AHC/WI: Lycoming R-7755 Powered Aircraft

Delta Force

Banned
The Lycoming R-7755 was the largest piston aircraft engine ever designed, having 36 cylinders and displacing 7,755 cubic inches (127 liters). The versions tested had an output of 5,000 horsepower, and it expected that the engine could eventually be developed to produce 7,000 horsepower. To illustrate how massive this engine was, the B-36 was the largest military combat aircraft ever produced, and it was powered by "only" six Pratt & Whitney R-4360 Wasp Major engines with 28 cylinders, a displacement of 4,363 cubic inches (71.5 liters), and an output of 3,500 horsepower with the R-4360-41 Wasp Major engines that powered the B-36B variant. Just about everything about the R-7755 was double that of the R-4360 Wasp Major. The R-7755 even required two propellers (contra-rotating), because a single propeller would have been unable to achieve ground clearance on the B-36!

To my knowledge, no aircraft was ever planned to receive the R-7755, although it was at one point planned for use on the European bomber project that led to the B-36. The challenge is thus to find a use for this massive amount of power.
 

Just Leo

It seems to be comparable with a Rolls Royce Tyne for power, but the Tyne weighs 2400 lbs and doesn't need a cooling system. Fuel consumption of Tyne at full take-off is the same as the beast at 70% cruise. It coulda been a contender in a world where Wright and Pratt & Whitney didn't rule the market, and bean counters figured out the bills. There weren't enough made to outfit a single Hughes Sprucey Goosey.
 

Kevin Renner

Maybe somthing like an enlarged Douglas MixMaster. The B-36 could of been designed around four of these beasts but I'm pretty sure that P&W had a significant lead time in terms of development. The US engine under development at the time I would love to hear run is Wright's Tornado
 

Delta Force

Banned
Just Leo said:
It seems to be comparable with a Rolls Royce Tyne for power, but the Tyne weighs 2400 lbs and doesn't need a cooling system. Fuel consumption of Tyne at full take-off is the same as the beast at 70% cruise. It coulda been a contender in a world where Wright and Pratt & Whitney didn't rule the market, and bean counters figured out the bills. There weren't enough made to outfit a single Hughes Sprucey Goosey.
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Turboprop conversions and/or developments of piston engined aircraft would have been interesting. Would a pusher design such as the B-36 have any problems with turbprops?

Kevin Renner said:
Maybe somthing like an enlarged Douglas MixMaster. The B-36 could of been designed around four of these beasts but I'm pretty sure that P&W had a significant lead time in terms of development. The US engine under development at the time I would love to hear run is Wright's Tornado
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The Tornado had 42 cylinders. That has to be close to the most cylinders for any single engine.
 

Delta Force

Banned
Uruk said:
How about using it on a twin engined B-50?
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Large and/or long distance twin engine aircraft didn't really become popular until the 1970s and 1980s because engines weren't reliable enough. Their would probably be a preference for four smaller engines over two larger engines in such roles.
 

Just Leo

Delta Force said:
Large and/or long distance twin engine aircraft didn't really become popular until the 1970s and 1980s because engines weren't reliable enough. Their would probably be a preference for four smaller engines over two larger engines in such roles.
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Look up Lockheed P2V-1 Truculent Turtle.
 

Delta Force

Banned
Grey Wolf said:
Wasn't the B52 originally designed to be prop driven?
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I know that Boeing and Douglas both studied propeller driven strategic bombers that would have been used in the same role as the B-52. I think the B-52 as we know it (that is, the one that was built and flies today) was always designed for jet engines.
 

Just Leo

The nature of flame propagation in spark ignition engines tends to limit cylinder bore size. Compression ignition is different.
 

Delta Force

Banned
Just Leo said:
The nature of flame propagation in spark ignition engines tends to limit cylinder bore size. Compression ignition is different.
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True, but what I mean is that there were piston engines with much higher displacements that still had less cylinders than the Tornado. Why would an engine designed in 1940 need so many cylinders of fairly small displacement?
 

bsmart

Since Lycoming doesn't have a track record of producing large radial engines I question their ability to develop this engine in a timely manner. This engine is something like an order of magnitude larger than any production engine they had produced. They had also only produced one other radial engine that I can find (R-680 used in the Stearman trainer)

Lycoming builds very good engines, and they probably could pull it off but there would be problems. Since it is not a 'corncob' design (offset cylinders in rear rows of cylinders the way the R-4360 was designed) I foresee problems with cooling of the rear cylinders
 

Delta Force

Banned
bsmart said:
Since Lycoming doesn't have a track record of producing large radial engines I question their ability to develop this engine in a timely manner. This engine is something like an order of magnitude larger than any production engine they had produced. They had also only produced one other radial engine that I can find (R-680 used in the Stearman trainer)

Lycoming builds very good engines, and they probably could pull it off but there would be problems. Since it is not a 'corncob' design (offset cylinders in rear rows of cylinders the way the R-4360 was designed) I foresee problems with cooling of the rear cylinders
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The R-7755 was liquid cooled, so I don't know how much of an issue the lack of spiraling would be. I don't think air cooling would contribute much to an engine that uses 700 gallons of water per minute for cooling.
 

bsmart

Delta Force said:
The R-7755 was liquid cooled, so I don't know how much of an issue the lack of spiraling would be. I don't think air cooling would contribute much to an engine that uses 700 gallons of water per minute for cooling.
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Yea in looking back at it (when looking into the Wright Tornado engine you mentioned I noticed that.) I'm not used to Radial engines that aren't air cooled. I thinbk this is another strike against it. Lycoming didn't have much expereince with liguid cooled engines (and the ones they tried were failures) So I can see the reluctance to use such a revolutionary engine design in a critical program.
 

Kevin Renner

All of the multibank engines above the v type* were pretty much failures. It can't of been from excessive mass on the crank throws as evidenced by 9 and 18 cylinder radials. I think in the long run the Lycoming would of worked. The Tornado I have my doubts. The layshaft setup bothers me.

*By this I mean all of the 4 or 6 bank star configurations. I suspect there were vibration issues common to the type due to uneven firing orders.The Sabre was multi bank true. But it was a compound engine of basically two flat 12s
 
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