Hyper engine

Liberty L-12 engine
Liberty L-12 engine, from which Hyper Engine No.1 was derived
Type	One cylinder converted into "Hyper Engine No. 1"
National origin	United States
Manufacturer	Continental Motors
Designer	Sam Heron
First run	1932
Major applications	Experimental Engine
Number built	1

The hyper engine was not an aircraft engine at all, but a 1930s study project by the United States Army Air Corps (USAAC) to develop a high performance aircraft engine that would be equal to or better than the aircraft and engines then under development in Europe. The project goal was to produce an engine capable of delivering 1 hp/in³ (46 kW/L) of engine displacement that weighed less than 1 lb/hp. It was clear that this sort of performance would not be easy to achieve, although this milestone had been met by special purpose-built racing engines.

At the time, no production engine could come close to the requirements. A typical large engine of the era, the Pratt & Whitney R-1830 Twin Wasp, developed about 1,200 hp (895 kW) from 1,830 in³ (30 L) so an advance of at least 50% would be needed. The ultimate design goal was an increased power-to-weight ratio suitable for long-range airliners and bombers. Simply scaling up an existing design was no solution. While it would have increased the total available power, it would not have any dramatic effect on the power-to-weight ratio; for that, more radical changes were needed.

Design and development

Improvements in construction and lighter materials had already delivered some benefits. Aluminum was being introduced in place of steel as the quality and strength of aluminum alloys improved during the 1930s; this lowered engine weight noticeably, but not enough to achieve a 50% improvement.

The solution would include a combination of:

• Increasing the mean effective pressure (MEP)
• Increasing the engine speed
• Decreasing the engine's losses (friction, combustion inefficiencies, scavenging losses etc.)

The USAAC engineers determined that it would study all three for. Before long, they concluded that increasing the combustion temperature and scavenging efficiency promised the greatest increases of all of the possibilities. To meet that goal, increasing engine speed seemed to be the most attractive solution. A number of problems blocked this process.

Most notable were:

• Problem: At that time, aircraft engines ran on 80/87 octane gasoline, which had been pushed nearly to its limit with the engine designs then in use. Exhaust valves were typically solid metal, and ran nearly hot enough to ignite the fuel,
  • Solution: hey solved with sodium-cooled poppet type valves. The stem of the poppet valve was made tubular instead of solid metal as in the past. Sodium was inserted in the hollow valve stem and permanently sealed in. The sodium filled valve was better than solid metal in drawing the heat from the head of the poppet valve, quickly transferring the heat up the valve stem and into the coolant circulating in the cylinder head passages. By moving the heat faster, the temperature of the valve came down to a reasonable level.
• Problem: Increasing the cylinder compression ratio, although mechanically simple, was found to cause Engine knocking (also called pre-ignition) and, if not controlled, would result in serious damage to the engine.
  • Solution: Raising the octane rating became a necessity for the improvements needed. It was found that adding a lead based additive to the fuel, higher compression ratios became possible.
• Problem: There were problems with the poppet valve design. At high operating speeds, the valves do not completely close before the cam opens them again, a problem called "valve float". Valve float allows gases in the cylinder to escape through the partially open valve, reducing the engine efficiency. Increasing valve spring pressure to close the valves faster led to rapid cam wear and increased friction, reducing overall performance by more than any horsepower gained.
  • Solution: Several solutions to the valve problem were known in the 1930s. In England, Harry Ricardo had developed the sleeve valve system for exactly these reasons, and had some success convincing British engine companies to invest in the idea, most notably Bristol Aeroplane Company Engines, where Roy Fedden became "a believer". Ricardo's friendly competitor, Frank Halford, designed his own sleeve valve engine, which was chosen by Napier & Son, another prominent British engine maker.

Ironically it was one of Ricardo's papers on the sleeve valve design that led to the USAAC's hyper engine efforts. In one late 1920s paper he claimed that the 1 hp/in³ goal was impossible to achieve with poppet valve type engines. The USAAC engineering team at Wright Field decided to test this claim by beating it.

The USAAC proposed an engine of about 1200 cubic inches (20 L), hoping the engine's smaller size would lead to better streamlining and improved range.

Hyper No.1

Sam Heron, head of development at Wright Field, started working on the problem with a single cylinder test engine that he converted to liquid cooling, using an L-12 Liberty engine cylinder. He pushed the power to 480 psi BMEP, and the coolant temperature to 300 degrees F before reaching the magic numbers.

By 1932, the the USAAC's encouraging efforts led the Army to sign a development contract with Continental Motors Company for the continued development of the engine design. The contract limited Continental's role to construction and testing, leaving the actual engineering development to the Army.

Starting with the famous Liberty L-12 engine, they decreased the stroke from 7 in to 5 in in order to allow higher RPM, and then decreased the cylinder bore from 5 in to 4.62 in, creating the 84 in³ cylinder that was to be used in a V-12 engine of 1008 in³ displacement.

They used the L-12's overhead camshaft to operate multiple valves of smaller size, which would improve charging and scavenging efficiency. Continental's first test engine, the single-cylinder Hyper No.1, first ran in 1933.

They eventually determined that exhaust valves could run cooler when a hollow core filled with sodium is used - the sodium liquefies and considerably increases the heat transfer from the valve's head to its stem and then to the relatively cooler cylinder head where the liquid coolant picks it up.

Liquid cooling systems at that time used plain water, which limited operating temperatures to about 180°F. The engineers proposed using ethylene glycol, which would allow temperatures up to 280°F. At first they proposed using 100% glycol, but their was little improvement due to the lower specific heat of the glycol (about 2/3 that of an water). They eventually determined that a 50/50 mixture (by volume) of water and glycol provided optimal heat removal.

Hyper No.2

A second cylinder was added to Hyper No. 1 to make a horizontal opposed engine for evaluation of an opposed piston 12 cylinder engine. After running the modified engine with different combinations of cylinder bore and stroke, it was found that the high coolant temperatures required to maintain the required output was impractical. A third high performance single cylinder engine was then constructed with lower operating parameters. This engine was designated "Hyper No. 2", and became the test bed for developing the cylinders that would become the O-1430-1.

Continental O/V/IV/XIV-1430

Main article: Continental O/V/IV/XIV-1430

IV-1430-9 in the National Museum of the United States Air Force

The Army apparently became concerned about the development of a suitable supercharger for high-altitude use, and for further development in 1934 they asked for a newer cylinder with slightly less performance and an increased volume of 118.8 in³ from its 5.5 in bore and 5.0 in stroke. This size cylinder would then be used in a 1425 in³ 12-cylinder engine, delivering the same 1000 hp, with a performance of 0.7 hp/in³. This placed its performance on a par with newer experimental engines from Europe like the Rolls-Royce Merlin, at least when running on the higher-octane fuels the Army planned to use.

Another change was to the engine layout. The Army, convinced that future aircraft designs would use engines buried in the wings for additional streamlining, asked Continental to design a full-sized flat-Opposed-piston engine for installation inside a wing. The resulting engine was the Continental O-1430, which would require a ten year development period which changed the layout to first an upright V-12 engine and later, an inverted V-12 engine before becoming reliable enough to consider for full production as the Continental IV-1430 in 1943. By then other engines had already passed its 1,600 hp (1,200 kW) rating, and although the IV-1430 had a better power-to-weight ratio, there was little else to suggest setting up production in the middle of the war was worthwhile.

The project was eventually guided by the requirements in the "Request for data R40-C", which was included as a part of the FY 1940 aircraft procurement program.

Request for data R40-C

As 1938 came to an end, the war in Europe heated to its boiling point. American military planners could easily see that aviation engineering was vastly superior to the resources available to them should the war become global.

America's top front-line fighters just would not do if placed against an opponent such as the Messerschmitt bf-109. American two top fighters, the Republic P-35 and the Curtiss P-36A, were just able to hit 300 mph, and if pitted against the 340+ mph Messerschmitt, neither would not have a chance. In the wings, the Lockheed XP-38 was undergoing an extended test program. The XP-38 was able to fly at speeds in excess of 413 mph, it was big and heavy, and was therefore not as maneuverable as its stablemates.

The XP-38 also had a newly introduced liquid cooled engine, the Allison V-1710. The Allison's in-line vee cylinder arrangement allowed for a narrow aerodynamic shape that had much less drag than the air-cooled radial engine fighters that predominated America at the time.

The fighter aircraft procurement program for FY 1940 was contained in a document that was approved by Assistant Secretary of War Louis K. Johnson on 9 June, 1939. That document was the "Request for Data R40-C", and unlike previous aircraft procurement requests, it was sent to only a limited number of aircraft manufacturers. The original document was to be sent to:

• Bell Aircraft Corporation
• Consolidated Aircraft Corporation
• Curtiss-Wright Corporation, Curtiss Airplane Division
• Curtiss-Wright Corporation, St. Louis Airplane Division
• Grumman Aircraft Engineering Corporation
• Lockheed Aircraft Corporation
• Republic Aviation Corporation
• Vought-Sikorsky Aircraft Division, United Aircraft Corporation
• Vultee Aircraft Division, Aviation Manufacturing Corporation

After final review and approval as Air Corps Type Specification XC-622, these four manufacturers were added to the distribution:

• Hughes Aircraft Corporation
• McDonnell Aircraft Company
• Boeing Aircraft Company
• Northrup Aircraft, Incorporated

These companies had only 10 days to agree to the terms of the document, and only 30 days to submit their designs.

FY 1940

A total of 26 designs, with a mix 16 engine models from six engine companies, were submitted by seven of the selected companies. These engines became known as the "Hyper Engines", a contraction of High performance engines. These submittals were graded using a "Figure of merit" (FOM) rating system, and then, using the FOM results (which ranged from 444.12 for the Allison V-1710-E8 to 817.90 for the Pratt and Whitney X-1800-A4G), they were separated into one of three groups.

• Those placed in the first group were little more than modifications to existing designs. They were not considered to be sufficiently advanced.
• Those placed in the third group proposed using am engine that was unlikely to be developed into flying condition by the time the airframe was ready to fly. They were not considered to be viable in the time frame allowed.
• The remaining ten submittals were placed in the second group, those that were an advancement in aeronautical engineering, with an engine that would be ready to fly, when needed.

Only three of these ten submittals were approved, and contracts were made for a limited prototype run of three aircraft each.

The three aircraft/engine combinations that were selected:

1. Vultte Aircraft's Model 70 Alternate 2, (FOM score: 817.9), which became the XP-54, powered by the Pratt & Whitney X-1800-A4G engine
2. Curtiss-Wright St Louis' Model P248C, (FOM score: 770.6), which became the XP-55, powered by the Continental IV-1430-3 engine
3. Northrup's Model N2-B (FOM score: 725.8), which became the XP-56, powered by the Pratt & Whitney X-1800-A3G engine

The high performance engines of FY 1940

Engine Model	Displacement	Horsepower	Specific horsepower	Weight	Power to weight ratio
Continental IV-1430-3	1,430 in³	1,600 hp at 3,200 rpm	1.12 hp/in³	1,615 lb	.99 hp/lb
Pratt & Whitney X-1800-A3G	2,600 in³	2,200 hp	.85 hp/in³	3,250 lbs	.68 hp/lb
Pratt & Whitney X-1800-A4G	2,600 in³	2,200 hp	.85 hp/in³	3,250 lbs	.68 hp/lb

FY 1941

Three additional high performance engines were considered for the USAAC's FY 1942 "Hyper" engine procurement program. They were:

• Wright R-2160 "Tornado"
• Pratt & Whitney H-3130
• Allison V-3420

Not to be left out, the US Navy selected the Lycoming XH-2470 for funding in FY 1942 as well.

The high performance engines of FY 1940

Engine Model	Displacement	Horsepower	Specific horsepower	Weight	Power to weight ratio
Allison V-3420	3,421.2 in³	2,100 hp	.61 hp/in³	2,600 lb	.81 hp/lb
Lycoming XH-2470	2,470 in³	2,300 hp	.93 hp/in³	2,430 lb	.96 hp/lb
Pratt & Whitney H-3130	3,130 in³	2,650 hp	.84 hp/in³	3,250 lbs	.82 hp/lb
Wright R-2160	2,160 in³	2,350 hp	1.09 hp/in³	2,400 lb	.98 hp/lb

Hyper engine program ends

In the end, all of these programs were canceled, and the surviving engines became museum pieces. One survivor, a Continental IV-1430, is privately owned, and is displayed publicly from time to time.

Ironically, engines that were not considered under the program; the Allison V-1710, the Pratt and Whitney R-2800 and the Wright R-3350, all passed the USSAC requirements, and continue flying into the 21st century.

References

Bibliography

• Balzer, Gerald H. (2008). American Secret Pusher Fighters of World War II. Specialty Press. ISBN 13-978-1-58007-125-3. {{cite book}}: Check |isbn= value: length (help)
• Biermann, Arnold E, Corrington, Lester C. and Harries, Myron L. (1942). Effects of Additions of Aromatics on Knocking Characteristics of Several 100-octane Fuels at Two Engine Speeds. Cleveland, Ohio, May,: Aircraft Engine Research Laboratory.{{cite book}}: CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
• Bingham, Victor. Major Piston Aero Engines of World War II. Airlife Publishing. ISBN 1-84037-012-2.
• Schlaifer, Robert and Herron S.D. Development of Aircraft Engines and Development of Aviation Fuels. Harvard University.
• Taylor, C. Fayette (1971). Aircraft Propulsion, Smithsonian Press, GPO.
• White, Graham (1995). Allied Piston Engines of World War II. SAE International. ISBN 1-56091-855-9. {{cite book}}: Check |isbn= value: checksum (help)
• Connors, Jack (2010). The Engines of Pratt & Whitney: A Technical History. Reston. Virginia: American Institute of Aeronautics and Astronautics. ISBN 78-1-60086-711-8. {{cite book}}: Check |isbn= value: length (help)
• Gunston, Bill (2006). World Encyclopedia of Aero Engines, 5th Edition. Phoenix Mill, Gloucestershire, England, UK: Sutton Publishing Limited. ISBN 0-7509-4479-X.