Author Archives: William Pearce


Rail Zeppelin Propeller-Driven Railcar (Schienenzeppelin)

By William Pearce

During World War I, German engineer Otto Steinitz had the idea of testing aircraft engines and propellers on railcars. Carl Geissen designed the engine mount, and testing was carried out on a special track at the German Aviation Research Institute (Deutschen Versuchsanstalt für Luftfahrt, DVL) in Berlin. The test car reached speeds of up to 97 mph (140 km/h). After the war, the propeller-driven railcar concept led Steinitz to design a special two-axle car with a mount for an aircraft engine at each end. An enclosed area between the engines housed the crew, passengers, and equipment. Known as the Dringos-Wagen, the machine made a 25-mile (40-km) test run from Grunewald to Beelitz on 11 May 1919. Loaded with approximately 40 people (possibly 35 passengers and five crew), the Dringos-Wagen experienced slow acceleration and a limited top speed of about 37 mph (60 km/h). Interest in Steinitz’s Dringos-Wagen declined after the test, but Geissen continued to design propeller-driven railcars for passenger service into the early 1920s.


The Dringos-Wagen testing the concept of a propeller-driven railcar in 1919. Note the radiators installed on the deck

Also in the early 1920s, fellow German engineers Kurt Wiesinger and Franz Friedrich Kruckenberg had similar ideas of using propellers to improve and quicken rail traffic. Wiesinger envisioned propelling railcars along the tracks with propellers, while Kruckenberg was considering a streamlined, propeller-driven gondola suspended from a single overhead track as a Zeppelin-on-rails. Kruckenberg’s design was similar to George Bennie’s Railplane of the same period. The pair met in 1923 but soon had a falling out and went their separate ways.

Kruckenberg had studied shipbuilding at the Technical University in Danzig (now Gdańsk University of Technology). One of his professors, Johann Schütte, had partnered with industrialist Karl Lanz to form Luftschiffbau Schütte-Lanz (Airship Construction Schütte-Lanz) in April 1909. After his graduation in August 1909, Kruckenberg joined the firm as a developmental engineer. Kruckenberg was involved with both airship and aircraft constructions while working at Schütte-Lanz, and he was the firm’s chief designer and director of aircraft production during World War I.

After World War I, Kruckenberg left Schütte-Lanz and began to focus on ways to improve rail travel, which is when he met Wiesinger. In July 1924, Kruckenberg partnered with Curt Stedefeld, an associate from university who had also worked for Schütte-Lanz and had founded the Company for Traffic Engineering (Gesellschaft für Verkehrstechnik, GVT) to promote the overhead rail system. Despite a forecasted top speed of 224 mph (360 km/h), the German Ministry of Transportation (Reichsverkehrsministerium) and the German State Railroad Company (Deutschen Reichsbahn-Gesellschaft, DRG) were not willing to offer any financial support. The main objection was the cost of the overhead rail system, which required the support and construction of a completely new infrastructure.


The DVL’s Propellerwagen was strictly a test machine and not intended to transport passengers. However, the Propellerwagen provided important information on suspension and handling that was applied to the Rail Zeppelin.

In April 1928, Kruckenberg and Stedefeld founded the Trajectory Company (Flugbahn-Gesellschaft, FG) in Heidelberg. The purpose of the new company was to build a propeller-driven railcar for experimentation on existing rail lines to validate the concepts of the overhead rail system. Once FG had demonstrated reliable performance on existing rails, it was hoped that the DRG would be willing to support the overhead rail system.

Around the same time, the DVL was interested in constructing a Propellerwagen to revive the testing of engines and propellers on railcars. Both FG and DVL had petitioned the DRG for the use of a straight, 5-mile (8-km) long, unused track between Langenhagen and Celle. The DRG proposed that the FG and the DVL work together to build a test rig that could be used to test engines and propellers and validate the concepts of propeller-driven railcars.

The DVL Propellerwagen test railcar was completely enclosed with an engine and propeller at each end. The narrow machine was tall with flat sides and had two axles. The rear engine drove its propeller directly via a long shaft, while the front engine drove an elevated propeller shaft via a wide belt. Both engines were six-cylinder, inline BMW IVs that produced 250 hp (186 kW) at 1,400 rpm. The test car weighed around 30,865 lb (14,000 kg) and had a top speed of 109 mph (175 km/h). After operating under its own power for the first time in April 1929, the test railcar eventually made 82 runs that totaled approximately 620 miles (1,000 km). While the DVL test machine did not help advance GVT/BG’s study of aerodynamics, it did provide important information about suspension, handling, and the operation of a propeller-driven railcar.


The bodyless Rail Zeppelin on 30 August 1930 illustrating the machine’s intricate frame. Note the numerous lightening holes in the truss frame. The engine-driven centrifugal fan drew in air via the circular opening (one on each side). The air was then forced through the large, square radiator in the lower rear of the railcar.

With information from the RVL tests in hand, Kruckenberg and his team compared diesel-electric drives against propeller drives for their railcar. They found that the diesel-electric would cost about 19 times more than the propeller drive and would weigh around 19,842 lb (9,000 kg), compared to 772 lb (350 kg) for the propeller and engine. In June 1929, the design of a streamlined, propeller-driven Trajectory Express Car (Flugbahn-Schnellwagen) was laid out and designated Propeller Railcar A (Propellertriebwagen A). This machine was undoubtedly inspired to some degree by the earlier designs of Geissen and Wiesinger. Detailed design work was done in October 1929, and wind tunnel models were tested the following month. Due to its design, construction, and appearance, the streamlined, high-speed railcar became commonly known as the Rail Zeppelin (Schienenzeppelin).

The Rail Zeppelin consisted of a steel chassis with an aluminum truss frame. The engine supports and some other components were also made of steel. The aluminum frame was perforated with extensive lightening holes. The machine was supported on two axles and had a wheelbase of 64 ft 4 in (19.60 m). The axles used rubber ball dampeners for their suspension. Each of its four wheels were 39 in (1.0 m) in diameter. The inner flange of the wheels was made taller than normal to help prevent any possible derailments caused by the machine’s anticipated high speeds. Air-powered friction brakes were used to slow the Rail Zeppelin. An electric drive motor powered the front axle for moving the machine in a limited manner up to 12.4 miles (20 km) and at relatively slow speeds.


The completed Rail Zeppelin displaying its streamlined form for press photographers. Note the two exhaust stacks at the rear of the machine and its long wheelbase.

Above the rear axle was a single BMW VI liquid-cooled V-12 engine. The BMW VI had a 6.30 in (160 mm) bore and a 7.48 in (190 mm) stroke. The engine displaced 2,797 cu in (45.84 L) and produced 500 hp (373 kW) at 1,410 rpm and 600 hp (447 kW) at 1,540 rpm. The engine’s exhaust was expelled through two vertical stacks. The drive end of the engine pointed toward the rear of the Rail Zeppelin and was elevated seven degrees. A shaft, which was also angled at seven degrees, extended approximately 7 ft 7 in (2.3 m) back to the rear of the machine and turned a four-blade, fixed-pitch Heine propeller made from ash wood. The seven-degree angle on the propeller applied downward force on the Rail Zeppelin and directed the propwash up and away from people on rail platforms. The propeller was 9 ft 2 in (2.80 m) in diameter and was comprised of two stacked two-blade units.

Also attached to the drive end of the engine was a centrifugal fan that circulated cooling air through the engine compartment. Air was drawn in via vents on each side of the Rail Zeppelin and entered a duct at the center of the machine. The air then passed through radiators and was expelled out from the bottom of the Rail Zeppelin. The engine also powered the compressor for the air brakes and two generators for the electrical system. Storage batteries were located in the train’s nose.

The Rail Zeppelin was covered by a streamlined, aerodynamic body. The front, lower sides, and rear of the machine were covered by aluminum sheeting. Windows extended along the sides of the passenger compartment. Due to the expected speed of the Rail Zeppelin, none of the windows opened, and ventilation was provided by forced air. The top of the railcar was covered with fire-proof canvas.


Rear view of the Rail Zeppelin with its four-blade propeller. The grate on the side was the cooling air intake. The circular housing under the propeller was for lights.

Two drivers sat side-by-side at the front of the train in a raised cockpit, which also had seats for two observers. Passenger compartment access doors were positioned at the front, middle, and rear on each side of the Rail Zeppelin. The 8 ft 2 in (2.5 m) wide and 52 ft 6 in (16 m) long passenger cabin was insulated and had wood paneling. As designed, the passenger compartment consisted of six sections, with each section accommodating four passengers, and a central aisle extended through each section. In addition to the 24-seat configuration, an alternative configuration with bench seating could accommodate 44 passengers. A lavatory was provided at the rear of the cabin. As built, only the forward three compartments were completed, and the rear three compartments held test equipment. The Rail Zeppelin was 84 ft 10 in (25.85 m) long, 8 ft 9 in (2.66 m) wide, and 9 ft 2 in (2.80 m) tall. The railcar weighed 40,962 lb (18,580 kg).

Construction of the Rail Zeppelin started in early 1930 at the DRG repair works in Leinhausen, near Hannover. Without its body, the railcar was mostly complete in August 1930 and moved under its own power with the electric motor. The body was added, and the Rail Zeppelin was completed in September. The first test with propeller power occurred on 25 September 1930. During the first high-speed test, the Rail Zeppelin reached 62 mph (100 km/h) after 66 seconds and 3,232 ft (985 m) of forward travel. The machine hit 93 mph (150 km/h) after two minutes, and the throttle was pulled back just past three minutes at 113 mph (182 km/h).


The Rail Zeppelin with its two-blade propeller sits at Spandau (Berlin) station after its run on 21 June 1931. The two-blade propeller improved the machine’s top speed but slowed acceleration.

The initial testing was done in secret and revealed that braking was an issue. Due to the Rail Zeppelin’s streamlining and relatively light weight, light breaking took a long distance, and heavy breaking had a tendency to lock the rear axle. In one instance, the brakes locked the rear axle at 112 mph (180 km/h), and it took 1.2 miles (2 km) for the railcar to come to a stop. A flat spot on the rear wheels about .14 in (3.5 mm) deep was discovered during a quick inspection, but the Rail Zeppelin was still operated up to 87 mph (140 km/h) on its return trip.

On 18 October 1930, the Rail Zeppelin was debuted to the press. Tests continued, some of which involved DRG officials. To test the concept of using a propeller with adjustable blades, a propeller with reverse pitch was installed (this may have been the normal propeller installed backward), and the Rail Zeppelin was run in reverse at 37 mph (60 km/h). With the propeller back to its normal forward thrust configuration, propeller braking tests were conducted. The electric motor was used to reverse the train at 28 mph (45 km/h). Then the propeller was engaged, and it alone halted the Rail Zeppelin in 20 seconds. These tests indicated that a fully reversible pitch propeller would greatly enhance the Rail Zeppelin’s braking and improve its safety.


This upper view of the Rail Zeppelin in Berlin illustrates the machine’s canvas covering over its upper body. Note the windshield wipers and the two-blade propeller.

Testing on the isolated track continued until May 1931, when the Rail Zeppelin was operated on the main line. However, no German insurance company would cover the propeller-driven train, and arrangements had to be made with Lloyd’s of London for coverage. The main line test was a 12.2-mile (19.7-km) stretch between Plockhorst and Lehrte. The Rail Zeppelin drew quite a crowd wherever it operated, necessitating a police presence to control the spectators. On 10 May, the machine covered the distance in 10 minutes and reached a top speed of 127 mph (205 km/h).

Testing over a longer distance was needed, so the 160-mile (257-km) route between Hamburg and Berlin was selected. The four-blade propeller was switched in favor of a two-blade unit that would provide a higher top speed at the cost of acceleration. The two-blade propeller was of the same construction as the previous propeller—fixed pitch, wood, and 9 ft 2 in (2.80 m) in diameter.

On 21 June 1931, the Rail Zeppelin left the Hamburg-Bergedorf station at 3:27 AM with a number of observers and crew on board. As the train traveled, its speed continued to increase. However, the track speed limit around many of the curves was 62 mph (100 km/h), which caused the Rail Zeppelin to slow often and accelerate on the straight stretches. Over the 7.5 miles (12-km) separating Karstädt and Dergenthin, the Rail Zeppelin averaged 143.0 mph (230.2 km/h)—a new speed record for passenger rail travel that would stand until 1954. The train arrived in Berlin at 5:05 AM with an average speed of 97.7 mph (157.3 km/h). Along the way, the Rail Zeppelin burned only 48.6 US gal (40.5 Imp gal / 184 L) of fuel, which averaged to 3.3 miles per US gal (1.4 km/L).


With its propeller spinning, the Rail Zeppelin awaits departure at a station. Although the propeller did not really extend beyond the railcar’s body, this view illustrates the rather disconcerting proposition of passengers coming into close proximity of the large propeller. Note the open middle access door.

After its record run, the Rail Zeppelin was put on display at the Rennbahn-Stadion (now Olympiastadion) railway station in Berlin until 25 June 1930. After the display, the train embarked on a short tour of Germany. The four-blade propeller was reinstalled for the tour, and the speed was kept down to conform with normal scheduled traffic on the line. Once again, the Rail Zeppelin drew large crowds wherever it went. The machine returned to Hannover on 28 June.

A new electromagnetic braking system was installed on the Rail Zeppelin and was tested in March 1932. The system was able to stop the train from 103 mph (165 km/h) in 2,067 ft (630 m). While this was a definite improvement, the distance was still longer than desired. Although the Rail Zeppelin had achieved some level of success, the practicality of such a machine was in question. The train’s long wheelbase caused issues on tight curves, and its ineffective brakes necessitated long stopping distances. The propeller-driven design did not allow coupling multiple units together, and the machine was unable to easily maneuver forward and back for short distances. The large propeller always presented a level of danger to anyone in close proximity to the Rail Zeppelin, and that included passengers waiting on rail platforms.


Image of the modified Rail Zeppelin with propeller removed and the engine installed in the nose. The nose and cockpit were revised for the installation of the engine and the hydraulic drive. Barely visible is the dual-axle front bogie.

Kruckenberg and his team took another look at the future of rail travel, and the propeller-driven railcar concept was discarded in favor of a diesel-hydraulic drive that was much lighter than diesel-electric. In May 1932, modifications were started on the Rail Zeppelin to convert the machine to the new power system. The BMW engine and propeller were removed from the rear, and the engine was temporarily installed in the nose of the train until the intended Maybach GO 5 was available. The GO 5 was a 2,588 cu in (42.4 L) diesel V-12 that produced 410 hp (305 kW) at 1,400 rpm. The engine’s exhaust was collected in a central duct that split the center of the cockpit’s windscreen. Via a Föttinger fluid coupling, the engine drove a double-axle bogie positioned under the cockpit. The bogie had a wheelbase of 6 ft 7 in (2.0 m). To accommodate the changes, the train’s nose was elongated, and its cockpit was raised. Its length was increased to 95 ft 2 in (29.0 m) and its weight increased to 62,832 lb (28,500 kg).

The revised Rail Zeppelin was completed in November 1932. The train was tested in early 1933 and reached 87 mph (140 km/h) in under two minutes after traveling 1.5 miles (2,426 m). It was also run at least to 99 mph (160 km/h). However, the DRG had become interested in other trains, namely those powered by diesel-electric engines. The Rail Zeppelin continued to be tested through 1934 and accumulated over 1,491 miles (2,400 km) with its new drive system. The GO 5 engine was finally installed in 1934, and the machine was sold to the DRG. It does not appear that much testing was done with the GO 5 engine. While Kruckenberg and his team continued to design more conventional locomotives throughout the 1930s, the Rail Zeppelin was placed into storage. In 1939, the Rail Zeppelin was scrapped so that its metal could be used to rebuild the German armed forces.

The Rail Zeppelin and its diesel-hydraulic drive served as the basis for the Kruckenberg-designed SVT 137 155, which could accommodate 100 passengers. A single example of the SVT 137 155 was completed in 1938, and the three-section express train set a conventional passenger train speed record on 23 June 1939 at 134 mph (215 km/h). The SVT 137 155 never entered regular service, and it was scrapped in 1967.


The SVT 137 155 built upon the Rail Zeppelin’s diesel-hydraulic experiments. Note the exhaust stack splitting the windscreen.

Der Schienenzeppelin by Alfred Gottwaldt (2006)
BMW Aero Engines by Fred Jakobs, Robert Kroschel, and Christian Pierer (2009)


Eldridge FIAT Mephistopheles LSR Car

By William Pearce

In 1907, FIAT won the French Grand Prix and had a good racing season overall. The manufacturer’s success inspired Scotsman George Abercromby to order his own FIAT race car with the hope of winning the 1908 Montagu Cup Race held at the Brooklands raceway in Surrey, England. Abercromby’s car was designated SB4 Corsa (Race) by FIAT, and was an improvement of the 1907 Grand Prix racer.


Felice Nazzaro sits behind the wheel of the original FIAT SB4 built for George Abercromby in 1908. A leather panel could be added to enclose the side of the very open racer.

The FIAT SB4 consisted of two straight frame rails that supported the engine at the front of the car, followed by two very open seats just before the rear wheels and a fuel tank at the extreme rear. The four-cylinder engine had two cast cylinder blocks, each with two cylinders. Reportedly, each cylinder had one intake valve and two exhaust valves. The intake valve and one exhaust valve of each cylinder were actuated by pushrods from the right side of the engine, while the remaining exhaust valve was actuated from the left side of the engine. The cylinders had a 7.48 in (190 mm) bore and a 6.30 in (160 mm) stroke. The SB4 engine displaced 1,107 cu in (18.15 L) and produced around 175 hp (130 kW) at 1,200 rpm.

The engine was concealed in the SB4 racer under a cowling and had an underpan. Mounted behind the engine was a four-speed transmission that powered a differential shaft just forward of the rear wheels. Sprockets and chains delivered power to the rear wheels. All of the wheels were made of wood. A foot pedal engaged a brake on the gearbox, and a hand lever operated a brake on the differential shaft. There were no front brakes.


Ernest Eldridge sits in the highly-modified FIAT SB4, now lengthened and powered by a 300 hp (223 kW) A.12bis engine. The car is pictured at Brooklands in 1924.

Abercromby’s SB4 was delivered to England in the spring of 1908, and FIAT driver Felice Nazzaro raced the car at Brooklands in June. Nazzaro defeated Frank Newton driving the Napier Samson and averaged 94.75 mph (152.49 km/h) over the 27.25-mile (43.85-km) race with one lap recorded at 121.64 mph (195.76 km/h). However, Abercromby was not pleased with the car (or perhaps FIAT) and refused its delivery. Therefore, the FIAT was not entered in the 1908 Montagu Cup Race held in August. A legal skirmish ensued between Abercromby and FIAT and was won by FIAT, with Abercromby ultimately taking delivery of the vehicle.

Abercromby raced the FIAT a bit in 1910, but mechanical issues prevented success. The car passed through a few owners before World War I but was run very little. After World War I, John Duff discovered the FIAT stored in a garage and was able to purchase the car. Duff somewhat restored the racer, replaced the wood wheels with wire ones, and had a new body made that enclosed more of the car and improved its aerodynamics. Duff and co-driver R F Cooper entered the car for various Brooklands meets in 1921, but mechanical issues prevented it from starting most of these races. The Fiat did place second in a Lightning Short held in August, but cracked pistons took it out of subsequent races.


Eldridge and Jim Ames in Mephistopheles at Arpajon, France for an LSR attempt. Note the chain drive.

In 1922, Duff had replaced the pistons with lighter ones designed by Harry Ricardo. With co-driver L G Callingham, Duff finished third in a sprint race held in May, turning a lap at 107.10 mph (172.36 km/h). However, the FIAT’s engine blew up spectacularly during a longer race, with parts flying in all directions. Duff decided that the FIAT was not worth his time, and he sold the damaged, 14-year-old car to Ernest Arthur Douglas Eldridge.

Eldridge had started racing at Brooklands in 1921 behind the wheel of a 1907 Isotta Fraschini Grand Prix car powered by a 488 cu in (8.0 L) four-cylinder engine that produced around 100 hp (75 kW). Disappointed by his lackluster performance, Eldridge decided to modify the car with a six-cylinder, inline Maybach AZ engine that displaced 1,251 cu in (20.5 L) and produced 180 hp (134 kW) at 1,200 rpm. The Isotta Fraschini car required extensive modifications to support the large Maybach engine, which originally powered an airship. The modified car was known as the Isotta-Maybach, and Eldridge debuted it in April 1922. Eldridge found success with the Isotta-Maybach and was able to lap Brooklands in excess of 100 mph (161 km/h).


Mephistopheles about to make a record run at Arpajon. Eldridge always did an excellent job handling the car’s power, and only the tires suffered.

In search of more power, Eldridge was able to acquire a war-surplus FIAT A.12bis engine, a type that powered various Italian aircraft during World War I. The six-cylinder, inline A.12bis had two intake and two exhaust valves for each cylinder, all actuated by a single overhead camshaft. Two spark plugs were fitted on each side of each cylinder. The engine had a 6.30 in (160 mm) bore and a 7.09 in (180 mm) stroke. The A.12bis displaced 1,325 cu in (21.7 L) and normally produced around 260 hp (194 kW) at 1,700 rpm. Eldridge had made some modifications to the engine, including improving its ignition system, and his example produced 300 hp (233 kW) at 1,400 rpm and 320 hp (239 kW) at 1,800 rpm. Rather than modifying the Isotta-Maybach, Eldridge sought a new chassis for the engine and purchased the FIAT racer from Duff as the basis for his new project. The Isotta-Maybach was sold to Loftus Claude Gerald Moller Le Champion, and Eldridge focused on his FIAT racer.

In order to fit the A.12bis engine, Eldridge added about 17 in (432 mm) to the FIAT racer’s chassis. Some sources state that this section was originally from a bus frame, but it is more likely that the metal was supplied by the London General Omnibus Company and that it was not from a scrapped bus. A new, more enclosed body was made to cover the longer car, but the transmission and chain drive were retained. The car used a 176 lb (80 kg) flywheel, and the clutch had 57 plates. The underpan was extended the entire length of the car. Eldridge’s 300 hp FIAT was 16 ft 8 in (5.09 m) long, 6 ft 1 in (1.85 m) wide, 4 ft 7 in (1.40 m) tall, and weighed approximately 3,858 lb (1,750 kg). Mounted on the car’s 21 in (533 mm) wire wheels were 33 x 6 in (838 x 152 mm) tires.


Mephistopheles streaks along the public road in Arpajon as it makes a record attempt. The road had a 4.5-mile (7.2-km) straight.

Eldridge debuted his 300 hp FIAT at Brooklands for the Summer Meeting held on 23 June 1923. The car was run without the body, as it had not yet been completed. Various issues were encountered, but Eldridge was able to complete a lap from a standing start at 88.77 mph (142.86 km/h), which was a good speed but not fantastic. After repairs, Eldridge pushed his standing start speed up to 91.17 mph (146.72 km/h), but trouble persisted, and the car was withdrawn.

In late October 1923, the 300 hp FIAT was back at Brooklands where Eldridge set a world half-mile (.8 km) standing start record, averaging 77.68 mph (125.01 km/h) over two runs. In April 1924, Eldridge completed a Brooklands lap at 122.37 mph (196.94 km/h) and finished second in the Founder’s Gold Cup Race, coming in behind Le Champion driving Eldridge’s old Isotta-Maybach, which had a 20 second head start. The powerful car had an extreme tendency to quickly destroy tires. In early June, Eldridge was back at Brooklands and lapped the track at 107.10 mph (172.36 km/h) from a standing start and 123.89 mph (199.38 km/h) the next time around. Eldridge had become as comfortable as possible in the 300 hp monster FIAT.


Eldridge with the new radiator cowling installed on Mephistopheles. Note the engine’s 12 open exhaust stacks. The car was run in this configuration at Montlhéry in 1925.

The Automobile Club de France was sponsoring speed trials in Arpajon, France in early July 1924, and Eldridge decided to take the 350HP FIAT and attempt a Land Speed Record. At the time, the LSR stood at 133.75 mph (215.25 km/h) over the flying km (.6 mi) and 129.17 mph (207.88 km/h) over the flying mile (1.6 km) and was set by Kenelm Lee Guinness driving the Sunbeam 350HP at Brooklands on 17 May 1922. The course for the trials was a 4.5-mile (7.2-km) straight section of a tree-lined public road that linked Arpajon to Paris.

The aero-engined FIAT, now with white ‘FIAT’ lettering, caused quite a commotion in France, and the car was nicknamed Mephistopheles (Mefistofele in Italian) by the press. Mephistopheles is a folklore demon that collects the souls of the damned. The name stuck, and the car became known as the FIAT Mephistopheles / Mefistofele.


Eldridge and Ames in Mephistopheles leads John Godfrey Parry-Thomas in his Leyland-Thomas racer at Brooklands on 11 July 1925. Thomas would come back to win the three-lap match race, which involved both cars operating beyond their limits. Thomas set a Brooklands lap record during the race. (Brooklands Museum image)

On 6 July 1924, Eldridge and his co-driver Jim Ames took Mephistopheles out for a record run. The co-driver had the tasks of actuating a pump to maintain fuel pressure and of opening an oxygen bottle, which Eldridge had devised to feed the gas into the engine in an attempt to make more power. The pair ran at the record-breaking speed of 146.8 mph (236.3 km/h) over the km (.6 mi). However, Frenchman René Thomas protested the run, as Mephistopheles had no reverse gear, which new rules stipulated was required. Earlier in the day, Thomas had established a new record in his V-12-powered Delage DH at 143.312 mph (230.638 km/h) for the km (.6 mi) and 143.26 mph (230.55 km/h) for the mile (1.6 km). Thomas’ protest was upheld, and he retained the LSR while Eldridge was disqualified.

Not to be outdone, Eldridge modified Mephistopheles to conform to the rules. Exactly how this was done is up for debate. Some sources state that he flipped the drive chain to make a figure eight and spin the drive axle in reverse. Others contend that while this would make the car back up, it would not be able to move forward without having the chain put right again, and such a modification was unlikely to conform to the rules. More likely, a simple reverse gear was made incorporating an auxiliary shaft from the transmission.


Thomas (left) and Eldridge (right) shake hands after the match race. Both men were the epitome of the sportsman. The cowling of Mephistopheles is in the foreground.

Whatever the ‘fix,’ the modifications to Mephistopheles satisfied the officials, and another record attempt was planned for 12 July 1924. At this point, the time trials were over, and the public road was open to normal traffic. In the early morning, with police standing-by to hold traffic, Eldridge and co-driver D. W. R. Gedge ran the 16-year-old Mephistopheles on the road and established a new LSR at 146.014 mph (234.986 km/h) over the km (.6 mi) and 143.260 mph (234.794 km/h) over the mile (1.6 km). True to its nature, Mephistopheles destroyed its tires along the way. This was the last LSR set on a public road. They also set a standing start 1 km (.6 mi) record at 85.477 mph (137.562 km/h). Eldridge held the LSR until 25 September 1924, when Malcolm Campbell set his first LSR at 146.16 mph (235.22 km/h) over the km (.6 mi) in Guinness’ old Sunbeam 350HP, which became the first Blue Bird.

After the record run, Eldridge had Mephistopheles modified slightly with a new, more-streamlined radiator cowling. In October 1924, the car competed against John Godfrey Parry-Thomas in the Leyland-Thomas racer at the opening of the Autodrome de Linas-Montlhéry track south of Paris, France. Mephistopheles won the six-lap race at 121.04 mph, but both cars suffered tire failure along the way. On 27 November 1924, Eldridge attempted to better his LSR but was only able to establish a new 10-mile (16.1-km) record at 121.443 mph (195.444 km/h). In December, a new 5 km (3.1 mi) record was set at 128.53 mph (206.85 km/h). Back at the Montlhéry track on 29 March 1925, Eldridge and Mephistopheles set new records covering 5 km (3.1 mi) at 129.23 mph, 5 mi (8.0 km) at 128.20 mph, and 10 km (6.2 mi) at 128.34 mph (206.5 km/h).


FIAT Mephistopheles as seen at the Goodwoood Festival of Speed in 2011. The car is owned by Fiat and normally kept at the Centro Storico Fiat (Fiat Historic Center) in Turin, Italy. (Fiat image)

Since the debut of the 300 hp FIAT, there had been much interest in a match race against Thomas in the Leyland-Thomas racer. That head-to-head race was finally held at Brooklands on 11 July 1925, and no one in attendance was disappointed. Mephistopheles’ new radiator cowling had been discarded by this point. The Leyland-Thomas used a highly-turned, straight-eight engine that had a 3.5 in (89 mm) bore and a 5.75 in (146 mm) stroke. The engine displaced 443 cu in (7.26 L) and produced an impressive 240 hp at 3,500 rpm. Thomas got off the line first but was soon passed by Eldridge. Both men pushed their machines to the limit, skidding around the track at times. Thomas was able to get back by Eldridge and take the win, although both cars lost one tire near the end of the three-lap race. Eldridge and the FIAT had a best lap of 125.45 mph (201.89 km/h) and finished at an average of 121.19 mph (195.04 km/h). During the race, Thomas set a Brooklands lap record at 129.70 mph (208.73 km/h) and finished at an average of 123.23 mph (198.21 km/h).

In late July 1925, Eldridge sold Mephistopheles to Le Champion. Le Champion campaigned the car off and on for some time, but Mephistopheles’ habit of devouring its tires did not serve it well during most races. The car was acquired by W.G.S. Wike and George Gregson in October 1931. After racing it for a short time, Wike and Gregson regularly drove the car on public roads. Gregson eventually took full ownership of Mephistopheles but was killed at the Battle of Dunkirk during World War II. In 1945, the car was acquired by Charles Naylor, who later sold it to Fiat around 1960. Mephistopheles was restored and participated in a vintage race in 1961 and in other races over the years. It has most recently appeared at the Goodwood Festival of Speed in 2001 and 2011. Mephistopheles is preserved at the Centro Storico Fiat (Fiat Historic Center) in Turin, Italy. Although Eldridge did not make any further LSR attempts, he was involved with George Eyston’s Speed of the Wind and Thunderbolt cars.


FIAT Mephistopheles on display giving a glimpse at the car’s A.12 engine. While not the original engine installed by Eldridge, the power plant is more than enough to push Mephistopheles to speeds beyond that at which any sane person would travel. (Fiat image)

This article is part of an ongoing series detailing Absolute Land Speed Record Cars.

Brooklands Giants by Bill Boddy (2006)
The Land Speed Record 1920-1929 by R. M. Clarke (2000)
Reid Railton: Man of Speed by Karl Ludvigsen (2018)


Lockheed Model 1249 Turboprop Super Constellation

By William Pearce

In 1938, the Lockheed Corporation in Burbank, California began design work on a large commercial airliner intended to outperform other transports then in service. Initially known as the Model 44 Excalibur, the aircraft’s design changed as feedback provided by Pan American Airways was evaluated. In 1939, Transcontinental and Western Air (TWA) approached Lockheed in search of an aircraft with performance superior to that of the planned Model 44. Lockheed decided to redesign its airliner based on TWA’s requirements, and the new design became the Model 049 Constellation (originally Model 49 and known as Excalibur A).


The Lockheed Model 1249 was a turboprop-powered Super Constellation originally ordered by the US Navy as the R7V-2. The aircraft was the fastest of the Constellation series by far, but other turboprop and jet aircraft were favored by all parties.

The Model 049 Constellation was an all-metal, low-wing aircraft with tricycle landing gear. The airliner was powered by four 2,200 hp (1,641 kW) Wright R-3350 engines and carried 60 passengers in its pressurized cabin. The Model 049 had a 123 ft (37.5 m) wingspan and was 95 ft 2 in (29.0 m) long and 23 ft 8 in (7.2 m) tall. The aircraft’s tail had three vertical stabilizers with rudders to keep the aircraft’s overall height down so that it would fit in TWA’s existing hangars. The Model 049 had a top speed of 329 mph (529 km/h) at sea level, a cruising speed of 275 mph (443 km/h) at 20,000 ft (6,096 m), an initial climb rate of 1,620 fpm (8.2 m/s), and a range of 2,290 miles (3,685 km) with a maximum payload of 18,400 lb (8,346 kg). The aircraft had an empty weight of 55,345 lb (25,104 kg) and a maximum weight of 86,250 lb (39,122 kg).

In 1940, the design of the Model 049 was mostly finalized, and three airlines had placed orders for a total of 84 aircraft (30 of these were long-range Model 349s). In May 1941, the United States Army Air Corps ordered 180 Model 349s to be used as transports. Lockheed tooled-up for aircraft production, and construction of the first Model 049 was underway when the United States entered World War II after the bombing of Pearl Harbor on 7 December 1941. With the United States at war, production priorities shifted, and all of the aircraft intended for the airlines would be completed as C-69s, the military designation for the Model 049/349.


Installation of the Pratt & Whitney T34 turboprop engines onto the Super Constellation airframe was well-executed. The tight-fitting cowling was much smaller than those needed to cover the larger-diameter R-3350 piston engine. The aircraft’s main gear was unchanged, which resulted in an awkward hump under the No. 2 and 3 engines. Note the wide cord of the three-blade propeller.

The C-69 received a low priority compared to Lockheed’s other commitments, and the prototype made its first flight on 9 January 1943. Only 15 C-69s were completed by the end of the war. After the war, Lockheed again focused on the Constellation for airline use, and new orders were received. In May 1945, Lockheed made use of new 2,500 hp (1,864 kW) R-3350 engines and designed the Model 649 and the Model 749, which had increased range. The United States Air Force also used the Model 749 as the C-121A. The Model 749 had a top speed of 358 mph (576 km/h) at 19,200 ft (5,852 m), a cruising speed of 304 mph (489 km/h) at 20,000 ft (6,096 m), an initial climb rate of 1,280 fpm (6.5 m/s), and a range of 1,760 miles (2,834 km) with a payload of 16,300 lb (7,394 kg). The aircraft had an empty weight of 58,970 lb (26,748 kg) and a maximum weight of 107,000 lb (48,534 kg).

In late 1949, Lockheed investigated ways to improve the Constellation’s performance and keep the aircraft on the frontline of airline service. The result was the Model 1049 Super Constellation, which had two new fuselage sections added that increased the aircraft’s length by 18 ft 5 in (5.6 m). In addition, 2,700 hp (2,013 kW) R-3350 engines were installed, and the height of the vertical stabilizers was increased by 1 ft 3 in (.38 m). The aircraft could accommodate up to 92 passengers. The Model 1049 was 113 ft 7 in (34.6 m) long, 24 ft 9 in (7.6 m) tall, had a top speed of 338 mph (544 km/h) at sea level, a cruising speed of 302 mph (485 km/h) at 20,000 ft (6,096 m), an initial climb rate of 1,100 fpm (5.6 m/s), and a range of 2,880 miles (4,635 km) with a payload of 18,800 lb (8,528 kg). The aircraft had an empty weight of 69,210 lb (31,393 kg) and a maximum weight of 120,000 lb (54,431 kg). The Model 1049 made its first flight on 13 October 1950. The Model 1049B was a military transport version of the Super Constellation, designated R7V-1 (originally R7O-1) for the US Navy and C-121C for the US Air Force.


The first R7V-2 (BuNo 131630) seen on a test flight without the wingtip fuel tanks. The Constellation-series of aircraft is known as one of the more graceful airframes, and the turboprop engines made the aircraft that much more impressive.

From the start of the Model 1049’s design, Lockheed had envisioned using 3,250 hp (2,424 kW) R-3350 Turbo Compound (TC) engines, which used three power recovery turbines to harness energy from the exhaust and feed it back to the crankshaft via fluid couplings. However, Wright’s development of the engine lagged behind that of the aircraft. The R-3350 TC engines were first incorporated into the Model 1049C, which made its first flight on 17 February 1953. The pinnacle of the Super Constellations was the Model 1049G, powered by 3,400 hp (2,535 kW) R-3350 TC engines. The aircraft made its first flight on 7 December 1954. The Model 1049G had a top speed of 370 mph (595 km/h) at 20,000 (6,096 m), a cruising speed of 310 mph (499 km/h) at 20,000 ft (6,096 m), an initial climb rate of 1,165 fpm (5.9 m/s), and a range of 4,165 miles (6,704 km) with a payload of 18,300 lb (8,301 kg). The aircraft had an empty weight of 73,016 lb (33,120 kg) and a maximum weight of 137,500 lb (62,369 kg).

The US Navy had been instrumental in supporting Wright’s development of the turbo compound engine, but in the early 1950s, the turboprop engine was making its way onto the aviation scene. In June 1950, Lockheed considered a turboprop-powered Super Constellation airliner as the Model 1149, but the design did not procced. In November 1951, Lockheed proposed to the Navy a turboprop R7V-1 (Model 1049B) powered by Pratt & Whitney T34 turboprop engines. The Navy was interested, and Lockheed proceeded with design work on the turboprop Super Constellation as the Model 1249. The Navy ultimately amended its R7V-1 order to include two airframes converted to turboprop-power. These aircraft were designated R7V-2 by the Navy and carried the Lockheed serial numbers 4131 and 4132 and the Navy BuNos 131630 and 131631.


Side view of the R7V-2 shows the reinforcements on the rear fuselage above and below the large cargo door, which hinged up. The turboprop aircraft used standard Super Constellation fuselages, and most were reused on piston-powered aircraft once their days of testing were over.

Two additional airframes were ordered in May 1953. They carried the Lockheed serial numbers 4161 and 4162 and Navy BuNos 131660 and 131661. In October 1953, BuNos 131660 and 131661 were slated to be completed as YC-121Fs for the Air Force and were also assigned Air Force serial numbers 53-8157 and 53-8158. The YC-121F was the Lockheed Model 1249A. Since the order originated with the Navy, all four turboprop Super Constellations carried the Navy designation R7V-2, with the last two also assigned the Air Force designation. All four aircraft were purely intended to test the serviceability of the turboprop engine.

The Model 1249 was based on the Model 1049B, with a modified wing and new engines. The R-3350-powered Constellations had the engine nacelle’s centerline mounted below the wing. The Model 1249 had the engine nacelle’s centerline mounted above the wing, and the nacelle extended back to the wing’s trailing edge. Exhaust from the turboprop engine was expelled from the back of the nacelle and generated thrust. The Model 1249 could also accommodate removable 600 US gallon (500 Imp gal / 2,271 L) wingtip tanks that were first installed on Navy Super Constellations and later used by airlines. Additional fuselage fuel tanks were fitted, and the landing gear was strengthened.


The first YC-121F, still with Navy BuNo 131660 painted on the tail, seen on a test flight over Pacific Palisades, just north of Santa Monica, California. Note the large, removable wingtip fuel tanks.

The T34 turboprop was an axial-flow engine that consisted of a 13-stage compressor powered by a three-stage turbine. Sources indicate that the R7V-2s for the Navy used T34-P-12 engines, while the YC-121Fs for the Air Force used T34-P-6 engines. The T34-P-12 produced 5,005 shp (3,732 kW) and 1,360 lbf (6.05 kN) of thrust, for a total of 5,550 eshp (4,139 kW) at 11,000 rpm for takeoff power. Continuous power for the T34-P-12 was 4,210 shp (3,139 kW) and 1,165 lbf (5.18 kN) of thrust, for a total of 4,675 eshp (3,486 kW) at 10,500 rpm.

The T34-P-6 produced 5,500 shp (4,101 kW) and 1,250 lbf (5.56 kN) of thrust, for a total of 6,000 eshp (4,474 kW) at 11,000 rpm for takeoff power. Continuous power for the T34-P-6 was 4,750 shp (3,542 kW) and 1,125 lbf (5.57 kN) of thrust, for a total of 5,200 eshp (3,878 kW) at 10,750 rpm. Each engine turned a three-blade Hamilton Standard A-3470 propeller at .0909 engine speed. The propeller was 15 ft in (4.57 m) diameter, and each blade was 24 in (610 mm) wide.

The Model 1249 had a 117 ft (35.7 m) wingspan without wingtip fuel tanks and a 119 ft (36.3 m) wingspan with wingtip fuel tanks. The aircraft was 116 ft 2 in (35.4 m) long and 25 ft 6 in tall (7.8 m). The Model 1249 had a top speed of 444 mph (715 km/h) at 15,000 ft (4,572 m) and could maintain 420 mph (676 km/h) at 25,000 ft (7,620 m). The aircraft had an initial climb rate of 4,600 fpm (23.4 m/s) at maximum power and 2,310 fpm (11.7 m/s) at normal power. The Model 1249’s ceiling was 32,900 ft (10,028 m) at maximum power and 26,400 ft (8,047 m) at normal power. The aircraft’s range was 2,230 miles (3,589 km) with a payload of 24,210 lb (10,981 kg), and it had an empty weight of 72,387 lb (32,834 kg) and a maximum weight of 148,540 lb (67,377 kg). The Model 1249 could accommodate 106 passengers and four crew members for short flights, 87 passengers and 15 crew members for long flights, or 35,500 lb (16,103 kg) of cargo. For medical evacuations, the aircraft could accommodate 73 litters, four attendants, and four crew members.


The second YC-121F, Air Force serial number 53-8158, seen with flaps and gear extended. Note the exhaust outlet at the rear of the engine nacelles.

The Model 1249 / R7V-2, BuNo 131630, made its first flight on 1 September 1954. The aircraft was not initially fitted with the wingtip tanks, and it was accepted by the Navy on 10 September 1954. The second R7V-2 soon followed and was accepted by the Navy on 30 November 1954. The Navy put the R7V-2 aircraft through various tests. A top speed of 479 mph (771 km/h) was achieved in a slight dive, and the aircraft took off overweight at 166,400 lb (75,478 kg). However, the R7V-2’s career was short. In December 1956, and with just 109 total hours, BuNo 131630 was put into storage at Naval Air Station (NAS) Litchfield Park in Arizona. The aircraft was struck off charge in April 1959 and provided spare parts for other Constellations.

In late 1956, BuNo 131631 was loaned back to Lockheed as an engine testbed for the L-188 Electra airliner and later the P-3 Orion maritime patrol aircraft. At the time, BuNo 131631 had accumulated 120 hours of operation. Rohr Aircraft in Chula Vista, California removed the T34 engines and replaced them with Allison 501-D (T56) engines in new nacelles intended for the Electra. The 501-D produced 3,460 shp (2,580 kW) and 726 lbf (3.23 kN) of thrust, for a total of 3,750 eshp (2,796 kW) for takeoff power. The engines turned four-blade Aeroproducts 606 propellers that were 13 ft 6 in (4.11 m) in diameter. The modified aircraft was nicknamed ‘Elation,’ a combination of Electra and Constellation. Elation made its first flight in July 1957 and was used until July 1959 when it was damaged at Palmdale, California. With 882 hours, BuNo 131631 was delivered to NAS Litchfield Park. In May 1960, the aircraft was sold to California Airmotive. The fuselage and some other parts were used to rebuild 1049G Super Constellation N7121C, and the remainder was scrapped. N7121C went through various air cargo owners until it was scrapped in March 1968.


Lockheed serial 4132, the second R7V-2 (BuNo 131631), fitted with Allison 501-D engines to test their installation for the L-1888 Electra. Known as the Elation, the aircraft flew more with the Allisons than it did with its original Pratt & Whitney engines. Note the four-blade propellers.

The Model 1249A / YC-121F, serial no 53-8157, made its first flight on 5 April 1955 and was accepted by the Air Force in July. The second aircraft, serial number 53-8158, took to the air in August 1955. Both YC-121Fs were assigned to the 1700th Test Squadron of the Military Air Transport Service, based at Kelly Air Force Base in San Antonio, Texas. In April 1956, a YC-121F set a point-to-point speed record, traveling the 1,445 miles (2,326 km) between Kelly, Texas and Andrews Air Force Base, Maryland in 2 hours 53 minutes, an average of 501.16 mph (806.54 km/h). Between 25 and 26 January 1957, another record was set flying from Long Beach, California to Andrews Air Force Base, Maryland. The 2,340-mile (3,766-km) route was covered in 4 hours 43 minutes at an average speed of 496.11 mph (798.41 km/h). Both record flights were most likely made by 53-8157.

In June 1957, 53-8158 was assigned to McClellan Air Force Base in Sacramento, California; 53-8157 followed a year later. In February 1959, the two YC-121Fs were placed in storage at Davis Montham Air Force Base in Tucson, Arizona. Both aircraft were sold to the Flying Tiger Line 1963. The fuselages of the two YC-121Fs were used with wings, engines, and tails from two 1049Gs and pressed into cargo transport service in 1963. In 1966, both aircraft were sold to North Slope Aviation Company in Alaska. Serial number 53-8158 (N174W) was written off in May 1970. Serial number 53-8157 (N173W) was sold to Aviation Specialties and written off in June 1973.

Along with the military versions, Lockheed had designed a turboprop Super Constellation airliner in 1952 designated as the Model 1249B. The aircraft was planned to have a maximum speed of 451 mph (726 km/h) and a maximum range of 4,125 miles (6,639 km). However, the 1249B was not pursued, and the L-188 Electra eventually took its place.


An ad for the turboprop Super Constellation as Lockheed made a light push to interest airlines in the concept. There were no takers, and Lockheed developed the L-188 Electra instead.

The Lockheed Constellation by Peter J. Marson (2007)
Lockheed Constellation by Curtiss K. Stringfellow and Peter M. Bowers (1992)
Lockheed Aircraft since 1913 by René J. Francillon (1987)
Lockheed C-121 Constellation by Steve Ginter (1983)
Characteristics Summary YC-121F by US Air Force (1 April 1957)
Lockheed Constellation by Dominique Breffort (2006)


Blackburn B-20 Experimental Flying Boat

By William Pearce

On 13 February 1935, John Douglas Rennie submitted a patent application for “Improvements in and relating to Seaplanes.” Rennie was the Chief Seaplane Designer for the Blackburn Aeroplane and Motor Company, which was renamed in 1936 as Blackburn Aircraft Ltd. Rennie’s design idea was for the lower portion of the flying boat’s hull to be sealed and extend for takeoff and landing. The extendable hull would essentially act as the aircraft’s main float.


An excellent view of the Blackburn B-20 highlighting the aircraft’s extended hull, retracted wingtip floats, and well-engineered cowlings for the Vulture engine.

In order to provide clearance for the propellers, traditional flying boats have some combination of a parasol or strut-mounted wing positioned above the fuselage, a gull wing, and a tall hull. In addition, the hull and wing are designed for the essential task of lifting the aircraft from the water, but they are far from optimized for cruise flight. All of these compromises add significant drag to the aircraft. With Rennie’s hydraulically-operated extendable hull, the flying boat’s cross section with the hull retracted was much more like that of a conventional aircraft, and drag was significantly reduced. In addition, when the hull was extended, the aircraft assumed the ideal angle for takeoff and landing, which allowed the aircraft’s wing to have an angle of incidence optimized for cruise flight when the hull was retracted. Rennie’s patent also included retractable wingtip floats.

Rennie was granted Great Britain patent 433,925 on 22 August 1935. In 1936 the British Air Ministry issued Specification R.1/36 for a small, general purpose flying boat capable of cruising at 230 mph (370 km/h). Rennie and Blackburn responded with a twin-engine flying boat that featured a retractable hull. Blackburn’s design carried the company designation B-20. The Air Ministry ordered the Saunders-Roe A.36 Lerwick for Specification R.1/36, but they were sufficiently intrigued by the Blackburn B-20 to order a prototype, which was later assigned serial number V8914.

Technically, the B-20 was more of a floatplane with a retractable center main float than a flying boat. However, when the float was retracted, the aircraft took on the appearance and configuration of a flying boat. The B-20 had a high wing and was of all-metal, stressed-skin construction. All of the control surfaces were fabric covered. With the exception of the extending hull, the aircraft had a conventional layout. The B-20 had a standard crew of six. The fuselage housed a bombardier’s compartment in the nose. The fight deck was located well forward of the wing attachment and provided the pilot and copilot a good view. Behind and slightly below the cockpit was the flight engineer, navigator, and observer’s compartment. Under the wing was a wardroom with sleeping accommodations for two, followed by the crew’s quarters with accommodations for four, a galley, and a lavatory.


This side view of the B-20 illustrates how the hull moved forward as it was extended. The rear member of each of the four hull mounts was a hydraulic cylinder that actuated the extension and retraction of the hull.

The one-piece wing had three main spars, a straight leading edge, and a tapered trailing edge. Mounted in a nicely streamlined nacelle on each wing was a Rolls-Royce Vulture II X-24 engine capable of 1,800 hp (1,342 kW) for takeoff. The engine had an international rating of 1,780 hp (1,327 kW) at 4,000 ft (1,219 m) and 1,660 hp (1,237 kW) at 13,500 ft (4,115 m). A scoop under the engine nacelle housed the engine’s coolant radiator and oil cooler. Each engine turned a three-blade, constant-speed, de Havilland propeller. Unlike the patent design, which featured wing floats that retracted into the engine nacelles, the wing floats of the B-20 retracted outward to be flush with the wing and form the wingtip.

The extendable hull had five watertight compartments. The center compartment housed four fuel tanks with a total capacity of 1,172 US gallons (976 Imp gal / 4,437 L). The hull also housed most of the mooring equipment. Four hydraulic cylinders mounted in the fuselage controlled the extension and retraction of the 48 ft 9 in (14.86 m) hull. The hydraulic cylinders extended the hull approximately 5 ft 8.25 in (1.73 m) down from the fuselage for operating on the water’s surface. Forward of each hydraulic cylinder was a hinged triangular frame mounted to one point on the fuselage and two points on the hull. As the hull extended down, it also traversed forward. This movement of the hull gave the aircraft the proper angle for landing and taking off. Entry to the fuselage was achieved with the hull extended. Hatches under the fuselage led to the bombardier’s station, the wardroom, and the galley. A ladder that hinged down from the hatch under the bombardier’s station was the main access point.

Although the prototype was unarmed, the B-20’s planned armament consisted of two .303 machine guns in the nose, a dorsal turret with two .303 machine guns, and a tail turret with four .303 machine guns. In each wing, two compartments between the engine nacelle and the fuselage could each house a 500 lb (227 kg) bomb or two 250 lb (113 kg) bombs.


The B-20 on the water looked a little ungainly with its hull extended. Note the access ladder between the hull and the fuselage.

The Blackburn B-20 had a wingspan of 82 ft 2 in (25.04 m) with the floats retracted and 76 ft (23.16 m) with the floats extended. The aircraft was 69 ft 7.5 in (21.22 m) long, and was 25 ft 2 in (7.67 m) tall on its beaching gear with the hull extended. Without the turrets, the B-20 had a top speed of 322 mph (518 km/h) at 15,000 ft (4,572 m), 302 mph (486 km/h) at 5,750 ft (1,753 m), and 280 mph (451 km/h) at sea level. With the proposed turrets, the aircraft’s performance fell to a maximum speed of 306 mph (492 km/h) at 15,000 ft (4,572 m), 288 mph (464 km/h) at 5,750 ft (1,753 m), and 268 mph (431 km/h) at sea level. Cruising speed was 200 mph (322 km/h), and the B-20’s range was 1,500 miles (2,414 km). The aircraft had a normal weight of 35,000 lb (15,876 kg).

The B-20 was completed at Blackburn’s factory in Dumbarton, Scotland, near the River Clyde. The aircraft made its first flight on 27 March 1940, piloted by Blackburn’s test pilot Harry Bailey. Another four or five flights were made with some aileron trouble, but otherwise there were no issues. The extending hull worked well, although its extension and retraction in flight were not entirely smooth. Once extended, the hull offered an open platform from which to conduct mooring operations, and the aircraft was well-behaved on the water.


The B-20 providing a good view of the wing float design. Note the Short Sunderland and what appears to be a Short Empire framed nicely between the B-20’s hull and fuselage.

On 7 April 1940, Bailey was joined by Blackburn test engineer Fred Weeks, Blackburn aircraft riggers Sam McMillan and Duncan Roberts, and Rolls Royce flight engineer Ivan Waller. The task of the day was to complete high-speed tests in the B-20. During the fight, the aircraft reached an unofficial speed of 345 mph (555 km/h). On the next run, an aileron experienced flutter and failed, sending the B-20 out of control. The aircraft crashed in the Firth of Clyde off Garroch Head. Weeks and Waller were able to successful bail out and were picked up by the HMS Transylvania, a merchant ship converted to an auxiliary cruiser. Bailey also bailed out but was too low for his parachute to fully open. His body was recovered from the sea. However, the bodies of McMillan and Roberts were never found.

Even though its flight career was very short, the B-20 had given every indication that its hull design significantly improved performance. Based on the B-20 design, the Blackburn B-40 and B-44 were proposed. The B-40 was in response to Specification R.13/40. The aircraft was a twin-engine flying boat transport powered by two Bristol Centaurus radial engines and intended as a possible replacement for the Short Sunderland. The B-40 was larger and heavier than the B-20 and had twice the range. Two B-40 prototypes were ordered on 9 September 1941, but the aircraft’s poor single engine performance and other priorities led to its cancellation on 6 January 1942. The B-44 was a single-engine floatplane fighter designed to Specification N.2/43. The aircraft was armed with four 20 mm cannons and powered by a Napier Sabre H-24 engine turning contra-rotating propellers. Two B-44 prototypes were ordered in October 1942, but the project was cancelled shortly after a mockup was built. An analysis of the design indicated that the B-44 would be difficult to handle on the water.

In August 1998, one of the B-20’s Vulture engines was recovered after becoming tangled in the nets of a trawler. The B-20’s crash site was subsequently classified as a war grave. What remains of the Vulture engine is now on display at the Dumfries and Galloway Aviation Museum in Scotland.


Rear view of the B-20 helps visualize the defense the four .303 machine guns in the turret would have provided.

Aircraft of the Fighting Powers Volume 6 by Owen Theyford (1945/1980)
Blackburn Aircraft since 1909 by A. J. Jackson (1989)
British Experimental Combat Aircraft of World War II by Tony Buttler (2012)
British Prototype Aircraft by Ray Sturtivant (1990)
Jane’s All the World’s Aircraft 1945/46 By Leonard Bridgman (1946)
– “Improvements in and relating to Seaplanes” GB patent 433,925 by John Douglas Rennie (applied 13 February 1935).


Rolls-Royce Vulture X-24 Aircraft Engine

By William Pearce

In the mid-1930s, the British Air Ministry predicted the need for 2,000 hp (1,491 kW) engines to power new aircraft expected to enter service in the early 1940s. Rolls-Royce responded to this anticipated need with a 24-cylinder, liquid-cooled aircraft engine of an X-configuration, known as the Vulture. Initially, the Vulture design was based on utilizing four six-cylinder banks of the V-12 Kestrel engine. As the Vulture design developed, many changes were incorporated that shifted away from the Kestrel, and the Vulture ultimately had no parts in common with the Kestrel.


The Rolls-Royce Vulture X-24 was an attempt to create a 2,000 hp (1,491 kW) aircraft engine. A number of difficulties arose that complicated the engine’s development, leaving history to record the Vulture as a failure.

The Rolls-Royce Vulture was designed by Albert George Elliott, and its development was started in September 1935. The engine’s two-piece aluminum crankcase was split horizontally at the crankshaft’s centerline. Each crankcase half had two surfaces for mounting cylinder banks with an included angle of 90 degrees. The two crankcase halves were attached by 28 cross bolts and a series of smaller bolts along the parting flange. The cross bolts were tightened against the cylinder bank mounting surface and staggered to allow clearance for the cross bolts from the adjoining bank. Each side of the crankcase had two engine mounting pads. The single, hollow, six-throw crankshaft was secured between the two crankcase halves and supported by seven main bearings.

Each of the four monobloc cylinder banks was made of aluminum with an integral cylinder head. Steel liners were inserted for the six cylinders of each bank. Each cylinder bank was secured to the crankcase by 26 long studs that passed through to the top of the bank. The cylinder spacing was wider than that of the Kestrel to accommodate wider connecting rod bearings and to enable a future increase in bore diameter. Each cylinder had two intake valves and two sodium-cooled exhaust valves. The valves for each cylinder bank were actuated by a single overhead camshaft that was driven via bevel gears and by a vertical shaft from the gear reduction at the front of the engine.


Rear view of the Vulture shows the coolant pumps flanking the supercharger. All of the cylinder banks were spaced at 90 degrees.

The Vulture’s connecting rod consisted of a master rod extending at a 45-degree angle from a square big end, with three articulating rods extending from the other corners of the big end. Initially, the connecting rod’s big end cap had a hinged joined on one side and was secured to the crankshaft with two bolts on the opposite side. Although different versions were tried, this configuration proved problematic and was replaced by omitting the hinge and using four bolts (two long bolts on one side and two short bolts on the other) to secure the cap to the connecting rod around the crankpin. The mating surfaces of the big end had corresponding serrations to ensure a secure fit. Incidentally, this was the same type of big end employed on the connecting rods of the Rolls-Royce Exe, the development of which had slightly proceeded that of the Vulture. When viewed from the rear of the engine, the upper right cylinder bank was designated as the ‘A’ bank, and the designations proceeded counterclockwise. The master rod served the ‘D’ bank, which was the lower right.

At the front of the engine, a spur gear on the crankshaft engaged four compound layshafts, the opposite side of which drove the propeller shaft. This compound gear reduction resulted in the propeller turning .350 times crankshaft speed and being mounted on the engine’s centerline. Viewed from the rear, the crankshaft and propeller both rotated counterclockwise. A bevel gear on the back side of each compound layshaft drove the vertical shaft for the respective cylinder bank’s camshaft. A spur gear on the rear of the crankshaft supplied power to various accessory drives and to the two-speed, single stage supercharger. The supercharger’s impeller turned at 5.464 and 7.286 times crankshaft speed in low and high gears. A coolant pump was mounted by each side of the supercharger. The engine’s compression ratio was 6.0 to 1.


The mounting of the Vulture in the Manchester was similar to other installations—two pads on each side of the engine attached it to a tubular steel frame. The mounting pads were in the Vee formed by the upper and lower banks.

Air was drawn through the two-barrel SU carburetor and fed into the supercharger. The air/fuel mixture exited the supercharger via two outlets that respectively fed an upper or lower manifold. Each manifold was respectively positioned between the upper or lower cylinder banks. The manifold had three outlets on each side. The three outlets were connected to another manifold that was attached directly to and extended the length of the cylinder bank. The incoming charge for each cylinder was ignited by two spark plugs, one positioned in the intake side of the cylinder and the other on the exhaust side. This meant that access to the top, bottom, left, and right sides of the engine was needed to replace the spark plugs. The task was further complicated by the intake manifolds on the top and bottom and the exhaust manifolds and engine mounts on the left and right sides of the engine. Needless to say, the 24-cylinder Vulture was not a favorite with ground crews. The spark plugs were originally fired by a battery-powered coil ignition system, which was replaced by two magnetos and distributors driven from the gear reduction. The exhaust ports were on the left and right sides of the engine. A mixture of 70 percent water and 30 percent ethylene glycol was used to cool the engine.

The Vulture had a 5.00 in (127 mm) bore and a 5.50 in (140 mm) stroke. The engine’s total displacement was 2,591 cu in (42.47 L), and it had a takeoff rating of 1,800 hp (1,342 kW) at 3,200 rpm with 6 psi (.41 bar) of boost. At 3,000 rpm with 6 psi (.41 bar) of boost, the Vulture had a maximum rating of 1,845 hp (1,312 kW) at 5,000 ft (1,524 m) and 1,710 hp (1,223 kW) at 15,000 ft (4,572 m). At 2,850 rpm with 6 psi (.41 bar) of boost, the Vulture had an international rating of 1,780 hp (1,327 kW) at 4,000 ft (1,219 m) and 1,660 hp (1,237 kW) at 13,500 ft (4,115 m) and a maximum climb rating of 1,760 hp (1,312 kW) at 5,000 ft (1,524 m) and 1,640 hp (1,223 kW) at 15,000 ft (4,572 m). At 2,600 rpm with 5 psi (.34 bar) of boost, the engine had a maximum cruise rating of 1,540 hp (1,148 kW) in low gear and 1,460 hp (1,089 kW) in high gear. The Vulture was 87.2 in long, 35.8 in wide, and 42.3 in tall. The engine weighed 2,450 lb.


Installation Diagram for the Vulture II and IV engines. The main difference between the two variants was that the Vulture II drive an auxiliary gearbox via a right-angle drive mounted vertically behind the ‘A’ cylinder bank.

Preliminary testing of the Vulture engine included building an X-4 engine, and running this engine revealed the issues with the early two-bolt connecting rod design. Stresses on the bolts caused their failure, and the four-bolt connecting rod was developed. Another issue was insufficient lubrication of main bearings. The first complete 24-cylinder Vulture was run on 1 September 1937, the second in January 1938, and the third in May 1938. By November 1938, Vulture test engines had accumulated 1,150 hours of operation. Issues with the coil ignition system came to light while testing the complete engines, resulting in a switch to magnetos. In 1938, the Vulture produced 1,750 hp (1,305 kW) while on test.

Vulture engine development spanned from Mark I to Mark V. The Vulture I entered limited production and were mainly developmental engines. Refinements were incorporated into the Vulture II, which was intended for use in multi-engine aircraft. The Vulture II had a detached, five-drive, auxiliary gearbox that was driven from the engine by a flexible shaft. The flexible shaft connected to a right-angle drive mounted vertically behind the A (upper right when viewed from the rear) cylinder bank. The Vulture II was first run in September 1938. No descriptive information has been found regarding the Vulture III. The Vulture IV was nearly identical to the Vulture II but intended for single-engine aircraft. The Vulture IV had an engine-mounted three-drive auxiliary gearbox and different accessories.

The Air Ministry authorized engine production on 23 March 1939, anticipating a need for 1,560 Vultures, and true engine production started in January 1940. Issues with the Vulture necessitated a drop in its maximum speed to 3,000 rpm, but boost was increased to 9 psi (.62 bar) to maintain the engine’s takeoff rating of 1,800 hp (1,342 kW).


The Hawker Henley testbed (K5115) was the first aircraft to fly with a Vulture engine. The large scoop under the aircraft accommodated the coolant radiator and oil cooler.

Development of the Vulture V followed that of the Vulture IV and featured additional supercharging, with an impeller that turned at 6.018 and 8.111 times crankshaft speed in low and high gears. For takeoff, the engine had a rating of 1,995 hp (1,488 kW) at 3,000 rpm with 9 psi (.62 bar) of boost. Military power at the same rpm and boost was 2,035 hp (1,517 kW) at 5,000 ft (1,524 m) and 1,840 hp (1,372 kW) at 20,250 ft (6,172 m). At 2,650 rpm and with 7 psi (.48 bar) of boost, the Vulture V had a cruise rating of 1,650 hp (1,230 kW) at 3,500 ft (1,067 m) and 1,525 hp (1,137 kW) at 17,500 ft (5,334 m).

The Hawker Henley light-bomber prototype (K5115) was converted with a Vulture engine to serve as a testbed. A ventral scoop was added to the aircraft’s bomb bay that housed the radiator and oil cooler. The cowling was modified for the Vulture with its four rows of exhaust stacks, and a scoop for the carburetor was added just forward of the cockpit. The Vulture-powered Henley was first flown on 17 April 1939, and the Vulture passed a type-test with an 1,800 hp (1,342 kW) takeoff rating in August 1939. A second Henley (L3302) was converted to a Vulture testbed in 1940. The Vulture engine was intended for a number of aircraft under development, four of which were flown.

The Avro 679 Manchester medium bomber used two Vulture I engines and was ordered in mid-1937, before the aircraft’s design was finalized. Eventually, orders for some 700 examples were placed. The Manchester prototype (L7246) made its first flight on 24 (some sources state 25) July 1939. When Vulture II engines became available, they were used in the Manchester, and the type entered service in November 1940.


A production Avro Manchester I (L7288) running up one of its Vulture engines. A shroud covered each exhaust manifold to help cool the exhaust so that the discharge did not heat the wing. The two-engine bomber was quite a handful when one of the Vultures failed, and a number of aircraft and their crew were lost due to engine issues.

The Vickers Type 284 Warwick medium bomber was originally ordered in October 1935, but a change for the first prototype (K8178) to be powered by two Vulture I engines rather than the Bristol Hercules occurred in January 1937. K8178 made its first flight on 13 August 1939, and Vulture II engines were installed in November 1940.

Two prototypes of the Hawker Tornado fighter were ordered in December 1938. The first prototype (P5219) was powered by a Vulture II engine and made its first flight on 6 October 1939. Production contracts were issued in November 1939, with the Vulture V selected as the intended powerplant. The second prototype (P5224) used a Vulture V engine and made its first flight on 7 December 1940.

The Blackburn B-20 flying boat (V8914) was ordered in 1936 and made its first flight on 26 March 1940. The experimental aircraft was powered by two Vulture II engines and featured an extendable hull and retractable wing floats. The aircraft was lost on 7 April 1940 after aileron flutter was experienced during a high-speed test flight.

In March 1941 the improved Vulture II was type tested with a takeoff rating of 2,010 hp (1,499 kW) at 3,000 rpm with 9 psi (.62 bar) of boost. At the same rpm and boost, the engine’s military power rating was 1,845 hp (1,376 kW) at 5,000 ft (1,524 m) and 1,710 hp (1,275 kW) at 15,000 ft (4,572 m). At 2,850 rpm and with 6 psi (.41 bar) of boost, the Vulture II had a normal rating of 1,780 hp (1,327 kW) at 4,000 ft (1,219 m) and 1,660 hp (1,238 kW) at 13,500 ft (4,115 m). However, the Vultures in service were taking a turn for the worse.


The Vickers Warwick prototype (K8178) was the only example of the type fitted with Vulture engines.

The Manchester’s rush into production and subsequent rush into service meant that a number of deficiencies with the airframe and serious issues with the Vulture engine were not discovered until it was too late. The engines proved to be unreliable and prone to failure. As a result, all Manchesters were grounded numerous times. Manchesters with a failed Vulture were often unable to maintain height on one engine, and about 75 percent of the time, the aircraft crashed before an emergency landing could be executed at a suitable location. A contributing factor to the Vulture’s issues was that the Battle of Britain forced Rolls-Royce to focus on the Merlin engine, which delayed Vulture development.

Some engine failures were attributed to cooling issues. One of the coolant pumps would cavitate, halting the flow of coolant to that side of the engine. The affected cylinder banks would subsequently overheat, and the engine would seize; an engine fire resulted on a number of occasions. To fix the issue, a balance tube was installed which connected the inlet of the pumps to equalize pressure between the two. The crankshaft main bearings were also prone to failure. Numerous issues resulted in the failed bearings: over-heating due to the already mentioned coolant issues, poor lubrication, ineffective bearing material, and a slight misalignment of the two crankcase halves. The Vulture’s lubrication system was reworked to prevent aeration, and a new LA4-type bearing material was adopted. The misalignment issue was solved by including locating dowels through which cross bolts passed. A dowel was positioned on each side of the main bearings between the crankcase halves. The most vexing issue was the random failure of bolts securing the connecting rod cap. This typically created cascading failures that resulted in the sudden and catastrophic loss of the engine. The issue was traced to brittle bolts, and new measures were implemented to ensure they were tightened to the new, lower toque standard to prevent excessive strain and stretching. The connecting rod was also modified slightly. In addition, the Vulture’s maximum speed was reduced again to 2,850 rpm to minimize the risk of failure. The last of these changes were detailed by Rolls-Royce under Vulture Modification No. 44. By August 1941, engines with these changes were installed in some Manchesters, and the Vulture began to reliably make it 120-hours between major inspections. In addition, Manchesters were now able to make it to an airfield on a single engine more often than not. Eventually, the time between inspections was raised to 180 hours, and the engine’s maximum takeoff speed was increased to 3,000 rpm. However, another issue with Vulture engines came to light in late 1941. Exhaust manifolds were cracking and failing, resulting in a jet of hot gasses flowing against the engine, cowling, or other internal components. The failed manifolds caused engine failures or airframe damage or both. A new manifold was designed, and all of the older units were replaced in December 1941.


The second Hawker Tornado prototype (P5224) with its Vulture V engine. The Vulture was relatively well-behaved during testing of the Tornado, which was very similar to the Sabre-powered Typhoon.

Even though the main problems with the Vulture were mostly resolved, engines continued to encounter various random issues, including failures, overheating, lack of power, and excessive fuel consumption. Overall, there was little faith in the Vulture engine. The Manchester itself continued to have issues, and production was halted in November 1941. Of the 202 aircraft built, approximately 33 (16.3 percent) crashed or were struck off charge due to engine failures or fires. This number does not include aircraft that were repaired after an engine failure, nor does it include the six or so aircraft lost due to propeller issues (some of which precipitated an engine failure). Tragically, also not included are the numerous Manchesters that crashed after one engine was knocked out from battle damaged only to have the “good’ engine fail after it was overstressed trying to keep the underpowered aircraft aloft. The Manchester was withdrawn from operations in mid-1942 and served in various secondary roles through 1943, when all examples were scrapped.

The Manchester was redesign to use four Merlin engines and became the Lancaster (originally Manchester III), one of the greatest World War II bombers. Production Warwicks were fitted with either Pratt & Whitney R-2800 or Bristol Centaurus engines. While around 1,760 Tornados were ordered at one point, only three Vulture-powered examples were built, and the Napier Sabre-powered Typhoon took over in place of the Tornado.


The Blackburn B-20 was an experimental aircraft which tested a retractable hull to improve the aerodynamics of flying boats. With a top speed of over 300 mph (483 km/h), the B-20 showed potential, but it was lost during an early test flight.

By September 1942, a Vulture engine with a contra-rotating gear reduction was installed in the sole-production Tornado (R7936). The engine and aircraft were used to test Rotol and de Havilland contra-rotating propellers. Some sources report that one Vulture engine was built with its bore increased by .4 in (10 mm) to 5.4 in (137 mm), the same as the Merlin. This increased the engine’s displacement by 432 cu in (7.08 L) to 3,023 cu in (49.54 L). However, no further information on these engines has been found.

From as early as August 1939, Rolls-Royce wanted to cancel Vulture development so that the company could focus its resources on other engines, mainly the Merlin and Griffon. However, the Air Ministry felt that it needed the Vulture engine, so development continued. Vulture development was halted in October 1941, and production ended in March 1942, with 538 engines built. The Vulture was the only X-24 aircraft engine to enter production.

Rolls-Royce had designed a number of changes to be incorporated into the Vulture engine if production had continued. The connecting rod was redesigned with the three articulated rods attached to the bearing cap, and the cap was secured to the master connecting rod via four long bolts made from improved material. The cylinder banks were redesigned to incorporate a detachable cylinder head. A lighter planetary gear reduction for the propeller would have replaced the four compound layshafts. The two-speed supercharger was redesigned to include two-stage supercharging to improve the engine’s performance at higher altitudes.


The sole-production Tornado (R7936) seen in 1943 with a Vulture engine turning de Havilland contra-rotating propellers. The aircraft was also used to test Rotol contra-rotating propellers.

Only a small number of Vulture engines survive, and most were recovered from Manchester wrecks. Two recovered Manchester engines (engine 1 and engine 2) are held by the Luchtoorlogmuseum (Aerial Warfare Museum) Fort Veldhuis in Heemskerk, near Amsterdam in the Netherlands. A Vulture engine from the B-20, consisting mainly of the crankshaft, connecting rods, and cylinder barrels, is displayed in the Dumfries and Galloway Aviation Museum in Scotland. Three engines are part of the Royal Air Force Museum’s collection, and all are believed to have been recovered from Manchester wrecks. One of these engines is on loan to the Rolls-Royce Heritage Trust and is displayed at the Hucknall Flight Test Museum.

Note: Many sources state that the Vulture I used an updraft carburetor, and the Vulture II and later variants used a downdraft carburetor. However, the only aircraft that appears to have had an updraft carburetor was the first Tornado prototype, which reportedly flew with a Vulture II. Early Manchesters that reportedly flew with Vulture Is appear to have downdraft carburetors. In my opinion, the most logical explanation, although still questionable, is that all Vultures had downdraft carburetors and that the early installation in the Tornado prototype that incorporated the carburetor inlet with the belly scoop was an attempt to maximize the pilot’s forward vision and minimize the number of external protuberances.


The shattered remains of a Vulture II engine from Manchester R5779 shot down on 9 March 1942 near Oranje, Netherlands. The engine is actually on its side, and the view is of the induction manifold on the bottom of the engine. Note the severe deformation of the cylinder bank. The engine is displayed at the Luchtoorlogmuseum (Aerial Warfare Museum) Fort Veldhuis in Heemskerk. (Fort Veldhuis Airwarmuseum image)

Major Piston Engines of World War II by Victor Bingham (1998)
The Avro Manchester: The Legend Behind the Lancaster by Robert Kirby (2015)
Rolls-Royce Piston Aero Engines – a designer remembers RRHT 16 by A. A. Rubbra (1990)
Rolls-Royce Vulture II and IV Description: Air Publication 1801A Volume I, via the Aircraft Engine Historical Society (December 1940)
Rolls-Royce Aero Engines by Bill Gunston (1989)
Aircraft Engines of the World 1945 by Paul H. Wilkinson (1945)
Hawker Aircraft since 1920 by Francis K. Mason (1991)
Avro Aircraft since 1908 by A. J. Jackson (1990)
Vickers Aircraft since 1908 by C. F. Andrews and E. B. Morgan (1988)
Blackburn Aircraft since 1909 by A. J. Jackson (1989)


Hawker Tornado Fighter

By William Pearce

In early 1937, Hawker Aircraft Limited and the company’s chief designer, Sydney Camm, began to consider the next generation of fighter aircraft for the Royal Air Force. The British Air Ministry was also considering the future of fighter airframes as well as the incorporation of powerful, new engines under development—specifically the Napier Sabre H-24, the Rolls-Royce Vulture X-24, and the Bristol Centaurus 18-cylinder radial.


The first Hawker Tornado prototype P5219 in its original form with the belly radiator. The Vulture’s two rows of exhaust stacks are evident. The aircraft’s resemblance to the Hurricane is apparent.

In July 1937, Hawker proposed two Camm-designed aircraft—the N-type and the R-type, named for their respective Napier and Rolls-Royce powerplants. The Air Ministry told Hawker to wait until an official request was issued, which came in March 1938 in the form of Specification F.18/37 seeking a fighter capable of 400 mph (644 km/h) at 20,000 ft (6,096 m). Hawker was notified in August 1938 that they had won the design contest for Specification F.18/37, and two prototypes of each N-type and R-type were ordered. However, an official contract was not issued until December 1938. The N-type went on to become the Sabre-powered Hawker Typhoon, while the R-type became the Vulture-powered Hawker Tornado. The two Tornado prototypes were assigned serial numbers P5219 and P5224.

The Tornado was a single-engine fighter of all-metal construction with a conventional taildragger layout. The aircraft somewhat resembled an enlarged Hawker Hurricane. From the engine to just behind the cockpit, the fuselage consisted of a tubular frame covered with aluminum panels. The rear fuselage and tail were of monocoque construction. The pilot sat in an enclosed cockpit that was accessible via side entry doors. A fairing extended behind the cockpit and limited the pilot’s rearward vision.

The Tornado’s wing was mounted to the tubular frame of the center fuselage. Because of the Vulture’s installation, the wing was mounted to the fuselage about 3 in (76 mm) lower than on the Typhoon. The wing had two main spars and consisted of an inner and outer section. The inner section had a 1.0-degree anhedral and housed the inward-retracting main landing gear. The landing gear had a wide track of 13 ft 8 in (4.17 m). A 48 US gal (40 Imp gal / 182 L) fuel tank was located in each wing between the main gear leg well and the rear spar, and a 42 US gal (35 Imp gal / 159 L) fuel tank was located in the leading edge of each inner wing section. The Tornado’s total fuel capacity was 180 US gal (150 Imp gal / 682 L). Each outer wing section had a 5.5-degree dihedral and housed six Browning .303 machine guns with 500 rpg. The thick wing was originally designed for the possible installation of six 20 mm cannons, but this configuration was never tried. Each wing had a two-section, hydraulically actuated split flap and featured a large aileron. Except for the fabric-covered rudder, all control surfaces were covered with metal.


Another shot of the newly completed P5219 displays the aircraft’s original short tail. Note the opaque fairing behind the cockpit that blocked the pilot’s vision.

The Tornado’s Rolls-Royce Vulture II engine had 24 cylinders arranged in an X configuration. The engine was mounted to the forward part of the tubular fuselage frame and produced 1,760 hp (1,312 kW). Two rows of exhaust stacks protruded from each side of the engine’s cowling. A belly scoop between the main gear wells housed the engine’s coolant radiator and oil cooler. A door in the aft section of the scoop regulated temperatures. Two intakes between the belly scoop and the underside of the fuselage fed air to the engine’s carburetor. The engine turned a three-blade, constant-speed Rotol propeller that was 14 ft (4.27 m) in diameter.

The Hawker Tornado had a wingspan of 41 ft 11 in (12.78 m), a length of 32 ft 10 in (10.01 m), and a height of 14 ft 8 in (4.47 m). The aircraft had a top speed of 398 mph (641 km/h) at 23,000 ft (7,010 m) and stalling speeds of 82 mph (132 km/h) clean and 61 mph (98 km/h) with flaps and gear extended. The Tornado had an empty weight of 8,377 lb (3,800 kg) and a loaded weight of 10,668 lb (4,839 kg). The aircraft’s initial rate of climb was around 3,500 fpm (17.8 m/s), and its ceiling was 34,900 ft (10,638 m).


The second Tornado prototype P5224 with the chin radiator and windows behind the pilot to help improve vision. The aircraft now resembles a Typhoon, with which it shared many components.

The Tornado prototype P5219 was built at the experimental shop in Hawker’s Canbury Park Road facility in Kingston, but it was sent to Hawker’s new facility in Langley for final assembly in July 1939. The Vulture II engine was delivered in September 1939, and ground tests were started later that month. Piloted by Philip Lucas, P5219 made its first flight on 6 October 1939. During the preliminary flight tests in October and November, the aircraft achieved a speed of 370 mph (595 km/h) at 15,000 ft (4,572 m). However, the Tornado’s tail was lacking in surface area, and the rudder did not have sufficient authority to hold a straight course during takeoff and proved ineffective at speeds under 150 mph (241 km/h). Engine cooling was a constant issue, especially during ground operations. While in flight at higher speeds, turbulence from the wings disrupted airflow into the radiator, which impaired engine cooling. A new radiator was designed that would relocate the cooling system from its ventral position to a chin location under the engine. Metal was also found in the engine oil, indicating a possible issue with the Vulture’s bearings.

While the Vulture engine was undergoing maintenance, the Tornado airframe was modified with the new chin radiator and oil cooler, which shifted the aircraft’s appearance away from that of the Hurricane. In November 1939, an order for Hawker to produce 1,000 Tornados was placed. The contract was later changed to Typhoons, but then amended for 800 Typhoons and 200 Tornados, with the Tornados to be built by Avro due to Hawker’s production commitments of other aircraft, namely the Hurricane. Other Tornado production contracts were later issued, including 200 aircraft to be built by Cuncliffe-Owen and another 760 aircraft to be built by Avro. The revised Tornado took to the air on 6 December 1939, but Lucas reported that the aircraft was even more directionally unstable with the chin radiator. Performance tests in March 1940 indicated a top speed of 384 mph (618 km/h) at 20,500 ft (6,248 m), but the engine was not making full power. Various modifications were made to improve the aircraft’s stability. The exit of the radiator was extended 3 in (76 mm); the vertical stabilizer and rudder were enlarged in May 1940; and tailwheel doors were added in June 1940.


P5224 in flight displaying the aircraft’s aggressive appearance and enlarged tail. Note the carburetor intake atop the engine cowling.

With stability improved, P5219 was sent to Rolls-Royce’s flight-testing facility at Hucknall to improve the engine’s performance. The aircraft was returned to Langley in mid-July 1940 with a new engine and a new Rotol propeller that was 13 ft 2.5 in (4.02 m) in diameter. Performance flight testing continued, and on 27 July, the Tornado climbed to 20,000 ft (6,096 m) in 6 minutes and 36 seconds and achieved a speed of 396.5 mph (638.1 km/h) at 20,800 ft (6,340 m). On 31 July, the Vulture engine failed in flight, and the aircraft was damaged in the subsequent forced landing.

While P5219 was being repaired, the second Tornado prototype, P5224, was flown on 7 December 1940. Construction of the second prototype was delayed by other priority war work. P5224 was built from the start with the chin radiator and an enlarged tail. The aircraft also had the carburetor intake atop the engine cowling, inner gear doors to completely enclose the main gear, and side windows behind the cockpit to improve the pilot’s vision (which was still restricted). However, engine cooling was still an issue, as were excessive vibrations with the Vulture engine.

The repaired P5219 returned to active flight testing with a 1,980 hp (1,476 kW) Vulture V engine installed by March 1941, but the future of the Vulture engine was in doubt. P5224 suffered an engine failure on 21 March 1941, and its Vulture II was subsequently replaced by a Vulture V. P5224 first flew with the Vulture V on 11 June 1941. Around June 1941, Avro was instructed to halt work on producing the Tornado fighter, and the Tornado contracts were cancelled. The Vulture engine was stalled by Rolls-Royce so they could focus on the Merlin, and the Vulture was officially cancelled in October 1941. The Sabre-powered Typhoon fighter would be produced and take over resources previously allocated to the Tornado.


The first and only production Tornado, R7936, was used as a propeller testbed after its initial flight testing. The aircraft is seen here with Rotol contra-rotating propellers, which had a smaller diameter than the standard, single-rotation propellers used on the Tornado and Typhoon. Note that the aircraft did not have the windows behind the pilot like the second prototype.

P5219 continued flight testing with Hawker until at least April 1943, and the aircraft was scrapped in August 1943. P5224 was tested by the Aeroplane & Armament Experimental Establishment at Boscombe Down starting in October 1941. The aircraft was then delivered to the Royal Aircraft Establishment at Farnborough in December 1941. P5224 was scrapped in late 1944.

After the Tornado contracts were cancelled, construction of the first production Tornado, serial number R7936, was allowed to continue as well as components for two other examples that were nearing completion. R7936 was powered by a Vulture V engine and made its first flight on 29 August 1941, piloted by Lucas. In general, pilots that flew R7936 were impressed by its handling and performance. The aircraft recorded a speed of 402 mph (647 km) at 21,800 ft (6,645 m) and climbed to 20,000 ft (6,096 m) in 6 minutes and 54 seconds. With the Tornado program dead, R7936 was used as a testbed for Rotol and de Havilland contra-rotating propellers. Little information has been found on these tests, but the aircraft was delivered to Rolls-Royce in March 1942 for the installation of a Vulture engine with a contra-rotating gear reduction. The six-blade Rotol contra-rotating propeller was 11 ft (3.35 m) in diameter, and the aircraft was flown with the unit in September 1942. The de Havilland contra-rotating propellers were installed as early as December 1942. It appears R7936 continued with propeller tests until April 1944, when it was scrapped.


Typhoon HG641 was built to serve as a testbed for the Bristol Centaurus engine. Seen here with its original three-blade propeller, cowling, and single large exhaust manifold. The silhouette of the oil cooler can just be seen between the main landing gear.

From the first discussion with the Air Ministry before Specification F.18/37 was issued, Camm and Hawker had given some consideration to a Centaurus-powered Tornado, but little progress was undertaken beyond the preliminary design. With the Vulture and Sabre engines running into development issues by late 1940, more-serious consideration was given to installing a 2,210 hp (1,678 kW) Centaurus engine in a Tornado airframe. In September 1940, Hawker was given permission to proceed with the Centaurus-powered Tornado prototype, but the official contract was not issued until February 1941. Some work was also done on using a Wright R-3350 engine, but this design was dropped in June 1941.

The Centaurus Tornado was assigned serial number HG641. The aircraft was built by Hawker at Langley using components from uncompleted Tornado production airframes and a new center fuselage. The Centaurus engine turned a 12 ft 9 in (3.89 m) diameter, three-blade, Rotol propeller and was covered by a conventional cowling. Exhaust from the engine was expelled via a single manifold protruding from the cowling under the left side of the engine. An oil cooler was mounted between the wells for the main landing gear. The air-cooled radial reduced the aircraft’s weight by about 350 lb (159 kg). Lucas took the Centaurus Tornado up for its first flight on 23 October 1941.


HG641 with the new four-blade propeller and revised cowling. The oil cooler was located in the large duct under the engine.

Initial flight tests of HG641 indicated that airflow through the oil cooler was not efficient and led to the engine running near its upper temperature limit. Even so, a speed of 378 mph (608 km/h) was recorded at 20,000 ft (6,096 m). The oil cooler was modified, and testing continued until December 1941. At that time, the aircraft was modified to improve the installation of the engine package, including exhaust and oil cooler. The cowling was revised, and a new oil cooler duct was faired into the lower cowling. Two exhaust stacks were incorporated into the left and right sides of the fairing. A four-blade propeller, also 12 ft 9 in (3.89 m) diameter, was installed, and the modified Centaurus Tornado took its first flight on 23 December 1942, piloted by Lucas. Cooling was improved, and the aircraft achieved 403 mph (649 km/h) at 22,000 ft (6,706 m) and had a ceiling of 32,800 ft (9,997 m). In February 1943, the aircraft was transferred to Bristol’s facility in Filton, where a speed of 412 mph (663 km/h) at 18,000 ft (5,486 m) was reportedly recorded. The Centaurus Tornado continued engine testing until August 1944, when the aircraft was scrapped.

The testing of Tornado aircraft provided information for developing the Typhoon fighter, contra-rotating propellers, and the Bristol Centaurus engine, which was particularly helpful when applied to the Centaurus-powered Hawker Tempest II fighter. Although the Tornado has been mostly forgotten, both the Typhoon and the Tempest served with distinction during World War II.


Side view of HG641 with the new cowling. The aircraft did not have the windows behind the pilot and used hinged doors on the landing gear to completely conceal the main wheels. This was also tried on the prototypes before switching to a separate inner door.

The Hawker Typhoon and Tempest by Francis K. Mason (1988)
Hawker Typhoon, Tempest and Sea Fury by Kev Darling (2003)
British Experimental Combat Aircraft of World War II by Tony Buttler (2012)
Fighters Volume Two by William Green (1964)
Hawker Typhoon and Tempest: A Formidable Pair by Philip Birtles (2018)
Aircraft of the Fighting Powers Volume V by H. J. Cooper and O. G. Thetford (1944)
The Secret Years: Flight Testing at Boscombe Down 1939 – 1945 by Tim Mason (1998)
Hawker Aircraft since 1920 by Francis K. Mason (1991)


SNCM 130 and 137 24-Cylinder Aircraft Engines

By William Pearce

The history of the SNCM 130 and 137 aircraft engines detailed here has been derived from the research of Sébastien Faurès, which he consolidated into his amazing book, Lorraine-Dietrich.

In mid-1935 the French Service technique de l’aéronautique (STAé / Technical Service of Aeronautics) sought the design of a relatively compact aircraft engine that would produce 600 hp (447 kW) at 13,123 ft (4,000 m), displace around 732 cu in (12 L), and weigh 661 lb (300 kg). The air-cooled engine was intended to power the next generation of light fighter aircraft. Albert Lory was put in charge of the new engine design. Lory had previously worked for Delage automobiles and designed the company’s 15S8 Grand Prix racer that won the Manufacturers’ Championship in 1927. Lory also designed the Delage 12 GVis and 12 CDirs inverted V-12 aircraft engines. Working with the STAé, Lory quickly focused on a 24-cylinder engine of either an X, H, or coupled V-12 configuration.


The SNCM 130 / 137 displayed at the Argenteuil factory in mid-1939. This engine was either a mockup or incomplete, but it was outfitted with the envisioned cowling to make it a complete power package. The radiator would be housed between the ducted spinner and engine. Note the induction scoop positioned above the engine and how the valve train covers form part of the cowling. The holes in the cowling were individual exhaust ports. (image Sébastien Faurès/Lorraine-Dietrich)

Throughout 1936, the STAé engine concept changed quite radically, as did Lory’s design. By late 1937, the liquid-cooled engine was made up of four V-6 engine sections joined by a common crankcase and driving a common crankshaft. Each section would produce 600 hp (447 kW), creating a complete engine capable of 2,400 hp (1,790 kW). Few established engine manufacturers were interested in taking on such an unconventional engine, especially one designed outside of their company. On 31 March 1937, France had nationalized the Société des moteurs et automobiles Lorraine (Lorraine Motor and Automobile Company) and created the state-run Société nationale de construction de moteurs (SNCM / National Society of Engine Construction) in its place, with Claude Bonnier as SNCM’s Managing Director and General Manager. In October 1937, the STAé tasked SNCM to develop the new engine.

The 2,400 hp (1,790 kW) engine design was seen as a little too ambitious, and another redesign occurred. The proposed liquid-cooled, 24-cylinder engine was now formed from three V-8 engine sections on a common crankcase. With six banks of four inline cylinders spaced radially around the crankcase, this engine configuration is often called an inline radial. In addition, the outer points of the six banks formed a hexagon, which qualifies the powerplant as part of the family of rare hexagonal engines. Other hexagonal engines include the Curtiss H-1640 Chieftain, the Wright H-2120, the Junkers Jumo 222, and the Dobrynin series of aircraft engines.

The SNCM engine had an ultimate goal of 1,800 hp (1,342 kW), but it would initially be configured to produce 1,600 hp (1,193 kW). Once this power was obtained, the cylinder’s bore would be increased to achieve an output of 1,800 hp (1,342 kW). The 1,800 hp (1,342 kW) engine was designated SNCM 130. The 1,600 hp (1,193 kW) prototype version, with a reduced bore, was designated SNCM 137 and would be built first. Due to the similarity between the engines and their rather confusing genesis, the SNCM 137 engine is often referred to as the SNCM 130.


Left, French patent 870,367 drawing showing the four Vee engine sections and the valve train for each cylinder bank pair. Note that the induction was illustrated under the camshaft, which was not the case on the engine as built. Right, French patent 870,359 drawings showing two views of the engine’s combustion chamber. Ports e1 and e2 opposite of the inclined valves were for the spark plugs. Port f was for the fuel injector.

The SNCM 137 had a cast aluminum crankcase made of two-pieces and split horizontally (more like diagonally). The two crankcase halves joined around the four-throw crankshaft, which was supported via five main bearings. A connecting rod consisting of one master rod and five articulating rods was mounted to each of the crankshaft’s throws. Six cylinder banks were mounted at 60-degree intervals around the crankcase. Each cylinder bank consisted of a four-cylinder cast aluminum block with forged steel liners and a detachable cast aluminum cylinder head. The cylinder banks were paired together, forming three groups of eight cylinders. Mounted between each cylinder bank pair was an overhead camshaft that was driven by the crankshaft via a series of gears at the back of the engine. In this configuration, one camshaft served two cylinder banks, and the engine had three camshafts. Each of the two upper camshafts drove a fuel distribution pump from their rear. The single lower camshaft drove an oil pump from its rear and a water coolant pump from its front.

Via rockers, the camshaft actuated the single intake valve and single exhaust valve for each cylinder. The valve train between each cylinder pair was concealed by a large, arched valve cover. The valve cover between the lower cylinder banks extended deeper, past the cylinder heads to act as an oil sump. The valves were inclined in the cylinder head, which had a wedge-shaped combustion chamber. On the side of each cylinder opposite from the valves were two spark plugs and a single fuel injector. The spark plugs were fired by two magnetos driven from the rear of the engine. The engine’s compression ratio was 7 to 1.

A centrifugal single-stage, single-speed supercharger made by Szydlowski-Planiol was located at the rear of the engine, and it provided 3.7 psi (.25 bar) of boost. Air entered the rear of the supercharger, was compressed, and was distributed to each cylinder bank via six separate runners. Each runner was connected to an intake manifold that was cast integral with the cylinder bank. The intake manifolds ran along the outer side of the cylinder bank pairs, although a patent drawing shows the intake located under the camshaft between the cylinder pairs. Exhaust was expelled from a port above each cylinder. An engine mount extended between the intake manifolds in the open Vee between the cylinder banks.


Two images of the SNCM 130 / 137 under construction at the former Lorraine factory. On the left, the valve train is apparent between each cylinder bank pair. Note the diagonal split on the end of the crankcase, which illustrates the crankcase’s two halves. On the right is the rear of the completed engine with its supercharger and intake runners. Note the arched valve train covers. (image Sébastien Faurès/Lorraine-Dietrich)

Mounted to the front of the engine was a propeller gear reduction. Different reductions were available between .333 and .667 crankshaft speed. The gear reduction housing was elongated, and an annular radiator was intended to encircle the housing. A shroud enclosed the radiator, and the propeller’s spinner incorporated a duct to deliver air to the radiator. Three blades in the duct acted as a cooling fan to aid the flow of air through the radiator while the aircraft was on the ground. After flowing through the radiator, the air exited via cowl flaps positioned just before the cylinder banks. As designed, the engine and radiator came fully cowled and represented a power package ready for installation. The gear train covers doubled as part of the engine cowling, with removable panels covering the rest of the engine.

The SNCM 137 had a 5.31 in (135 mm) bore and a 5.12 in (130 mm) stroke. The engine’s total displacement was 2,725 cu in (44.66 L). The SNCM 137 was 46 in (1.18 m) in diameter and was 75 in (1.90 m) long. While Lory continued to lead the project and oversee the engine’s construction, former Lorraine engineer Charles Salusse was also involved with the SNCM 137’s design. Salusse was awarded French patents 870,359 for the combustion chamber design and 870,367 for the Vee-type configurations. Both patents were submitted in November 1940, after Lory had left SNCM following the German occupation, and awarded on 12 December 1941. The second patent illustrates the valve train for the paired cylinder banks and shows the intake positioned under the camshaft. One of the example engines has four Vee-section pairs (eight banks), as considered in an earlier STAé design.

The SNCM 137 was constructed at the former Lorraine plant in Argenteuil, near Paris, France. A mockup, or a partially completed engine, was displayed at the Argenteuil plant in mid-1939. The prototype SNCM 137 was completed by early 1940, and tests were quickly started. By the end of March 1940, 2,000 hours had been completed on a valve test rig, 500 hours of single-cylinder testing had been completed, and the SNCM 137 prototype engine had run for 80 hours. The SNCM 137 had achieved 1,638 hp (1,221 kW) at 3,000 rpm at a simulated altitude of 9,843 ft (3,000 m). However, all further development was stopped with the German invasion on 10 May 1940. Most likely, only the single SNCM 137 prototype engine was built. The SNCM 137 engine was captured by German forces and taken to Germany. The final disposition of the engine has not been found, and no parts of the engine are known to exist.

The SNCM 130 would have been the main production version of the engine, but it was not built. The engine had the same architecture as the SNCM 137, but its bore was enlarged .20 in (5 mm) to 5.51 in (140 mm). This gave the SNCM 130 a total displacement of 2,931 cu in (48.03 L), and its anticipated output was 1,800 hp (1,342 kW) at 3,200 rpm. It was expected to maintain this power to 18,045 ft (5,500 m). Most likely, the small increase in displacement would not alter the engine’s diameter or length from that of the SNCM 137. The SNCM 130 had a forecasted weight of 2,094 lb (950 kg). Some sources refer to the SNCM 130 as the 24E Taurus, with ‘24’ representing the number of cylinders, and ‘E’ standing for étoile, meaning ‘star,’ which is often a foreign term used to describe a radial engine.


The SNCM 130 / 137 undergoing tests in early 1940. Note the exhaust stacks protruding directly above each cylinder bank and the robust, three-point engine mount. The water pump is visible, attached to the front of the lower camshaft. (image Sébastien Faurès/Lorraine-Dietrich)

Lorraine-Dietrich by Sébastien Faurès Fustel de Coulanges (2017)
– “La S.N.C.M. construit un moteur de 1600 cv,” Les Ailes (6 July 1939)
Les Moteurs a Pistons Aeronautiques Francais Tome I by Alfred Bodemer and Robert Laugier (1987)


Beardmore Inflexible / Rohrbach Ro VI Transport

By William Pearce

In 1914, Adolf Karl Rohrbach started working for Luftschiffbau Zeppelin GmbH as the company began to diversify from airship construction into building heavier-than-air aircraft. Claude Dornier was also employed by Zeppelin and was tasked with designing airframes out of metal, rather than wood. Rohrbach worked with Dornier on the design of several aircraft before Rohrbach was reassigned in 1917 to the Zeppelin plant in Staaken, near Berlin, Germany. At Staaken, Rohrbach worked with Alexander Baumann and was involved in the design of large R-Plane (Riesenflugzeuge, or giant aircraft) bombers.


The duralumin fuselage skin of the Beardmore Inflexible exhibited significant wrinkling. The staining above the wings was caused by engine exhaust and oil. Note the cable running from the wing to the lower fuselage.

Immediately following World War I, Rohrbach designed the Zeppelin-Staaken E.4/20. Like Dornier and Hugo Junkers, Rohrbach was pioneering the construction of aircraft using metal and stressed skin. The E.4/20 was an all-metal, four-engine airliner that made its first flight on 30 September 1920. However, the Treaty of Versailles prevented Germany’s possession of large aircraft, and the E.4/20 was scrapped in 1922. That same year, Rohrbach founded Rohrbach Metall-Flugzeugbau GmbH (Rohrbach Metal Aircraft, Ltd) in Berlin. To work around the Treaty of Versailles, aircraft designed at Rohrbach in Berlin were built at an assembly plant in Copenhagen, Denmark or licensed to be constructed elsewhere.

Following World War I, the British Air Ministry became increasingly interested in all-metal aircraft. In 1923, the Air Ministry issued specification No. 18/23 for a large, all-metal, experimental transport, and order No. 445337/23 was awarded to William Beardmore & Company, Ltd in Dalmuir, Scotland for the construction of such an aircraft. At the time, Beardmore was involved in building ships, locomotives, aircraft engines, and airships. In addition, the company had built aircraft under license during World War I. Beardmore was to collaborate with Rohrbach on the design of the transport aircraft. Beardmore outlined the aircraft’s basic specifications, Rohrbach supplied some of the detailed drawings, and Beardmore built the transport. The aircraft was known as the Beardmore AV 1 Inflexible, or the Rohrbach Ro VI, or the BeRo 1—a combination of Beardmore and Rohrbach. Most commonly, the aircraft is referred to as the Beardmore Inflexible. It was not until 1924 that Beardmore obtained the license from Rohrbach and construction of the aircraft began.


The Inflexible at Martlesham Heath. In the lower right of the image are the wheel trollies used to move the aircraft sideways into the hangar.

At Beardmore, the design of the Inflexible was initially laid out and modified by William. S. Shackleton. The project was later taken over by Rollo A. de Haga Haig. The aircraft’s design was tested in the Royal Aircraft Establishment’s wind tunnel at Farnborough. Except for its size, the aircraft possessed a fairly conventional layout. The monoplane trimotor had shoulder-mounted wings and taildragger landing gear. One engine was mounted in the nose, and an engine was mounted on each wing. Each engine was a water-cooled Rolls-Royce Condor II that produced 650 hp (485 kW) and turned a wooden, fixed-pitch, two-blade propeller. The radiator for the nose-mounted engine was directly below the fuselage, and the radiator for each wing-mounted engine was located under the wing between the engine nacelle and the fuselage. The two-place, side-by-side, open cockpit was positioned just forward of where the wings mounted to the fuselage. Below the cockpit on the left side of the fuselage was a small propeller for a wind-driven pump. The pump supplied oil to a servo system that boosted movement of the ailerons and elevator.


The group posing in front of the Inflexible gives scale to the aircraft’s immense size. The radiator for the fuselage-mounted engine can be seen under the nose. Exhaust manifolds carried the gasses from the center engine away from the cockpit. Just under the cockpit is the windmill for the servo system pump.

The Inflexible was made of duralumin, an aluminum alloy that incorporates copper, manganese, and magnesium for increased strength. The fuselage had a rectangular cross section and consisted of front and rear sections that were bolted together. Both sections were made of duralumin sheets riveted to a duralumin frame. Mounted to the rear of the fuselage were the horizontal and vertical stabilizers. The elevator spanned the entire length of the horizontal stabilizer. A Flettner servo tab trailed behind the rudder and controlled its movement.

The wings were formed by a wing box that bolted to the fuselage and made up the center wing section. An outer wing section bolted to each side of the wing box and was supported by two spars. Like the fuselage, the wing was covered with sheets of duralumin. A cable that kept each wing in tension while in flight connected the rear spar, at about two-thirds the span of the wing, to the lower fuselage. This cable was tensioned to about 3,000 lb (1,361 kg). The wings had a six-degree dihedral. Sections of the leading and trailing edges of the wings were hinged for access and inspection of the inner wing. The aircraft’s 656 US gal (546 Imp gal / 2,482 L) of fuel was carried in four wing tanks. The Inflexible did not have any flaps, but its large ailerons spanned the outer half of each wing’s trailing edge. Extending from each of the aircraft’s control surfaces was an aerodynamic balance horn.

The Inflexible was on hand at the Royal Air Force Display at Hendon in late June 1928. The aircraft now has “9” painted on the fuselage. In a size comparison, the Inflexible was displayed with a de Havilland DH.71 Tiger Moth (far left). The Tiger Moth’s 22 ft 6 in (6.59 m) wingspan was about one-eighth that of the Inflexible.

The aircraft’s immense weight was supported by two large main wheels and a steerable tailwheel. During component testing, wire wheels collapsed under the expected weight of the Inflexible. New wheels were designed and made from steel and aluminum. Mounted to the wheels were 90-in (2.29-m) tall tires, specially developed by the Dunlop Rubber Company. The weight of the large tires increased by 70 lb (32 kg) when they were filled with air. Each main wheel was supported by a shock-absorbing strut that extended from just inside the engine nacelle. An A-frame mounted to the lower fuselage secured each main wheel. The main gear had a track of 25 ft 7 in (7.80 m). For landing, the main wheels had a hydraulic braking system that could be automatically applied when the tail wheel connected with the ground. This system was designed by Rohrbach engineer Kurt Tank.

The Beardmore Inflexible had a wingspan of 157 ft 6 in (48.01 m), a length of 75 ft 6 in (23.01 m), and a height of 21 ft 2 in (6.45 m). The aircraft had a top speed of 110 mph (177 km/h) at sea level and 101 mph (163 km/h) at 6,500 ft (1,981 m). Its landing speed was 65 mph (105 km/h). The Inflexible had a climb rate of 359 fpm (1.8 m/s) and took 18 minutes and 06 seconds to reach 6,500 ft (1,981 m). The aircraft’s service ceiling was 9,350 ft (2,850 m). The Inflexible had an empty weight of 24,923 lb (11,305 kg), a gross weight of 31,400 lb (14,243 kg), and a maximum weight of 37,000 lb (16,783 kg). Reportedly, the aircraft could seat 20 passengers, but it does not appear that such accommodations were ever installed.


Underside of the Inflexible as it overflies the Royal Air Force Display at Hendon. The radiators for the wing-mounted engines are visible by the fuselage. Note the aerodynamic balance horns extending from all of the control surfaces.

Construction of the Inflexible progressed slowly and was often delayed by various material shortages. The aircraft was initially given civil registration G-EBNG on 29 December 1925. This registration was cancelled on 12 July 1927, and military serial number J7557 was assigned. The aircraft was completed at Dalmuir, near Glasgow, Scotland, in mid-1927. It was then broken down into various sections and transported by sea from Glasgow to Ipswich, England. However, the Aeroplane and Armament Experimental Establishment had no way to transport the large components from the Ipswich docks to the nearby Martlesham Heath Airfield. Disassembled, the two fuselage sections were 41 ft (12.50 m) long, and the outer wing sections were 61 ft (18.59 m) long. Moving the large sections of the Inflexible to Martlesham Heath required the construction of a special transport with steerable axles. Once assembled, the Inflexible’s wingspan was larger than any hanger opening at Martlesham Heath. Special trollies were built that supported each of the aircraft’s wheels and enabled movement in all directions. With the trollies, the aircraft could be moved sideways into the hanger.

Initial ground tests were started in January 1928, and the Inflexible was soon ready for flight tests when the weather was clear. The aircraft’s first flight occurred on 5 March 1928 and was flown by Jack Noakes. A Beardmore mechanic was also on the flight. The Inflexible took off in about 1,014 ft (309 m) and flew for 15 minutes; at the time, it was the world’s largest aircraft to fly. The Inflexible was stable in flight and exhibited good controls. Further flight testing revealed the aircraft to be underpowered, and its pitch and roll control was lacking in rough weather and at slow speeds. Wake turbulence from the fuselage-mounted engine also caused vibration issues with the aircraft’s tail.


The Inflexible makes a pass during the Royal Air Force Display. The pilot, Jack Noakes, is just visible in the open cockpit.

The Inflexible was displayed for the public on at least three different occasions. On 27–30 June 1928, the aircraft was flown during the Royal Air Force Display at Hendon, near London. On 18–20 May 1929, it appeared at the Norwich Aero Club Air Display at the Mousehold Aerodrome. On 10 June 1929, the Inflexible was at the Cambridge Aero Club Display in Conington.

Beardmore struggled financially after World War I, and the aircraft department closed in February 1929. Rohrbach also suffered financial difficulties, and the company merged with a Deschimag subsidiary to form Weser Flugzeugbau GmbH in 1934. Although the Inflexible had demonstrated the feasibility of all-metal, stressed-skin construction, it would be a few years before the technique was fully adopted by the British aircraft industry. In January 1930, the Inflexible was disassembled for static tests at Martlesham Heath. The aircraft had accumulated 47 hours and 55 minutes of flight time. The engines were removed and placed into storage. After the static tests, the wings, fuselage, and other components were left exposed to the elements for corrosion tests. Occasionally, parts of the duralumin skin were removed and repurposed, and the fuselage served as a space for guards to get out of the weather. The remains of the Inflexible were eventually scrapped in 1931. The only surviving component of the aircraft is one main wheel, which is on display in the Science Museum, London.


Aerodynamic wheel covers were added to the aircraft sometime in early 1929. The Flettner tab controlling the rudder extended some distance behind the aircraft. The aerodynamic balance horns of the rudder and aileron are clearly visible.

Beardmore Aviation 1913-1930 by Charles Mac Kay (2012)
British Prototype Aircraft by Ray Sturtivant (1990)
Jane’s All the World’s Aircraft 1928 by C. G. Grey and Leonard Bridgman (1928)
British Flight Testing: Martlesham Heath 1920-1939 by Tim Mason (1993)
– “Die Monster von Beardmore” by Philip Jarrett, Flugzeug Classic (May 2002)


Alfa Romeo 1101 28-Cylinder Aircraft Engine

By William Pearce

In the early 1930s, Alfa Romeo began to build aircraft engines based on foreign designs that it licensed for production. By 1938, Alfa Romeo had obtained licenses to produce the Armstrong Siddeley Lynx, Bristol Jupiter and Pegasus, De Havilland Gypsy Major and Gypsy Six, and Walter Sagitta inverted V-12. The company had also used its knowledge and experience with licensed production to design its own engines. However, Alfa Romeo’s own D-series radial engines of the early 1930s were not successful, and its 135 engine, an 18-cylinder air-cooled radial first run in 1938, suffered from reliability issues. Giustino Cattaneo had designed the 135, but he left Alfa Romeo in 1936, before the first engine was built. Still, the design of these original Alfa Romeo engines owed much to the foreign engines built under license.


The Alfa Romeo 1101 28-cylinder engine with its remote, two-speed supercharger. Note the induction system from the supercharger to the cylinders. The fuel injection pump and magnetos can be seen on the back of the engine. One cylinder bank has a seemingly restrictive exhaust manifold attached.

In 1938, Ugo Gobbato, Managing Director of Alfa Romeo, tasked the Special Studies Service (Servizio Studi Speciali / SSS) to design an entirely new aircraft engine. The SSS was Alfa Romeo’s secret or special projects department. Wifredo Ricart, a Spaniard who escaped his country’s civil war and fled to Italy in 1936, was in charge of the new engine’s design, which was designated 281.

The 281 was an inline radial that consisted of seven cylinder banks, each with four cylinders. The liquid-cooled engine was equipped with a single-speed, single-stage centrifugal supercharger. The 281 engine had a 4.72 in (120 mm) bore, a 4.33 in (110 mm) stroke, and displaced 2,126 cu in (34.83 L). With the bore larger than the stroke, the oversquare engine was designed have a relatively small diameter and operate at higher rpm. The engine had an estimated output of 1,480 hp (1,089 kW) at 3,000 rpm. The 281 was designed with then-current power requirements in mind, but did not consider future demands for power increases. The 281 design produced basically the same power as the 135, although it was 35 in (.88 m) in diameter compared to 55 in (1.40 m) for the 135. Realizing that a more powerful engine was needed, Ettore Pagani, also of the SSS, completed a design study in 1939 of an enlarged 281 to produce an excess of 2,000 hp (1,471 kW). This engine became known as the 1101. The 281 was never built.

The Alfa Romeo 1101 was initially designated 101, but it was also referred to as the 1.101 and 1.1.01. However, 1101 has become the most common designation. The design team for the 1101 consisted of Ricart, Orazio Satta, and Giuseppe Busso. The engine had a cast aluminum crankcase with seven cylinder banks mounted radially around its center and spaced at 51.4 degrees. The upper cylinder bank extended vertically from the crankcase. Each cylinder bank contained four cylinders and was made from cast aluminum with an integral cylinder head. Wet cylinder liners made of nitrided steel were installed in the cylinder block. Each cylinder had one intake valve and one sodium-cooled exhaust valve. The intake valve was 2.56 in (65 mm) in diameter, and the exhaust valve was 2.20 in (56 mm) in diameter. The valves for each cylinder bank were actuated via hydraulic tappets by a single overhead camshaft. The camshaft was driven by bevel gears and a vertical shaft from the front of the engine. The one-piece crankshaft was supported by five main bearings. The pistons for each row of cylinders were served by a master connecting rod with six articulated connecting rods. The cylinders had a compression ratio of 6.5 to 1.


Front view of the 1101 illustrates the vertical drives for the camshafts. The four mounts on the front of the gear reduction are visible. A sump is positioned between the two lower cylinder banks.

Mounted to the front of the engine was a propeller gear reduction. Via planetary bevel gears, the propeller shaft rotated at .400 times crankshaft speed. Mounted to the rear of the engine were two fuel injection pumps and two magnetos. The primary injection pump had a maximum flow of 423 gallons (1,600 L) per hour and delivered fuel to the injectors mounted in the intake side of the cylinder head. The secondary fuel injection pump had a maximum flow of 132 gallons (500 L) per hour and delivered methanol (methyl alcohol) to injectors located in the intake manifold just before the intake port of each cylinder. The methanol was used to increase maximum power and reduce detonation. Each of the two magnetos fired one of the two spark plugs mounted in each cylinder.

A shaft extending from the rear of the engine powered a remote, two-speed, centrifugal supercharger. The 1101 engine as built did not have a supercharger mounted in a housing that attached directly to the rear of the crankcase. Some sources indicate that the engine had a two-stage supercharger, but photos show just the remote supercharger with no other stage apparent. Two-stage supercharging was certainly planned for future versions of the 1101 engine. Air entered the back of the supercharger, where it was compressed to provide 11.4 psi (.78 bar) of boost. A duct extending from the supercharger was intended to incorporate an aftercooler, but surviving photos do not show one installed. From the duct, the air entered a semi-annular manifold located at the rear of the engine. Seven individual runners extended from the semi-annular manifold and connected to each cylinder bank. The runners had four outlets grouped in two pairs of two and mounted to the left side of the cylinder bank. Each cylinder bank had four exhaust ports on its right side, and the exhaust ports for the middle two cylinders of each bank were grouped together.

A centrifugal water pump, most likely mounted to the lower rear of the engine, flowed coolant at 14,530 gallons (55,000 L) per hour. The coolant was a mix of 70 percent water and 30 percent ethylene glycol. Double dynafocal engine mounts were located on the back side of each cylinder bank. The propeller gear reduction housing also had four mounts.

The engine was officially designated Alfa Romeo 1101 RC37/87. The “RC” stood for Riduttore de giri (gear reduction) and Compressore (supercharged), and 37/87 designated the critical altitudes (in hectometers) at which maximum continuous power was obtained with its two-speed supercharger. The engine had a 5.31 in (135 mm) bore and a 4.92 in (125 mm) stroke. This gave the 1101 a displacement of 3,057 cu in (50.10 L). However, since the strokes of the articulated rods were slightly longer than that of the master rod, the engine had an actual displacement of 3,066 cu in (50.25 L). Takeoff power was 2,200 hp (1,618 kW) at 2,625 rpm. For one minute at emergency power and 2,800 rpm, the engine produced 2,300 hp (1,692 kW) at 7,546 ft (2,300 m) in low gear and 2,150 hp (1,581 kW) at 26,247 ft (8,000 m) in high gear. For five minutes at military power and 2,700 rpm, the engine produced 2,000 hp (1,471 kW) at 10,827 ft (3,300 m) in low gear and 1,900 hp (1,398 kW) at 28,215 ft (8,600 m) in high gear. Maximum continuous power was achieved at 2,625 rpm, with the engine producing 1,850 hp (1,361 kW) at 12,139 ft (3,700 m) in low gear and 1,750 hp (1,287 kW) at 28,543 ft (8,700 m) in high gear. The 1101 had a diameter of 44.7 in (1.14 m) and was 97.2 in (2.47 m) long. The engine weighed 2,535 lb (1,150 kg) without accessories.


The 1101’s aftercooler was to be incorporated into the induction pipe between the supercharger and the ring manifold. Note the shaft housing extending back from the engine to power the supercharger.

The 1101 was designed and built at Alfa Romeo’s plant in Pomigliano d’Arco, near Naples, Italy. As the 1101 was being built, Italy had secured licenses from Germany to build the Daimler-Benz DB 601 and DB 605 engines and tasked Alfa Romeo with their production. This led to the formation in 1941 of Alfa Romeo Avio, a division focused solely on producing aircraft engines. The 1101 engine was completed in late December 1941 and first run in early January 1942. Under tests, the 1101 experienced detonation issues that damaged the pistons and cylinder heads. These issues were caused by the 87 octane fuel and the timing of the fuel injection system.

Development of the engine progressed until early 1943, when the war situation required the dispersal of factories away from populated areas. The 1101 engine project was moved to Armeno in northern Italy, near the Swiss border. The move caused delays, but the entire project was suspended on 8 September 1943, following news of the Italian armistice. The Armeno plant housing the 1101 fell in the territory controlled by the newly formed Italian Social Republic (Repubblica Sociale Italiana), which was mostly controlled by Germany. It is not clear if work on the 1101 engine was resumed or stayed suspended, but by mid-1943, the Armeno plant housed nearly all of the engine’s documentation, the prototype engines, and parts for approximately 20 pre-production examples. On 18 June 1944, all of the materiel in the Armento plant was destroyed by Italian partisans (resistance fighters) to prevent its use by the German military.

Future development of the 1101 included two-stage supercharging to increase the engine’s military power rating to 2,300 hp (1,692 kW). Most likely, this configuration would include an additional centrifugal supercharger incorporated in a housing mounted directly to the rear of the crankcase and mechanically driven from the crankshaft. Investigations were also conducted into turbocompounding the engine. The turbocompounded 1101 would utilize five turbines. Three turbines would be positioned at the front of the engine to recover power from the exhaust and feed it back to the propeller shaft. The remaining two turbines were turbosuperchargers (first stage of supercharging) positioned at the rear of the engine to feed air into the engine’s centrifugal supercharger (second stage of supercharging). The turbocompounded engine was expected to weight 20 percent more, increase fuel efficiency by 15 percent, and produce 2,600 (1,912 kW) hp. However, no such engines were built.


The 1101 mounted on what appears to be a test bed. This image gives a good view to the spacing of the intake and exhaust ports. Note the two dynafocal mounts on the back of each cylinder bank. It is not clear if the remote supercharger has been omitted or is just obscured by the mounting frame.

Other developments included enlarging the engine’s cylinder, possibly with a 5.71 in (145 mm) bore and a 5.12 in (130 mm) stroke, so that total displacement was 3,668 cu in (60.1 L). Studies were also undertaken to create a 42-cylinder engine by having six cylinders per bank. Some sources indicate that this engine had a displacement of approximately 4,270 cu in (70 L). However, the bore and stroke of the 1101 would displace 4,586 cu in (75.1 L) with 42 cylinders. Therefore, the bore and stroke of the 4,270 cu in (70 L) 42-cylinder engine are not known.

The 1101 was proposed for at least three aircraft projects: the Alfa Romeo 1902—apparently a development of the Aeronautica Umbra MB-902 design, with the two engines buried in the fuselage and driving propellers on each wing via extension shafts and right-angle drives; the Caproni Vizzola MCT (Monoposto Caccia Trigona / Tr.1207)—a single seat fighter of a taildragger configuration with the engine buried in the fuselage behind the cockpit and driving a tractor propeller via an extension shaft; and the Savoia-Marchetti SM-96 (II)—a single seat taildragger fighter of a conventional tractor layout with the engine installed in the nose. None of these projects were built.

Two Alfa Romeo marine engines utilized 1101 components: the inline, four-cylinder 1001 engine used a single cylinder bank, and the V-8 1002 engine used two cylinder banks. Both of these engines were built during World War II and neither appear to have entered quantity production. The only known part of an 1101 engine to survive is a fuel injection pump stored at the Alfa Romeo Museum (Museo Storico Alfa Romeo) in Arese, Italy.

Note: The horsepower (hp) figures in this article are actually Cavalli Vapore (CV), which is 1.387% more than a standard hp (100 CV = 98.6 hp). The kilowatt (kW) values are based on CV.


A composite drawing of the Caproni Vizzola MCT (Monoposto Caccia Trigona / single seat fighter, designed by Emmanuele Trigona) with the 1101 engine installed in the fuselage.

– “Destini incrociati” by Luigi Montanari, epocAuto Anno 14, N.1 (January 2019)
– “Le attività aeronautiche in Alfa Romeo fino al 1945” by Fabio Morlacchi, L’Alfa Romeo di Ugo Gobbato 1933-1945, Monografi AISA 92 (2 April 2011)


Martin XB-51 Attack Bomber

By William Pearce

In February 1946, the United States Army Air Force (AAF) sought design proposals for an attack aircraft to replace the Douglas A-26 Invader. The Glenn L. Martin Company (Martin) responded with its Model 234, a straight-wing aircraft of a rather conventional layout, except that the engine nacelle on each wing housed a turboprop and a turbojet engine. The Model 234 had a crew of six and was forecasted to carry 8,000 lb (3,629 kg) of ordinance over 800 miles (1,287 km).


The Martin XB-51 was a unique attack bomber designed at the dawn of the jet age. The first prototype is seen here with its original tail. Note the inlet for the fuselage-mounted engine. The dark square behind the canopy is a window over the radio operator. (Martin/USAF image)

Martin was awarded a contract to develop the Model 234 on 23 May 1946, and the aircraft was designated XA-45. A few weeks later, the AAF decided to discard the “Attack” category, and the XA-45 was subsequently redesignated XB-51. The AAF then requested new requirements for the XB-51 with an emphasis on speed. The AAF’s new desired specifications for the A-26 replacement was a top speed of 640 mph (1,030 km/h) and the ability to carry 4,000 lb (1,814 kg) of ordinance over 600 miles (966 km). The new requirements necessitated a complete redesign of the XB-51, which Martin completed and submitted to the AAF in February 1947. After slight modifications, the design was somewhat finalized by July 1947. The AAF ordered two prototypes, which were assigned serial numbers 46-685 and 46-686.

The Martin XB-51 was a radical departure from the firm’s previous aircraft designs. The XB-51 was an all-metal aircraft that featured a relatively large fuselage supported by relatively small swept wings. The aircraft had a crew of two and was powered by three General Electric J47-GE-13 engines, each developing 5,200 lbf (23.13 kN) of thrust. Two of the engines were mounted on short pylons attached to the lower sides of the aircraft in front of the wings. The third engine was buried in the extreme rear of the fuselage.


The XB-51 with its flaps up and its wing at an incidence of three degrees as the aircraft is rolled out on 4 September 1949. The circle on the side of the fuselage just behind the cockpit is a side window for the radio operator. There is no window mirrored on the left side of the aircraft. Note that the intake for the fuselage-mounted engine has its cover rotated closed. (Martin/USAF image)

The pilot sat in the front of the aircraft under what appeared to be a small canopy in contrast to the large fuselage. Behind the pilot and completely within the fuselage was the radio operator, who was also in charge of the short range navigation and bombing (SHORAN) system. The crew compartment was pressurized, and access was provided by a door on the left underside of the fuselage, between the pilot and radio operator’s stations. In case of an emergency, both crew were provided with upward firing ejection seats.

The engine housed in the rear fuselage was fed by an inlet duct located atop the fuselage. A rotating assembly was installed forward of the inlet to either cover the inlet with an aerodynamic fairing when the engine was not in use, or rotate to provide a duct to feed air to the engine. The rear engine could be shut down in flight to extend the aircraft’s range. When not in use, a door in the intake duct prevented the back flow of air through the rear engine. Large doors swung open beneath the fuselage to access the rear engine.


The first XB-51 with flaps down and its wing at an incidence of 7.5 degrees. Note that only one of the wingtip outrigger gears is touching the ground. (Martin/USAF image)

Mounted above the rear engine was the vertical stabilizer, with the horizontal stabilizer mounted to its top. Originally, the XB-51’s design had the horizontal stabilizer mounted midway up the vertical stabilizer, but the aircraft was not built with this configuration. The horizontal stabilizer was swept back 35 degrees, and its incidence could be changed for trimming. Two rocket assisted takeoff (RATO) bottles could be fitted to each side of the rear fuselage. The RATO packs would be ignited to shorten the XB-51’s takeoff distance, then discarded once the aircraft was in flight. Each bottle provided 1,000 lbf (4.44 kN) of thrust. Hydraulically operated air brakes were located on each side of the fuselage, under the intake for the rear engine. A braking parachute was housed in the left side of a fairing located below the rudder.

The XB-51 used tandem (bicycle) main gear that consisted of front and aft trucks, and outrigger wheels that deployed from the aircraft’s wingtips for support. Martin had used a similar gear arrangement for the straight-wing XB-48 jet medium bomber and had initially tested the setup using the Martin XB-26H, a B-26 Marauder specially modified for to test the tandem landing gear. The main trucks could swivel to counteract the aircraft’s yaw while taking off or landing with a crosswind.


Ordinance for the XB-51 that would fit in the bomb bay. From left to right, four 1,600 lb (726 kg) bombs, eight 5 in (127 mm) High Velocity Aircraft Rockets (HAVR), one 4,000 lb (1,814 kg) bomb, four 2,000 lb (907 kg) bombs, four 1,000 lb (454 kg) bombs, and nine 500 lb (227 kg) bombs. The 4,000 lb (1,814 kg) bomb required an enlarged bomb bay door. (Martin/USAF image)

The aircraft’s bomb bay was located in the fuselage between the main wheels. The bomb bay had a single rotating door to which the bomb load was attached. Opening the rotating door did not create any buffeting or require any speed restriction normally required by two conventional doors. In addition, the rotating door was removable and could be quickly replaced with another door already loaded with ordinance. The standard door could accommodate nine 500 lb (227 kg) bombs, four 1,000 lb (454 kg) bombs; four 1,600 lb (726 kg) bombs; or two 2,000 lb (907 kg) bombs. Two additional 2,000 lb (907 kg) bombs could be accommodated on exterior bomb racks mounted on the bottom of the door. A special enlarged door could be fitted to carry a single 4,000 lb (1,814 kg) bomb or a Mk 5 or Mk 7 nuclear bomb. The XB-51’s maximum bomb load was 10,400 lb (4,717 kg). Eight 5 in (127 mm) High Velocity Aircraft Rockets (HAVR) could be carried in the bomb bay in place of internal bombs.

Three fuel tanks were installed in the aircraft’s fuselage. The forward tank was located above the front main gear and held 640 US gal (2,426 L). The center and aft tanks were both located above the bomb bay and held 745 US gal (2,820 L) and 1,450 US gal (5,489 L) respectively. All the standard fuel tanks could be filled via a single fueling receptacle. A 160.5 US gal (607.6 L) water/alcohol tank to boost engine performance during takeoff was mounted between the front and center fuel tanks. Two 350 US gal (1,325 L) tanks could be carried in the bomb bay for ferrying the aircraft over long distances. The XB-51 had a total normal fuel capacity of 2,835 US gal (10,732 L), and 3,535 US gal (13,381 L) with the bomb bay tanks.


The XB-51 executing a high-performance takeoff provides a good view of the aircraft’s leading-edge slats and large flaps. No RATO bottles are fitted. (Martin/USAF image)

In the nose of the XB-51 were eight fixed 20 mm cannons with 160 rpg and a forward strike camera. The nose of the second XB-51 was detachable, and different noses could be fitted depending on the aircraft’s mission. In addition to the standard gun nose, other noses featured equipment for precision bombing and equipment for photo-reconnaissance. As standard, the XB-51 had a reconnaissance camera installed under the cockpit and a strike assessment camera installed in the lower rear fuselage.

With fuel, engines, and the main landing gear all housed in the fuselage, the XB-51’s mid-mounted wings were very thin. The wings were swept back 35 degrees and had six degrees of anhedral. Outrigger wheels deployed from the wingtips to steady the aircraft on the tandem main gear. Slats extended along the outer 70 percent of the wing’s leading edge. Large, slotted flaps covered 75 percent of the wings trailing edge, with small ailerons taking up 15 percent of the trailing edge. While the ailerons contributed to aircraft’s roll control, their main purpose was to provide feedback for the pilot. The majority of roll control was provided by spoilers positioned on the wing’s upper surface, just forward of the flaps. The spoilers extended about 40 percent of the wing’s span. The incidence of the entire wing could vary from 2 to 7.5 degrees and would automatically change with deployment of the flaps. The wing incidence increased at lower speeds to decrease the aircraft’s stall speed and make the aircraft assume the correct attitude for landing, which was with the nose high approximately six degrees. The tandem landing gear required the simultaneous touchdown of both the forward and aft trucks. To prevent the accumulation of ice, hot air was bled off from the engines, directed through a passageway in the wing’s leading edge, and exhausted out the wingtip.

The Martin XB-51 had a 53 ft 1 in (16.18 m) wingspan, was 85 ft 1 in (25.93 m) long, and was 17 ft 4 in (5.28 m) tall. The track between the outrigger landing gear was 49 ft 5 in (15.06 m). The aircraft had a top speed of 645 mph (1,038 km/h) at sea level and 580 mph (933 km/h) at 35,000 ft (10,668 m). Cruising speed was 532 mph (856 mph) at 35,000 ft (10,668 m), and the aircraft’s landing speed was around 140 mph (225 km/h). The XB-51’s initial rate of climb was 6,980 ft (35.5 m/s) at maximum power and 3,600 ft (18.3 m/s) at normal power. The service ceiling was 40,500 ft (12,344 m); normal range was 980 miles (1,577 km), and ferry range was 1,445 miles (2,326 km). The XB-51 had an empty weight of 30,906 lb (14,019 kg), a combat weight of 44,000 (19,958 kg), and a gross weight of 55,930 lb (25,369 kg).


The first XB-51 undergoing an engine run. The bullet fairing has been added to the tail. Note the covered ports in the nose for the 20 mm cannons. (Martin/USAF image)

On 24 February 1948, a mockup of the XB-51 was inspected by the United States Air Force (USAF), which had become a separate branch of the US Armed Forces on 18 September 1947. Construction of the first prototype (46-685) proceeded swiftly at the Martin plant in Middle River, Maryland, and the completed aircraft was rolled out on 4 September 1949. After completing ground tests, aircraft 46-685 made is first flight on 28 October 1949, piloted by Orville Edward ‘Pat’ Tibbs. Initial flight testing went well until the rear main gear collapsed after landing on 28 December. The aircraft was repaired and returned to flight status in early 1950. High-speed testing had revealed some vibrations with the tail and a tendency to Dutch roll. A bullet faring was added at the intersection of the horizontal and vertical stabilizers in March 1950 to mitigate the issues.

The second prototype (46-686) made its first flight on 17 April 1950, piloted by Frank Earl ‘Chris’ Christofferson. Although 46-686 was initially flown with the original tail, bullet fairings were soon added. Both aircraft were involved in numerous landing accidents, mostly attributed to the tandem landing gear and the pilot’s lack of familiarity with its nuances. Nose high landings resulted in tail strikes that damaged the aft fuselage. Nose low and hard landings resulted in the collapse or shearing of the front main gear. Despite the landing difficulties, pilots seemed to like the aircraft and its performance. While the XB-51 could perform rolls and outpace some fighters, the aircraft was not stressed for aggressive maneuvers.


Another image of the first XB-51 with its bullet tail fairing. Note the RATO bottles attached to the rear fuselage. The shield painted under the cockpit says “Air Force Flight Test Center.” (Martin/USAF image)

The USAF considered putting the XB-51 into production, but the role for which the aircraft was intended had changed again with the outbreak of the Korean War. Speed was no longer the main focus, and the USAF now desired an aircraft that could loiter in an area until needed by ground forces. The USAF compared the XB-51 against the North American AJ-1 Savage and B-45 Tornado, the Avro Canada CF-100 Canuck, and the English Electric Canberra. Under the new criteria, the USAF selected the Canberra as the winner in February 1951, and the XB-51 program was essentially cancelled. The Canberra had more than twice the range and loiter time of the XB-51. The following month, Martin was awarded a contract to build the Canberra as the B-57, and the rotary-style bomb bay pioneered on the XB-51 was installed on the B-57. Ultimately, 403 B-57 aircraft would be produced. Both XB-51 aircraft continued to be evaluated and tested. The two XB-51s underwent performance and armament tests at Edwards Air Force Base (AFB) in California and Elgin AFB in Florida.

On 9 May 1952, the second prototype XB-51 was destroyed at Edwards AFB when Major Neal Lathrop executed a roll at low altitude and collided with the ground. Lathrop was the sole occupant on board. At the time of the accident, 46-686 had accumulated 151 hours of flight time and had made 193 flights.


The second (left) and first (right) XB-51 aircraft at the Martin plant in Middle River. Both aircraft have the bullet tail fairings, and the second prototype (left) has RATO bottles attached. The Martin plant in the background still has the camouflage paint scheme applied during World War II. Compare the different flap and wing positions between the two aircraft. (Martin/USAF image)

The first prototype played the role of the “Gilbert XF-120” fighter in the 1956 movie “Toward the Unknown.” The movie was shot mostly at Edwards AFB in 1955. On 25 March 1956 the 46-685 was destroyed while taking off from El Paso Municipal (now International) Airport in Texas. The stop in El Paso was to refuel as the aircraft traveled from Edwards AFB to Eglin AFB. The accident occurred due to a premature rotation and subsequent stall. The radio operator, Staff Sergeant Wilbur R. Savage, was killed in the crash, and the pilot, Major James O. Rudolph, died of his injuries on 16 April 1956. The first XB-51 prototype had accumulated 432 hours and made 453 flights.

Performance of the Martin XB-51 had exceeded the manufacturer’s guarantees. However, the aircraft was designed and built at a time when USAF’s desires and priorities were rapidly shifting, and it turned out that the service did not really want the aircraft they had originally asked for. Pilots held the XB-51 in a high regard despite its demanding landing characteristics. Ultimately, the XB-51 faded into history as a short-lived experimental aircraft investigating a new direction at the dawn of the jet age.


The second (right) and first (left) XB-51 aircraft make a low pass over Martin Field on 11 October 1950. Note the shadows of the aircraft on the runway. (Martin/USAF image)

The Martin XB-51 by Scott Libis (1998)
“Martin XB-51” by Clive Richards, Wings of Fame Volume 14 (1999)
Martin Aircraft 1909–1950 by John R. Breihan, Stan Piet, and Roger S. Mason (1995)
Standard Aircraft Characteristics XB-51 by U.S. Air Force (11 July 1952)
Jane’s All the World’s Aircraft 1951-1952 by Leonard Bridgman (1951)
U.S. Bombers 1928 to 1980s by Lloyd S. Jones (1980)