Engine Design Gone Wild! Lycoming R-7755

Discussion in 'Engines' started by syscom3, Nov 5, 2009.

  1. syscom3

    syscom3 Pacific Historian

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    Lycoming R-7755 - Wikipedia, the free encyclopedia

    The Lycoming R-7755 was the largest piston-driven aircraft engine ever produced; with 36 cylinders totaling about 7,750 in³ (127 L) of displacement and a power output of 5,000 horsepower (3,700 kilowatts). It was originally intended to be used in the "European bomber" that eventually emerged as the Convair B-36. Only two examples were built before the project was terminated in 1946.
    Contents

    Development
    Lycoming had not been successful in designing a high-power engine. They had started with an attempt to make a hyper engine that led to the 1,200 hp (890 kW) O-1230; by the time the engine was ready, however, new aircraft designs were all calling for more power. They tried again by "twinning" the engine to produce the H block H-2470, which saw some interest in the Vultee XP-54 Swoose Goose project. Work on the H-2470 ended when the XP-54 was cancelled.

    In one final attempt, Lycoming decided to go all out and build the largest engine in the world. They put together a team under the direction of VP of Engineering Clarence Wiegman at their main Williamsport factory in the summer of 1943 and started work.

    Design
    The resulting design used nine banks of four cylinders arranged around a central crankshaft to form a four-row radial engine. Unlike most multi-row radials, which splay the cylinders to allow cooling air to reach them, the R-7755 was water-cooled and so the cylinder heads were in-line under a cooling jacket. Contrast this with the Junkers Jumo 222, which looked similar from the outside but ran on a V-style cycle instead of a radial. The R-7755 was 10 ft (3 m) long, 5 ft (1.5 m) in diameter, and weighed 6,050 lb (2,740 kg). At full power it was to produce 5,000 hp (3,700 kW) at 2,600 rpm, maintaining that with a turbocharger to a critical altitude that was apparently never published.

    Each cylinder bank had a single overhead cam powering the poppet valves. The camshaft included two sets of cams, one for full takeoff power, and another for economical cruise. The pilot could select between the two settings, which would shift the camshaft along its axis to bring the other set of cams over the valve stems. Interestingly, the design mounted some of the accessories on the "front side" of the camshafts, namely two magnetos and four distributors. The seventh camshaft was not used in this fashion, its location on the front of the engine was used to feed oil to the propeller reduction gearing.

    The original XR-7755-1 design drove a single propeller, but even on the largest aircraft the propeller needed to absorb the power would have been ridiculously large. This led to a minor redesign that produced the XR-7755-3, using a new propeller gearing system driving two shafts to power a set of contra-rotating props. The propeller reduction gearing also had two speed settings to allow for a greater range of operating power than adjustable props alone could deliver. Another minor modification resulted in the XR-7755-5, the only change being the replacement of carburetors with a new fuel injection system.

    Operational history
    The engine first started testing at 5,000 hp (3,700 kW) in 1944 with the XR-7755-3, but demonstrated terrible reliability problems. A second example was provided, as planned, to the United States Army Air Forces at Wright Field in 1946. However, by this time the Air Force had lost interest in new piston designs due to the introduction of jet engines, and the Lycoming delivery team was instructed to simply "dump it on the ground". This engine has since disappeared. The original test engine was later delivered to the Smithsonian Institution, where it was recently restored.

    Studebaker was also working on a very large engine, a 24-cylinder H-type. The H-9350 (8.0 x 7.75 = 9349.4 in³/153.21 L) was being designed to deliver over 5,000 hp (3,700 kW). It is not known what became of the project.

    Specifications (R-7755)
    General characteristics
    * Type: 36-cylinder turbosupercharged liquid-cooled "star" (9 banks of 4 cylinders) aircraft piston engine
    * Bore: 6 3⁄8 in (161.9 mm)
    * Stroke: 6 3⁄4 in (171.4 mm)
    * Displacement: 7,756.3 in3 (127.1 L)
    * Length: 120 in (3,050 mm)
    * Diameter: 60 in (1,525 mm)
    * Dry weight: 6,050 lb (2,745 kg)

    Components
    * Valvetrain: Single overhead camshaft with separate cams for takeoff and economical cruise (Variable valve timing)
    * Cooling system: Liquid-cooled
    Performance
    * Power output:
    o 5,000 hp (3,730 kW) at 2,600 rpm takeoff
    o 4,000 hp (2,985 kW) at 2,300 rpm cruise
    * Specific power: 0.64 hp/in³ (29.3 kW/L)
    * Specific fuel consumption:
    o 0.70 lb/(hp·h) (0.43 kg/(kW·h)) at takeoff power
    o 0.485 lb/(hp·h) (0.29 kg/(kW·h)) at 70% power
    o 0.37 lb/(hp·h) (0.22 kg/(kW·h)) at minimum cruise power
    * Power-to-weight ratio: 0.82 hp/lb (1.36 kW/kg)
     

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  2. engguy

    engguy Member

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    Yeah its too bad these and or similar engines aren't powering the aircraft of nowdays, instead of jets.
    If this was a diesel with a .25 BSFC in a TC configuration, the fuel savings would be fantastic compaired to turbines.
     
  3. syscom3

    syscom3 Pacific Historian

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    The maintenance costs would have been enormous. Plus the wide profile meant there was going to be quite some drag created.
     
  4. engguy

    engguy Member

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    Naaa, just some good jobs available.
     
  5. mudpuppy

    mudpuppy Member

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    It looks like from the photo this engine may be at the Udvar-Hazy annex of the Smithsonian in northern Virginia...I'm way overdue for another trip there. :)
    Derek
     
  6. Colin1

    Colin1 Active Member

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    What a monster
    it weighs almost the same as a whole Spitfire Mk V at max take-off weight :)
     
  7. davebender

    davebender Well-Known Member

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    A powerful engine but not powerful for that amount of weight. I can see why they were told to dump it on the ground.
     
  8. Colin1

    Colin1 Active Member

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    Strictly speaking
    was it an R-7755, or a V-7755?
    It seemed to possess more of the characteristics of an inline, a bunch of inlines arranged radially.
     
  9. Shortround6

    Shortround6 Well-Known Member

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  10. Degs

    Degs New Member

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    #10 Degs, Nov 13, 2009
    Last edited: Nov 13, 2009
    Finally found out what Dr Who has in the middle of his TARDIS !!!:):):)
     
  11. barney

    barney Member

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    The XR-7755 was intended for the B-36. The 4360's on the B-36 were originally rated at about 3000 hp and later upgraded 3600 hp or 21,600 hp per plane. If the 5000 hp XR-7755 could undergo a similar upgrade it would have been putting out 6000 hp or 36,000 hp per plane. So, had the B-36 used the XR-7755 engines there might have been no need for the jets.
     
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  12. Piper106

    Piper106 Member

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    #12 Piper106, Dec 30, 2009
    Last edited: Dec 30, 2009
    Second the comment on the Lycoming R-7775 being way too heavy.

    A P&W R-2800 CB16 (or a -99W military engine) engine would do 2500 HP (wet) takeoff for 2390 pounds (source"R-2800; Pratt Whitney's Dependable Masterpiece" by Graham White). Doubled and you have 5000 HP takeoff HP from 4780 pounds, compared to the 6050 pounds for the Lycoming. The weight difference is even more pronounced since the weight of the R-7775 does not include the radiators, which a R-2800 does not need. Two R-2800s could drive a single propeller if needed; use the military -50 drive drive nose case, and then a remote combining gearbox, much like Bristol did with the coupled Centaurus engines in the Babrazon airliner.

    If you just have to have liquid cooling, couple two R-R Griffon 57s (like two Allison V-1710s were coupled to make the V-3420). Each Griffon 57 gives 2450 HP take-off from 2020 pounds. Coupled you would have 4900 HP from 4040 pounds or less.

    Piper106
     
  13. barney

    barney Member

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    Well, the war was over, jets were flying and nobody in the military was interested in spending development money on piston engines anymore. The 4360 was ready and that is what the B-36 got.

    I love these hyper engines. They are huge, complicated and so powerful. And, when at their zenith, along comes something that looks like a glorified stove pipe and it makes more power. It is like the last days of the dinosaurs.

    My car has overhead cams, fuel injection and a turbocharger. Cars have finally evolved to the level of WWII aircraft. I'm ready to switch to jets. 8)
     
  14. engguy

    engguy Member

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    I agree with you on this. Yeah look how long it took the car makers to get as far as those old airplane engines of years past.
     
  15. Burmese Bandit

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    Gentlemen, I reply in two words:

    Napier Sabre.

    This under supported and under reported engine in its final form, with a decent supercharger, gave up to 5500 hp in its highest form, and had WAY smaller frontal area!!!
     
  16. AJStew22

    AJStew22 New Member

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    Yes, but this engine STARTED at 5,000, and had the potential to exceed 7,000 hp. look at the Wright R-3360, it started at 2,200 hp and ended up producing over 4,000 hp in the lockheed constellation. for a reference, even at 5,000 hp this engine still has a better power to weight ratio than the bristol hercules did, the BH came in at .7 hp/lbs or 1.4 lbs/hp.
     
  17. GregP

    GregP Well-Known Member

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    Never did like the Sabre.
     
  18. johnbr

    johnbr Well-Known Member

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  19. MiTasol

    MiTasol Active Member

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    #19 MiTasol, Oct 16, 2016
    Last edited: Oct 16, 2016
    Actually the Russian Yakovlev M-501 intended for the four-engine Tupolev 487 and Ilyushin IL-26 is bigger at 8760 cubic inches and there are many of its derivatives still in existence, including a much modified one in the Dragonfire drag racer.
    (https://get.google.com/albumarchive...lWVytgBiI2Fn24W_TuBPEEJ1tZInNtbzKz?source=pwa)

    To quote Yakovlev M-501 and Zvezda M503 and M504 Diesel Engines

    The Yakovlev M-501 was a large, water-cooled, diesel, four-stroke, aircraft engine. The 42-cylinder engine was an inline radial configuration consisting of seven cylinder banks positioned around an aluminum crankcase.

    The M-501 had a 6.30 in (160 mm) bore and a 6.69 in (170 mm) stroke. The engine displaced 8,760 cu in (143.6 L) and produced 4,750 hp (3,542 kW) without the turbosupercharger. With the turbosupercharger and the thrust it provided, the engine produced 6,205 hp (4,627 kW). The engine weighed 6,504 lb (2,950 kg) without the turbocharger and 7,496 lb (3,400 kg) with the turbocharger.

    For engine lovers (and odd airframe lovers) the whole Old Machine Press site is worth a visit because it has a lot of well researched data and photos of engines I had either never heard of or could never find reasonable information about. For example
    • Allison X-4520 24-Cylinder Aircraft Engine
    • Armstrong Siddeley ‘Dog’ Aircraft Engines
    • Beardmore Cyclone, Typhoon, and Simoon Aircraft Engines
    • Bréguet-Bugatti 32A and 32B Quadimoteurs
    • Clerget 16 H Diesel Aircraft Engine
    • Curtiss H-1640 Chieftain Aircraft Engine
    • Deissner ‘Paradox’ Rotary Aircraft Engine
    • Deschamps V 3050 Diesel Aircraft Engine
    • FIAT AS.8 Engine and CMASA CS.15 Racer
    • FKFS Gruppen-Flugmotor A, C, and D
    • General Airmotors / Moore Three Valve Aircraft Engine
    • Junkers Jumo 224 Aircraft Engine
    • Lancia V-12 Aircraft Engine
    • (American) Marchetti Cam-Action Engines
    • Menasco 2-544 Unitwin Aircraft Engine
    • Napier Cub (E66) – First 1,000 hp Aircraft Engine
    • R.E.P. Fan (Semi-Radial) Aircraft Engines
    • Reggiane Re 101 to Re 105 Aircraft Engines
    • Rolls-Royce Exe (Boreas) and Pennine Aircraft Engines
    • Wright Aeronautical R-4090 Cyclone 22 Aircraft Engine
    Happy reading

    Mi
     
  20. WJPearce

    WJPearce Active Member

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    Hello,

    I’m glad you liked my article on the Soviet/Russian 48-cylinder engine and my Old Machine Press site. I’m always happy to see my articles getting around.

    There were only a couple engines larger than the XR-7755 that I am aware of, and they are so obscure that it is easy to see why they are mostly unknown. The thing that makes me cringe is when I read or hear that the R-4360 is the “world’s largest piston engine.” Such a statement is wrong on so many levels.

    Larger than the XR-7755:

    In 1933, the Soviets developed a V-12 that had an 8.74 in (222 mm) bore, an 11.26 in (286 mm) stroke, and a displacement of 8,107 cu in (132.8 L). The engine was built by the Institute of Aviation Motors (Институт авиационного моторостроения/ИАМ or Institut aviatsionnogo motorostroyeniya/IAM) and designated M-44. Two were built for aircraft use and a third for marine use. I doubt the 2,000 hp (1,491 kW), 3,968 lb (1,800 kg) engine ever flew.

    The 8,760 cu in (143.6 L) Yakovlev M-501 that has already been mentioned.

    Under Construction but cancelled:

    In 1942, Studebaker went to work on the 5,000 hp (3,728 kW) XH-9350 (153.21 L). The 24-cylinder engine had an 8 in (203 mm) bore and a 7.75 in (197 mm) stroke. Single- and twin-cylinder testing was been done and some components were made, but the engine was cancelled in October 1945.

    In France in 1946, SNECMA's GEHL (Groupe d'étude des moteurs à huile lourde, or study group of heavy oil engines) designed the 32 HL. The engine was a four-row radial with eight liquid-cooled cylinders per row (32 cylinders total). Its bore was 7.09" (180 mm) and its stroke was 7.87" (200 mm), giving a total displacement of 9,938 cu in (162.86 L). The diesel engine was to produce 4,000 hp (2,983 kW) and weighed 7,716 lb (3,500 kg). Some cylinder testing (probably only single) and crankcase construction was underway when the project was cancelled in 1948. The 32HL was cancelled because the ATAR 201 turboprop SNECMA was developing was to produce the same hp but at one sixth the weight.

    Normally I would not count coupled engines, but I’ll include the two below (because it is easy):

    The Hispano-Suiza 48Z was comprised of two 24Z engines. The 48-cylinder 48Z engine displaced 8,800 cu in (144.20 L) and had a takeoff rating of 7,200 hp (5,369 kW). I don’t think this late 1940s design was ever built.

    The Arsenal 24H Tandem consisted of two 24H engines connected by a 39 in (1.0 m) shaft. It displaced 8,541 cu in (139.96 L) and had a takeoff rating of 7,200 hp (5,369 kW), with some sources stating 8,000 hp (5,966 kW). Some sources claim that a 24H Tandem was constructed and run in the late 1940s.

    Of course, I’m sure there are numerous other paper engine projects that were considered, but the ones above progressed past the design phase. It all shows that the XR-7755 and other really large engines were not the idea of crazed engineers, but a serous effort to solve the power question for the next generation of large piston-powered aircraft—those beyond the B-36, Spruce Goose, and Brabazon. Fortunately, jet engines changed everything.

    Regards,
     
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