Author Archives: William Pearce

Fairey P24 Monarch engine

Fairey P.24 Monarch Aircraft Engine

By William Pearce

The first original engine made by the Fairey Aviation Company (FAC) was the P.12 Prince. Designed by Captain Archibald Graham Forsyth, the Prince was a 1,559 cu in (25.5 L) V-12 that was ultimately rated at 750 hp (559 kW) for normal output and 900 hp (671 kW) for maximum output.

Fairey P24 Monarch engine

The Fairey P.24 Monarch was a final attempt by Fairey Aviation to produce a piston aircraft engine. The engine proved to be reliable and had some unique features, but nothing about it was revolutionary. Both Britain and the United States passed at the opportunity to produce the engine.

Seeking more power, Forsyth investigated a 16-cylinder engine designated P.16 that displaced 2,078 cu in (34.1 L). A V-16 design was initially considered, but the configuration was changed over concerns regarding the engine’s length combined with excessive torsional vibrations and stress of the long crankshaft. The P.16 configuration was switched to an H-16 with four banks of four cylinders. However, by switching to an H-24 configuration with four banks of six cylinders, a more powerful engine could be developed that would possess the same frontal area as the H-16. In fact, there is little evidence from primary sources that indicates a P.16 engine or an H-16 configuration were ever seriously considered. Design work on the H-24 engine had begun by October 1935. The H-24 engine was designated P.24 and may have been initially named “Prince” (like the P.12). For a time, the P.24 was called “Queen,” but the name was later changed to “Monarch.”

The Fairey P.24 Monarch was a vertical H engine in which the left and right 12-cylinder engine sections could be operated independently of each other. The aluminum crankcase was made of an upper and lower half. Each bank of six cylinders was mounted to the crankcase. An aluminum cylinder head attached to the cylinder bank. The P.24 retained the bore and stroke of the P.12 (and P.16) engine. Each cylinder had two intake valves and one exhaust valve, all actuated by a single overhead camshaft driven from the rear of the engine. The 1.8125 in (46 mm) diameter intake valves were operated by a T-type tappet, and the 2.25 in (57 mm) diameter exhaust valve was operated directly by the camshaft. It is interesting to note that various British patents (no. 463,501 and 465,540) filed by FAC and Forsyth show four valves per cylinder. No information has been found of a four-valve head being fitted to a P.24 engine.

Fairey P24 integral passageways

Drawings taken from British patent 463,501 illustrate the integral passageways of the P.24’s induction system. The drawn configuration was nearly identical to that used on the actual engine. The sectional view on the right illustrates the numerous sharp turns the air/fuel mixture made on its way into the cylinders.

Mounted to each side of the engine was a single-stage, two-speed supercharger with two carburetors mounted on its inlet. The superchargers were driven from the rear of the engine at 8.3475 times crankshaft speed through three step-up gears. Via a short manifold, each supercharger delivered air into passageways cast integral with the crankcase, cylinder bank, and cylinder head. A single passageway brought air into two cylinders. It was noted in British patent 463,501 that having intake passageways cast integral with the crankcase made the engine cleaner, more rigid, and opened the vertical space between the cylinder banks for either an oil cooler or gun. However, if a gun were to be considered, the crankcase construction did not allow it to fire through the propeller hub. Rather, the gun would need to be synchronized to fire through the propellers.

The air/fuel mixture was ignited by two spark plugs—one on each side of the cylinder. The spark plugs were fired by four magnetos mounted to the rear of the engine. The upper two magnetos fired the spark plugs located on the inner side of the cylinders, and the lower two magnetos fired the spark plugs located on the outer side of the cylinders. The left and right sides of the P.24 had the same firing order: 1U, 5L, 4U, 1L, 2U, 4L, 6U, 2L, 3U, 6L, 5U, and 3L. The first and last cylinders had their own exhaust stack, but the middle four cylinders were paired off with a shared exhaust stack. This arrangement gave the P.24 16 exhaust stacks, which often caused the engine to be mistaken for an H-16.

Fairey P24 valves

Another drawing from British patent 463,501 details the induction, valves, and exhaust. Although the drawing has two exhaust valves per cylinder, the P.24 as built had only one exhaust valve. Note that each bank of six cylinders only has four exhaust stacks. This gave a total of 16 stacks for the P.24 engine, which is why it is occasionally mistaken for an H-16.

At the front of the engine, each crankshaft was geared to a separate propeller shaft at a .5435 reduction. The two propeller shafts made up a coaxial, contra-rotating unit. The crankshafts and accessories for each engine section rotated in opposite directions. When viewed from the rear, the left crankshaft rotated clockwise and powered the front propeller. The right crankshaft rotated counterclockwise and powered the rear propeller. The P.24’s fully-adjustable, contra-rotating propeller was developed by FAC. Each crankshaft had six throws and was supported by eight main bearings. The pistons were connected to the crankshaft by fork-and-blade connecting rods, with the fork rod servicing the lower cylinders and the blade rod servicing the upper cylinders. Since they rotated in opposite directions, the crankshafts and engine accessories were not interchangeable.

When either the left or right side of the engine was shut down, the other side of the engine would continue to operate and power its propeller. This gave any aircraft powered by a P.24 engine the reliability of two engines without the drawback of asymmetrical thrust in an engine-out situation. This configuration also allowed half of the engine to be shut down to extend the aircraft’s range or loiter time. Although the cooling and oil systems of the engine sections were separate, they used common tanks and coolers during engine tests. It was noted that completely separate coolers and tanks could be installed in an aircraft to make the engine sections truly independent of one another.

Fairey P24 Monarch installation drawing

The P.24 installation drawing illustrates the H-24 engine as built. British patent 463,501 mentioned the possibility of installing a gun between the upper cylinder banks, but no provisions for such equipment were incorporated into the actual engine.

The Fairey P.24 Monarch had a 5.25 in (133 mm) bore, a 6.0 in (152 mm) stroke, and a compression ratio of 6 to 1. The engine displaced 3,117 cu in (51.1 L) and was originally rated for 2,000 hp (1,491 kW) at 2,600 rpm. However, Forsyth felt the engine could be developed to 2,600 hp (1,939 kW) at 3,000 rpm. The two-speed superchargers gave critical altitudes of 6,000 and 13,000 ft (1,829 and 3,962 m). Fuel consumption was .63 lb/hp/hr (383 g/kW/h) at takeoff, .55 lb/hp/hr (335 g/kW/h) at full power, and .45 lb/hp/hr (274 g/kW/h) at 60% throttle. The P.24 engine was 86.25 in (2.19 m) long, 43.0 in (1.09 m) wide, and 52.5 in (1.33 m) tall. The engine weighed around 2,330 lb (1,057 kg), although 2,180 lb (989 kg) is given by many sources. Perhaps the discrepancy in reported weight is a result of the engine’s weight changing with the installation of various accessories.

The P.24 was first run in 1938. The test cell at FAC was not built for the full power of the P.24, so just half of the engine was run at a time. By 6 October 1938, the engine was successfully completing two-hour runs without issues. Arrangements were made to install the P.24 in a Fairey Battle light bomber, and the engine was being considered for use in the Hawker Tornado fighter. The P.24 started its 50-hour civil type test on 13 May 1939 and successfully completed the test on 14 June 1939. For the test, the engine ratings were a normal output of 1,200 hp (895 kW) at 10,500 ft (3,200 m) and 2,400 rpm, and a maximum output of 1,450 hp (1,081 kW) at 10,500 ft (3,200 m) and 2,750 rpm. It appears that a single-speed supercharger delivering just .5 psi (.04 bar) of boost was used for the 50-hour test.

Fairey P24 Monarch Battle GB side

This side view of the P.24 engine installed in Fairey Battle K9370 illustrates the very large radiator installed under the aircraft. It is easy to understand why the engine, with its 16 prominent exhaust stacks, is often thought to be an H-16. Note that the propellers do not have a complete spinner, which was installed later.

The P.24-powered Battle (K9370) first flew on 30 June 1939, piloted by Christopher S. Staniland. A short time later, a P.24 test engine achieved 1,540 hp (1,148 kW) at 2,600 rpm with 3 psi (.21 bar) of boost for takeoff. With P.24 tests moving forward, FAC looked to apply the engine to new aircraft designs. On 19 October 1939, FAC proposed using the P.24 engine in aircraft designed to specifications N8/39 and N9/39. Designed by FAC chief designer Marcel Lobelle, the same basic single-engine, two-seat fighter design was used to satisfy both specifications, with the addition of a turret for N9/39. In Lobelle’s drawings, the FAC engine was labeled as the “Queen,” but it was visually identical to the P.24 as built. In addition, the late-1939 time frame was after FAC had moved away from 16-cylinder engine designs. In the late-1939 proposals, the engine was rated at 1,320 hp (984 kW) for takeoff and 1,170 hp (872 kW) at 15,000 ft (4,572 m).

During 1940, a number of short runs were made up to 1,750 hp (1,305 kW), but there were no long periods of running at these high outputs. Trouble was experienced with the superchargers and main bearings. A maximum of 2,200 hp (1,641 kW) was achieved, but not with both halves of the engine running at the same time. Each individual engine half achieved an output of 1,100 hp (820 kW), adding up to the 2,200 hp (1,641 kW) figure. In fact, each engine half made two runs at 1,100 hp (820 kW), but the runs were only a short duration of two minutes each.

Fairey P24 Monarch Battle GB front

A well circulated image of the P.24-powered Battle in Britain. Taken at the same time is another image that shows the front propeller turning (left side of the engine running). A doctored set of these images had the exhaust stacks removed to keep the engine’s configuration a secret. Note the complete spinner.

In October 1940, the Air Ministry made it clear that no production orders for the P.24 engine would be placed. Instead, the focus was on other engines already further developed and being designed by established engine manufacturers with greater facilities for production. In April 1941, the Fleet Air Arm (FAA) expressed some interest in the P.24. Since the P.24 had twin-engine reliability, and its contra-rotating propellers eliminated torque reaction, the engine was ideally suited for carrier operations. However, the Air Ministry again asserted that there would be no production of the engine. This did not stop FAC from continuing to push the P.24 engine, even proposing in mid-1942 that the Fairey Firefly carrier fighter should be re-engined with a P.24 that would produce 2,150 hp (1,603 kW) at 3,000 rpm. The Air Ministry was not interested, and the plan went no further. The P.24-powered Battle was turned over to Royal Aircraft Establishment Farnborough on 12 July 1941. By this time, P.24 engines on test had been run 20 hours at 2,000–2,100 hp (1,491–1,566 kW) and five hours at 2,100–2,300 hp (1,566–1,715 kW).

Fairey had discussed the P.24 engine with United States Army Air Force (AAF) officials in June 1941. The following month, Forsyth visited the US to give more details about the engine. Fairey and Forsyth felt that the Air Ministry had made a mistake in exclusively backing the Napier Sabre and not providing any support for the P.24. They wanted P.24 development and production to continue in the US; production in the US by an established engine manufacturer would be easier than FAC undertaking the task themselves. By this time, the name “Monarch” was applied to the P.24 engine. In August 1941, the AAF stated that they were not interested in the development or production of the P.24 engine, but they were interested the in the contra-rotating propellers developed for the engine. However, Fairey stated in a letter dated November 1941 that Wright Field in Dayton, Ohio had prepared three-view drawings of the P.24 installed in the Republic P-47 Thunderbolt fighter and the Curtiss A-25 Shrike (SB2C Helldiver) dive bomber. Fairey also stated that the Ford Motor Company was engaged in discussions about producing the engine.

Fairey P24 Monarch Battle US side

The P.24 was flown extensively in the US, but the AAF was mostly interested in the contra-rotating propeller. The Battle retained its serial number, but the British roundels were painted over, and US markings were applied. Note the star under the wing and the stripes on the tail. Some contend the Battle was designed to be powered by the P.24. However, the Battle’s origin can be traced to 1933, and the P.24’s design was initiated over two years later, in 1935. An early design of the Battle was powered by the Fairey P.12 Prince.

The apparent reversal of the AAF’s interest in P.24 production seems odd, and it may have been more optimism on Fairey’s part than what was really expressed by the AAF. Fairey did want to get the engine to the US, and claiming that the AAF was interested was the quickest way to get the cooperation of the Air Ministry, who had been battling Fairey for quite some time. Regardless of the AAF’s level of interest in the engine, they were certainly interested in the contra-rotating propellers. The P.24-powered Battle was shipped to the US on 5 December 1941. Another P.24 engine was delivered to Farnborough for further testing, and a third Monarch engine was prepared for shipping to the US. With the Japanese attack on Pearl Harbor, the second P.24 engine was never sent to the US.

Many sources state that the P.24 engine was considered to replace the Pratt & Whitney R-2800 in the P-47. It should be noted that an order for 773 P-47Bs (602 were finished as P-47Cs) was placed in September 1940; the XP-47B made its first flight on 6 May 1941, and an order for 805 P-47Ds was placed in October 1941. All of this P-47 activity occurred before the AAF touched the P.24 engine and before the US entered World War II. An additional 1,050 P-47Ds and 354 P-47Gs were ordered in January 1942, before the AAF had much, if any, time to evaluate the P.24. It would seem that the AAF was quite content with the R-2800 engine, since full-scale P-47 production was underway, and 2,982 aircraft were on order. A request from Fairey dated January 1943 sought a new set of propellers for a P.24 engine installed in a P-47. At the time, the P-47 was two months away from entering combat, with hundreds of aircraft produced and thousands on order. It seems highly unlikely that any engine change would have been seriously considered by the AAF.

Fairey P24 Monarch FAA side

The sole surviving P.24 Monarch engine and its propellers are preserved and housed in the Fleet Air Arm Museum at Yeovilton. Only around three P.24 engines were built. (Rory57 image via

When the AAF received the P.24-powered Battle at Wright Field in Dayton, Ohio, it had around 87 hours of flight time. The P.24 engine had a takeoff rating of 2,100 hp (1,566 kW) and military ratings of 2,100 hp (1,566 kW) at 6,000 ft (1,829 m) and 1,850 hp (1,380 kW) at 13,000 ft (3,962 m); all ratings were at 3,000 rpm with 9 psi (.62 bar) of boost and using 87 octane fuel. Forsyth believed the engine was capable of 2,600 hp (1,939 kW) with 100 octane fuel. The AAF found the coaxial propellers and the “double engine” concept novel, but found the rest of the engine conventional. The AAF felt the design of the P.24 limited its further development. Since the intake manifolds were cast into the engine’s crankcase, a complete redesign would need to be undertaken to improve their flow. As it was, the intake manifolds fed the air/fuel mixture clumsily into the cylinders through five turns, some of which were fairly sharp 90-degree bends. The integrally cast manifold also caused the air/fuel mixture to be heated as it flowed to the cylinders. Another issue was that the gear reduction housing was cast integral with the crankcase. If a failure caused damage to the gear reduction housing, the entire crankcase would need to be scrapped. With all of the integral components, the two crankcase castings were large and complex. The AAF also noted the non-interchangeability of the crankshafts and other components. The AAF remarked that BMEP (brake mean effective pressure) achieved by the P.24 at 3,000 rpm with 9 psi (.62 bar) of boost was matched by the Allison V-3420 with 3.75 psi (.26 bar) of boost at the same rpm. In addition, the relatively low critical altitude of the P.24 meant the Rolls-Royce Merlin 60 series had a 160 hp (119 kW) advantage at 30,000 ft (9,144 m).

Of course, enhancements to the P.24 could be made, and Forsyth suggested that further development of the engine be conducted in the US. This included increasing the bore of the P.24 to 5.5 in (140 mm), which would give a displacement of 3,421 cu in (56.1 L) and an output of 3,000 hp (2,237 kW). In addition, a P.32 could be built with four banks of eight cylinders for a total displacement of 4,156 cu in (68.1 L). The bore of the 32-cylinder P.32 could also be increased to 5.5 in (140 mm) for a total displacement of 4,562 cu in (74.8 L). A 24-cylinder engine with a 6.0 in (152 mm) bore and stroke could be developed that would displace 4,072 cu in (66.7 L) and produce 3,400 hp (2,535 kW).

Additions to the basic P.24 included developing a two-stage supercharger that would enable the engine to produce around 1,800 hp (1,342 kW) at 36,000 ft (10,973 m). The AAF mentioned that the stages would be separate, with one stage driven from the propeller gear reduction at the front of the engine. In May 1942, Forsyth applied for a US patent (no. 2,470,155) that addressed some of the AAF’s concerns regarding the engine’s gear reduction and supercharger. The patent outlines the basic P.24 engine but with a detachable propeller gear reduction. The engine could be used in a variety of aircraft, and different gear reductions would be fitted to provide the desired propeller rpm based on the aircraft’s role. An extension could be installed between the engine and propeller gear reduction that had a mounting to drive an additional supercharger on each side of the engine. In addition, different superchargers with their own gearing could be installed on the engine to provide different levels of boost based on the needs of the aircraft. In some configurations, superchargers could be engaged as the aircraft gained altitude. In addition, US patent 2,470,155 described how P.24 engines could be coupled to create an H-48 engine. A 48-cylinder engine would displace 6,234 cu in (102 L) and produce over 4,400 hp (3,281 kW).

Fairey P24 Turbosuperchargers

Forsyth envisioned adding turbosuperchargers to the P.24 as another stage of charging. This concept is outlined in British patent 463,984 (top, granted in 1937) and US patent 2,395,262 (bottom, granted 1946). In addition, a front mounted supercharger driven from the propeller gear reduction was contemplated. All of these arrangements were to give the P.24 better high-altitude performance, but none were built.

In June 1942, FAC and Forsyth applied for another US patent (no. 2,395,262) that detailed another supercharger configuration, but with a turbosupercharger mounted to the front of the engine. This configuration was briefly mentioned in US patent 2,470,155. In US patent 2,395,262, the turbosupercharger was the first stage and was powered by the exhaust gases from the top row of cylinders. Exhaust from the lower cylinders was combined with the exhaust from the turbosupercharger. The pressurized air flowed from the turbosupercharger to the gear-driven supercharger at the rear of the engine. The air was pressurized further and directed into the engine via manifolds as seen on the P.24.

Forsyth had been considering the combined turbo and supercharger arrangement since before the P.24 first ran. This concept was outlined in a British patent (no. 463,984) applied for in 1935 and granted in 1937. In this patent, the turbosuperchargers would be mounted on the sides of the engine, outside of the induction manifolds. The gear-driven supercharger would be run alone for low altitude operation, and the turbosupercharger would provide additional boost at higher altitudes. At a certain altitude, valves would open, allowing engine exhaust into the turbosupercharger to start its operation. At the same time, valves on the gear-driven supercharger’s inlet pipes would close. The turbosupercharger would become the first stage of charging and feed air into the gear-driven supercharger, in which fuel would be added and the mixture further pressurized before being fed into the cylinders.

Fairey P24 with compressors

As the jet age dawned, Forsyth looked to incorporate the new technology into the P.24. The top drawing is from British patent 591,048 and describes a single compressor (H) mounted behind the engine (A) and supercharger (F). Induction pipes (34) lead from the supercharger to the engine. The bottom drawing is from British patent 591,189 and describes a compressor (M) mounted behind each engine section. Both configurations allow the engine to drive the propellers, the compressor, or both. In addition, fuel could be injected and ignited into combustion chambers (I top and S bottom) for additional thrust. The patents were applied for in 1944 and granted in 1947.

Forsyth also suggested developing a jet engine section to be added to the P.24. British patent 591,048 described the P.24 employed in a semi-motorjet configuration. Behind the piston engine was a supercharger, and behind the supercharger was a large, engine-driven compressor. Fuel was injected and ignited in the compressor to generate thrust. Three different power options were available: the engine could drive the propellers only; the engine could drive both the propellers and the compressor; or the propellers could be disengaged, and the engine would drive the compressor alone, the compressor generating the thrust needed to maintain flight. A series of clutches connected or disconnected the propellers, piston engine, and compressor.

British patent 591,189 described a very similar engine concept as the semi-motorjet listed above; however, two compressors were used. Each engine section had its own compressor section, and the piston engine’s superchargers were again located on the side of the engine. In addition to the power options listed in the previously mentioned patent, one engine section could drive one propeller, while the other engine section could drive one compressor. Both of the patents that incorporated compressors with the P.24 engine were applied for in 1944 and granted in 1947.

Forsyth even thought about using P.24 components to create a marine engine. US patent 2,389,663 outlines P.24 cylinder banks being used in a U-12 configuration. Two U-12 engine sections would be combined to create a U-24 engine. The drive for the contra-rotating marine propellers would come from between the two U-12 engine sections. The patent notes that the six-cylinder engine sections could be run independently and that the superchargers could be engaged or disengaged. Low-speed operation would consist of running one six-cylinder engine section without supercharging. High-speed operation would employ all 24 cylinders and four superchargers.

Fairey U-24 marine engine

For marine use, Forsyth mounted the four banks of the P.24 on a new crankcase to create a U-24 engine. This drawing from US patent 2,389,663 shows the engine and how it would drive a contra-rotating propeller. The bevel drive to the supercharger is shown by number 10.

All of these inventive propulsive ideas came to naught. As previously mentioned, the British supported the Sabre and not the P.24. The AAF felt that only 2,460 hp (1,834 kW) at 3,000 rpm would be obtained from the P.24 (as built) with 100 octane fuel and that no part of the engine was so remarkable that it warranted production in the US. This opinion did not stop the AAF from adding 250 hours of flight time to the P.24 before the Battle was returned to Britain in 1943. The aircraft logged around 340 hours powered by the P.24 engine.

Some suggest that if FAC had received the resources given to Napier for development of the Sabre, the P.24 would have been a phenomenal engine. The P.24 was a good engine, but its performance does not appear to be exceedingly remarkable for the era in which it was developed. While it is true that the P.24 performed reliably, the 3,117 cu in (51.1 L) engine was producing under 2,000 hp (1,491 kW) for most of its developmental life. A P.24 Monarch engine and its contra-rotating propellers survived and are currently on display in the Royal Navy Fleet Air Arm Museum at Yeovilton. The engine and propellers were most likely those used on the Battle.

Fairey P24 engine configurations

A variety of P.24 engine configurations were illustrated in US patent 2,470,155. All of the different configurations are reminiscent of what Allison envisioned for the V-1710 and V-3420. Note the bevel gear drives for the power shafts.

Fairey Aircraft since 1915 by H. A. Taylor (1988)
British Piston Aero-Engines and their Aircraft by Alec Lumsden (2003)
World Encyclopedia of Aero Engines by Bill Gunston (2006)
Fairey Firefly by W. Harrison (1992)
Report on 50 Hours Civil Category Type Test Fairey P.24 – Series I (October 1939)
Memorandum Report on Fairey P-24 (Monarch) Engine by B. Beaman, F. L. Prescott, E. A. Wolfe, and Opie Chenoweth (22 August 1941)
Memorandum Report on Evaluation of P-24 Engine and Coaxial Rotating Propellers by Air Cops Material Division (27 August 1941)
“Improvements in or relating to Gaseous Fuel Induction Pipes for Internal Combustion Engine” British patent 463,501 by Fairey Aviation Company and Archibald Graham Forsyth (granted 1 April 1937)
“Improvements in or relating to Supercharging Internal Combustion Engines” British patent 463,984 by Fairey Aviation Company and Archibald Graham Forsyth (granted 9 April 1937)
“Improvements in or relating to Valve Mechanism for Internal Combustion Engines” British patent 465,540 by Fairey Aviation Company and Archibald Graham Forsyth (granted 10 May 1937)
“Improvements in or relating to Power Plants for Aircraft” British patent 469,615 by Fairey Aviation Company and Archibald Graham Forsyth (granted 29 July 1937)
“Marine Power Unit” US patent 2,389,663 by Archibald Graham Forsyth (granted 27 November 1945)
“Supercharging Arrangement” US patent 2,395,262 by Archibald Graham Forsyth (granted 19 February 1946)
“A Power Unit for Aircraft and the like” British patent 591,048 by Fairey Aviation Company and Archibald Graham Forsyth (granted 5 August 1947)
“Improvements in or relating to Power Units” British patent 591,189 by Fairey Aviation Company and Archibald Graham Forsyth (granted 11 August 1947)
“Supercharged Multiple Motor Internal-Combustion Unit for Aircraft” US patent 2,448,789 by Archibald Graham Forsyth (granted 7 September 1948)
“Power Plant Assembly” US patent 2,470,155 by Archibald Graham Forsyth (granted 17 May 1949)

Fairey Fox II P12 engine run

Fairey P.12 Prince Aircraft Engine

By William Pearce

Charles Richard Fairey founded the Fairey Aviation Company (FAC) in 1915. Fairey was at Cowes, Isle of Wight, United Kingdom in September 1923 to witness a practice session for the Schneider Trophy seaplane race over the Solent. What he saw both impressed and disappointed him.

Curtiss D-12 Fairey Felix

The Curtiss D-12 so impressed Richard Fairey that he went to the United States and acquired a license to produce the engine. Named the Fairey Felix, the engine was actually never produced, but 50 D-12 engines were imported.

Fairey was impressed by the Curtiss CR-3 racers, each with its compact 450 hp (336 kW) Curtiss D-12 engine turning a Curtiss-Reed metal propeller. When the race was run, the two CR-3 aircraft from the United States (US) proved to be 20 mph (32 km/h) faster than the British Supermarine Sea Lion racer. The Sea Lion was powered by a 550 hp (410 kW) Napier Lion W-12 engine that turned a wooden propeller. The two CR-3s finished the race averaging 177.266 mph (285.282 km/h) and 173.347 mph (278.975 km/h), while the Sea Lion averaged 157.065 mph (252.772 km/h). Fairey was disappointed that the British Air Ministry was not pushing its aircraft industry to make the same technological strides that were taking place in the US. Fairey was already frustrated by the constraints the Air Ministry placed on their specifications for new aircraft. With the world-beating performance of the Curtiss CR-3 aircraft fresh in his mind, Fairey resolved that if the Air Ministry would not push technology, he would.

Fairey went first to the Air Ministry seeking support for his new aircraft and was promptly turned down. Fairey then traveled to the US where, at great expense, he obtained manufacturing licenses for the Curtiss D-12 engine and Curtiss-Reed propeller. This agreement included some 50 D-12 engines to be used while FAC tooled up to manufacture their version, which was called the Felix. Fairey was so enthusiastic about the D-12, that he somehow smuggled an engine into his stateroom for his return sea voyage to Britain.

Fairey Fox bomber D-12 Felix

The Fairey Fox I light bomber was powered by the D-12/Felix engine. The aircraft was a private venture, and its performance surpassed other bombers and most fighters then in service. The British Air Ministry did not appreciate Fairey’s non-conformist attitude or the aircraft’s foreign power plant.

The D-12/Felix was a normally aspirated, liquid cooled, 60 degree, V-12 engine. The engine had a 4.5 in (114 mm) bore and a 6.0 in (160 mm) stroke. The D-12/Felix’s total displacement was 1,145 cu in (18.8 L), and it produced 435 hp (324 kW) at 2,300 rpm. The engine had four valves per cylinder that were operated by dual overhead camshafts.

With the engine situation under control, Fairey had his design department drew up plans for a new aircraft to be powered by the D-12/Felix. What came off the drawing board was the Fairey Fox I light bomber. Piloted by Norman Macmillan, the Fox I was flown for the first time on 3 January 1925. The Fox I had a top speed of 156 mph (251 km/h), some 50 mph (80 km/h) faster than comparable bombers then in service and also faster than most frontline fighters. Although it was built as a private venture, the Air Ministry was forced to buy a few Fox I bombers because of the aircraft’s unparalleled performance. The Air Ministry was not pleased with the situation and was downright appalled that the aircraft was powered by a US engine. Moreover, they did not want another aircraft engine manufacturer in Britain.

The Air Ministry tasked Rolls-Royce to develop an engine superior to the D-12. This new engine was developed as the Rolls-Royce Kestrel (type F) and was a stepping stone to the Merlin. The whole situation did nothing to improve the relationship between Fairey and the Air Ministry. However, had Fairey not forced the D-12 upon the Air Ministry, it is entirely possible that there may not have been a Merlin engine ready for the Battle of Britain in 1940.

Fairey P12 induction side

British patent 402,602 outlined how passageways cast into an engine’s crankcase could bring induction air into the cylinders. The patent also states how special oil lines (h) could traverse the passageway. This would help cool the oil and heat the incoming air/fuel mixture (which is not a good idea when higher levels of supercharging are applied to the engine).

The small order of Fox aircraft meant that the Fairey Felix engine never went into production. Only 28 Fox I aircraft were built, and a number were either built with or re-engined with Kestrel engines. FAC also built the D-12-powered Firefly I fighter, which first flew on 9 November 1925 and had a 185 mph (298 km/h) top speed. No orders were placed for the Firefly I.

Failing to enter the aircraft engine business on his first attempt did not stop Fairey from trying again. In 1931, FAC had hired Captain Archibald Graham Forsyth as chief engine designer. Forsyth had previously worked with Napier and Rolls-Royce while he was with the Air Ministry. Forsyth went to work designing a new aircraft engine. During this same period, Rolls-Royce started work on their PV-12 engine, which would become the Merlin.

Forsyth developed a liquid-cooled, 60 degree, V-12 engine known as the P.12. The upper crankcase and cylinder banks of the P.12 were cast together. Each detachable cylinder head housed four valves per cylinder. Reportedly, the P.12 used a dual overhead camshaft valve train similar to that used on the D-12/Felix. Cast into the Vee of the engine was the intake manifold and the runners, which branched off from the manifold. The intake runners aligned with passages cast integral with the cylinder head that led to the cylinders. The integral intake manifolds increased the engine’s rigidity, eliminated many pipe connections, and gave the engine a much cleaner appearance.

Fairey P12 engine section

A drawing from British patent 406,118 illustrates the induction passageways (d, e, and f) cast integral with the engine’s crankcase and head. The drawing also shows the water circulation from the crankcase to up around the cylinders and into the cylinder head. Although the valve arrangement is not specified, it is easy to see how four valves per cylinder with dual overhead camshafts could be accommodated.

The Fairey P.12 had a 5.25 in (133 mm) bore and a 6.0 in (152 mm) stroke. The engine’s total displacement was 1,559 cu in (25.5 L). Two versions of the P.12 were designed that varied in their amount of supercharging. The lightly-supercharged (some sources say unsupercharged) P.12 Prince produced 650–710 hp (485–529 kW) at 2,500 rpm. The moderately-supercharged P.12 Super Prince (or Prince II) produced 720–835 hp (537–623 kW) at 2,500 rpm. The P.12 engine weighed around 875 lb (397 kg).

The P.12 engine was first run in 1933. By 1934, three engines had been built and had run a total of 550 hours. One engine had run non-stop for 10 hours at 520 hp (388 kW) and had made three one-hour runs at 700 hp (522 kW). In late 1934, a P.12 Prince engine was installed in a Belgium-built Fox II (A.F.6022) aircraft (A.F.6022). The Prince-powered aircraft made its first flight on 7 March 1935. Ultimately, P.12 engines were run around 1,000 hours and had a final rating of 750 hp (559 kW) for normal output and 900 hp (671 kW) for maximum output.

Fairey Fox II P12 engine run

The Fairey Fox II was used as a testbed for the P.12 Prince engine. Unfortunately, little information has been found regarding the engine or its testing. Note the two exhaust stacks for each cylinder. The arrangement was similar to that used on the D-12/Felix engine.

In 1933, the Air Ministry issued specification P27/32 for a new light bomber. Marcel Lobelle, chief designer at FAC, drew up a number of designs, including one powered by two P.12 Prince engines. However, the Air Ministry wanted a single-engine aircraft. Lobelle altered the twin-engine design into what was basically a P.12-powered early design of the Fairley Battle. The Air Ministry made it clear to FAC that it would not consider any P.12-powered aircraft, because FAC was not a recognized engine manufacturer, and the Air Ministry did not want any other firms entering the aircraft engine field. Consequently, the FAC design for the P27/33 specification was switched to A Rolls-Royce Merlin I engine in 1934. This design was contracted as the Fairey Battle. The Battle was first flown on 10 March 1936 by Christopher Staniland, but an order for 155 aircraft (under specification P.23/35) had already been placed in May 1935. The Battle was the first production aircraft powered by the Merlin engine. With no support from the Air Ministry, the P.12 Prince faded into history.

Encouraged by the early bench tests of the P.12, Forsyth designed a more powerful 16-cylinder engine in January 1935 that was designated P.16. Initially, the P.16 design was basically a P.12 with four additional cylinders to make a V-16 engine. The P.16 used the same bore and stroke as the P.12 but displaced 2,078 cu in (34.1 L). Some sources state the P.16 was guaranteed to produce 900 hp (671 kW) at 12,000 ft (3,658 m) with a weight of only 1,150 lb (522 kg). The 900 hp (671 kW) output seems low, especially when compared to the anticipated performance of the Super Prince.

Fairey P27-32

FAC’s proposal to specification P27/32 included two twin-engine aircraft powered by P.12 Prince engines. The Air Ministry wanted a single-engine aircraft and would not consider anything powered by FAC engines. The specification and design eventually became the Fairey Battle.

Numerous sources suggest the P.16’s configuration was changed over concerns regarding the engine’s length combined with excessive torsional vibrations and stress of the V-16’s long crankshaft. The new, revised layout of the P.16 was an H-16 engine with two crankshafts, four banks of four cylinders, and an output of 1,540 hp (1,148 kW). This power level seems more reasonable than the 900 hp (671 kW) listed previously, but some sources give the 1,540 hp (1,148 kW) figure as an early power rating of a different engine (the P.24 Monarch). On occasion, the H-16 engine has been referred to as the P.16 Queen, but “Queen” was an early name for the P.24 Monarch. It may be that the H-16 engine never existed and has been mistaken for the P.24 over the years.

A third P.16 layout is described by other sources, which details the engine as a U-16 with two straight-eight engines mounted in parallel and geared to a common propeller shaft. FAC and Forsyth applied for a patent on 31 January 1936 (British patent 469,615) for such an engine configuration, but that date is after FAC moved away from the P.16, and the drawings depict a 12-cylinder engine. Both the H-16 and U-16 configurations would result in a much heavier engine of around 1,500 lb (680 kg).

Rather than proceed with a 16-cylinder engine, a new design had been started by October 1935. In fact, there is little evidence from primary sources that indicates a P.16 engine or an H-16 configuration were ever seriously considered. The new engine would keep the bore and stroke of the P.12 and use an H layout with four banks of six cylinders for a total of 24 cylinders. The H-24 engine design was called the Fairey P.24 Monarch.

Fairey U engine

Some sources state the P.16 engine was really two inline-eight engines coupled together as a U-16. While no drawings of a U-16 have been found, FAC and Forsyth did take out a British patent (no. 469,615) for a similar engine. This U-12 design was probably more of a stepping stone to the P.24 than a development of the P.16. Note the barrel (c) drawn between the cylinder banks.

Fairey Aircraft since 1915 by H. A. Taylor (1988)
British Piston Aero-Engines and their Aircraft by Alec Lumsden (2003)
World Encyclopedia of Aero Engines by Bill Gunston (2006)
Memorandum Report on Fairey P-24 (Monarch) Engine by B. Beaman, F. L. Prescott, E. A. Wolfe, and Opie Chenoweth (22 August 1941)
“Improvements in or relating to the Induction and Lubrication Systems of an Internal Combustion Engine” British patent 402,602 by Fairey Aviation Company and Archibald Graham Forsyth (granted 7 December 1933)
“Improvements in or relating to the Cylinder Block and Crank Case of an Internal Combustion Engine” British patent 406,118 by Fairey Aviation Company and Archibald Graham Forsyth (granted 22 February 1934)
“Improvements in or relating to Power Plants for Aircraft” British patent 469,615 by Fairey Aviation Company and Archibald Graham Forsyth (granted 29 July 1937)
“Fairey Battle Database” by W. A Harrison Aeroplane (June 2016)

Irving-Napier Golden Arrow museum

Irving-Napier Golden Arrow LSR Car

By William Pearce

On 29 March 1927, Henry O’Neil de Hane Segrave set a new Land Speed Record (LSR) in the Sunbeam 1,000 hp Mystery Slug. Segrave achieved a speed of 203.793 mph (327.973 km/h) over the one mile course on Dayton Beach in Florida. Segrave was the first to travel over 200 mph (322 km/h) on land and returned to Britain a hero. However, he wanted to go faster.

Irving-Napier Golden Arrow model

John Samuel Irving holds a model of the Irving-Napier Special / Golden Arrow. Irving was responsible for the car’s design, as well as the previous car Henry Segrave used to break the 200 mph (322 km/h) mark, the Sunbeam 1,000 hp Mystery Slug.

Shortly after his return to Britain, Segrave parted ways with the Sunbeam Motor Car Company and joined the Portland Cement Manufacturers as a high-profile salesman. Segrave worked quickly to get the financial backing of his employer and from some of the sponsors involved with his previous record attempt. With funding secured, Segrave turned to John Samuel Irving to design the new LSR car. Irving had designed the Sunbeam Slug and had also left the company shortly after the successful record runs.

Segrave’s 203.793 mph (327.973 km/h) record stood for less than a year before it was beaten by Malcom Campbell. Driving his updated Blue Bird racer, Campbell averaged 206.956 mph (333.064 km/h) on 19 February 1928. Campbell’s record stood for only two months before it was slightly bettered by American Ray Keech driving the White Triplex at 207.553 mph (334.024 km/h) on 22 April 1928.

The new records did not worry Segrave; much higher speeds were planned with the car Irving had designed. Segrave’s new car was initially called the Irving Special. Once the Napier Lion VIIA aircraft engine was acquired to power the car, its name was updated to Irving-Napier Special. The direct drive Lion VIIA had powered the Supermarine S5 aircraft that finished second in the 1927 Schneider Trophy, while the geared Lion VIIB engine powered the S5 that won the trophy. Once the car was painted its gold finish, it was often referred to as the Golden Arrow.

Irving-Napier Golden Arrow construction

This image of the Golden Arrow being built shows just how closely the cowling fit over the Napier Lion engine. The front two screw jacks can be seen passing through the car’s body. The holes and fins on the brake drums were to help dissipate heat. Note the stout frame rail.

The Napier Lion VIIA was a W-12 (or broad arrow) engine design with a 5.5 in (140 mm) bore and a 5.125 in (130 mm) stroke. The engine displaced 1,461 cu in (23.9 L) and produced 930 hp (694 kW) at 3,400 rpm. The Lion engine was installed in the Golden Arrow’s narrow frame, just behind the front wheels. The car’s frame rails were made of channel section steel 13 in (330 mm) tall and 4 in (102 mm) wide. Each corner of the frame had a threaded jacking point. The rest of the Golden Arrow’s structure was made from tubular steel and wood.

A three-speed transmission was mounted behind the Lion engine. First gear maxed out at 81 mph (130 km/h), second at 166 mph (267 km/h), and third gave a theoretical top speed of 246 mph (396 km/h). The transmission took the engine’s power and distributed it to two drive shafts that rotated in opposite directions. The shafts passed along both sides of the cockpit and to the rear axle. This arrangement allowed the driver’s seat to be placed some 8 in (200 mm) lower than if the driveshaft passed under the seat.

Irving-Napier Golden Arrow crate

The Golden Arrow was carefully packed for its trip across the Atlantic. The covers over the surface radiators were regularly used when the car was not being run. Note the black “aiming” stripe on the upper engine cowling. The car’s narrow cockpit was designed especially for Segrave, and the cockpit side panels were attached after Segrave was in the driver’s seat.

The offset driver’s seat in the Sunbeam Slug had made driving the car at speed slightly more challenging. Irving decided to have the driver positioned right on the centerline of the Golden Arrow. Steel plating .25 in (6 mm) thick encased the cockpit to protect the driver. A telescopic sight was placed in front of the driver, and a sighting tab was located in front of the engine on the upper cowl. In addition, a black stripe was painted along the center of the car. This was all done to make driving the Golden Arrow as easy as possible at well over 200 mph (322 km/h). The steering gearbox was positioned on top of the transmission. A drag link extended from each side of the box to the front wheels. The wheels themselves were not linked together by a tie rod. The car’s drum brakes and clutch were vacuum assisted.

The Golden Arrow’s tires were specially made by the Dunlop Rubber Company. The tires were 37 x 7 in (940 x 178 mm) and filled with 125 psi (8.6 bar) of air. Dunlop had guaranteed the tires to last 25 seconds at 240 mph (386 km/h). At that speed, it would only take 15 seconds to travel the measured mile, and the tires would be changed after each run. A streamlined fairing extended back from each front wheel to each rear wheel. The fairing improved the aerodynamics of the car and was covered in surface radiators built by the Gloster Aircraft Company. Special covers were placed over the surface radiators to protect them when the car was not running.

The surface radiators served as the primary means to cool water for the Golden Arrow’s engine. However, if the engine temperature rose too high, a secondary cooling system was employed. This system consisted of an isolated chemical compound in a tank positioned in the front of the car. When the engine got too hot, thermostats allowed water from the engine to flow through the tank where it would be cooled by the chemical. Unfortunately, which chemical was used has not been found (perhaps dry ice or cardice). The header water tank was located behind the engine, and two oil tanks were located in the frame rails.

Irving-Napier Golden Arrow Segrave Daytona

Segrave poses in the Golden Arrow on Daytona Beach. The telescopic sight has been installed in front of the cockpit, and the fore sight has been installed on the front of the top cowling. These sights were removed after the car’s first practice run. Note the aerodynamic wheel covers.

With the use of a wind tunnel, Irving designed the Golden Arrow’s body to minimize frontal area and drag. The body sloped to a point in front of the engine, and the engine’s three cylinder banks were very closely cowled. The car’s streamlined body flowed back to the cockpit, located in front of the rear wheels. Behind the cockpit was a 24 gallon (91 L) fuel tank, and the body transitioned into a tail to provide directional stability at high speeds. The Golden Arrow’s main body was inspired by the Supermarine S5 Schneider racer, and the entire body was designed to provide downforce to keep the car on the ground. The car’s aluminum body was built by coachbuilders Thrupp & Maberly.

The Irving-Napier Golden Arrow was 27 ft 6 in (8.38 m) long, 6 ft 1 in (1.85 m) wide, and 3 ft 8 in (1.12 m) tall. The car had a 14 ft (4.27 m) wheelbase, a 5 ft (1.52 m) track, and 7 in (178 mm) of ground clearance. The Golden Arrow weighed around 7,694 lb (3,490 kg) loaded. Irving and Segrave wanted to set the LSR at over four miles per minute—240 mph (386 km/h).

The Golden Arrow was built in 1928 at Kenelm Lee Guinness’ Robinhood Engineering Works. The car made its public debut at the end of January 1929. Virtually no testing occurred before the car, Segrave, and team left for Daytona Beach, Florida on 31 January 1929. Upon arrival, weather conditions were poor, and it was not until 20 February that Segrave took the car out for it first practice run. This was actually the first time Segrave drove the car. He went up and down the beach once, hitting a top speed of over 180 mph. Segrave then drove the Golden Arrow on public streets the short distance back to the garage. A few modifications were made, such as the removal of the telescopic sight and installing a smaller front sight. Segrave now thought the car was perfect and that it was time to make an attempt on the record.

Irving-Napier Golden Arrow Segrave radiator

A close-up of Segrave in the Golden Arrow shows details of the surface radiators, the telescopic sight, and Segrave’s rudimentary crash helmet. The cockpit side panels are not attached. Note that “Irving Napier Special” is painted behind the cockpit.

On 11 March 1929, the weather and beach conditions were acceptable to make a LSR attempt. Around 100,000 spectators turned out to watch, and large arc lights were strung at both ends of the measured mile. Segrave lined up the sights on the Golden Arrow as he rocketed north along the beach, shifting gears at 3,200 rpm. Fighting a cross wind, he passed through the measured mile in 15.55 seconds, averaging 231.511 mph (372.581 km/h). Suddenly, a radiator hose loosened, spraying hot water over Segrave, but he managed to maintain control. After the run, the water line was fixed, tires were changed, and water and fuel were replenished.

Segrave now made his run southward, still battling the crosswind. After using 4 miles to come up to speed, the Golden Arrow ran through the measured mile in 15.57 seconds, averaging 231.214 mph (372.103 km/h). The average of his two runs gave Segrave a new LSR of 231.362 mph (372.341 km/h)—23.809 mph (38.317 km/h) faster than the previous record set by Ray Keech in the Triplex. Some sources list the speed as 231.446 mph (372.478 km/h), which was Segrave’s speed for the flying kilometer, not the mile. At the end of the run, Segrave hit a gulley in the sand, and the Golden Arrow twisted sideways, damaging the right surface radiator.

Irving-Napier Golden Arrow Segrave front

Front view of the Golden Arrow as the car and Segrave pose for photographers. The exhaust stacks for the Lion’s side banks were on the bottom of the cowling. Segrave did not have any issues with exhaust fumes entering the cockpit.

The record had come easy. Segrave felt the Golden Arrow had more speed left, and the car was repaired for another run. However, Segrave decided that he would only make another record attempt if the White Triplex beat his speed. Driven by Lee Bible, the White Triplex took to the course on 13 March 1929. Bible’s first run was at 186 mph (299 km/h) and his second was at 202 mph (325 km/h). However, something happened at the end of the second run that caused Bible to lose control of the Triplex. The car crashed, killing Bible and Charles Traub, a British Pathé cameraman who was filming the record run. The accident put an end to the 1929 record season at Daytona.

Segrave returned to Britain and was knighted on 27 April 1929. A short time later, Segrave declared that he was done with LSRs. He found Water Speed Records more of a challenge and focused his efforts there. On 13 June 1930, Segrave made two good runs on Windermere lake in his Miss England II motorboat powered by two 1,800 hp (1,342 kW) Rolls-Royce R engines. Accompanying him were Mechanic Michael Willcocks and Rolls-Royce engineer Victor Halliwell. Although Segrave did not know it at the time, the runs established a new water speed record at 98.76 mph (158.94 km/h).

Irving-Napier Golden Arrow run south

Segrave and the Golden Arrow making their south run on Daytona Beach at 231.214 mph (372.103 km/h). Few images of the car at speed exist despite numerous photographers attending the record attempt. At the time, photographers had little experience capturing high-speed subjects. Note that the original sights have been removed.

Segrave had made the first two runs at less than full throttle and knew that he could do better. Without coming to shore, he immediately set out for another two runs. On his third run of the day, Miss England II was traveling around 120 mph when the boat hit some debris and violently capsized. Segrave, Halliwell and Wilcocks were all thrown into the water. Willcocks was pulled from the water alive. Halliwell was killed in the crash; his body was recovered two days later, still clutching his pencil and notepad. Segrave was found unconscious and taken to a shore-side house where he was treated by doctors. Segrave regained consciousness, asked about Willcocks and Halliwell, asked about the record, and then passed away from his injuries.

Segrave was the first person to simultaneously hold the World Land Speed Record and the World Water Speed Record. The Irving-Napier Golden Arrow was never raced again after its record run, and the car has been driven under its own power fewer than 40 miles (64 km). The Golden Arrow was preserved and is currently on display at the British National Motor Museum in Beaulieu, Hampshire, United Kingdom.

Irving-Napier Golden Arrow museum

A fantastic image of the Golden Arrow as it sits in the British National Motor Museum. The holes for the front screw jacks can be seen as well as the separate drag links for the front wheels. (Brian Snelson image via

The Land Speed Record 1920-1929 by R. M. Clarke (2000)
The Fast Set by Charles Jennings (2004)
Land Speed Record by Cyril Posthumus and David Tremayne (1971/1985)
Leap into Legend by Steve Holter (2003)

Sunbeam 1000 hp Mystery Slug top

Sunbeam 1,000 hp Mystery Slug LSR Car

By William Pearce

On 16 March 1926, Henry O’Neil de Hane Segrave blasted down Ainsdale Beach at Southport, England and set a new Land Speed Record (LSR) at 152.33 mph* (245.15 km/h). The speed was only 1.57 mph (2.53 km/h) faster than the previous record, set by Malcolm Campbell on 21 July 1925, and Segrave knew his record would not stand for long. What Segrave needed to achieve a truly impressive speed was a car designed especially for the LSR.

Sunbeam 1000 hp Mystery Slug top

The Sunbeam 1,000 hp Mystery Slug as it appears today. Note the side exhaust for the front engine and the individual stacks for the rear engine. ( image)

Segrave was born in the United States (US) to an American mother and an Irish father. He was raised in Ireland and England, and was a pilot in the First World War. He became a race car driver after the war and drove Sunbeam-Talbot-Darracq autos to many victories. The Sunbeam Motor Car Company found Grand Prix racing too expensive and quit competing in 1926. By 1927, Segrave had left auto racing completely to focus solely on setting land speed records.

Sunbeam had previously provided Campbell and Segrave’s LSR cars. These machines were little more than modified Grand Prix racers. Louis Hervé Coatalen was the managing director of Sunbeam and understood how speed records would translate into auto sales. Coatalen knew that a specially-designed LSR car would be able to achieve much higher speeds than the current record. Coatalen also knew that such a car could be built fairly inexpensively by utilizing many of the unused parts at the Sunbeam factory. Coatalen agreed to build a special LSR car for Segrave, and their target was 200 mph (322 km/h).

Sunbeam 1000 hp Mystery Slug test

The Slug being tested at the Sunbeam works. The steel guards over the tires and chain can be seen. Many pipes were needed to bring in cool water and take away hot water and exhaust. The front engine’s four magnetos can be seen between the front tires.

The new LSR car was designed by John Samuel Irving in 1926 and built by the Sunbeam works in Wolverhampton. Its frame and crossmembers were made of channel-steel. Two Sunbeam Matabele aircraft engines would be used to push the car to 200 mph (322 km/h). Coatalen had originally designed the V-12 Matabele engine around 1917. The engine had a 4.80 in (122 mm) bore and a 6.30 in (160 mm) stroke. Total displacement was 1,370 cu in (22.4 L), and the engine produced around 450 hp (336 kW) at 2,000 rpm but could be overrevved to 2,200 rpm. The two engines in the car had actually been salvaged from the four used in the Maple Leaf VII powerboat, which sunk during the 1921 Harmsworth Trophy Race on the Detroit River in the United States.

Although each of the two engines produced only 450 hp (336 kW), the racer was officially called the “1,000 HP Sunbeam.” As the car was constructed, the workmen dubbed it “The Slug” due to the shape of its body. When the car arrived in the US, the American newspapers called it the “Mystery S.” Perhaps it is most appropriate to combine all the names and call it the “Sunbeam 1,000 hp Mystery Slug.”

The driver sat in the middle of the car and was offset to the right. One engine was installed in front of the driver and the other behind. The front engine had a single radiator in the car’s nose, and its exhaust was expelled through a single stack on each side of the car. Louvers covered the front of the car to let the heat from the front engine escape. The rear engine had two radiators, one on each side of the car, positioned behind the driver. Cooling air was brought in through ducts on both sides of the car and escaped out an opening in the car’s tail. The rear engine’s exhaust was expelled through 12 stacks that protruded behind the driver.

Sunbeam 1000 hp Mystery Slug debut

When first shown to the press, the Slug had wheel covers over its rear tires. These were removed for the record run. Note the louvered scoop for the rear radiator. Airflow proved inadequate, and a larger scoop was fitted. Segrave is looking into the car.

The engines were installed back-to-back and were linked by a common shaft. The rear engine was started with compressed air. Once the rear engine was running, it was clutched to the front engine via the common shaft, which started the front engine. With both engines running, the common shaft locked the engines together to keep them at the same rpm. A three-speed transmission took power from the common shaft and drove a cross shaft. A sprocket and chain on each end of the cross shaft delivered power to the rear axle. The transmission actually stepped up the speed of the cross shaft over the speed of the common shaft, but the chain drive acted as a gear reduction, bringing the final drive ratio to 1.02:1. The Slug had a theoretical top speed of 212.5 mph (342.0 km/h) with the engines turning at 2,000 rpm.

The Slug’s innards were covered by a streamlined aluminum body developed after wind tunnel tests at the Vickers Aviation Department. To keep the driver safe, the frame was reinforced around the cockpit, and thick steel guards were installed around the drive chains and tires. A .25 in (6 mm) thick steel underbody was installed that allowed the Slug to slide along the ground if a tire failed. Covers were originally fitted over the rear wheels, but these were removed for the record runs. The 35 x 6 in (635 x 152 mm) tires were specially designed by the Dunlop Rubber Company and guaranteed to last 3.5 minutes at 200 mph (322 km/h). The tires would be changed after each record run. In the tail of the car, behind the rear engine, was a 28 gallon (106 L) fuel tank. The 1,000 HP Sunbeam had a wheelbase of 11 ft 9 in (3.58 m) and a track of 5 ft 2 in (1.57 m). The car was 3 ft 7 in (1.09 m) tall and over 23 ft (7.01 m) long. The Slug had 7 in (178 mm) of ground clearance and weighed around 7,790 lb (3,533 kg) empty.

Segrave sits in the 1,000 HP Sunbeam. The louvers on the front of the car allowed heat to escape the front engine bay. The “Co” painted on the side of the racer was changed to “CAR.” With the rear wheel cover removed, both “CAR” and “ENGLAND” were cut off. (Getty Images)

Once assembled, the car was run on a special test rig for six hours to resolve any issues. The 1,000 HP Sunbeam made its official debut on 21 February 1927. Segrave realized there was no place in Europe to safely run the car and made plans for a record attempt at Daytona Beach, Florida. Some of the car’s backers were unhappy about the runs being planned outside of Britain and forced Segrave to personally make his own arrangements to ship the car and travel overseas. Segrave rose to the challenge and got the Association Internationale des Automobile Clubs Reconnus (AIACR) to recognize the attempts which would be overseen by the American Automobile Association (AAA). This required much negotiation between the AIACR and the AAA.

Segrave, his crew, and the Slug left for the US in February 1927. Segrave’s earlier LSR has been beat on 28 April 1926** by John Godfrey Parry-Thomas at 170.624 mph (274.593 km/h) in his racer “Babs.” Campbell regained the record on 4 February 1927 with a speed of 174.224 mph (280.387 km/h) in his new “Blue Bird” racer. While attempting to win back the record, Parry-Thomas was killed on 3 March 1927. At the time, a chain was thought to have broken free and killed Parry-Thomas. As a result, Segrave decided to thoroughly inspect his chains throughout his record runs.

Sunbeam 1000 hp Mystery Slug Seagrave beach

Segrave stands by the Slug on Daytona Beach. The larger scoops for the rear radiator have been installed. The rear wheel covers have been removed, and wheel discs cover the spokes on the rear wheels. The removed cover behind the rear engine gave access to the fuel tank. At the front of the car, part of the underbody is visible.

Segrave and the Slug’s first test run was on 21 March 1927. The Daytona Beach course featured four miles (6.4 km) to accelerate, one measured mile (1.6 km), and four miles (6.4 km) to slow the car. This was the first time the car was driven for any real distance. Other than being difficult to steer and the rear engine getting hot, the car performed well on its rather sedate trips along the beach. A new steering box was installed, which required some modifications to the car. Larger scoops were added to the Slug’s sides to draw more air into the radiators for the rear engine. The biggest issue Segrave encountered was with the thousands of spectators who turned out to watch and got in the way of the car and the time measuring equipment. The car’s next run was on 24 March, and higher speeds were attained. More police were present to help control the crowds, but they were still an issue.

With increased crowd control and no technical issues to overcome, the decision was made to make a serious attempt at the record. On 29 March 1927, Segrave set off to the north, determined to get every bit of speed he could out of the Slug. Reportedly, 30,000 spectators were on the beach that day. Fighting against the wind, Segrave hit some marker flags that lined the prepared course, but he pushed on and flew through the measured mile (1.6 km) in 17.94 seconds, averaging 200.669 mph (322.945 km/h). Letting off the throttle, Segrave found that the Slug did not decelerate as quickly as he had anticipated. Nearing the end of the course, he hit the brakes hard only to have them melt. Segrave then drove the car into the sea along the shore to slow it down and regain control.

Sunbeam 1000 hp Mystery Slug beach

Given the cleanliness of the car, this image was probably taken before the record run. Note how the removal of the wheel covers chopped off “CAR” and “ENGLAND.” The large rear radiator scoops must have created a fair amount of drag.

The car was prepared for its second run: tires were changed, new brakes were installed, and fuel and water were replenished. A short time later, Segrave ran the Slug with the wind to the south. With the engines hitting 2,200 rpm, Segrave blasted through the measured mile (1.6 km) in 17.39 seconds, averaging 207.016 mph (333.160 km/h). With a little more control that in his previous run, he brought the car to a safe stop at the end of the course. Segrave and the Sunbeam 1,000 hp Mystery Slug had set a new LSR of 203.793 mph (327.973 km/h)—an astounding 29.569 mph (47.587 km/h) faster than the previous record (Campbell’s).

Segrave and the Slug’s record run represented the first time the 200 mph (322 km/h) mark was exceeded. Segrave was the first non-US citizen to make a record attempt at Daytona Beach. Likewise, the 1,000 HP Sunbeam was the first non-US car to make a record attempt at Daytona Beach. The Slug ushered in a new era of large, streamlined machines designed solely to break the LSR.

Sunbeam 1000 hp Mystery Slug run

Segrave and the Slug are seen racing down Dayton Beach on the second (south) record run. The marker flag is similar to those that Segrave hit on his first pass. The relative positions between the photographer and the flag give a sense of how narrow the course was.

Segrave’s record stood for less than a year before Campbell bettered the speed by only 3.163 mph (5.090 km/h). At the time, Segrave was busy working on a new LSR car, the Golden Arrow. The Slug’s one outing in Florida had gained the record but had also shown that the car’s chain-drive was antiquated and that its second-hand engines could be improved upon. The Sunbeam 1,000 hp Mystery Slug was preserved and eventually made its way to the British National Motor Museum in Beaulieu, Hampshire, United Kingdom, where it is currently on display. The car has been driven approximately 75 miles (120 km) under its own power.

*Segrave’s 152.33 mph (245.15 km/h) record was over 1 km (not 1 mile) and was officially recognized by the AIACR. The speed had already been exceeded by Tommy Milton, who drove his twin-engine Duesenberg-Milton racer to a recorded speed of 156.046 mph (251.132 km/h) on 27 April 1920. Milton’s car caught fire during the first run, and he was unable to make a return pass. Milton’s speed was recognized by the AAA as a US record, but it was not recognized by the AIACR as an international record.

** Parry-Thomas actually broke Segrave’s record on 27 April 1926 at a speed of 168.074 mph (270.489 km/h). Parry-Thomas then set a new record the following day.

Sunbeam 1000 hp Mystery Slug display

The Sunbeam 1,000 hp Mystery Slug on display in the British National Motor Museum. While the car has been preserved, the rear radiator scoops and rear tire covers seem to have been lost. Note the bulge in front of the cockpit meant to deflect some air away from the driver’s face. Segrave had much trouble with the wind trying to rip his goggles and helmet off. (David Chief image via Wikimedia Commons)

The Land Speed Record 1920-1929 by R. M. Clarke (2000)
The Fast Set by Charles Jennings (2004)
Land Speed Record by Cyril Posthumus and David Tremayne (1971/1985)
Sunbeam Aero-Engines by Alec Brew (1998)

Sikorsky S-67 Blackhawk airbrakes

Sikorsky S-67 Blackhawk Attack Helicopter

By William Pearce

In the late 1960s, Sikorsky Aircraft had many helicopter models in production, but they had lost contracts to develop new helicopters. In 1966, the United States Army’s Advanced Aerial Fire Support System (AAFSS) contract was awarded to Lockheed, but their AH-56 Cheyenne attack helicopter ran into serious design issues. On 20 November 1969, Sikorsky initiated development of a new helicopter to be used primarily as a gunship, but it could also be used in other roles. This helicopter was designated S-67 Blackhawk, and its design and construction was self-funded by Sikorsky.

Sikorsky S-67 Blackhawk airbrakes

The Sikorsky S-67 Blackhawk was a very versatile helicopter that exhibited great performance, but it also had various shortcomings that the US Army could not overlook. The helicopter’s narrow fuselage and air brakes are illustrated in this image.

The Sikorsky S-67 Blackhawk was designed as a high-speed attack helicopter with a small wing to generate lift. The pilot and copilot/gunner sat in tandem in the helicopter’s cockpit, with the copilot in the front seat and the pilot in the rear seat. The pilot accessed the cockpit from the left side of the helicopter and the copilot from the right. The narrow, streamlined fuselage was only 3 ft 10 in (1.2 m) wide, which decreased the helicopter’s drag and increased its survivability by presenting a smaller target to enemy gunners. Behind the cockpit was a compartment that could be used for additional equipment or to transport personnel.

Sikorsky S-67 Blackhawk tail

This image shows the S-67’s original tail that did not have any rudders. Note the tail’s camber. Air brakes can be seen on the upper wing surfaces. The main gear had a 7 ft (2.1 m) track.

To cut expense and development time, the S-67 was designed to use the dynamic drive power system from a Sikorsky S-61/SH-3 Sea King. This included two 1,500 hp (1,119 kW) General Electric T58-GE-5 turboshaft engines and their drive, rotor, hydraulic, and electrical systems. The S-67’s five-blade rotors had 22 in (559 mm) of their tips swept back 20 degrees to delay compressibility effects, lower vibration, and reduce noise. The net effect was that the blades allowed the helicopter to achieve higher speeds. The main rotors also had a hub fairing, and their collective pitch control was modified to increase sensitivity and range.

The S-67’s main gear retracted into sponsons mounted on the fuselage sides. The helicopter’s thin wings extended from the sponsons. Each wing featured two hardpoints for weapons, auxiliary fuel tanks, or equipment. Each wing also had three air brakes: two that deployed along its upper surface and one that deployed along the lower surface. With the air brakes deployed, the helicopter slowed twice as fast as without the air brakes. In addition, the air brakes could be deployed during combat to offer unrivaled maneuverability. The S-67 was the first helicopter with air brakes.

A five-blade, 10 ft 7 in (3.2 m) diameter tail rotor was mounted to the left side of the S-67’s vertical fin. A lower fin with a non-retractable tailwheel extended below the helicopter’s tail. The large upper and lower fins were cambered to counteract the torque of the main rotor at speeds above 46 mph (74 km/h). This enabled controlled flight without the tail rotor as long as the S-67’s forward speed was in excess of 46 mph (74 km/h). If the tail rotor was lost, the helicopter could be flown back to base and landed like a conventional aircraft. The S-67 used an all-moving horizontal stabilizer that increased the helicopter’s maneuverability and decreased rotor stress.

Sikorsky S-67 Blackhawk landing

Note the angle of the all-moving horizontal stabilizer as the S-67 comes in for a landing. The landing gear was found to be insufficient for operating from unimproved locations. The helicopter’s double main wheels sunk into soft ground, and the gear doors only had 9.75 in (248 mm) of clearance.

With a 7,000 lb (3,175 kg) payload, the S-67 could accommodate a variety of armaments. A removable Emerson Electric Company TAT-140 turret mounted under the cockpit could carry a 7.62 mm minigun (M134), a 20 mm three-barrel rotary cannon (M197), a 30 mm single-barrel cannon (XM140), a 30 mm three-barrel rotary cannon (XM188), or a 40 mm grenade launcher (M129). The four underwing hardpoints could carry two drop tanks, up to 16 TOW missiles, or up to eight rocket pods. Each 2.75 in (70 mm) rocket pod contained 19 rockets, for a total of 152 rockets.

Sikorsky S-67 Blackhawk side

The S-67’s rudders can be seen in this image. One is on the upper fin below the tail rotor, and the other is on the lower fin. Pylons have been installed on the wings’ hardpoints, with drop tanks mounted to the inner stations. The turret is installed with a M197 three-barrel 20 mm cannon.

The S-67 had a wingspan of 27 ft 4 in (8.3 m) and a rotor diameter of 62 ft (18.9 m). The fuselage was 64 ft 2 in (19.6 m) long, and the helicopter’s total length including the rotor was 74 ft 1 in (22.6 m). The S-67’s mast height was 15 ft (4.6 m), and the top of the tail rotor was 16 ft 4 in (5.0 m). The helicopter’s top speed was 213 mph (343 km/h); maximum cruise speed was 201 mph (324 km/h), and normal cruise speed was 167 mph (269 km/h). The S-67 could climb at 2,000 fpm (10.2 m/s) and had a service ceiling of 20,000 ft (6,096 m). The helicopter could hover in ground effect up to 9,700 ft (2,957 m) and could hover without ground effect up to 6,500 ft (1,981 m). Maximum range on internal fuel was 325 miles (523 km), but its normal combat range was 220 miles (354 km). With external fuel tanks, range was extended to over 600 miles (966 km). The S-67 had an empty weight of 12,525 lb (5,681 kg), a normal weight of 18,500 lb (8,391 kg), and a maximum takeoff weight of 22,050 lb (10,002 kg).

Sikorsky S-67 Colonge Germany 1972

The S-67 seen in the same configuration as the previous image. The helicopter is over Cologne, Germany on its European and Middle Eastern tour in 1972.

Construction on the S-67 started on 15 February 1970 and proceeded rapidly. The helicopter made its first flight on 20 August 1970. Flight testing proved the S-67 to be very responsive, maneuverable, smooth, and quiet. The helicopter was able to perform rolls, loops, and split-S turns—although, only rolls to the right were made. On 14 December 1970, Sikorsky test pilots Kurt Cannon and Byron Graham in the S-67 established a new absolute speed record by averaging 216.841 mph (348.971 km/h) over a 3 km (1.86 mile) course. They then set a new record on 19 December 1970 by averaging 220.888 mph (355.485 km/h) on a 15–25 km (9.3–15.5 mile) course.

In 1971, the S-67 covered 3,500 miles (5,633 km) touring 12 US military bases. In addition to Sikorsky demonstration flights, the helicopter was flown on 147 demo flights with military personnel. The S-67 completed 155 rolls and 140 split-S turns during these flights.

Sikorsky S-67 Blackhawk fan-in-tail

A fan-in-fin anti-torque system was tested in the S-67. Note the rudders above and below the fan. No issues were encountered with the fan-in-fin, but the helicopter was converted back to a conventional tail rotor.

Between 25 May and 13 June 1972, the S-67 was flown 26 hours for a series of flight evaluations by the US Army. The helicopter was competing against the Bell 309/AH-1 KingCobra to replace the AH-56 Cheyenne, which had been cancelled. For the AAFSS role, the S-67 was designated AH-3, and Sikorsky’s proposal included adding an additional hardpoint to each wing, bringing the total number to six. This would enable the S-67 to carry up to 24 TOW missiles. While the S-67 was praised for its performance and most of its flight characteristics, the evaluation recorded a number of shortcomings. The Army did not award either Sikorsky or Bell a contract and decided to initiate a new Armed Attack Helicopter program, which eventually was won by the Hughes AH-64 Apache.

The S-67 underwent a number of modifications in late 1972. Rudders were added to the ventral and dorsal fins to increase yaw control. The compartment behind the cockpit was altered to enable the transport of six troops. Hardpoints were added to the wingtips for each to carry a Sidewinder missile. A hoist was added under the helicopter that allowed the S-67 to transport a 7,000 lb (3,175 kg) external load.

Sikorsky S-67 Blackhawk cockpit

After the fan-in-tail rotor tests, a small door was added on the left side of the fuselage to access the compartment behind the cockpit. Initially, access was gained (with some difficulty) via the door under the fuselage (seen above). The S-67 was then painted a light desert camouflage, and this was the helicopter’s final configuration.

With no interest from the US Armed Forces, Sikorsky offered the S-67 for export. In late 1972, the S-67 was taken on a two-month tour of Europe and the Middle East. More than 7,500 miles (12,070 km) were covered, and the helicopter was flown for 136 hours. Despite interest from Israel, no orders were placed. Sikorsky then modified the S-67 to test a fan-in-fin tail rotor installation. A 4 ft 8 in (2.6 m), seven-blade rotor was installed in the modified tail. The helicopter underwent flight tests, including a dive at 230 mph (370 km/h). After the tests in 1974, the S-67’s tail was converted back to its previous configuration (with rudders), and a door to access the rear compartment was installed in the helicopter’s left side. The S-67 was then painted a light desert camouflage. The data from the fan-in-fin test was used for the Sikorsky H-76 fantail demonstrator, which tested the tail configuration later used in the Boeing-Sikorsky RAH-66 Comanche.

Sikorsky S-67 Blackhawk inverted

The S-67 made hundreds of rolls in its lifetime, but they were always to the right. The square in the fuselage above the wing is the window in the new rear compartment access door. What appear to be two rectangular windows can be seen father aft. Note the helicopter’s rudders and deployed air brakes.

On 26 August 1974, the S-67 arrived in the United Kingdom to start another European tour. On 1 September 1974, the S-67 was destroyed after failing to recover from a second roll during a practice session for the upcoming Farnborough Air Show. The copilot, Stu Craig, was killed in the crash, and the pilot, Kurt Cannon, died from his injuries nine days later. The accident was caused by the second roll being initiated in a less than ideal configuration combined with low altitude. However, the accident investigators believed that the crash was survivable had the helicopter been fitted with five-point harnesses rather than four-point harnesses. The S-67 had accumulated 598.7 hours at the time of the crash.

With the prototype destroyed and no interest from the US military, Sikorsky decided to end the S-67 Blackhawk program. Its swept-tip rotor blades were developed into those used on the Sikorsky S-70/UH-60 Black Hawk (the name similarity is a coincidence) and other helicopters. The S-67’s speed record stood for eight years until it was broken on 21 September 1978 by the Soviet Mil A-10 (modified Mi-24B) at 228.9 mph (368.4 km/h).

Sikorsky S-67 Blackhawk crash

The S-67 tries to recover from a roll a split second before it impacts the ground. The helicopter’s low altitude left no room to recover from the roll, which was rushed and initiated in a flawed manner. The crash would ultimately kill the pilot and copilot and end the S-67 program.

“Blackhawk’s Last Flight” Aeroplane Monthly (June 1976)
Attack Helicopter Evaluation, Blackhawk S-67 Helicopter by George M. Yamakawa, et al (July 1972)

Douglas XB-42 no1 in flight

Douglas XB-42 Mixmaster Attack Bomber

By William Pearce

In the early 1940s, Edward F. Burton began to investigate ways to simplify bomber aircraft. Burton was the Chief of Engineering at the Douglas Aircraft Company (Douglas), and he had noted that each subsequent generation of bomber aircraft was substantially larger, more complex, and more expensive than the preceding generation. Burton and his team started with a clean sheet of paper and designed what would become the XB-42.

Douglas XB-42 no1 in flight

The Douglas XB-42 Mixmaster had a unique design that provided very good performance. However, it was too late for World War II and too slow compared to jet aircraft. The first prototype (43-50224) is seen with its short tail on an early test flight.

Acting on their own, with no official United States Army Air Force (AAF) requirement, Burton and his team worked to design a two-engine tactical bomber with a top speed of over 400 mph (644 km/h) and that was capable of carrying 2,000 lb (907 kg) of bombs to a target 2,500 miles (4,023 km) away. The aircraft’s high speed would eliminate the need for extensive defensive armament, which would minimize the bomber’s crew and save weight. Burton’s team placed the wings, tail, and propellers in their optimal positions; the designers then filled in the rest of the aircraft with the needed equipment. What emerged from the drafting table was the Douglas Model 459: a mid-wing aircraft operated by a crew of three. At the rear of the aircraft were a set of coaxial contra-rotating pusher propellers driven by engines buried in the fuselage. In May 1943, Douglas proposed the aircraft to the AAF, and they were sufficiently impressed to order two prototypes and a static test airframe on 25 June 1943.

The AAF originally gave the aircraft the Attack designation XA-42. Douglas had presented the aircraft in a variety of roles that suited the Attack aircraft profile. However, the aircraft was reclassified as a bomber and redesignated XB-42 on 25 November 1943. Unofficially, the XB-42 was given the name Mixmaster, on account of its eight contra-rotating propeller blades loosely resembling a popular kitchen mixer.

The Douglas XB-42 Mixmaster was a very unique aircraft. It was an all-metal aircraft with a tricycle landing gear arrangement, which was novel at the time. A plexiglass nose covered the bombardier’s position. Atop the fuselage were two separate bubble canopies for the pilot and copilot. At the rear of the aircraft was a cruciform tail; its ventral fin contained an oleo-pneumatic bumper to protect the propellers from potential ground strikes during takeoff and landing.

Douglas XB-42 no1 nose

Nose view of the first prototype shows the twin bubble canopies to advantage. Both XB-42 aircraft were originally built with the canopies, but they were disliked. The second aircraft was later modified with a more conventional canopy.

The aircraft’s long wing used a laminar flow airfoil and was fitted with double-slotted flaps. An inlet in the wing’s leading edge led to the engine oil cooler and radiator, both fitted with electric fans for ground operation. After air flowed through the coolers, it was expelled out the top of the wing. The main landing gear retracted back into the sides of the fuselage, below and behind the wings. The complex retraction required the gear legs and wheels to rotate 180 degrees. Fuel tanks in each wing carried 330 gallons (1,249 L) of fuel. Four additional 275 gallon (1,041 L) fuel tanks could be installed in the bomb bay to extend the aircraft’s range. In addition, a 300 gallon (1,136 L) drop tank could be installed under each wing.

Housed in the fuselage behind the cockpit were two Allison V-1710 engines. Each engine was installed with its vertical axis tilted 20 degrees out from center, and the engines were angled toward the tail. Ducts flush with the aircraft’s skin and positioned below the cockpit on both sides of the aircraft brought induction air to the engines. A row of exhaust stacks was located above the leading edge of each wing, and two rows of exhaust stacks were positioned along the aircraft’s spine. The engines of the first XB-42 prototype produced 1,325 hp (988 kW) at takeoff and 1,820 hp (1,357 kW) at war emergency power. The second prototype had engines that produced 1,675 hp (1,249 kW) for takeoff and 1,900 hp (1,417 kW) for war emergency power.

Douglas XB-42 no2 gear retract

A unique view of the second prototype (43-50225) that displays the aircraft’s slotted flaps and uncommon main gear retraction that required the legs and wheels to rotate 180 degrees into the fuselage sides. Also visible are the wing guns and revised leading edge inlets, both features exclusive to the second prototype.

Extending from each engine was an extension shaft made up of six sections. The shaft sections were like those used in the Bell P-39 Airacobra (which used two sections). The shafts extended around 29 ft (8.8 m) and connected the engines to a remote, contra-rotating gear reduction box from an Allison V-3420-B engine. The gearbox had been slightly modified for the XB-42 and used a .361 gear ratio that was unique to the aircraft. Each engine turned a three-blade Curtiss Electric propeller. The left engine drove the forward propeller, which was 13 ft 2 in (4.01 m) in diameter. The right engine drove the rear propeller, which was 13 ft (3.96 m) in diameter. The engines and propellers were operated independently—if needed, one engine could be shut down and its propeller feathered while in flight.

To eliminate the danger the propellers presented to the crew during a bail out, a cord of explosives (cordite) was threaded through holes carefully drilled around the gearbox mount. Before bailing out, the crew could detonate the explosives, which would separate the gearbox and propellers from the aircraft.

Douglas XB-42 Allison engine test

Two Allison V-1710 engines connected to the V-3420 remote gear reduction for the contra-rotating propellers as used on the XB-42. The power system accumulated over 600 hours on the test stand and never caused serious issues during the XB-42 program.

The XB-42’s bomb bay was covered by two-piece, snap-action doors. The bay accommodated 8,000 lb (3,629 kg) of bombs, or a single 10,000 lb (4,536 kg) bomb could be carried if the doors were kept open six inches. The bay was long enough to carry two 13 ft 9 in (4.2 m) Mk 13 torpedoes. Two fixed .50-cal machine guns with 500 rpg were installed in the aircraft’s nose. Housed in the trailing edge of each wing, between the aileron and flap, were a pair of rearward-firing .50-cal machine guns, each with 350 rpg. The guns were concealed behind snap-action doors. Once exposed, the guns could be angled through a range of 30 degrees up, 15 degrees down, and 25 degrees to the left or right. Their minimum convergence was 75 ft behind the aircraft. The rear-firing guns were operated by the copilot, who rotated his seat 180 degrees to use the gun’s sighting system.

Douglas designers envisioned that the B-42 aircraft could be fitted with a solid nose containing different weapons for different roles. This is the same concept that was applied to the Douglas A-20 Havoc and A-26 Invader. Three of the possible B-42 nose configurations were as follows: eight .50-cal machine guns; two 37 mm cannons and two .50-cal machine guns; or a 75 mm cannon and two .50-cal machine guns. Douglas also thought the aircraft’s speed and range would make it very useful in a reconnaissance role. None of these plans made it off the drawing board.

The XB-42 had a 70 ft 6 in (21.49 m) wingspan and was 53 ft 8 in (16.4 m) long. Originally, the aircraft was 18 ft 10 in (5.7m) tall, but the tail and rudder were extended to cure some instability. The extension increased the XB-42’s height to 20 ft 7 in (6.3 m). A brochure published by Douglas in April 1944 predicted the B-42 would be able to carry 2,000 lb (907 kg) of bombs over 5,333 miles (8,583 km) and have a top speed of 470 mph (756 km/h). These numbers proved very optimistic. Perhaps the speed was a misprint, because some sources indicate the anticipated top speed was 440 mph (708 km/h). Regardless, the aircraft only achieved 410 mph (660 km/h) at 23,440 ft (7,145 m), and its cruising speed was 312 mph (502 km/h). The XB-42 had an empty weight of 20,888 lb (9,475 kg) and a maximum weight of 35,702 lb (16,194 kg). The aircraft’s service ceiling was 29,400 ft (8,961 m). Its combat range was 1,800 miles (2,897 km), but additional fuel tanks in the bomb bay could extend the XB-42’s range to a maximum of 5,400 miles (8,690 km).

Douglas XB-42 no2 rear

Rear view of the second prototype shows the ventral tail and rudder. Note the oleo-pneumatic bumper on the tail and its minimal ground clearance. The wing guns and new canopy are just barely visible.

Construction of the XB-42 proceeded rapidly. The AAF inspected and approved an aircraft mockup in September 1943, and the first prototype (43-50224) was completed in May 1944—one year after the aircraft was proposed and 10 months after the contract was awarded. The XB-42 flew for the first time on 6 May 1944, flown by Bob Brush and taking off from the Palm Springs Army Airfield in California. The second prototype (43-50225) flew for the first time on 1 August 1944, taking off from Santa Monica Airport in California.

Both XB-42s were originally fitted with separate bubble canopies. This cockpit layout was not very popular with the pilots. Although they could communicate via intercom, the pilots often found themselves leaning forward to speak with one another face to face under the canopies. The second aircraft was modified with a more conventional single canopy that encompassed both pilot and copilot. While the bubble canopies reduced drag, the single canopy was preferred. Another issue facing the aircraft was that cracks formed in the plexiglass nose. After the plexiglass was replaced several times, the nose was eventually covered with plywood.

Both prototypes were heavier than expected, which reduced performance. Some work went into lightening the second aircraft, like the use of hollow propeller blades. However, issues with vibrations occurred when disturbed air encountered the propellers, and this phenomenon was exacerbated by the hollow blades. No issues were encountered when the aircraft was clean, but when the bomb bay doors were open or when the gear or flaps were deployed, the vibration issue occurred. Some pilots lived with the vibrations and dismissed the issue, but other pilots found it very disconcerting. An improved propeller was designed that featured reversible blades to decrease landing roll and to slow the aircraft in flight. However, it was cancelled in March 1945 and was never built.

Douglas XB-42 no2 with canopy

Front view of the second prototype illustrates the aircraft’s revised canopy. The canopy on production aircraft would have been similar but more refined. Again, note the tail clearance and wing guns.

Some cooling issues were encountered, and modifications to the air intakes were made to improve airflow. The main gear was also modified a few times to improve its retraction and performance. Overall, the aircraft flew well, but the controls were not well harmonized. In addition, the XB-42 aircraft would encounter a slow dutch roll oscillation if not counteracted by the pilot. As previously mentioned, the tail of the aircraft was enlarged to resolve the issue, but it was never entirely solved. The XB-42 required a very long takeoff run of some 6,415 ft (1,955 m). Because there was only about 9 in (.23 m) of clearance between the ventral tail and the ground, the aircraft needed to build up a substantial amount of speed before it was carefully rotated for liftoff.

The second XB-42 prototype was the only aircraft to have revised wing inlets and to be fitted with its machine gun armament, although the guns were never tested. The second aircraft was flown around 70 hours before it was turned over to the AAF. On 8 December 1945, Lieutenant Colonel Henry E. Warden and Captain Glen W. Edwards flew the second XB-42 from Long Beach, California to Bolling Field in Washington, D.C. The record-setting, point-to-point flight covered 2,295 miles (3,693 km) in a time of 5:17:34—an average of 433.6 mph (697.8 km/h). The XB-42 had benefited from a favorable tailwind, and the aircraft’s average true airspeed was around 375 mph (604 km/h).

Douglas XB-42 wing guns

The guns in the left wing are seen aimed 30 degrees up and 25 degrees inboard. Only the second aircraft was fitted with the guns, and they were never tested. Note the snap-action doors that covered the guns. When open, the doors increased the XB-42’s directional stability, resulting in additional rudder force to give the desired yaw.

On 16 December 1945, the second XB-42 was lost during a test flight near Bolling Field. The aircraft was in a landing configuration when there was an issue with extending the landing gear. While the crew was troubleshooting the problem, the left engine began to overheat and then died. The right engine was taken to full power and began to overheat. The decision was made to bail out, and two of the crew safely jumped free before the pilot remembered to jettison the propellers. The propellers and their gearbox were successfully severed from the XB-42, and the pilot bailed out. All three crew members survived the ordeal without any injuries, but the aircraft was completely destroyed.

An exact cause of the crash was never determined, but it was speculated that the coolant doors were inadvertently left in their nearly-closed landing configuration while the crew investigated the gear issue. This resulted in the engines overheating. At the same time, a fuel tank switch was made a bit late and probably led to fuel starvation of the left engine. The second XB-42 had accumulated a little over 118 hours of flight time when it crashed.

The first XB-42 prototype had made 42 flights and accumulated over 34 flight hours by 30 September 1944. A year later, that number rose to around 150 flights, with the aircraft accumulating around 125 flight hours. Before the XB-42 had even flown, Douglas contemplated adding jet engines to the aircraft. An official proposal for the modification was submitted on 23 February 1945. The proposal was approved on 8 March 1946, and modifications to the aircraft began on 26 June 1946. At the time, the first XB-42 had made 168 flights and had flown around 144.5 hours. The two Westinghouse 19XB-2A (J30) jet engines were finally delivered in October 1946 and were installed on the aircraft.

Douglas XB-42A rear

Rear view of the XB-42A illustrates the notches in the new flaps to avoid the jet exhaust. The rest of the aircraft remained relatively unchanged from the XB-42 configuration. The cooling air exit can be seen on the right wing. Note the various Douglas aircraft in the background.

With the jet engines added to the first prototype, the aircraft was redesignated as the Douglas XB-42A. The 1,600 lbf (7.12 kN) thrust jet engines were mounted under the aircraft’s wings. New flaps were installed that were notched behind the jet engines. The notches allowed the flaps to avoid the jet exhaust when they were deployed. The fuel tanks in the wings were modified because of the jet engine mounts. Total wing tankage was decreased by 154 gallons (583 L), but two additional 74 gallon (280 L) tanks were installed in the fuselage. The jets themselves burned the same fuel as the piston engines. The aircraft’s instrumentation was also modified to accommodate the jet engines.

The XB-42A is listed as having a 70 ft 7 in (21.51 m) wingspan and a length of 53 ft 10 in (16.4 m). In reality, the wingspan was probably the same as the XB-42, and the length was slightly longer due to a different spinner. The aircraft’s height was 20 ft 7 in (6.3 m). The XB-42A had a predicted maximum speed of 488 mph (785 km/h) but only achieved 473 mph (761 km/h) at 14,000 ft (4,267 m); cruising speed was 442 mph (711 km/h). The XB-42A had an empty weight of 24,775 lb (11,238 kg) and a maximum weight of 44,900 lb (20,366 kg). The aircraft’s service ceiling was 34,500 ft (10,516 m). The XB-42A had a normal range of around 1,200 miles (1,931 km), but a maximum range of 4,750 miles (7,644 km) could be achieved with additional fuel tanks in the bomb bay.

Douglas XB-42A

The XB-42A makes a low pass over Muroc Air Base during an early test flight. Note the exhaust stains above the wing and the oil stains below the wing. The aircraft was outclassed by other jet aircraft, including its XB-43 cousin.

The first flight of the XB-42A (still 43-50224) occurred on 27 May 1947 at Muroc (now Edwards) Air Base in California. The aircraft required a lot of maintenance and did not prove remarkable in any category to justify further development. Despite the increased performance, the XB-42A was perched on the awkward dividing line between piston-powered aircraft of the past and jet-powered aircraft of the future. There is no better indicator of this than the fact that Douglas had already moved forward with an all-jet XB-42 aircraft, designated XB-43. The Douglas XB-43 Jetmaster had its jet engines buried in the fuselage, near were the Allison engines were installed on the XB-42. The first XB-43 was built using the XB-42 static test airframe. The jet-powered XB-43 made its first flight on 17 May 1946—little more than a year before the jet/piston-powered XB-42A first flew. The XB-42A made only 23 flights, accounting for a little under 18.5 hours of flight time.

With technological progress outpacing the XB-42A, the aircraft was donated to the Air Force Museum on 30 June 1949. It was later moved to the National Air and Space Museum’s Paul Gerber Facility in Silver Hill, Maryland, where it was stored for a number of years. In 2010, the XB-42A was transferred to the National Museum of the United States Air Force in Dayton, Ohio. The aircraft, along with second XB-43 prototype, will eventually be restored for static display.

Douglas persisted with the pusher configuration and designed a number of other military and commercial aircraft. The most developed design was that of the Model 1004, which was actually designated DC-8. Known as the Skybus, the aircraft was similar to an XB-42, but with an extended fuselage for airline service. The aircraft could seat a maximum of 48 passengers, and the extension shafts from the Allison engines travelled under the passenger compartment. First proposed in October 1945, the Skybus was never built, and the DC-8 designation was reapplied to Douglas’s first jet airliner.

Douglas DC-8 Skybus

Although visually similar to the XB-42, the Douglas DC-8 Skybus was an entirely new design. The aircraft’s excellent performance and great single-engine handling was not enough to justify its expense over more conventional designs.

American Bomber Development in World War 2 by Bill Norton (2012)
Vee’s for Victory! The Story of the Allison V-1710 Aircraft Engine 1929-1948 by Daniel D. Whitney (1998)
McDonnell Douglas Aircraft since 1920: Volume I by René J Francillon (1979/1988)
The Allison Engine Catalog 1915–2007 by John M. Leonard (2008)
“The First, The Last, and the Only” by Walt Boyne, Airpower Vol. 3 No. 5 (September 1973)
“The Douglas DC-8 Skybus” by R. E. Williams, Douglas Service Vol. 41 (second quarter 1984)

Dutheil Chalmers Eole props rear

Dutheil-Chalmers Éole Opposed-Piston Aircraft Engine

By William Pearce

In 1906, the French company Société L. Dutheil, R. Chalmers et Cie (Dutheil-Chalmers) began developing aircraft engines for early aviation pioneers. The company was headquartered in Seine, France and was founded by Louis Dutheil and Robert-Arthur Chalmers. Although most of their engines were water cooled, the Dutheil-Chalmers’ horizontal aviation engines may have been the first successful versions of the horizontal type that is now used ubiquitously in light aircraft. Continuing to innovate for the new field of aviation, Dutheil-Chalmers soon developed a line of horizontal, opposed-piston engines.

Dutheil Chalmers Eole patent

Taken from the Dutheil-Chalmers British patent of 1909, this drawing shows the layout of the horizontal, opposed-piston engine. The dashed lines represent the bevel-gear cross shaft that synchronized the two crankshafts.

On 23 November 1908, Dutheil-Chalmers applied for a French patent (number not found) that outlined their concept of an opposed-piston engine. The French patent is referenced in British patent 26,549, which was applied for on 16 November 1909 and granted on 21 July 1910. In the British patent, Dutheil-Chalmers stated that the engine would have two crankshafts. The output shaft would not be a power shaft that connected the two crankshafts. Rather, the crankshafts would rotate in opposite directions (counter-rotating), and a propeller would mount directly to each crankshaft. This is the same power transfer method used in the SPA-Faccioli opposed-piston aircraft engines. While the Dutheil-Chalmers and SPA-Faccioli engines shared a similar concept and were built and developed at the same time, there is no indication that either company copied the other.

The Dutheil-Chalmers opposed-piston engines are sometimes referred to as Éole engines. It is not clear if Dutheil-Chalmers marketed the engines for a time under a different name or if Éole was just the name they gave to their line of opposed-piston engines. Éole is the French name for Aeolus, the ruler of the winds in Greek mythology. The engines were primarily intended to power airships. The two counter-rotating propellers would cancel out the torque associated with a single propeller on a standard engine. In addition, the opposed-piston engine’s two-propeller design did not require the heavy and cumbersome shafting and gears necessary for a conventional single-crankshaft engine to power two propellers.

Dutheil Chalmers Eole 2 view

Top and side view drawings of the four-cylinder, opposed-piston engine. The drawings show no valve train and differ slightly from photos of the actual engine, but they give an idea of the engine’s general layout.

Four different horizontal, opposed-piston engine sizes were announced, all of which were water-cooled. Three of the engines had the same bore and stroke but differed in the number of cylinders used. These engines had two, three, and four cylinders. Each had a 4.33 in (110 mm) bore and a 5.91 in (150 mm) stroke, which was an 11.81 in (300 mm) stroke equivalent with the two pistons per cylinder. The two-cylinder engine displaced 348 cu in (5.7 L) and produced 38 hp (28 kW) at 1,000 rpm. The engine weighed 220 lb (100 kg). The three-cylinder engine displaced 522 cu in (8.6 L) and produced 56 hp (42 kW) at 1,000 rpm. The engine weighed 397 lb (180 kg). The four-cylinder engine displaced 696 cu in (11.4 L) and produced 75 hp (56 kW) at 1,000 rpm. The engine weighed 529 lb (240 kg). It is not clear if any of these engines were built.

The fourth engine was built, and it was the largest opposed-piston engine in the Dutheil-Chalmers line. The bore was enlarged to 4.92 in (125 mm), and the stroke remained the same at 5.91 in (150 mm)—an 11.81 in (300 mm) equivalent with the two pistons per cylinder. The four-cylinder engine displaced 899 cu in (14.7 L) and produced 97 hp (72 kW) at 1,000 rpm. Often, the engine is listed as producing 100 hp (75 kW). The four-cylinder engine weighed 794 lb (360 kg).

Dutheil Chalmers Eole front

This Drawing illustrates the front of the Dutheil-Chalmers opposed-piston engine. Note the cross shaft that synchronized the two crankshafts. The gear on the cross shaft drove the engine’s camshaft. The pushrods, rockers, and valves are visible.

Only the 97 hp (72 kW) engine was exhibited, but it was not seen until 1910. The engine was displayed at the Paris Flight Salon, which occurred in October 1910. The engine consisted of four individual cylinders made from cast iron. The horizontal cylinders were attached to crankcases on the left and right. Threaded rods secured the crankcases together and squeezed the cylinders between the crankcases. Each crankcase housed a crankshaft, and the two crankshafts were synchronized by a bevel-gear cross shaft positioned at the front of the engine. A two-blade propeller was attached to each crankshaft. The propellers were phased so that when one was in the horizontal position, the other was in the vertical position.

Near the center of the cross shaft was a gear that drove the camshaft, which was positioned under the engine. The camshaft actuated pushrods for the intake valves on the lower side of the engine and the exhaust valves on the upper side of the engine. The pushrods of the intake valves travel between the cylinders. All of the pushrods acted on rocker arms that actuated the valves positioned in the middle of the cylinder. Each cylinder had one intake and one exhaust valve.

No information has been found that indicates any Dutheil-Chalmers Éole opposed-piston engines were used in any airship or aircraft. Still, it is a unique engine conceived and built at a time of great innovation, not just in aviation, but in all technical fields.

Dutheil Chalmers Eole props rear

The 97 hp (72 kW), four-cylinder, eight-piston engine on display at the Paris Flight Salon in 1910. The engine has appeared in various publications as both a Dutheil-Chalmers and an Éole. Note the rods that secured the crankcases together. What appears to be the camshaft can be seen under the engine.

Les Moteurs a Pistons Aeronautiques Francais Tome II by Alfred Bodemer and Robert Laugier (1987)
“Improvements in or connected with Motors especially applicable to Aviation and Aerostation Purposes” GB patent 26,549 by L. Dutheil, R. Chalmers and Company (granted 21 July 1910)
“Motors for Aerial Navigation—V” by J. S. Critchley, The Horseless Age (26 October 1910)
“Aerial Motors at the Salon” by Oiseau, Flight (5 November 1910)