AHC/WI: Lycoming R-7755 Powered Aircraft

Delta Force

Banned
It looks like that engine was part of the USAAC Hyper Engine program of the 1940 timeframe
http://en.wikipedia.org/wiki/Hyper_engine

This was an attempt to get 1 HP per cubic inch

There are some interesting engines and aircraft listed in that article.

I don't necessarily know about power to volume ratios, but in terms of power to weight ratios wouldn't it be better to have a few large cylinders rather than many small cylinders? Volume scales exponentially relative to surface area (in this case, cylinder size), so it seems that from a purely mathematical point of view, the best design would take the largest cylinder capable of functioning properly (gasoline engines having a limit due to the need for spark ignition) and arrange them in a suitable configuration.

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

I haven't been able to find a source to really visualize this, but what's the difference between a multibank engine and something like an H, U, or W engine?
 
I figured out the perfect aircraft for this engine, the Bristol Brabazon. It was powered by eight Centaurus radials, buried in the wings in pairs driving four contra-rotating propellers. Unlike the R-2800 or R-3350, the Centaurus did not employ a dynamic balancer, so it shook like the bejeezus. The solution was to mount the engine on metalastic bushings, common as dirt nowadays. The propeller drive was not properly in tune with the engine harmonics, so the prop extentions suffered from fatigue cracks. A single big engine replacing a pair would probably solve this problem. Unfortunately, nobody bought any. They could also be recommended to power the Saro Princess, replacing the unreliable engines, but nobody bought them either.

I don't know what a U engine is either, but I think I know the rest of the alphabet. I tend to babble too much when I explain things as complex as the limits on engine size and volumetric efficiency, but don't spend too much time looking into the wartime engine program. They all failed. An additional engine was the Chrysler 16 cylinder inverted V, two hemi V8s end to end with the drive in between to shorten crankshaft length. Also failed, but it did keep them busy for 5 years. I would have been interested to see the Ford V-12 developed, but that's life. What was even more amazing was the number of aircraft developed to employ these mythical powerplants, in wartime.
 
A better POD would be that P&W finishes developmentg of its 24 cylinder sleeve valve engines. In some ways these reflect Pratt's radial experience as the cylinders are single bolt on units to ease servicing

A U type can be thought of as just one side of an H type. Two inline engines side by side on a common crankcase
http://en.m.wikipedia.org/wiki/Bugatti_U-16
 

NothingNow

Banned
I don't know what a U engine is either, but I think I know the rest of the alphabet.

It's a pair of separate inline engines hooked up to the same throttle and then joined by gears or chains after the crankshaft. It's not at all useful for most practical designs, because it's going to be heavier and more maintenance intensive than a V- or flat engine configuration for the same number of cylinders.

It got used on M4A2 Shermans with the GM 6046D engine because it was a fast, cheap solution and the 6-71 engine was reliable enough that it wouldn't cause any extra problems, while massively simplifying production and maintenance logistics for diesel vehicles in general. That's the only application I can remember for the configuration outside of auto racing.
 
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.

The Boeing Model 464, which was Boeing's internal designation for what became the B-52, was originally designed with 4 turboprops. The design evolved before the first prototype was built into the 8 jet engines we know today.
 
It looks like that engine was part of the USAAC Hyper Engine program of the 1940 timeframe
http://en.wikipedia.org/wiki/Hyper_engine

This was an attempt to get 1 HP per cubic inch

Interesting. Isnt it the case that modern high performance car engines (turbocharged, of course) hit 100 hp/L, or 1.6 hp/in^3? So modern massproduced car engines can have half again as much power cutting edge aero engines then? WithOUT using leaded superhigh octane AvGas?
 

Delta Force

Banned
Interesting. Isnt it the case that modern high performance car engines (turbocharged, of course) hit 100 hp/L, or 1.6 hp/in^3? So modern massproduced car engines can have half again as much power cutting edge aero engines then? WithOUT using leaded superhigh octane AvGas?

They can do more than that. The Koenigsegg One:1 engine generates 1,360 horsepower and weights only 434 pounds (197 kilograms), giving a power to weight ratio of 3.13 horsepower per pound (or 6.90 horsepower per kilogram). It has about 4.43 horsepower per cubic inch (0.272 horsepower per cubic centimeter).
 
The Rolls Royce Crecy was tested in a single cylinder testbed and produced power equivalent to 5,000 hp for the full V-12, in an engine smaller than Merlin. I myself produced a 60 cc rotary valve two cycle engine, normally aspirated, which produced the equivalent of 5340 hp, compared to Merlin size. Too late for the war, however. Still, Rare Bear, powered by R-3350 is still the fastest, and Merlin Mustangs seem to still be in abundance at air races. Apples and oranges, when a car blows up, you coast into the pits. When a plane blows up, it makes its own pit.
 

Delta Force

Banned
The Rolls Royce Crecy was tested in a single cylinder testbed and produced power equivalent to 5,000 hp for the full V-12, in an engine smaller than Merlin. I myself produced a 60 cc rotary valve two cycle engine, normally aspirated, which produced the equivalent of 5340 hp, compared to Merlin size. Too late for the war, however. Still, Rare Bear, powered by R-3350 is still the fastest, and Merlin Mustangs seem to still be in abundance at air races. Apples and oranges, when a car blows up, you coast into the pits. When a plane blows up, it makes its own pit.

Even producing 2,730 horsepower, the Crecy would have been a very interesting option. Designs with fewer cylinders (perhaps a production version of the development model V-8) and tandem and/or H-block designs could be produced based on it.
 

Delta Force

Banned
What would military and commercial aircraft built around the Lycoming R-7755 have looked like in terms of performance, size, and capacity? Obviously turboprop and turbofan engines would have been options by late World War II, but what if those had not been options or something even more capable than the B-36 had been required?
 
It got used on M4A2 Shermans with the GM 6046D engine because it was a fast, cheap solution and the 6-71 engine was reliable enough that it wouldn't cause any extra problems, while massively simplifying production and maintenance logistics for diesel vehicles in general. That's the only application I can remember for the configuration outside of auto racing.

M5 Stuarts with Cadillac Eights,and the Australian AC1 Sentinel did one better, using two Caddys side by side, with a third off to the rear, a cloverleaf. any of the engines could be clutched separately to a common gearbox
 

Delta Force

Banned
Could the Lycoming R-7755 have been used on variants/new aircraft based on ones powered by the Pratt & Whitney R-4360 Wasp Major and Wright R-3350 Duplex-Cyclone? It would be a few few longer and a five inches wider than both engines, as well as liquid cooled (as opposed to air cooled). However, it could have been another way of increasing power on aircraft instead of making them mixed propulsion with a combination of piston and turbojet engines. There would have had to be mixed fuel anyways, so the water coolant could be carried where the jet fuel tanks would have been located.

In terms of output, the R-7755 had a growth target of 7,000 horsepower. I'm not sure if this is the case, but I've read that one pound of thrust is about equivalent to one horsepower, so a B-36 with R-7755 engines would have had about as much power as one with the R-4360 and J47, a Hughes H-4 could use four R-7755 engines instead of eight R-4360, etc.
 
The Lycoming R-7755 was based on the unsuccessful H-2470. The dud H-2470 was based on the unsuccessful O-1230. The previous engines were not rejected based solely on unreliability, but the reports always were concluded with it mentioned. Having the world's most complex engine, without reliability seems like a consummation devoutly to be avoided.

Converting thrust to horsepower isn't at all simple, since they are different things. Converting equivalent shaft horsepower to horsepower is much easier.
 
just in case you've not heard of it...

Allison type-tested the V-3420, two V-1710s siamesed at the crankcase. They then geared two of these together to make the DV-6840. 48 cylinders and over 5,000 horsepower for anyone with a big plane needing a big push. That's takeoff power in the WW2 timeframe, not an imaginary 'growth' number.
 

Delta Force

Banned
The Lycoming R-7755 was based on the unsuccessful H-2470. The dud H-2470 was based on the unsuccessful O-1230. The previous engines were not rejected based solely on unreliability, but the reports always were concluded with it mentioned. Having the world's most complex engine, without reliability seems like a consummation devoutly to be avoided.

Converting thrust to horsepower isn't at all simple, since they are different things. Converting equivalent shaft horsepower to horsepower is much easier.

Didn't most of the high output engines have development issues, including the ones used on the B-29.

Allison type-tested the V-3420, two V-1710s siamesed at the crankcase. They then geared two of these together to make the DV-6840. 48 cylinders and over 5,000 horsepower for anyone with a big plane needing a big push. That's takeoff power in the WW2 timeframe, not an imaginary 'growth' number.

How well do single cylinder tests and existing engines illustrate the potential for larger engines?
 
Heh. Of course, some marks of the Sherman TANK had a 30 cylinder engine! (which has to be some sort of record of RubeGoldberg/power).

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Immediately after WW2, the U S Army "gifted" all its Chrysler Multi-bank powered Sherman to allies.
It would have been a nightmare to maintain those engines in the long-run. Which probably explains why so many Shermans got re-engined with diesels during the 1950s.
 
Immediately after WW2, the U S Army "gifted" all its Chrysler Multi-bank powered Sherman to allies.
It would have been a nightmare to maintain those engines in the long-run. Which probably explains why so many Shermans got re-engined with diesels during the 1950s.
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multibanks were surprisingly reliable, much more so than the R-975

Switched to diesel for the fuel economy, and for stopped making GA* V8s in 1945
 
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