Category Archives: Between the Wars

Packard X-2775 front

Packard X-2775 24-Cylinder Aircraft Engine

By William Pearce

In late 1926, Lt. Alford Joseph Williams approached the Packard Motor Car Company (Packard) regarding a high-power engine for a special aircraft project. Williams was an officer in the United States Navy and believed that air racing contributed directly to the development of front-line fighter aircraft. The United States had won the Schneider Trophy two out of the last three races, and another win would mean permanent retention of the trophy for the US. However, the US government was no longer interested in supporting a Schneider team.

Packard X-2775 front

The original Packard X-2775 (1A-2775) was a direct-drive engine installed in the Kirkham-Williams Racer. A housing extended the propeller shaft to better streamline the engine. Two mounting pads were integral with the crankcase, and a third was part of the timing gear cover at the rear of the engine. Note the vertical intake in the center of the upper Vee.

Williams was assembling a group of investors to fund the design and construction of a private racer to participate in the Schneider contest. In addition, the US Navy was willing to indirectly support the efforts of a private entry. With the Navy willing to cover the development of the engine, Packard agreed to build a powerful engine for Williams’ Schneider racer. On 9 February 1927, the US government officially announced that it would not be sending a team to compete in the 1927 Schneider race, held in Venice, Italy. On 24 March 1927, it was announced that a private group of patriotic sportsmen had formed the Mercury Flying Corporation (MFC) to build a racer for the Schneider Trophy contest that would be piloted by Williams. The aircraft was built by the Kirkham Products Corporation and was known as the Kirkham-Williams Racer.

Packard had started the initial design work on the engine shortly after agreeing to its construction, even though a contract had not been issued. Once the Navy had the funds, Contract No. 3224 was issued to cover the engine’s cost. To speed development of the powerful engine, Packard combined components of two proven V-1500 engines to create a new 24-cylinder engine. The new engine was designated the Packard 1A-2775, but it was also commonly referred to by its Navy designation of X-2775.

Packard X-2775 case drive rod crank

The X-2775’s hexagonal, barrel-type crankcase, timing gear drive and housing, connecting rods, and crankshaft. Note the walls inside of the crankcase, and the crankshaft’s large cheeks that acted as main journals.

The Packard X-2775 was designed by Lionel Melville Woolson. The engine was arranged in an X configuration, with four banks of six cylinders. The upper and lower banks retained the 60-degree bank angle of the V-1500. This left 120-degree bank angles on the sides of the engine. As many V-1500 components were used as possible, including pistons, the basic valve gear, and the induction system. At the front of the X-2775, the propeller shaft ran in an extended housing and was coupled directly to the crankshaft, without any gear reduction. The extended housing allowed for a more streamlined engine installation.

A single-piece, cast aluminum, hexagonal, barrel-type crankcase was used. Two engine mounting pads were provided on each side of the crankcase, and a third pad was incorporated into the side of the timing gear housing, which mounted to the rear of the engine. The crankcase was designed to support landing gear or floats connected to the forwardmost engine mounting pad. Seven integrally cast partitions were provided inside the crankcase. The partitions were hollow at their center and were used to support the crankshaft. The seven single-piece main bearings were made of Babbitt-lined steel rings, shrunk into the crankcase’s partitions, and retained by screws from the outer side of the flanged partition. The partitions had a series of holes around their periphery that allowed for the internal flow of oil as well as enabled assembly of the engine’s connecting rods.

Packard X-2775 manifold and valve spring

Upper image is the valve port arrangement that was integral with the valve and camshaft housing. The drawing includes the ports to circulate hot exhaust gases around the intake manifold to ensure fuel vaporization. The lower image is the unique valve spring arrangement designed by Lionel Woolson. Helically-twisted guides (left) held the seven small springs (center) to make the complete spring set (right).

The crankshaft was positioned about 1.5 in (38 mm) above the crankcase’s centerline and had six crankpins. The crankshaft’s cheeks acted as main journals. The cheeks were perfectly circular and were 7.75 in (197 mm) in diameter. This design increased the main bearing surface area to support the engine’s power but kept the crankshaft the same overall length as the crankshaft used on the V-1500 engine. A longer crankshaft would result in a longer and heavier engine, as well as necessitating the design and manufacture of new valve housings and camshafts. At 161 lb (73 kg), the crankshaft was around twice the weight of the crankshaft used in the V-1500 engine. The X-2775’s crankshaft was inserted through the center of the crankcase for assembly.

Each connecting rod assembly was made up of a master rod and three articulated rods. The end cap, with its two bosses for the articulating rods, was attached to the master rod by four studs. The articulated rods had forked ends that connected to the blade bosses on the master rod. The forked end of each articulated rod was tapped and secured to the master rod by a threaded rod pin. Once assembled, two bolts passed through the connecting rod assembly to further secure its two halves and also secured the pins of the articulated rods. To accommodate the crankshaft being approximately 1.5 in (38 mm) above center in the crankcase, the lower articulated rods were 1.5 in (38 mm) longer than the other rods. When the engine was viewed from the rear, the master rods were attached to pistons in the upper left cylinder bank.

Packard X-2775 section

Sectional view of the X-2775 engine. The engine mount is depicted on the left, and the landing gear or float mount is on the right. Note the spark plug position. The revised engine had provisions for four spark plugs—two on each side of the cylinder.

Individual steel cylinders of welded construction with welded-on steel water jackets were mounted to the crankcase via 10 studs. The cylinder’s combustion chamber had machined valve ports and was welded to the top of the cylinder barrel. Five studs protruded above each cylinder’s combustion chamber and were used to secure the cast aluminum valve and camshaft housing. Each bank of six cylinders had a single valve and camshaft housing.

Each cylinder had two intake and two exhaust valves. The valves were arranged so that one intake and one exhaust valve were on the Vee side of the cylinder, and the pairing was duplicated on the other side of the cylinder. The valve and camshaft housing collected the exhaust gases from two adjacent cylinders and expelled it out one of three exhaust ports. The valve and camshaft housing also had an integral intake manifold that fed three cylinders. The valves for each cylinder bank were actuated by a single overhead camshaft driven by an inclined shaft at the rear of the engine. The two inclined shafts for each Vee engine section were driven by a vertical shaft geared to the crankshaft. The lower vertical shaft was extended to drive one fuel, one water, and four oil pumps. The shafts were enclosed in the timing gear housing that mounted to the back of the engine. The valve covers of the lower cylinders also formed sumps for engine oil collection. Oil was circulated through various passageways in addition to the hollow crankshaft and hollow camshaft. The exhaust valve had a hollow stem for oil cooling.

The valve springs were designed by Woolson and were a unique design. Rather than the valve stem passing through the center of one or two valve springs, a set of seven smaller springs encircled the valve stem. Each of the seven springs was mounted on a guide, and the set was contained in a special retainer. The seven spring guides were given a slight helical twist. The special valve spring set distributed the spring load evenly around the valve stem, reduced the likelihood of a valve failure due to a spring breaking, prevented valve springs from setting, and also rotated the valve during engine operation. The valve rotation was one revolution for about every 40 revolutions of the crankshaft.

Packard X-2775 front and back

Front and rear views of the original X-2775 illustrate that the engine was narrow but rather tall. The ring around the propeller shaft was a fixed attachment point for the engine cowling.

Each cylinder’s combustion chamber had a flat roof with a spark plug on each side of the cylinder. The spark plugs were fired by a battery-powered ignition system via four distributors driven at the rear of the engine. Two distributors were positioned behind each 60-degree cylinder bank Vee. In each cylinder, one spark plug was fired by an upper distributor, and one spark plug was fired by a lower distributor. Separate induction systems were positioned in the upper and lower cylinder Vees. Each system consisted of a central inlet that branched into a forward and rear section. Each section had a carburetor and fed six cylinders. This gave the engine a total of four carburetors—two in each upper and lower vee. Control rods linked the carburetors to the distributors so that ignition timing was altered with throttle position. A port in the valve and camshaft housing fed exhaust gases through a jacket surrounding the manifold to which the carburetor mounted. The exhaust gases heated the intake manifold to better vaporize the incoming fuel charge.

Packard’s V-1500 engine had a 5.375 in (137 mm) bore and a 5.5 in (140 mm) stroke. The X-2775 had the same 5.375 in (137 mm) bore, but the stroke was shortened to 5.0 in (127 mm). However, the three articulated connecting rods had a slightly longer stroke of 5.125 in (130 mm). Each of the six cylinders served by a master rod had a displacement of 113.5 cu in (1.86 L), and each of the 18 cylinders served by an articulated rod had a displacement of 116.3 cu in (1.91 L). The total displacement for the engine was 2,774 cu in (45.5 L). The X-2775 produced a maximum of 1,250 hp (932 kW) at 2,780 rpm and was rated for 1,200 hp (895 kW) at 2,600 rpm. At 2,000 rpm, the engine had an output of 800 hp (597 kW). The X-2775 was 77.5 in (1.97 m) long, 28.3 in wide (.72 m), and 45.2 in (1.15 m) tall. The weight of the initial X-2775 was 1,402 lb (636 kg).

Packard X-2775 no 2 supercharged

The second X-2775 incorporated a Roots-type supercharger driven from the propeller shaft. Difficulty was encountered with fuel metering since the carburetors were positioned on the pressure side of the supercharger. The supercharged engine was never installed in an aircraft.

The X-2775 engine was completed in June 1927 and subsequently passed an acceptance test, which involved the engine running continuously at full throttle for one hour. Williams was involved with testing the X-2775 at Packard to gain experience with its operation. The engine was then shipped out for installation in the Kirkham-Williams Racer, which was finished in late July. The racer and the X-2775 made their first flight on 25 August. Despite achieving speeds around 270 mph (435 km/h), the racer had issues that could not be resolved in time for the Schneider Trophy contest, scheduled to start on 23 September. The Kirkham-Williams Racer was subsequently converted to a land plane, and Williams flew the aircraft over a 3 km (1.9 mi) course unofficially timed at 322.42 mph (518.88 km/h) on 6 November 1927. However, that speed was with the wind, and Williams later stated that the true speed was around 287 mph (462 km/h). Higher speeds had been anticipated. The aircraft was then shipped to the Navy Aircraft Factory (NAF) at Philadelphia, Pennsylvania.

Around late June 1927, rumors indicated that the Schneider competition would be faster than the Kirkham-Williams Racer. As a result, the Navy added a second X-2775 engine to its existing contract with Packard. The second engine incorporated a supercharger for increased power output. In the span of 10 weeks, Packard had designed, constructed, and tested the new engine. The second X-2775 engine was, again, direct drive. However, the propeller shaft also drove a Roots-style supercharger with three rotors (impellers). A central rotor was coaxial with the propeller shaft, and it interacted with an upper and lower rotor that supplied forced induction to the respective upper and lower cylinder banks. For the upper Vee, air was brought in the right side of the supercharger housing and exited the left side, flowing into a manifold routed between the upper cylinder banks. For the lower Vee, the flow was reversed—entering the left side of the supercharger and exiting the right. The supercharged X-2775 weighed around 1,635 lb (742 kg).

Because of the very tight development schedule, the rotors were given generous clearances. This reduced the amount of boost the supercharger generated to only 3.78 psi (.26 bar), which increased the X-2775’s output to 1,300 hp (696 kW) at 2,700 rpm. Tighter rotor tolerances would yield 4.72 psi (.33 bar) of boost and 1,500 hp (1,119 kW) at 2,700 rpm. However, it is not known if improved rotors were ever built. Although completed around August 1927, the supercharged engine was never installed in the Kirkham-Williams Racer.

Packard X-2775 NASM left

The first X-2775 engine was reworked with a propeller gear reduction, new cylinders, new valve housings, and a new induction system. This engine was installed in the Williams Mercury Racer. (NASM image)

The Navy felt that adding a propeller gear reduction to the engine would be more beneficial than the supercharger. To this end, the unsupercharged engine was removed from the Kirkham-Williams Racer as the aircraft was disassembled in the NAF around early 1928. The engine was returned to Packard for modifications. A new aircraft, the Williams Mercury Racer, was to be built, and the first X-2775 engine with the new gear reduction and other modifications would power the machine.

A planetary (epicyclic) gear reduction was built by the Allison Engineering Company in Indianapolis, Indiana. This gear reduction mounted to the front of the engine and turned the propeller at .677 crankshaft speed. Other modifications to the X-2775 included using cylinders and valve housings from an inverted 3A-1500 (the latest V-1500) engine and revising the induction and ignition systems.

The new cylinders increased the engine’s compression (most likely to 7.0 to 1) and had provisions for two spark plugs on both sides of the cylinder. Still, only two spark plugs were used, with one on each side of the cylinder. The new induction was a ram-air system with inlets right behind the propeller. The air flowed into a manifold located deep in the cylinder bank’s Vee. Two groups of two carburetors were mounted to the manifold. Each carburetor distributed the air/fuel mixture to a short manifold that fed three cylinders. The revised ignition system used two magnetos and did away with battery power. The magnetos were mounted to the rear of the engine and driven from the main timing gear. The improved X-2775 was occasionally referred to as the 2A-2775, but it mostly retained the same 1A-2775 Packard designation of its original configuration. The geared X-2775 produced 1,300 hp (969 kW) at 2,700 rpm and weighed around 1,513 lb (686 kg). The gear reduction added about 3 in (76 mm) to the engine, resulting in an overall length of 80.5 in (2.04 m). The width was unchanged at 28.3 in (.72 m), but the revised induction system reduced the engine height slightly to 43.25 in (1.10 m).

Packard X-2775 NASM front

The revised X-2775 took advantage of ram-air induction. Intakes directly behind the Williams Mercury Racer’s spinner fed air into manifolds at the base of the cylinder Vees. Note the spark plugs on both sides of the cylinders. (NASM image)

The updated X-2775 engine was installed in the Williams Mercury Racer in July 1929. In early August, flight testing was attempted on Chesapeake Bay near the Naval Academy in Annapolis, Maryland. While the aircraft was recorded at 106 mph (171 km/h) on the water, it could not lift off. The Williams Mercury Racer was known to be overweight, and there were questions about its float design. The trouble with the racer caused it to be withdrawn from the Schneider Trophy contest, scheduled to start on 6 September in Calshot, England. Later, it was found that the Williams Mercury Racer was some 880 lb (399 kg), or 21%, overweight. Some additional work was done on the aircraft, but no further attempts at flight were made.

Of the original X-2775, Woolson stated that the engine ran for some 30 hours, and at no time was mechanical trouble experienced or any adjustments made. Williams made some comments about the X-2775 losing power, but he otherwise seemed satisfied with the engine and did not report any specific issues. Assistant Secretary of the Navy for Aeronautics David S. Ingalls did not make any negative comments about the engine, but he said Commander Ralph Downs Weyerbacher of the NAF felt that the engine was not satisfactory. However, the basis for Weyerbacher’s opinion has not been found.

There were essentially no X-2775 test engines. Only two engines were made, and the second engine was never installed in any aircraft. The very first X-2775 built was installed in the Kirkham-Williams Racer, and the majority of the issues encounter seemed to come from the aircraft, and not the engine. This scenario repeated itself two years later with the Williams Mercury Racer. The X-2775 did not have any issues propelling the updated racer at over 100 mph (161 km/h) on the surface of the water, but it was the aircraft that was overweight and unable to take flight. If the engine were significantly flawed, it would not have survived its time in the Kirkham-Williams Racer, have been subsequently modified, and then installed in the Williams Mercury Racer. This same engine, Serial No. 1, was preserved and is in storage at the Smithsonian National Air and Space Museum.

Packard offered to build additional X-2775 engines for anyone willing to spend $35,000, but no orders were placed. In the late 1930s, Packard investigated building an updated X-2775 as the 2A-2775. The 2A-2775 was listed as a supercharged engine that produced 1,900 hp (1,417 kW) at 2,800 rpm and weighed 1,722 lb (781 kg). Some sources indicate the engine was built, although no pictures or test data have been found.

Packard X-2775 NASM top

Top view of the X-2775 illustrates the two sets of two carburetors, with each carburetor attached to a manifold for three cylinders. The intake manifold can be seen running under the carburetors. (NASM image)

“The Packard X 24-Cylinder 1500-Hp. Water-Cooled Aircraft Engine” by L. M. Woolson S.A.E. Transactions 1928 Part II. (1928)
“Internal Combustion Engine” US patent 1,889,583 by Lionel M, Woolson (granted 29 November 1932)
“Valve-Operating Mechanism” US patent 1,695,726 by Lionel M, Woolson (granted 18 December 1928)
“Lieut. Alford J. Williams, Jr.—Fast Pursuit and Bombing Planes” Hearings Before a Subcommittee of the Committee on Naval Affairs, United States Senate, Seventy-first Congress, second session, on S. Res. 235 (8, 9, and 10 April 1930)
“Packard “X” Type Aircraft Engine is Largest in World” Automotive Industries (8 October 1927)
Master Motor Builders by Robert J. Neal (2000)
Packards at Speed by Robert J. Neal (1995)
Jane’s All the World’s Aircraft 1929 by C. G. Gray (1929)

Kirkham-Williams Racer no cowl

Kirkham-Williams Seaplane Racer (1927)

By William Pearce

Lt. Alford Joseph Williams was an officer in the United States Navy and a major proponent of aviation. Williams believed that air racing contributed directly to the development of front-line fighter aircraft. In 1923, Williams won the Pulitzer Trophy race and later established a new 3 km (1.9 mi) absolute speed record at 266.59 mph (429.04 km/h). In 1925, Williams finished second in the Pulitzer race, but his main disappointment was not being selected as a race pilot for the Schneider Trophy team. Williams was also not selected for the 1926 Schneider team. That year was a particularly bad showing from the United States despite its advantage of hosting the Schneider contest.

Kirkham-Williams Racer front

The Kirkham-Williams Racer was built to compete in the 1927 Schneider Trophy contest and to capture the world speed record. Note how the large Packard X-24 engine dictated the shape of the aircraft.

Williams could see that racing was not a priority for the US military and decided to take matters into his own hands. In late 1926, Williams sought the support of investors to build a private venture Schneider racer. Since the US had won the Schneider Trophy two out of the last three races, another win would mean permanent retention of the trophy. Williams received further support from various departments in the US Navy, and the Packard Motor Car Company (Packard) was willing to design a new engine provided the Navy paid for it. On 9 February 1927, the US government officially announced that it would not be sending a team to compete in the 1927 Schneider race, held in Venice, Italy. The plans that Williams, the Navy, and Packard had implemented moved forward, and a syndicate to fund the private entry racer was announced on 24 March 1927. The Mercury Flying Corporation (MFC) was formed by patriotic sportsmen for the purpose of building the racer to compete in the 1927 Schneider Trophy contest, with Williams as the pilot.

Although the US government was not directly supporting MFC’s efforts, the US Navy was willing to lend indirect support by transporting the racer to Italy and providing a Packard X-2775 engine for the project. The X-2775 (Packard model 1A-2775) was a 1,200 hp (895 kW), water-cooled, X-24 engine that had been under development by Packard since 1926. The engine was a result of the talks initiated by Williams for a power plant intended specifically for a race aircraft. Ultimately, the engine was covered under a Navy contract. The X-2775 was one of the most powerful engines available at the time.

Kirkham-Williams Racer wing radiator

The racer had some 690 sq ft (64.1 sq m) of surface radiators covering its wings. Fluid flowed from a distributor line at the wing’s leading edge, through the tubes, and into a collector line at the wing’s trailing edge. Tests later indicated that the protruding radiator tubes doubled the drag of the wings.

Williams had decided that the racer should be designed along the same lines as previous Schneider racers built by the Curtiss Aeroplane and Motor Company (Curtiss). MFC contracted the Kirkham Products Corporation (Kirkham) to design and construct the racer. Kirkham’s founder was engineer and former Curtiss employee Charles K. Kirkham, and a number of other former Curtiss employees worked for the company, such as Harry Booth and Arthur Thurston. Booth and Thurston had been closely involved with the racers built at Curtiss. The aircraft was named the Kirkham-Williams Racer, but it was also referred to as the Kirkham-Packard Racer, Kirkham X, and Mercury X.

The Kirkham-Williams Racer was constructed in Kirkham’s faciality in Garden City, on Long Island, New York. The biplane aircraft consisted of a wooden fuselage built around the 24-cylinder Packard engine. The engine mount, firewall, and cowling were made of metal. The upper and lower surfaces of the wooden wings were covered with longitudinal brass tubes to act as surface radiators for cooling the engine’s water and oil. The specially-drawn tubes had an inverted T cross section and protruded about .344 in (8.73 mm) above the wing, creating a corrugated surface. The tubes were .25 in (6.35 mm) wide at their base and .009 in (.23 mm) thick. Around 12,000 ft (3,658 m) of tubing was used, and the oil cooler was positioned on the outer panel of the lower right wing. The water or oil flowed from the wing’s leading edge to a collector at the trailing edge. The aircraft’s twin floats were also made from wood and housed the racer’s main fuel tanks. The floats were attached by steel supports that were covered with streamlined aluminum fairings. The forward float supports were mounted directly to special pads on the engine. The cockpit was positioned behind the upper wing, and a headrest was faired back along the top of the fuselage into the vertical stabilizer. A framed windscreen protected the pilot. A small ventral fin extended below the aircraft’s tail.

Kirkham-Williams Racer starter

The Packard X-2775 engine barely fit into the racer. The engine cowling mounted to arched supports running from the cylinder banks to a ring around the propeller shaft. The Hucks-style starter, powered by four electric motors, is connected to the propeller hub. Note that the forward float strut is mounted to the engine’s crankcase.

The Kirkham-Williams Racer had an overall length of 26 ft 9 in (8.15 m). The fuselage was 22 ft 9 in (6.93 m) long, and the floats were 21 ft 3 in long (6.48 m). The upper wing had a span of 29 ft 10 in (9.09 m), and the lower wing’s span was 24 ft 3 in (7.39 m). The racer was 10 ft 9 in (3.28 m) tall and weighed 4,000 lb (1,814 kg) empty and 4,600 lb (2,087 kg) fully loaded. The aircraft carried 60 gallons (227 L) of fuel, 35 gallons (132 L) of water, and 15 gallons (57 L) of oil. The direct-drive Packard engine turned a two-blade, ground-adjustable, metal propeller that was 8 ft 6 in (2.59 m) in diameter and built by Hamilton Standard. A Hucks-style starter driven by four electric motors engaged the propeller hub to start the engine. Carburetor air intakes were positioned in the upper and lower engine Vees and were basically flush with the cowling’s surface.

Packard was involved with the aircraft’s construction, and Williams was involved with the engine’s development. The Kirkham-Williams Racer was finished in mid-July 1927 and transported later that month to Manhassest Bay, on the north side of Long Island. Weather delayed the first tests until 31 July. Taxi tests revealed that the float design was flawed and caused a large amount of spray to cover the aircraft and cockpit. The spray resulted in damage to the propeller during a high-speed taxi test. In addition, the aircraft was around 450 lb (204 kg) overweight.

Kirkham-Williams Racer launch

Lt. Al Williams prepares the racer for a test on Manhassest Bay. The cockpit was designed around Williams, and he was the only one to taxi or fly the aircraft. Note the support running between the vertical and horizontal stabilizers.

With the Schneider race just over a month away, little time was left to properly test the aircraft and transport it halfway around the world. Williams requested a postponement of the Schneider race for one month, but the British contingent declined the request. To make matters worse, Williams had been very optimistic about the aircraft’s test schedule and repeatedly promised an attempt on the world speed record. Issues with the Kirkham-Williams Racer resulted in a continual push-back of Williams’ proposed speed flights.

With a repaired propeller and new floats, the Kirkham-Williams Racer was ready for additional tests on 16 August. An oil leak and air in the water-cooling system caused Williams to cancel the day’s activities before any real testing had been done. On 17 August, high-speed taxi tests were finally sufficiently completed. Williams announced that the Kirkham-Williams Racer’s first flight would be the following day, but unfavorable weather caused that date to be pushed back. The racer’s first flight was on 25 August, and it should be noted that this was the first flight for the X-2775 engine as well. Some sources state that Williams made two speed runs at an estimated 250 mph (402 km/h). However, Williams stated that no speed runs were attempted on the first flight. While 250 mph (402 km/h) is an impressive speed for the time, it was most likely an estimation made by observers and not achieved over a set course. The second flight that day was cut short because of engine cooling issues caused by air in the cooling system.

Kirkham-Williams Racer runup

Williams is in the cockpit running up the X-2775 engine. The registration X-648 has been applied to the tail. The fuselage was painted blue, with the wings, floats, and rudder painted gold. Note the rather imperfect finish of the fuselage, just before the tail.

Unfavorable weather resulted in more delays, and it was not until 29 August that Williams was able to take the Kirkham-Williams Racer up for another flight during a brief break between two storm fronts. Williams made a high-speed run, and the racer was unofficially timed at 275 mph (443 km/h). Later, Williams would say the speed was probably around 269 mph (433 km/h), but he and others felt the aircraft was capable of 290 mph (467 km/h). Weather again caused delays, and three takeoff attempts on 3 September had to be aborted on account of pleasure boats straying into the aircraft’s path and causing wakes.

On 4 September, a good, extended flight was made, after which Williams reported the aircraft was nose-heavy and became increasingly destabilized at speeds above 200 mph. The issue was with the orientation of the floats. Modifications were made, and the aircraft flew again on 6 September. Williams reported improved handling, but some issues remained. The Navy had held the cruiser USS Trenton at the Brooklyn Navy Yard with the intention of transporting the Kirkham-Williams Racer to Italy in time for the Schneider contest, which was to start on 23 September. However, Williams cancelled any attempts to make the Schneider race on 9 September, citing the nose-heaviness and also float vibrations.

Kirkham-Williams Racer no cowl

Williams stands on the float, with work going on presumably to clear air from the cooling system, which was a reoccurring issue. The copper radiators covered almost all of the wing’s surface area. Note that the interplane struts protruded slightly above the wings.

During the time period above, it was felt that the Kirkham-Williams Racer may not have been competitive, and Packard was asked to build a more powerful engine. In the span of 10 weeks, Packard designed, constructed, and tested a supercharged X-2775 engine. The Roots-type supercharger was installed on the front of the engine and driven from the propeller shaft. Liberal tolerances were used because of the lack of time, and the supercharger generated only 3.78 psi (.26 bar) of boost. The supercharged engine produced 1,300 hp (696 kW), which was only a slight power increase. The engine was not installed, because the minor gain in power was offset by the added weight and complexity of the supercharger system.

With the Schneider race out of reach, the Kirkham-Williams Racer was converted to a landplane with the intent to set a new world speed record. The floats were removed, and two main wheels attached to streamlined struts were installed under the engine. A tail skid replaced the small fin under the aircraft’s rudder. In addition, the X-2775 engine was fitted with a new cowling and spinner that gave the aircraft a more streamlined nose.

Kirkham-Williams Racer landplane front

Williams reported making four emergency landings in the racer at Mitchel Field, but the causes of the forced landings have not been found. The aircraft was fitted with the same direct-drive X-2775 engine as the seaplane. The intake of the upper Vee engine section can just be seen above the cowling.

The modifications to the Kirkham-Williams Racer were completed by late October 1927, and the aircraft was taken to Mitchel Field on Long Island, New York. Williams’ initial tests found the plane heavy with a landing speed of around 100 mph (161 km/h). Williams felt Mitchel Field was not an ideal place for experimental work with the aircraft, but the MFC did not have funds to seek a better location. Williams ended up making four forced landings at Mitchel Field in the Kirkham-Williams Racer.

On 6 November, Williams flew the aircraft over a 3 km (1.9 mi) course and was unofficially timed at 322.42 mph (518.88 km/h). This speed was significantly faster than the then-current records, which were 278.37 mph (447.99 km/h) set by Florentin Bonnet on 11 November 1924 for landplanes, and an absolute record of 297.70 mph (479.10 km/h) set by Mario de Bernardi on 4 November 1927. Some were skeptical of Williams’ speed, especially since it was achieved in only one direction and with the wind reportedly blowing at 40 mph (64 km/h). Williams announced that an official attempt on the record would soon be made, but no further flights of the Kirkham-Williams Racer were recorded. Later, Williams stated that the racer’s still-air speed on the 6 November 1927 run was around 287 mph (462 km/h), which was much lower than anticipated.

Williams had the aircraft disassembled and shipped to the Naval Aircraft Factory (NAF) in Philadelphia, Pennsylvania to further evaluate ways to improve the racer’s speed. A section of the wing was removed and tested by the National Advisory Committee for Aeronautics in their wind tunnel at Langley Field, Virginia. The test results indicated that the corrugated surface radiators decreased lift, doubled drag, and slowed the aircraft by some 20 mph (32 km/h). While at the NAF, the disassembled Kirkham-Williams Racer was used as the basis for Williams’ 1929 high-speed aircraft—the Williams Mercury Racer.

Kirkham-Williams Racer landplane

In landplane form, the Kirkham-Williams Racer had a more streamlined nose and an added tailskid. The machine looked every bit a racer and was one of the fastest aircraft in the world, even at only 287 mph.

Schneider Trophy Seaplanes and Flying Boats by Ralph Pegram (2012)
Schneider Trophy Racers by Robert Hirsch (1993)
Master Motor Builders by Robert J. Neal (2000)
Racing Planes and Air Races Volume II 1924–1931 by Reed Kinert (1967)
Full Scale Investigation of the Drag of a Wing Radiator by Fred E. Weick (September 1929)
“Lieut. Williams’ Racing Seaplane” by George F. McLaughlin, Aero Digest (September 1927)
“Lieut. Alford J. Williams, Jr.—Fast Pursuit and Bombing Planes” Hearings Before a Subcommittee of the Committee on Naval Affairs, United States Senate, Seventy-first Congress, second session, on S. Res. 235 (8, 9, and 10 April 1930)

Lycoming O-1230 front

Lycoming O-1230 Flat-12 Aircraft Engine

By William Pearce

In the late 1920s, the Lycoming Manufacturing Corporation of Williamsport (Lycoming County), Pennsylvania entered the aircraft engine business. At the time, Lycoming was a major supplier of automobile engines to a variety of different manufacturers. Lycoming quickly found success with a reliable nine-cylinder radial of 215 hp (160 kW), the R-680. However, the company wanted to expand into the high-power aircraft engine field.

Lycoming O-1230 front

When built, the Lycoming O-1230 was twice as large as and three times more powerful than any other aircraft engine the company had built. Lycoming essentially achieved the hyper engine goals originally set for the O-1230, but other engine developments had made the engine obsolete by the time it would have entered production.

In 1932, Lycoming became aware of the Army Air Corps’ (AAC) program to develop a high-performance (hyper) engine that would produce one horsepower per cubic inch displacement and one horsepower per pound of weight. The AAC had contracted Continental Motors in 1932 to work with the Power Plant Branch at Wright Field, Ohio on developing a hyper engine. The engine type was set by the AAC as a 1,200 hp (895 kW), flat, liquid-cooled, 12-cylinder engine that utilized individual-cylinder construction. The flat, or horizontally-opposed, engine configuration was selected to enable the engine’s installation buried in an aircraft’s wings.

Lycoming saw an opportunity to quickly establish itself as a high-power aircraft engine manufacturer by creating an engine that would satisfy the AAC’s hyper engine requirements. On its own initiative, Lycoming began development of its own hyper engine. The AAC encouraged Lycoming’s involvement and provided developmental support, but the AAC did not initially provide financial support. Lycoming started serious developmental work on the new engine in 1933. Various single-cylinder test engines were built and tested in 1934. In 1935, the AAC became more interested in the engine and began supporting Lycoming’s efforts. Single-cylinder testing yielded positive results, with the engine passing a 50-hour test in May 1936. That same year, the AAC contracted Lycoming to build a complete engine. Lycoming had spent $500,000 of its own money and had finalized the design of its engine, which was designated O-1230 (also as XO-1230). Construction of the first O-1230 was completed in 1937, and the engine was ready for endurance testing in December of that year.

Lycoming O-1230 side

Intended for installation buried in an aircraft’s wing, the O-1230’s height was kept to a minimum. The long nose case would aid in streamlined wing installations. Note that the supercharger’s diameter was slightly in excess of the engine’s height.

The Lycoming O-1230 hyper engine had a two-piece aluminum crankcase that was split vertically. Six individual cylinders attached to each side of the crankcase. The cylinders were made of steel and were surrounded by a steel water jacket. Each cylinder had a hemispherical combustion chamber with one intake and one sodium-cooled exhaust valve. A cam box mounted to the top of each cylinder bank, and each cam box contained a single camshaft that was shaft-driven from the front of the engine.

A downdraft carburetor fed fuel into the single-speed, single-stage supercharger mounted at the rear of the engine. Lycoming had experimented with direct fuel injection on test cylinders, but it is unlikely that any O-1230 ever used fuel injection. The supercharger’s 10 in (254 mm) diameter impeller was driven at 6.55 times crankshaft speed. It provided air to the intake manifold that sat atop the engine. Individual runners provided air to each cylinder from the intake manifold. Exhaust was expelled out the lower side of the cylinders and collected in a common manifold for each cylinder bank. An extended nose case housed the .40 propeller gear reduction, with options for a .50 or .333 reduction. On the top of the O-1230, just behind the gear reduction, was the engine’s sole magneto. The magneto was connected to two distributors, each driven from the front of the camshaft drive.

Lycoming O-1230 Vultee XA-19A

The O-1230-powered Vultee XA-19A before it arrived at Wright Field. The scoop above the cowling brought air into the engine’s carburetor. Louvered panels allowed heat generated by the exhaust manifold to escape the cowling.

The O-1230 had a 5.25 in (133 mm) bore and a 4.75 in (121 mm) stroke. The engine’s total displacement was 1,234 cu in (20.2 L), and it had a 6.5 to 1 compression ratio. The O-1230 produced 1,200 hp (895 kW) at 3,400 rpm for takeoff, 1,000 hp (746 kW) at 3,100 rpm for normal operation, and 700 hp (522 kW) at 2,650 rpm for cruise operation. The engine had an overspeed limit of 3,720 rpm for diving operations. The O-1230 was 106.7 in (2.71 m) long, 44.1 in (1.12 m) wide, and 37.9 in (.96 m) tall. The engine weighed 1,325 lb (601 kg).

After completing a type test in March 1939, the O-1230 was rated at 1,000 hp (746 kW). Continued development pushed the engine’s rating up to 1,200 hp (895 kW). The O-1230 was installed in a Vultee YA-19 attack aircraft that had been modified as an engine testbed and redesignated XA-19A (38-555). Some sources list the designation as YA-19A, but “Y” was typically used for pre-production aircraft, while “X” was for experimental aircraft. The O-1230-powered XA-19A first flew on 22 May 1940, the flight originating at Vultee Field in Downey, California. The aircraft and engine combination were transferred to Wright Field, Ohio in June 1940 and then to Lycoming on 27 March 1941. By this time, the AAC had already moved away from the buried-engine-installation concept and was interested in more powerful engines.

Lycoming O-1230 Vultee XA-19A side

The XA-19A is seen with its Wright Field markings. The aircraft’s tail was modified to compensate for the larger and longer nose needed to house the O-1230. The radiator positioned under the engine added bulk to the O-1230’s installation. Note the large exhaust outlet.

While the O-1230’s power output was on par with many of its contemporaries, such as the Allison V-1710, the O-1230 did not offer the same development potential or reliability as other engines. The O-1230 was cancelled in favor of other projects, and the engine was subsequently removed from the XA-19A airframe. The XA-19A was transferred to Pratt & Whitney on 8 August 1941, where an R-1830 was subsequently installed, and the aircraft was redesignated XA-19C.

Lycoming was still interested in developing a high-power engine and used O-1230 components to create the 24-cylinder XH-2470. In some regards, the Lycoming XH-2470 was two O-1230 engines mounted to a common crankcase. Lycoming started initial design work on the engine as early as 1938. A single O-1230 survived and is on display at the New England Air Museum in Windsor Locks, Connecticut.

Lycoming O-1230 display

The restored O-1230 on display at the New England Air Museum. The engine’s electric starter is mounted vertically just in front of the supercharger. (Daniel Berek image via

Development of Aircraft Engines and Fuels by Robert Schlaifer and S. D. Heron (1950)
Aircraft Engines of the World 1941 by Paul Wilkinson (1941)
Jane’s All the World’s Aircraft 1942 by Leonard Bridgman (1942)
“The Evolution of Reciprocating Engines at Lycoming” by A. E. Light, AIAA: Evolution of Aircraft/Aerospace Structures and Materials Symposium (24–25 April 1985)
“Vultee Engine-Test Aircraft in World War II” by Jonathan Thompson, AAHS Journal Volume 39 Number 4 (Winter 1994)

Bristol Hydra front

Bristol Hydra 16-Cylinder Radial Aircraft Engine

By William Pearce

In 1930, the Bristol Aeroplane Company began to contemplate the future of aircraft engines. Their engine department was run by Roy Fedden, a prolific aircraft engine designer. At the time, Bristol was manufacturing its nine-cylinder, single-row Mercury radial engine that had an output of 510 hp (380 kW) and displaced 1,519 cu in (24.9 L). The Mercury engine was under continuous development to increase its output. However, to produce more power out of the same basic engine size, Fedden realized that a second cylinder row was needed.

Bristol Hydra front

The Bristol Hydra was an odd radial engine utilizing two inline rows of eight cylinders. The engine suffered from vibration issues due to a lack of crankshaft support. Note the dual overhead camshafts for each front and rear cylinder pair.

Fedden and Bristol evaluated at least 28 engine designs to determine the best path forward for a multi-row engine. At the same time, Fedden was investigating a switch to using sleeve valves, but their development at Bristol had just begun. The multi-row engine would continue to use poppet valves. At the end of 1931, a 16-cylinder, air-cooled engine design was selected for development. This engine was called the Double Octagon or Hydra.

The Bristol Hydra was designed by Frank Owner in 1932, and the project was overseen by Fedden. The radial engine was very unusual in that it had an even number of cylinders for each row. Nearly all four-stroke radial engines have an odd number of cylinders per row so that every other cylinder can fire as the crankshaft turns. In addition, the Hydra’s cylinder rows were not staggered—the first and second rows were directly in line with each other. The “Double Octagon” name represented the engine’s configuration, in which the eight cylinders on each of the engine’s two rows formed an octagon. The name “Hydra” was given to the engine because of its numerous “heads” (cylinders).

Bristol Hydra side drawing Perkins

A sectional view of the Hydra created by Brian Perkins and based on a drawing found in the Bristol archives. The numbers in the drawing relate to the number of gear teeth. Note the unsupported crankshaft center section that joined the front and rear crankshaft sections. (Brain Perkins drawing via the Aircraft Engine Historical Society)

Unlike a traditional radial engine, the Hydra’s design resembled four V-4 engines mounted to a common crankcase and using a common crankshaft. In fact, a V-4 test engine was built to refine the Hydra’s cylinder and valve train design before a complete engine was built. The V-4 cylinder sections were mounted at 90-degree intervals around the crankcase, and their cylinders had a 45-degree bank angle. This configuration spaced all cylinder banks at 45-degree intervals. The V-4 cylinder sections had their exhaust ports located on the outer sides and their intake ports positioned in the Vee of each V-4 cylinder section. Two supercharger-fed intake manifolds delivered air to the Vee of each V-4 cylinder section, with each manifold servicing one front and rear cylinder. The engine’s supercharger turned at over four times crankshaft speed.

The Hydra used an aluminum cylinder that was machined all over with cooling fins. A steel barrel lined the inside of the cylinder. Each cylinder had one intake and one exhaust valve. Each front and rear cylinder formed a pair, and each cylinder pair had separate overhead camshafts that directly operated the intake and exhaust valves. At the rear of the cylinder pair, the exhaust camshaft was driven via beveled gears by a vertical shaft that was powered from the crankshaft by a gear set. A short cross shaft extended from the exhaust camshaft to power the intake camshaft. Each cylinder had two spark plugs.

Bristol Hydra 16-cylinder

Front and side view of the Hydra. Note the exhaust stacks protruding slightly above the cylinders.

The engine’s crankshaft was built-up from three pieces. The center piece joined the front and rear sections via four clamping bolts. The crankshaft only had two main bearings and no center support. Single-piece master connecting rods were used. A bevel gear reduction at the front of the engine reduced the propeller speed to .42 times that of the crankshaft. The relatively high-level of gear reduction was needed because of the engine’s high operating speed.

The Hydra had a 5.0 in (127 mm) bore and stroke. The engine’s total displacement was 1,571 cu in (25.7 L). The Hydra had a 6 to 1 compression ratio and produced 870 hp (649 kW) on 75 octane fuel. On 87 octane fuel, the engine reportedly produced 1,020 hp (761 kW). The power outputs were achieved at 3,620 rpm, a very high speed for a radial engine. The engine was 46.5 in (1.18 m) in diameter, 57 in (1.45 m) long, and weighed approximately 1,500 lb (680 kg). With its unusual cylinder configuration, the Hydra had the following cylinder firing order: 1F, 2F, 7R, 4F, 1R, 6F, 3R, 8F, 5R, 6R, 3F, 8R, 5F, 2R, 7F, and 4R.

Bristol Hydra Hawker Harrier

Hydra engine installed in the sole Hawker Harrier. Note the baffling on the engine. The four-blade test club propeller was fitted for ground runs.

The Hydra V-4 test engine underwent runs in mid-1932 and eventually produced around 190 hp (142 kW) with no cooling issues. A complete 16-cylinder Hydra was first run in 1933. Later that year, the engine was installed in the sole Hawker Harrier biplane bomber prototype, J8325. The engine’s configuration made installation very easy, and the intake Vees were baffled to improve cooling airflow.

The Hydra-powered Harrier encountered some oil leaks and ignition issues, but the main trouble was with excessive engine vibration. The lack of a center main bearing on the crankshaft caused the vibration issues, which could be quite severe at certain RPMs. The short stroke of the engine combined with a short crankshaft gave the designers the false hope that the center main bearing would not be needed. A redesign of the engine was required to cure the vibration issues.

Bristol Hydra Hawker Harrier side

The Hydra-powered Harrier completely cowled and with its three-blade flight propeller. The aircraft was flown in this configuration during 1933, but engine vibration issues at critical RPMs limited the testing.

By 1934, the Mercury was approaching the 800 hp (597 kW) level, and the new nine-cylinder, 1,753 cu in (28.7 L) Pegasus was giving every indication that 900 hp (671 kW) was just around the corner. In addition, the sleeve valve, 1,519 cu in (24.9 L) Perseus engine had proved reliable and was producing around 700 hp (522 kW), and more ambitious sleeve valve engines were being designed. Rather than proceed with the Hydra and its double-octagon configuration, Bristol chose to develop its existing production engines and also focus on new sleeve valve engines.

The Hydra engine project was funded entirely by Bristol, although Fedden tried to get Air Ministry support. Only two Bristol Hydra engines were built; remarkably, both are reported to still exist. One is housed at the Sir Roy Fedden Heritage Centre, Bristol Branch of the Rolls-Royce Heritage Trust, in Bristol, United Kingdom. The other engine is stored at the Royal Air Force Museum London, located on the old Hendon Aerodrome.

Bristol Hydra display

A preserved Bristol Hydra engine held by the Bristol Branch of the Rolls-Royce Heritage Trust. Note the extensive finning on the aluminum cylinders. (Brain Perkins image via the Aircraft Engine Historical Society)

Fedden – the life of Sir Roy Fedden by Bill Gunston (1998)
British Piston Aero-Engines and their Aircraft by Alec Lumsden (2003)
An Account of Partnership – Industry, Government and the Aero Engine by George Bulman and edited by Mike Neale (2002)
“My Wife Calls it an Obsession!!!! Part 2: Bristol Hydra” by Brian Perkins Torque Meter Volume 4, Number 2 (Spring 2005)
“The Future of the Air-Cooled Engine” Flight (25 February 1937)

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)