Pennsylvania Railroad 6-4-4-6 S1 Locomotive

By William Pearce

PRR S1 6100 top

The Pennsylvania Railroad S1 engine 6100 in February 1939, shortly after completion. The S1 was the longest and heaviest rigid frame reciprocating steam passenger locomotive ever built. Note the dual stacks protruding slightly above the engine’s streamlined claddin

The Pennsylvania Railroad (PRR) was founded in 1846 and headquartered in Philadelphia, Pennsylvania. In the first half of the 20th century, PRR was the largest railroad by traffic and revenue in the United States. At one time, PRR was the largest publicly traded corporation in the world, with a budget larger than that of the U.S. government and a workforce of approximately 250,000 people.

In 1937, PRR sought to design a coal-burning steam locomotive that would pull heavy passenger trains for long runs at better than 60 mph (97 km/h). Accomplishing such tasks typically required the use of two engines pulling a single train (double-heading). PRR also hoped that the performance of the new engine would match that of the new electric locomotives just then coming into service. The new steam locomotive would serve as an experimental prototype for the railroad as it worked to modernize its fleet. The new locomotive was designated as the S1 class, and PRR collaborated with the American Locomotive Company, the Baldwin Locomotive Works, and the Lima Locomotive Works in designing and building the engine. The S1 was built in PRR’s Altoona Works in Altoona, Pennsylvania during 1938. The S1 was given the Altoona serial number 4341 and the PRR number 6100.

The PRR S1 was a unique duplex locomotive that utilized a 6-4-4-6 wheel arrangement. A six-wheel leading truck with 36 in (.91 m) wheels was positioned at the front of the engine. A set of four 84 in (2.13 m) drive wheels followed, trailed by another identical set of four drive wheels. A six-wheel trailing truck with 42 in (1.07 m) wheels was positioned at the rear of the engine. What made the S1 a duplex locomotive was its use of two separate pairs of cylinders mounted to a rigid frame. Each cylinder pair drove a set of four drive wheels. The two trucks and four pairs of drive wheels were mounted to a single-piece frame bed made of cast steel by General Steel Castings in St Louis, Missouri. The cylinders and their valve chests were integrally cast with the frame. The frame was 77 ft 9.5 in (23.7 m) long, weighed 97,620 lb (44,280 kg), and was the largest locomotive bed casting ever made. However, the use of a long rigid frame meant that the engine would not be able to operate on tracks with significant curves.

PRR S1 6100 construction

The S1 under construction with its large firebox and boiler being attached to the engine’s huge cast steel frame. While mostly concealed, the single-piece frame can be seen supporting the leading and trailing truck

With an overall length of 140 ft 2.5 in (42.7 m), the S1 was the longest rigid frame reciprocating steam passenger locomotive ever built, a fact that earned it the nickname The Big Engine. The S1 was made up of an 81 ft 1.75 in (24.7 m) long engine and a 59 ft .75 in (18.0 m) long tender that carried the locomotive’s coal and water. The engine weighed 608,170 lb (275,862 kg), and its weight was distributed with 135,100 lb (61,280 kg) on the leading truck, 191,630 lb (86,922 kg) on the trailing truck (326,730 lb / 148,202 kg total on the trucks), and 281,440 lb (127,659 kg) on the driving wheels. This distribution meant that less than half (46.28%) of the engine’s weight was on the driving wheels, a configuration that often led to wheel slip.

The tender was supported by two eight-wheel trucks with 36 in (.91 m) wheels. It carried 53,000 lb (24,040 kg) of coal in a front compartment and 24,230 gallons (91,720 L) of water in a rear compartment. When combined with the engine, the 451,840 lb (204,951 kg) tender gave the S1 a total weight of 1,060,010 lb (480,813 kg). The locomotive was 15 ft 6 in (4.7 m) tall and 10 ft 7 in (3.2 m) wide.

PRR S1 6100 NY Fair

The S1 atop its special display stand at the 1939 New York World’s Fair. The stand enabled the engine to operate daily at up to 60 mph (97 km/h). Note that the tender is painted as “American Railroads.”

An HT type mechanical stoker auger transported coal from the tender to the engine’s firebox. The firebox was 198 in (5.03 m) long and 96 in (2.44 m) wide. Coal was burned in the firebox at around 2,000 °F (1,093 °C). Heat from the firebox flowed through the boiler via 219 tubes that were 2.25 in (57.2 mm) in diameter and 69 flues that were 5.5 in (139.7 mm) in diameter. Each of the tubes and flues was 22 ft (6.7 m) long. The 288 tubes and flues would stretch for 6,336 ft (1,931 m) if laid end to end. The boiler was made from approximately 1 in (254 mm) thick nickel steel. After passing through the tubes, the soot, embers, smoke, and heat from the burning coal flowed into a smokebox at the front of the engine and was subsequently vented into the atmosphere via dual vertical stacks. The stacks were approximately 21 in (533 mm) in diameter and protruded 4.875 in (124 mm) above the top of the engine.

The tubes, flues, and firebox of the S1 had a combined evaporative surface area of 5,661 sq ft (525.9 sq m). Heat radiating from these surfaces turned water in the boiler to steam and built up a working pressure of 300 psi (20.7 bar). With a temperature of over 420 °F (215 °C), the wet, saturated steam was collected from slots along the top of a pipe inside the boiler shell. The steam then flowed to the modified Type A superheater, which had a surface area of 2,085 sq ft (193.7 sq m). From the superheater, 69 small superheater elements (tubes) took the wet steam back into the flues. The steam inside the superheater elements was heated well above its saturation value and converted to dry, superheated steam. The superheater elements delivered the dry steam to the steam chamber in the superheater.

PRR S1 6100 Raymond Loewy

Raymond Lowey proudly poses with the S1 at the 1939 New York World’s Fair. The engine is mounted on its display stand, and a roller can be seen under the front drive wheel.

The flow of steam in and out of each of the engine’s four cylinders was controlled by a Walschaerts valve gear. A 12 in (305 mm) diameter piston valve was mounted in a valve chest above each cylinder. The valve slid back and forth 7.5 inches (191 mm) to allow steam to enter one side of the double-acting cylinder while simultaneously opening the other side to exhaust the previous steam charge. The steam flowed into the front of the cylinder and filled its 9,883 cu in (162 L) volume, pushing the 22 in (558.8 mm) diameter piston back 26 in (660.4 mm) to the rear of the cylinder. The valve then slid rearward to direct steam into the rear part of the cylinder and allow the front part of the cylinder to exhaust. Steam entering the rear part of the cylinder pushed the piston forward to its original position. The cylinder had a smaller return volume of approximately 9,321 cu in (153 L) on account of the 5.25 in (133 mm) diameter piston rod taking up some room. The piston rod extended straight back from the cylinder and was attached to the connecting rod via a crosshead. The connecting rod linked the piston rod to the rear driving wheel in the two-wheel set on each side of the engine. Here, the connecting rod was attached to the coupling rod, which connected the two driving-wheel sets together. The reciprocating parts for each of the four two-wheel driving sets weighed 1,010 lb (458 kg). To aid traction, sand could be deposited on the rails in front of all four front drive wheels and in front of the last pair of rear drive wheels. Two sand boxes were positioned on each side of the engine.

The S1 was designed to haul a 1,200-ton (1,089-t) passenger train at 100 mph (161 km/h). The engine developed around 6,500 indicated hp (4,847 kW) at 100 mph (161 km/h) and had a maximum tractive force of some 76,400 lb (34,654 kg) based on an 85% efficiency factor. Without any slip, each rotation of the drive wheels moved the engine 22 ft (6.7 m). At 100 mph (161 km/h), each drive wheel rotated 400 times a minute, and each double-acting piston made 800 strokes. This resulted in roughly 17,781 cu ft (503.5 cu m) of steam passing through the S1’s four cylinders every minute.

PRR S1 6100 Englewood snow

Early in its life, the S1 heads east from Englewood Union Station as the “Manhattan Limited.” The nameplate at the front of the engine says “Manhattan.” Note that all of the engine’s skirting and paneling is in place.

The S1 was encased in Art Deco-styled cladding designed by Raymond Loewy. The streamlined cladding consisted of aluminum panels that covered the boiler and extended to a bullet-shaped nose at the front of the engine. Skirt panels covered the lower part of the engine and partially concealed the running gear. The cladding was adorned with chrome handrails and trim accents. The S1’s low-profile stacks were concealed in a fairing atop the engine. Loewy had worked with PRR when he designed the streamlined cladding for the K4 engine 3768 in 1936. Additional K4 engines were streamlined, but not to the extent of 3768. Loewy’s S1 styling was a direct development of his work on engine 3768. It is often claimed that Loewy was awarded US patent 2,128,490 for his S1 design, but this patent was applied for on 17 July 1936 and actually details his work on the K4 engine 3768.

Completed on 31 January 1939, the S1 cost PRR approximately $669,780 USD to build, which is equivalent to $11,912,085 USD in 2018. After undergoing some initial testing, the S1 was showcased at the 1939 World’s Fair held at Flushing Meadows Corona Park on Long Island, New York from 30 April 1939 to 27 October 1940. The entire railroad display was sponsored by 27 railroads from the eastern United States. Still numbered as 6100, the S1 was branded “American Railroads” rather than the “Pennsylvania” it wore later in life. The S1 sat atop a special stand that enabled the locomotive to be operated at speed under its own power. In the stand, the engine’s drive wheels powered generators. Electricity created by the generators was used to power motors that turned the 12 wheels of the leading and trailing trucks and the 16 wheels on the tender. The drive system in the stand was configured so that all wheels turned at the same rpm. While the display was open during the 16-month fair, the S1 was operated daily from 12:00 PM to 8:00 PM at 60 mph (97 km/h). By the end of the fair, the S1 had traveled some 50,000 miles (81,467 km) without moving from the stand.

PRR S1 6100 NYC

The S1 moves east from Englewood Union Station as the “Trailblazer.” In service, the S1 began to lose some of its skirting and paneling, like the piece at the front of the engine. The panels were removed for access and often never replaced. A New York Central J-3a 4-6-4 Hudson occupies another track.

After the fair, the S1 was finally pressed into service for the PRR in December 1940. While the S1 made for an impressive sight on its special display stand, operating the engine on standard track presented some difficulties. The wide, long, and heavy rigid locomotive could not operate on tracks with tight turns or obstructions, which included most of PRR’s system. PRR sent the S1 to operate on a 283-mile (455-km) straight route of the main line from Chicago, Illinois to Crestline, Ohio. Special facilities were built in Crestline to house and maintain the S1. Even so, the locomotive occasionally derailed during turning operations on a special section of wye track.

In the early 1940s, the S1 was operated in profitable service pulling one of the longest passenger trains for PRR—a 2,000-ton (1,814-t) train consisting of 22 cars. The S1 was popular with crews because of its speed, power, and smooth ride. However, the majority of the S1’s weight rested on the leading and trailing trucks rather than on the engine’s eight drive wheels. Frequent wheel slip was an issue—the engineer needed to be careful opening the throttle, and the duplex engine arrangement made it difficult to quickly detect when the drive wheels were slipping. Wheel slip at speed would quickly damage drive components. Some of the S1’s aerodynamic skirting was removed to ease inspection and maintenance. The discarded skirting also allowed better access to the engine’s 350 grease fittings that needed daily servicing. On a standard 283-mile (455-km) run between Chicago and Crestline, the S1 consumed 48,000 lb (21,772 kg) of coal and 36,000 gallons (136,275 L) of water.

PRR S1 6100 no skirts

All of the skirting has been removed from the S1’s drive wheels and trailing truck. While the S1 proved to be quite capable of pulling passenger trains at high speeds, it was too big for most tracks and suffered from wheel slip.

In service, the S1 would regularly top 100 mph (161 km/h). On a test run with 12 loaded cars, Charlie Wappes, assistant road foreman of PRR’s Fort Wayne division, observed the S1’s speedometer needle pegged at the gauge’s 110 mph (177 km/h) maximum. Wappes pulled out his stopwatch and timed the train from the Wanatah, Indiana station to the Hanna, Indiana station. The S1 covered the 6.3-mile (10.1-km) distance in 170 seconds, a time that averages to 133.4 mph (214.7 km/h). Other second-hand reports indicate the S1 traveling over 140 mph (225 km/h) on multiple occasions, and an inconceivable top speed of 156 mph (251 km/h) was claimed on a run between Fort Wayne, Indiana to Chicago, Illinois. PRR was reportedly fined for this speed, as the track’s limit was 80 mph (129 km/h). The official (and still current) speed record for a steam locomotive was set by the British LNER (London and North Eastern Railway) Class A4 4468 Mallard at 125.88 mph (202.58 km/h) on 3 July 1938. While it seems possible that the S1 may have been able to break the record, the S1 never made any official speed record attempts, and there is no official documentation that corroborates these high-speed claims.

The S1 was purely an experimental engine, and its operation was very limited. The locomotive was too long for almost all railway turntables, and its long rigid frame could not take the curves into most railyards. But, the S1’s wheel slip trouble, caused by the majority of the engine’s weight resting on the trucks rather than the drive wheels, was perhaps the engine’s biggest issue. After just a few years of operation, the sole S1 was removed from service. Some sources indicate the S1’s last run was in December 1945, while other sources give the date as May 1946. Regardless, the impressive, powerful, and ultimately unsuccessful S1 engine 6100 was scrapped in 1949. However, some of the lessons learned from the S1 were applied to the last steam locomotives built by the PRR, the 4-4-4-4 engines of the T1 class.

PRR S1 6100 color

The S1 under power late in its life with all of its skirting removed. In addition, the trim is gone from the front of the engine, and the tender has been repainted without any striping. Note the separate cylinders connected to the drive wheels.

Sources:
Loco Profile 24: Pennsylvania Duplexii by Brian Reed (June 1972)
Pennsy Power (I) by Alvin F. Staufer (1962)
“High-Capacity Locomotive for Fast Service” Railway Age Vol. 106, No. 25 (24 June 1939)
“Riding the Gargantua of the Rails” by Roderick M. Grant, Popular Mechanics (December 1941)
https://en.wikipedia.org/wiki/Pennsylvania_Railroad_class_S1
https://en.wikipedia.org/wiki/Pennsylvania_Railroad
http://www.steamlocomotive.com/locobase.php?country=USA&wheel=Duplex&railroad=prr
http://www.crestlineprr.com/duplexexperimentals.html
http://www.dieselpunks.org/profiles/blogs/sunday-streamline-14-the-big
http://streamlinermemories.info/?p=5258

Vickers Type 432 in flight

Vickers Type 432 High-Altitude Fighter

By William Pearce

In March 1939, The British Air Ministry issued Specification F.6/39 for a 400 mph (644 km/h) two-seat fighter. The aircraft was to carry four 20-mm cannons, with the possibility of later mounting two 40-mm cannons. Under a design team led by Rex Pierson, Vickers-Armstrongs Ltd. (Vickers) had been working on a fighter with a single flexibly-mounted 40-mm cannon installed in the aircraft’s nose. The twin-engine aircraft was powered by Rolls-Royce Griffon engines and met the requirements of F.6/39, aside from its armament. Vickers met with the Air Ministry in April 1939 to discuss the aircraft’s potential. The Air Ministry was sufficiently impressed and issued Specification F.22/39 that covered the Vickers fighter, which carried the internal designation Type 414. Specification F.6/39 was subsequently cancelled in November 1939.

Vickers Type 432 front right

The Vickers Type 432 prototype DZ217 appears shortly after its completion at Foxwarren. The bystander gives some indication to the aircraft’s size. Note the bubble canopy.

Two Type 414 prototypes were ordered on 30 August 1939, and they were assigned serial numbers R2436 and R2437. After inspection of the Type 414 mockup in early February, the Air Ministry inquired about the possibility of installing several 20-mm cannons in place of the single 40-mm cannon. Vickers responded with aircraft proposals incorporating eight 20-mm cannons or two 40-mm cannons.

Vickers designated the fighter with 20-mm cannons as the Type 420. Two cannons were positioned in the aircraft’s nose, and three were on each side of the cockpit. Vickers and the Air Ministry discussed the Type 420 in June 1940, and Specification F.16/40 was issued for the aircraft’s development. The Type 420 was given a high priority, and an order for two prototypes was expected. The order for two Type 414 prototypes was still in place. However, the Type 420 took precedence, and work on the Type 414 slowed substantially.

In early January 1941, the Air Ministry requested a design change to reduce the number of 20-mm cannons to six. At the same time, Vickers had designed a high-altitude fighter that used many components from the Type 420. The high-altitude aircraft was armed with four 20-mm cannons and powered by two Rolls-Royce Merlin engines. The Air Ministry was interested in Vickers’ proposal, as they felt there was an urgent need for a heavily armed, high-altitude fighter aircraft to intercept high-altitude German bombers that were expected in the skies over Britain. However, high-altitude German bombing raids were never undertaken en masse and did not present a significant threat to Britain during World War II.

Vickers Type 432 rear right

Rear view of the Type 432 displays the aircraft’s long engine nacelles and ventral pod for the six 20-mm cannons. Note how the aircraft’s tail resembles that of a de Havilland Mosquito. The completed aircraft was disassembled at Foxwarren and taken to Farnborough for flight testing.

In March 1941, work on the Type 414 was stopped completely, and discussions with Rolls Royce commenced regarding the acquisition of Merlin engines. In May 1941, Vickers detailed the specifics of the high-altitude aircraft, which it had designated as Type 432. Specification F.22/39 was cancelled, thus halting work on the Type 420. Design work on the Type 432 continued, resulting in the switch to a single-seat cockpit placed in the nose of the aircraft and six 20-mm cannons installed in a ventral fairing. Each cannon had 120 rounds of ammunition. The Air Ministry ordered two Type 432 prototypes on 9 September 1941, and the aircraft would be built to the new Specification F.7/41. The two Type 432 prototypes were issued serial numbers DZ217 and DZ223.

The fuselage of the Vickers Type 432 was made of stressed-skin aluminum panels that were flush-riveted to the closely-spaced circular structures that made up the airframe. The forward part of each wing was made of a similar stressed-skin construction. The thick skins and their supports created a torsion box of sufficient strength so that conventional wing spars and ribs were omitted. Fabric covered the aft section of the wings and the aircraft’s control surfaces. The wings had a unique elliptical planform with a slight forward-sweep outside of the engines. The wing leading edges between the engines and fuselage housed the coolant radiators.

The aircraft was powered by two-stage, two-speed Merlin 61 engines capable of 1,580 hp (1,178 kW) at 23,500 ft (7,163 m). The engines were housed in long, streamlined nacelles mounted to each wing. The main landing gear retracted rearward into the nacelle behind the engine. The cockpit consisted of a pressure cabin topped by a small canopy that hinged to the side for entry.

The Type 432 was a rather large aircraft with a wingspan of 56 ft 10 in (17.3 m), a length of 40 ft 7 in (12.4 m), and a height of 13 ft 9 in (4.9 m). Forecasted top speeds were estimated at 320 mph (515 km/h) at sea level, 435 mph (700 km/h) at 28,000 ft (8,534 m), and 400 mph (644 km/h) at 40,000 ft (12,192 m). Cruise speed was estimated at 400 mph (644 km/h) at 29,500 mph (8,992 m). The aircraft had a 2,750 fpm (14.0 m/s) initial climb rate and a service ceiling of 43,500 ft (13,259 m). The Type 432 weighed 16,373 lb (7,427 kg) empty and had a maximum takeoff weight of 20,168 lb (9,148 kg). With 506 gallons (421 Imp gal / 1,914 L) of fuel, the aircraft had a 1,500 mi (2,414 km) range.

Vickers Type 432 left side

During its initial taxiing tests at Farnborough, the Type 432 exhibited tracking issues and snaked from side-to-side. The landing gear was moved aft 3 in (76 mm) to improve handling. Flight tests revealed other undesirable characteristics, and modifications were made to the aircraft’s ailerons and tail to improve its handling.

The Type 432 mockup was inspected in late December 1941, and the first prototype, DZ217, was built throughout 1942. The aircraft was built at Foxwarren, a special Vickers dispersal site for experimental work near Brooklands in Surrey, England. The site did not have an airfield, so the Type 432 was disassembled and transported to Royal Aircraft Establishment Farnborough for its first flight. The Type 432 was first flown on 24 December 1942, piloted by Tommy Lucke. On 29 December, the Ministry of Aircraft Production cancelled the partially-built second prototype. This decision was not made official until 1 May 1943. The entire Type 432 program was cancelled at the end of 1943.

The sole Type 432 aircraft continued to fly occasionally until November 1944. Some efforts were made throughout the aircraft’s existence to improve its handling and flight qualities, as the Type 432 was noted as having heavy controls. Only 28 flights were made, and the aircraft was never submitted for official trials or tested to its maximum performance. Additionally, the 20-mm armament and the pressurized cabin were never installed. Although the Type 432 exceeded 400 mph (644 km/h) in a slight dive, the highest speed obtained in level flight was 380 mph (612 km/h), recorded on 14 May 1943. One of the factors that limited flight testing was that the Merlin engines installed in the Type 432 did not run well above 23,000 ft (7,010 m). Since the Type 432 had no future as a production aircraft, the performance issues of its Merlins were never fully investigated.

Aircraft observers were a regular fixture during World War II, keeping an eye out for any enemy action in the skies over Britain. The rarely-seen and oddly-shaped Type 432 was only listed as “AP1480” in the recognition handbooks. This non-descript designation led the spotters to dub the Type 432 as the “Tin Mossie” on account of the aircraft’s resemblance to the wooden de Haviland Mosquito. Some source list the aircraft as being referred to as “Mayfly,” but the origin of this name has not been found.

Vickers Type 432 in flight

The Type 432 made only 28 flights in its two-year life. The aircraft was noted as having some handling deficiencies that were never completely resolved, because the project was a dead end. Note the slight forward sweep of the Type 432’s outer wing panels.

Sources:
British Secret Projects: Fighters & Bombers 1935-1950 by Tony Buttler (2004)
Vickers Aircraft since 1908 by C. F. Andrews and E. B. Morgan (1988)
RAF Fighters Part 3 by William Green and Gordon Swanborough (1981)
The British Fighter since 1912 by Francis K. Mason (1992)
Aircraft of the Fighting Powers Volume VII by Owen Thetford (1946)

Sunbeam Silver Bullet debut Kaye Don

Sunbeam Silver Bullet LSR Car

By William Pearce

During the 1920s, race cars built by the Sunbeam Motor Car Company in Wolverhampton, England captured the World Land Speed Record (LSR) five times. The last record for the company was set by the Sunbeam 1,000 hp Mystery Slug, a specially-built LSR car designed by John Irving that Henry Segrave used to achieve 203.793 mph (327.973 km/h) on 29 March 1927. Segrave and Irving then parted ways with Sunbeam, and the record held by Sunbeam was broken in 1928. Segrave recovered the record on 11 March 1929, hitting 231.362 mph (372.341 km/h) in the Irving-Napier Golden Arrow. Wanting to recapture the record, Sunbeam went to work on a new LSR car to push the record up to 250 mph (402 km/h).

Sunbeam Silver Bullet debut Kaye Don

The Sunbeam Silver Bullet with Kaye Don in the cockpit during the car’s public debut in February 1930. Exhaust from the engines was collected in the long black manifold that ran along the side of the cockpit. The bulge along the lower side of the body covered the steering drag link.

Designed by Sunbeam’s chief engineer Louis Coatalen and chief designer Hugh Rose, the new Sunbeam LSR car was specially-built and powered by two engines. The car was named Silver Bullet, most likely a retort to Segrave and Irving’s Golden Arrow. Unlike the 1,000 hp Mystery Slug that was built using what was available at the Sunbeam factory, construction of the Silver Bullet was an entirely scratch-built affair. The car’s design was refined by model testing in the Vickers Aviation Department’s wind tunnel.

The Sunbeam Silver Bullet was composed of very stout steel frame rails that were 13.5 in (343 mm) in height at their tallest point. The frame rails were joined by various crossmembers and supports that arched from rail to rail. The body of the LSR car was made up of streamlined aluminum panels, and an underbody enclosed the bottom of the chassis. The wheels sat outside of the Silver Bullet’s body and were trailed by aerodynamic fairings. The Dunlap tires were 37 in (940 mm) tall and 6 in (152 mm) wide. Steering was achieved by separate drag links that extended from the cockpit at the rear of the car to the front wheels. A long bulge on each side of the body covered the drag link. Twin fins at the rear of the car helped stabilize the racer at high speeds. A horizontal member between the fins rotated down to act as an air brake. The car used water-cooled hydraulic brakes at all four wheels.

Sunbeam Silver Bullet no body

The incomplete Silver Bullet with engines installed. Note the routing of the induction pipe from the supercharger and around the rear (left) engine. The empty space in front of the forward (right) engine was for the ice tank. The steering drag link for the right wheel can be seen on the outside of the right frame rail.

The Silver Bullet was powered by two water-cooled V-12 engines built especially for the racer. To keep the engine and the car as narrow as possible, the engine’s bank angle was set at 50-degrees. The engine was made of aluminum and had four valves per cylinder. Two overhead camshafts actuated the valves for each cylinder bank. Each cylinder bank was composed of two three-cylinder blocks. The single spark plug per cylinder was positioned between the valves in the top of the combustion chamber. The two engines in the Silver Bullet were installed in tandem, with the front of both engines toward the rear of the racer. A secondary shaft integral with the crankcase and positioned under the crankshaft of each engine coupled the engines together and transferred their combined power to the transmission. Engine exhaust for each cylinder bank was collected in separate manifolds that extended back along both sides of the Silver Bullet and under the engine cowling. Just behind the rear engine, the exhaust manifolds on each side of the car joined into a single manifold and emerged from under the cowling. These large exhaust manifolds ran alongside the cockpit and extended back to just before the Silver Bullet’s tail.

Sunbeam Silver Bullet supercharger

Detail view of the Silver Bullet’s single supercharger. The two carburetors are on the left, with the steering box just below. Note the relatively sharp bends of the induction pipe.

The engine had a 5.51 in (140 mm) bore and a 5.12 in (130 mm) stroke. It displaced 1,465 cu in (24.01 L) and produced 490 hp at 2,400 rpm normally-aspirated, but a supercharger was incorporated into the Silver Bullet’s design. Initially, four Roots-type superchargers were to provide each engine with induction air, and this configuration was tested on one engine in November 1929. However, the final supercharging system was a single unit of the centrifugal type providing air to both engines. The supercharger was driven at up to 17,000 rpm by the rear engine and provided around 7 psi of boost. Separate induction pipes extended from the supercharger along both sides of the rear engine. The pipes connected to an induction manifold positioned in the Vee of the front and rear engines. Exactly how much power the engines produced with supercharging is not known. It is entirely possible that a true power test was never undertaken. Regardless, Coatalen had no problem claiming the engines would produce 2,000 hp (1,491 kW) each at 3,000 rpm, making the Silver Bullet a “4,000 hp car.” Both the peak engine output and rpm seem to be rather optimistic figures. Two carburetors fed fuel into the air as it was drawn into the supercharger.

The secondary shaft from the engines to the transmission spun at over twice engine rpm. The higher speed decreased torque and allowed the use of a smaller diameter shaft. At 2,600 rpm engine speed, the three-speed transmission had theoretical top speeds of 135 mph (217 km/h) in first gear, 180 mph (290 km/h) in second gear, and 266 mph (428 km/h) in third gear. While Sunbeam wanted to break the record of 231 mph (372 km/h) and planned to reach 250 mph (402 km/h), it was hoped that the car would ultimately hit 265 mph (426 km/h). The output of the transmission was in the form of two drive shafts that extended back on either side of the cockpit to the rear axle. The two-drive-shaft arrangement lowered the driver’s seat and the overall height of the Silver Bullet.

Sunbeam Silver Bullet test

The Silver Bullet chassis with both engines installed undergoing a test run. By all accounts, there was no time for any serious testing of the engines or the car before it was shipped to the United States. The reinforced structure on the right sits just before the cockpit.

An 11.5 cu ft (.33 m3) ice tank that held 616 lb (279 kg) of ice was installed in the nose of the Silver Bullet. Water from the engines was cooled by the ice and then returned to the engines. The 30-gallon (25-imp gal / 114 L) fuel tank was positioned in the streamlined fairing behind the cockpit. The cockpit was sized specifically for Kaye Don (Kaye Ernest Donsky), who raced for Sunbeam and had shown exceptional talent on the Brooklands race track, setting numerous records. The steering wheel was detachable for cockpit entry and exit. A fireproof bulkhead was positioned between the engines and the cockpit.

The Silver Bullet was 31 ft 1 in (9.47 m) long and 6 ft (1.83 m) across at its widest point. However, the body was under 3 ft (.91 m) wide. The car had a 4 ft 11 in (1.50 m) track, a 15 ft 5 in (4.70 m) wheel base, and 7.75 in (197 mm) of ground clearance. The top of the cowling over the engines was 44 in (1.12 m) tall, and the highest point of the car, just behind the cockpit, was around 53 in (1.35 m) above the ground. The Silver Bullet weighed around 6,000 lb (2,722 kg) dry and around 7,500 lb (3,402 kg) record-ready.

Sunbeam Silver Bullet rear air brake

Rear view of the Silver Bullet illustrates the air brake in the deployed position. It is interesting to consider how much drag the horizontal member created when it was in its normal position.

The engines were installed by 1 February 1930, and the Silver Bullet made its public debut on 21 February. Very little testing was done before the car left for Daytona Beach, Florida on 26 February. The Silver Bullet and crew arrived in Daytona on 8 March and immediately began work on the car. The Silver Bullet was started on 13 March and was ready for a run the next day. However, the timing equipment was not ready, and no run was made. The first test run was made on 15 March, and the Silver Bullet recorded an unofficial speed of around 150 mph (240 km/h).

An attempt was made on 17 March, but serious trouble was encountered when the air/fuel mixture self-ignited due to excessive heat in the long induction manifolds. This phenomenon created a backfire that routinely damaged the supercharger housing and its impeller. Part of the issue was that the induction pipes from the supercharger ran in close proximity to the exhaust manifolds, including a point where the intake crossed under the exhaust from the front engine. This created a localized area of high temperature in the induction system.

Sunbeam Silver Bullet rear

On first glance, the Silver Bullet gives the impression of a sleek and powerful vehicle that is ready to set speed records. On closer inspection, one begins to wonder just how much drag was created by the complex drag link covers, elaborate exhaust ducting, irregular body panels, and exposed fasteners. At the time, the science of aerodynamics was in its infancy.

The single supercharger arrangement and its complex piping left no way to cure the issue without significant modifications. Regardless, the Silver Bullet team tried to fix what they could and strove for a decent run up and down the beach. Modifications were made to vent exhaust from the front engine out the cowling rather than collecting it in the manifolds, but induction issues persisted. To make matters worse, the course was rough, and Don had to fight the car the whole way. Don tried again on 18 March, recording an official and disappointing two-way average speed of 171.019 mph (275.229 km/h). However, the Silver Bullet did manage to set a new American record for the flying 5 miles (8 km), averaging 151.623 mph (244.014 km/h).

Bad weather, poor course conditions, underperforming engines, and other teething issues on the untested LSR car all combined to delay further record attempts. During this time, various modifications were applied to the Silver Bullet. Another attempt was finally made on 31 March. The speed recorded for one direction was 186.046 mph (299.412 km/h), but issues caused further runs to be aborted. More delays were encountered and modifications undertaken. The next significant run occurred on 10 April, with 175.72 mph (282.79 km/h) speed in one direction being recorded.

Sunbeam Silver Bullet Daytona 14-03-1930

Don sits in the Silver Bullet on Daytona Beach. The image was taken on 14 March 1930, before any real issues with the car had been encountered. Note the slight exhaust staining just before the tail fin. It is doubtful that the wheel fairings improved aerodynamics much, given their distance from the tires.

After over 18 record attempts, the Silver Bullet’s issues proved to be too much to overcome, and the timing crews could not stay on the beach indefinitely. Coatalen ordered a return to England on 13 April. Sunbeam was struggling financially, and little further effort or expense was expended on the Silver Bullet.

The Silver Bullet was sold to Jack Field, a hotel and garage owner and gentleman racer. Field modified the car to resolve its issues and improve its reliability. All of the modifications are not known, but the exhaust manifolds running along the car’s sides were completely discarded in favor of 12 individual exhaust stacks that protruded from the cowling. Incidentally, the eight Roots-type superchargers originally planned for the car were included with the spare parts sold to Field. On 21 March 1934, Field made an attempt to capture the British absolute speed record (top speed achieved on British Empire soil), which then stood at 217.52 mph / 350.065 km/h (set by Malcolm Campbell at Verneuk Pan, South Africa on 21 April 1929). Field averaged 174.09 mph (280.17 km/h) in one direction on Southport beach, but the Silver Bullet caught fire, and further attempts were abandoned. Field sold the damaged car to famed motorcycle racer Freddie Dixon. Reportedly, the sale price was only £10, and adult beverages were involved. Dixon later determined that the car possessed little that he could use, and the Silver Bullet was scrapped.

Sunbeam Silver Bullet Jack Field Getty

Jack Field campaigning the Silver Bullet on Southport beach in 1934. Note the individual exhaust stacks protruding from the engine cowling. Field did not have any better luck than Don, and the Silver Bullet soon caught fire. (Getty image)

Sources:
The Land Speed Record 1930-1939 by R. M. Clarke (2000)
The Land Speed Record 1920-1929 by R. M. Clarke (2000)
Land Speed Record by Cyril Posthumus and David Tremayne (1971/1985)
Sunbeam Aero-Engines by Alec Brew (1998)
https://www.motorsportmagazine.com/archive/article/april-1976/46/inside-story-sunbeam-silver-bullet
https://www.motorsportmagazine.com/archive/article/february-1990/45/racing-cars-jack-field
http://www.historywebsite.co.uk/Museum/Transport/Cars/Sunbeam/Bullet.htm

Lycoming XR-7755-3

Lycoming XR-7755 36-Cylinder Aircraft Engine

By William Pearce

Since 1933, the Lycoming Division of the Aviation Manufacturing Corporation had worked to create a high-power engine for the United States Armed Forces. Its first attempt was the 1,200 hp (895 kW), 12-cylinder O-1230, which was outclassed by the time it first flew in 1940. Lycoming’s second attempt was the 2,300 hp (1,715 kW), 24-cylinder XH-2470. The engine had shown some promise, but its performance was eclipsed by other engines when the XH-2470 was first flown in 1943. Lycoming set out to design an engine that was more powerful than any other and that would meet the power needs of future large aircraft.

Lycoming XR-7755-3

The Lycoming XR-7755 was the most powerful aircraft engine in the world when it was built. The XR-7755 was the culmination of Lycoming’s experience with radial and liquid-cooled engines. Conceived in 1943, such a large engine was not needed by the time it first ran in 1946.

In mid-1943, Lycoming engaged in talks with personnel from the US Army Air Force (AAF) at Wright Field, Ohio. Different sources list the involvement of the Air Materiel Command, Air Technical Service Command, and the Power Plant Lab. By December 1943, the engine concept had been solidified as a very large displacement, high-compression, liquid-cooled engine designed for optimum fuel economy and intended to power the next generation of very large aircraft. Lycoming’s experimental engine was designated XR-7755 and given the “Materiel, Experimental” code MX-434.

Clarence Wiegman headed the Lycoming XR-7755 design team. The engine consisted of nine banks of four inline cylinders positioned radially with 40-degrees of separation around a forged steel crankcase. This formed a 36-cylinder inline radial engine. The crankcase was made up of five sections, each split vertically through the cylinders. The crankcase sections were secured together by nine bolts that extended the length of the case. The individual steel cylinders each had their own water jacket. Each bank of four cylinders shared a common cast aluminum cylinder head. Each four-cylinder bank was secured to the crankcase by 16 long studs that passed through the cylinder head.

Lycoming XR-7755-3 stand

The worker gives some perspective to the XR-7755’s large size. However, the engine’s three-ton (2.74 t) weight is hard to imagine. The engine’s two magnetos and four distributors are visible on the front of the cylinder banks.

Each cylinder had one intake and one exhaust valve. Both valves were sodium cooled, with a hollow stem for the intake valve and a hollow stem and head for the exhaust valve. The valves for each bank of cylinders were actuated by a single overhead camshaft, driven via a vertical shaft at the front of the engine. Each camshaft had two sets of lobes for different valve timing—one lobe set was optimized for power and the other set for economic cruise. The camshafts shifted axially to engage the desired set of lobes. When the camshaft was shifted, the spark plug timing was automatically changed. Ignition was provided by two magnetos and four distributors. Each unit was camshaft-driven and mounted to the front of a separate cylinder bank. The spark plug leads passed through the valve covers and to the spark plugs, which were positioned in opposite corners of each cylinder.

Lycoming XR-7755-1 test stand

The XR-7755-1 on the test stand with its single propeller shaft. With each of the 36-cylinders displacing 215 cu in (3.5 L), witnessing the XR-7755 run was most likely a very memorable event. Note the robust upper engine support.

The crankshaft had four crankpins, each spaced at 180 degrees. The crankshaft was made up of five sections and assembled through the four one-piece master connecting rods. The crankshaft sections were joined at the rear of the crankpin via face splines and secured by four bolts. Five roller bearings supported the crankshaft in the crankcase.

At the rear of the engine was a single-stage, single-speed supercharger. The supercharger’s impeller was 14.4 in (366 mm) in diameter and spun at six times crankshaft speed. The supercharger fed air to nine intake manifolds, each mating with the right side of a cylinder bank. Fuel was provided to the cylinder via either a carburetor or fuel injection. Individual exhaust stacks were attached to the left side of each cylinder. Provisions were also made to incorporate two turbosuperchargers.

Although a single rotation engine was tested, the engine accommodated contra-rotating propellers using SAE #60L-80 spline shafts. The inner shaft rotated counterclockwise, and the outer shaft rotated clockwise. A two-speed propeller gear reduction was hydraulically shifted and used planetary gears. A .2460 reduction was available for high engine speeds, and a .3536 reduction was used for cruise operations with low engine rpm.

Lycoming XR-7755-1 Maxwell and Cervinsky

Lycoming workers Red Maxwell (left) and Paul Cervinsky (right) pose next to the completed XR-7755-1. It appears Maxwell is ready for the big engine to be stuffed in an airframe to see what it will do. Note the ring on the nose case and around the propeller shaft. No other image found has that ring.

The XR-7755 had a 6.375 in (162 mm) bore and a 6.75 in (171 mm) stroke. The engine displaced 7,756 cu in (127.1 L) and had a compression ratio of 8.5 to 1. The XR-7755 produced 5,000 hp (3,728 kW) at 2,600 rpm (.2460 propeller gear) for takeoff, 4,000 hp (2,983 kW) at 2,300 rpm (.2460 propeller gear) for normal operation, and 3,000 hp (2,237 kW) at 2,100 rpm (.3536 propeller gear) for cruise power. Specific fuel consumption at normal cruise power was .43 lb/hp/hr (262 g/kW/hr), but the rate dropped to around .38 lb/hp/hr (231 g/kW/hr) at low cruise power of around 1,500 hp (1,119 kW). The engine was 61.0 in (1.55 m) in diameter, 66.25 in (1.68 m) tall, and 121.35 in (3.08 m) long. The XR-7755 weighed 6,050 lb (2,744 kg).

Lycoming XR-7755 ad Dec 1946

Lycoming ad from December 1946 featuring the XR-7755. If the engine was not going to go into production, Lycoming might as well get some press out of it. One can only wonder how those responsible for marketing imagined the huge, liquid-cooled engine would factor into the decision-making process of a person buying a small, air-cooled engine.

The XR-7755 was first run in July 1946. At the time, some 10,000 hours of single-cylinder testing had been completed. The Lycoming factory was located near a residential area. Reportedly, a nearby grocery store’s canned goods would vibrate off the shelves as the XR-7755 underwent high-power tests. A good neighbor, Lycoming went to the store and installed strips on the shelf edges to keep the cans from falling. At takeoff power, the XR-7755’s fuel consumption was 580 gallons (2,196 L) per hour, or 20.62 fl oz (.61 L) per second. The engine’s coolant pump flowed 750 gpm (2,839 l/m) to dissipate 95,600 BTUs (23,956 kcal) per minute. The flow rate was enough to fill a 55 gallon (208 L) drum every 4.4 seconds. The oil pump circulated 71 gpm (269 l/m) at 100 psi (6.89 bar). Lycoming had an optimistic opinion of the engine and believed that an output of 7,000 hp (5,220 kW) was possible.

Most sources indicate that two XR-7755 engines were built: an XR-7755-1 with a single rotation propeller shaft and an XR-7755-3 with a contra-rotating propeller shaft. Both of these engines used carburetors. There is some indication, including the recollections of those who had family members involved with the project, that a third engine was built: an XR-7755-5 with fuel injection. Reportedly, the -1 underwent a 50-hour test run, but the results are not known. The -3 was delivered to the AAF in 1946, but it is unlikely this engine underwent much testing. It is not clear what happened to the -5, if it was completed. By the time the XR-7755 had run, the concept of an aircraft larger than the Convair B-36 Peacemaker had fallen out of favor, as had the idea of modifying the B-36 with larger piston engines. Rather, jets would be used to improve performance of the aircraft. There was no application for the XR-7755 in a post-war world with the performance of jet aircraft quickly being realized. The XR-7755 never flew.

Lycoming XR-7755 AAF Fair Oct 1945

The XR-7755 on display at the Army Air Forces Fair held at Wright Field, Ohio in October 1945. Note what appears to be a mockup of the contra-rotating propeller shafts.

One curious anomaly in the XR-7755’s story is an appearance of the engine at the Army Air Forces Fair held at Wright Field, Ohio in October 1945. This predates the engine’s run date and its supposed delivery to the AAF. However, the engine appears to have a mockup of its contra-rotating propeller shafts installed. It would seem that the engine is not complete and was shipped the 460 miles (740 km) from Lycoming’s factory in Williamsport, Pennsylvania to Dayton, Ohio to be displayed with other unusual treasures from the war. Presumably, the engine was returned to Lycoming after the show and was subsequently completed and tested in 1946.

The sole XR-7755-3 has been preserved by the Smithsonian National Air and Space Museum and is on display in the Steven F. Udvar-Hazy Center in Chantilly, Virginia. Many consider the XR-7755 the largest aircraft engine ever built. However, the Soviet IAM M-44 (8,107 cu in / 132.8 L) of 1933 and Yakovlev M-501 (8,760 cu in / 143.6 L) of 1952 were larger engines. At the time it first ran, the XR-7755 was the world’s most powerful reciprocating aircraft engine.

Lycoming XR-7755-3 NASM

The restored XR-7755-3 on display in the Steven F. Udvar-Hazy Center of the Smithsonian National Air and Space Museum. The bottom of the engine is on the left, marked by the drain tube from the gear reduction housing and the sump built into the valve cover. Note the two spark plug leads for each cylinder passing through opposite sides of the valve covers. (Sanjay Acharya image via Wikimedia Commons)

Sources:
“5,000-Hp. Lycoming Revealed” by J. H. Carpenter, Aviation (December 1946)
“The Evolution of Reciprocating Engines at Lycoming” by A. E. Light, AIAA: Evolution of Aircraft/Aerospace Structures and Materials Symposium (24–25 April 1985)
Aircraft Engines of the World 1948 by Paul Wilkinson (1948)
The History of North American Small Gas Turbine Aircraft Engines by Richard A. Leyes II and William A. Fleming (1999)
Studebaker’s XH-9350 and Their Other Aircraft Engines by William Pearce (to be published)
https://generalaviationnews.com/2007/04/20/the-xr-7755-the-whole-story/
https://airandspace.si.edu/collection-objects/lycoming-xr-7755-3-radial-36-engine

Lycoming XH-2470 side

Lycoming XH-2470 24-Cylinder Aircraft Engine

By William Pearce

The Lycoming Division of the Aviation Manufacturing Corporation was located in Williamsport (Lycoming County), Pennsylvania. The company had started producing aircraft engines in the late 1920s. In 1937, Lycoming became aware that its most powerful engine to date, the 12-cylinder O-1230, would not produce the power needed for future frontline military aircraft. Development of the O-1230 engine started in 1933, but the anticipated power needs of state-of-the-art aircraft were beyond what the 1,200 hp (895 kW) engine could provide. Lycoming moved quickly to apply knowledge gained from the O-1230 to a new aircraft engine.

Lycoming XH-2470 side

The design of the Lycoming XH-2470 started with the concept of mounting two O-1230 engines to a common crankcase. Note that the propeller shaft is raised above the centerline of the engine.

Lycoming started the design of its new engine in 1938, and detailed design work commenced in mid-1939. The 24-cylinder engine had an H-configuration and consisted of components from two O-1230 engines combined with a new crankcase. The new two-piece aluminum crankcase was split horizontally and accommodated a left and right crankshaft. Each crankshaft served two banks of six cylinders, with one bank above the engine and the other bank below. Fork-and-blade connecting rods were used, with the forked rods serving the lower cylinders. The H-24 engine was designated XH-2470 and given the “Materiel, Experimental” code MX-211. The US Army Air Corps (AAC) initially felt that the engine was too small, but the US Navy supported the design. The Navy ordered a single prototype engine on 11 December 1939, and the AAC started to show some interest in the engine in 1940.

The Lycoming XH-2470 utilized individual cylinders that consisted of a steel barrel screwed and shrunk into an aluminum head. The liquid-cooled cylinder was surrounded by a steel water jacket. The aluminum head had a hemispherical combustion chamber with one intake valve and one sodium-cooled exhaust valve. A cam box was mounted to the top of each cylinder bank, and each cam box contained a single camshaft that was shaft-driven from the rear of the engine.

Lycoming XH-2740 top

Top view of the XH-2470 shows the intake manifold positioned between the cylinder banks. The narrow engine could be installed horizontally (on its side) in an aircraft’s wing. Bell and Northrop pursued this installation for project aircraft, but the designs were not built.

A downdraft carburetor fed fuel into the supercharger’s 12 in (305 mm) diameter impeller mounted to the rear of the engine. Lycoming had experimented with direct fuel injection on test cylinders and planned to have fuel injection available for the XH-2470, but it is unlikely that any complete engines ever used fuel injection. The XH-2470-1, -3, and -7 engines had a single-speed, single-stage supercharger that was driven at 6.142 times crankshaft speed. The XH-2470-5 had a two-speed supercharger that was driven at 6.06 and 7.88 times crankshaft speed. Intake manifolds ran between the upper and lower cylinder banks. Depending on the installation, exhaust gases were either expelled from the outer side of the cylinders via individual stacks or collected in a manifold common to each cylinder bank. Provisions were made for the engine to accommodate a turbosupercharger.

The XH-2470-1, -3, and -5 were available with a single-rotation propeller shaft using a SAE #60 spline shaft. The -1 and -3 had a .38 gear reduction. The -5 was listed as having a two-speed reduction, but the ratios have not been found. The XH-2470-7 had contra-rotating propeller shafts and a two-speed gear reduction with speeds of .433 and .321. The contra-rotating shafts were SAE #40-60 splines, with the inner shaft rotating counterclockwise and the outer shaft rotating clockwise. The gear reduction for all engines was achieved through spur gears, and the propeller shaft was positioned above the engine’s centerline. The engine could be installed in either a vertical or horizontal position.

Lycoming XH-2470-2 drawing

The XH-2470-2 and -4 were engines intended for the Navy. The -2 was similar to the AAF’s engine with a single propeller shaft. The -4 had contra-rotating propeller shafts and was similar to the -7.

The H-2470 had a 5.25 in (133 mm) bore and a 4.75 in (121 mm) stroke. The engine’s total displacement was 2,468 cu in (40.4 L), and it had a 6.5 to 1 compression ratio. The H-2470 produced 2,300 hp (1,715 kW) at 3,300 rpm at 1,500 ft (457 m) for takeoff, 2,000 hp (1,491 kW) at 3,100 rpm at 3,500 ft (1,067 kW) for normal operation, and 1,300 hp (969 kW) at 2,400 rpm at 15,000 ft (4,572 m) for cruise operation. In addition, the two-speed supercharged engine could achieve 1,900 hp (1,417 kW) at 3,300 rpm at 15,000 ft (4,572 m) for emergency power and 1,750 hp (1,305 kW) at 3,100 rpm at 15,000 ft (4,572 m) for normal operation. The XH-2470 had a 3,720-rpm overspeed limit for diving operations. The single-rotation engines were 89.9 in (2.28 m) long, 30.5 in (.77 m) wide, 50.3 in (1.28 m) tall, and weighed 2,430 lb (1,102 kg). The contra-rotating XH-2470-7 was approximately 114 in (2.90 m) long and weighed 2,600 lb (1,179 kg).

Before the XH-2470 had even run, Lycoming proposed a variant of the engine to satisfy the AAC’s Request for Data R40-D, which was issued on 6 March 1940. R40-D sought the design of a 4,000 to 5,500 hp (2,983 to 4,101 kW) aircraft engine for use in long-range bombers. Lycoming proposed coupling two H-2470 engines together, creating a 48-cylinder XH-4940. The XH-4940 would produce 4,800 hp (3,579 kW) at 3,100 rpm up to 8,500 ft (2,591 m) with the aid of a single-speed, single-stage supercharger. The engine had a projected maximum speed of 3,400 rpm and would weigh 6,200 lb (2,812 kg). The AAC’s R40-D ended up going nowhere, and the request was cancelled in mid-1940.

Lycoming XH-2470 test stand

An XH-2470 mounted on a test stand with a tractor propeller. Installed in the XP-54 as a pusher; the blades on the XH-2470 had their angle reversed. Note the individual exhaust stacks.

The XH-2470 was first run in July 1940. The engine was proposed for the Curtiss XF14C Naval fighter and the Vultee XP-54 Swoose Goose AAC fighter. The XP-54’s original power plant was the Pratt & Whitney X-1800 (XH-2240 / XH-2600), but development of this engine stopped in October 1940. It was the cancellation of the X-1800 that led to the AAC’s interest in the XH-2470, and the AAC ordered 25 (later increased to 50) engines in October 1940. The AAC was also interested in potentially using the XH-2470 to power the Lockheed XP-58 Chain Lightning. Bell and Northrop also expressed interest in the engine for future projects.

The XH-2470 completed a Navy acceptance test in April 1941. At the time, the XF14C and XP-54 prototypes were in the detailed design stage. However, the Army Air Force (AAF—the AAC had changed its name in June 1941) continued to alter the XP-54 requirements throughout 1941. Added to the Vultee project were Turbosuperchargers, a pressurized cockpit, and the option of the Wright R-2160 Tornado engine. It was not until 1942 when R-2160 development was seriously behind schedule that the engine was dropped from the XP-54 and a more focused installation of the XH-2470 was presented. An XH-2470-7 engine with contra-rotating propellers was intended for the XP-54, but a single rotation engine was substituted because of delays with the contra-rotating gearbox. The AAF specified two Wright TSBB turbosuperchargers for the first XP-54 prototype and a single, experimental General Electric (GE) XCM turbosupercharger for the second aircraft. Reportedly, the Navy ordered 100 XH-2470 engines in May 1942. However, this may have been a total of 100 engines on order with 50 going to the AAF and 50 to the Navy.

The first XP-54 (41-1210) made its first flight on 15 January 1943, taking off from Muroc (now Edwards) Air Force Base, California. With the exception of the first flight, the XH-2470 engine installed in the XP-54 turned a 12 ft 2 in (3.71 m) Hamilton Standard propeller. Although the aircraft handled well, its development had suffered through constant changes in design and intended role. The aircraft underperformed, and the XH-2470 engine had some issues, such as oil foaming at high RPM or at altitudes above 20,000 ft (6,096 m).

Lycoming XH-2470 Vultee XP-54

The Vultee XP-54 was a very large aircraft. Even so, the installation of the XH-2470 appears to be quite cramped. Note the large exhaust manifold linking the engine to the turbosupercharger, which was positioned behind the cockpit.

The first XP-54 was flown to Wright Field, Ohio on 28 October 1943. After the next flight, a close inspection of the XH-2470 revealed some minor issues as well as damage to the supercharger impeller. The engine was removed and sent to Lycoming for repairs. The cost to fix the engine was more than the AAF was willing to pay, which showed the AAF’s lack of interest in the XH-2470 program. The first XP-54 was removed from flight status and used as a source of spare parts for the second XP-54 aircraft. The first XP-54 had completed 86 flights and accumulated 63.2 hours of flight time.

To make matters worse, the Navy cancelled its XH-2470 order in December 1943, deciding to power the XF14C with a turbosupercharged Wright R-3350 instead. Factors that influenced this change were the Navy’s long-standing preference for air-cooled engines, a shift of the XF14C’s role to that of a high-altitude fighter, issues with the XH-2470’s developmental progress, and doubts that the engine would be ready in time to see combat during World War II. At the same time, Lycoming had moved on to another aircraft engine project, the 36-cylinder XR-7755. Lycoming had invested over $1,000,000 of its own money into the XH-2470 engine.

Lycoming XH-2470 Vultee XP-54 top

The two exhaust outlets from the turbosupercharger protrude quite visibly behind the cockpit. The panel behind the exhaust was stainless steel, and hot exhaust burned the paint off the cowling on early flights. The upper cowling was later replaced with an unpainted stainless steel unit, and the rudders were painted around the same time. (Aerospace Legacy Foundation Archive image)

The second XP-54 prototype (42-108994, but incorrectly painted as 41-1211) made its first flight on 24 May 1944, taking off from Vultee Field. After at least three flights, the GE XCM turbosupercharger and the XH-2470 were removed from the aircraft. Some incompatibility between the turbosupercharger and engine had caused damage to both units. A new engine and turbosupercharger were installed, and the XP-54 flew again in December 1944. The second XP-54 made at least 10 flights, the last ending with an engine failure on 2 April 1945. The airframe had accumulated 10.7 hours of flight time.

At least one XH-2470 engine has been preserved. An XH-2470-7 is in storage at the Smithsonian National Air and Space Museum. The engine, which was never installed in any aircraft, has contra-rotating propellers and a two-speed gear reduction. The Smithsonian also lists an XH-2470-1 engine from the XP-54 in its inventory. However, no further evidence of this engine’s existence has been found.

The preserved XH-2470-7 is in storage at the Smithsonian National Air and Space Museum. Although the engine was never installed in any aircraft, at least it may be displayed one day. (NASM image)

The preserved XH-2470-7 is in storage at the Smithsonian National Air and Space Museum. Although the engine was never installed in any aircraft, at least it may be displayed one day. (NASM image)

Sources:
Aircraft Engines of the World 1947 by Paul Wilkinson (1947)
American Secret Pusher Fighters of World War II by Gerald H. Balzer (2008)
Development of Aircraft Engines and Fuels by Robert Schlaifer and S. D. Heron (1950)
U.S. Experimental & Prototype Aircraft Projects Fighters 1939–1945 by Bill Norton (2008)
Experimental & Prototype U.S. Air Force Jet Fighters by Dennis R. Jenkins and Tony R. Landis (2008)
The History of North American Small Gas Turbine Aircraft Engines by Richard A. Leyes II and William A. Fleming (1999)
Studebaker’s XH-9350 and Their Other Aircraft Engines by William Pearce (to be published)
Preliminary Model Specification for Engine Aircraft Model XH-2470-4 for Opposite Rotating Propellers by Aviation Manufacturing Corporation Lycoming Division (18 April 1940)
“The Evolution of Reciprocating Engines at Lycoming” by A. E. Light, AIAA: Evolution of Aircraft/Aerospace Structures and Materials Symposium (24–25 April 1985)
https://airandspace.si.edu/collection-objects/lycoming-xh-2470-7-h-24-engine
https://airandspace.si.edu/collection-objects/lycoming-xh-2470-1-h-24-h-type-engine