Large Aircraft Engine

[Christopher R.]

A while back, there was a discussion about big aircraft engines. I wanted to comment, but I wasn't sure of my facts. Now I am. Talk about big.

World's largest reciprocating aircraft engine ever built. Lycoming XR-7755. 7755 cubic inch radial. 36 pistons, 4 banks of 9. Weighed 6050 lbs. 10' long, 5' diameter. Put out 5,000 HP @ 2600 rpm. Burned 580 GPH of 100 octane avgas at rated HP. Development started in 1943 for the B36 bomber. Cancelled in 1945. Lots of other mechanical innovations including a gearbox, 2 shafts, and other stuff I didn't write down. I've got a picture, but I can't figure out how to open it. Beautiful thing.

[John M.]

Re: Large Aircraft Engine

Chris,
Here is a link to a pic of one.

http://www.aviation-history.com/engines/xr-7755.htm

I was schooled on the R-4360 engine when I first started in the aircraft industry, even though it was already an obsolete engine by that time. The B-36 allways needed something bigger than the "tiny" 4360 engine to get it off the ground. They had at least a couple of variants with both rocket and jet assisted take-off. I hated changing plugs on the 4360, because with 28 cylinders and 56 plugs, you would be there a while after pulling all the shrouding off.

Regards, John McGraw

[Joseph T.]

Re: Large Aircraft Engine

Any connection between the 4360 engine and the 4360 Rochester Fuel Injection?

Joe

[John M.]

Re: Large Aircraft Engine

Joe,
The 4360, just refered to the total cubic inch displacement of the engine.
This sounds pretty impressive until you consider that there were6 of them used on the B-36, and they were anticipating replacing them with the 7755 which was better than twice the size of the old 4360!

Regards, John McGraw

[Duke W.]

Re: Large Aircraft Engine

There were many engine development projects during WWII, but none ever went into production. All production engines were developments of designs that were already in production or on the drawing board, including the R-3350 that powered the B-29, at the time of the Pearl Harbor attack. The R-4360 didn't go into production until after the war, and the R-3350 had a lot of development problems, which delayed combat deployment of the B-29.

An EXCELLENT book on the subject is "Allied Aircraft Engines of World War II", that is available from SAE and other sources. It also includes British developments including the Bristol sleeve valve radials, and my all time favorite, the Napier Saber H-24 sleeve valve engine that powered Hawker Tempests and Typhoons into the sixties!

The problem with spark ignition recips is detonation, which limits practical bore size to about six inches. They aren't "scalable" like diesels and turbines, so to increase power you have to keep adding cylinders, which greatly increases complexity.

The Lycoming XR-7755 was essentially nine inline fours displaced radially on a common crankshaft. US aircraft engines of the era were named by type (R for radial and V for inline) followed by the cubic inch displacement.

Thus the XR-7755 was an experimental radial of 7755 cubic inches.

Duke

[Donald M.]

Re: Large Aircraft Engine

I installed a 7755 in a Vette once and when I started it the CAR started spinning at 2000 RPM at idle!

[Clem Z.]

some radials the crank stood still

and the engine(cylinder case) rotated correct??????

[Joe L.]

Re: some radials the crank stood still

clem-----

Yes, I believe so. However, I don't think that there were any US-built engines of this type. I think the British had some. I'm not sure, though.

[William C.]

Re: some radials the crank stood still

Can be seen on some of the WW-1 era shows on cable from time to time...

[Michael W.]

Re: some radials the crank stood still

The fr_nch LeRhone engine was probably the best known example. Fell out of popular use after the manufacturer recommended regular valve clearance adjustments while the engine was running.

[John H.]

Re: Large Aircraft Engine

"Six turnin' and four burnin'" was the magic formula to get the "aluminum overcast" off the ground. When I was an instructor at the Army Helicopter School at Fort Wolters, Texas in 1963, the B-36 Wing at Carswell AFB in Fort Worth lost one into the lake at the end of their main runway when only five of the six were pulling - one was pushing, which gave them a net of only four pulling - that ain't enough

[John H.]

Re: some radials the crank stood still

Some of the WWI radials (like the French LeRhone and some others) had a fixed crank with the prop bolted to the rotating crankcase; the main downside to that arrangement was no throttle control - they were either "on" or "off", which made final approach lots of fun

[Rich G.]

Re: some radials the crank stood still

They were actually called "Rotary" engines. They burned castor oil mixed with the gas and the "Throttle" was done by a kill switch that cut out a variable number of cyliders to reduce power for decent and landing. They would tend to burst into flames if the kill switch was held down too long and then released. Hence, the "blipping" of the engine when you hear a Camel or Tri-Plane coming in to land.

Also, with all that metal spinning, if the engine quit producing thrust on take-off the gyroscopic precession effect would usually render the airplane uncontrollable. More Sopwith Camels were lost in accidents than were shot down by the foe. Gnome and LeRhone were two manufacturers that come to mind.

The Old Rhinebeck Aerodrome in NY flies these engines on most summer weekends. They are amazing to see run.

Rich Giannotti 38594

[John M.]

Re: Large Aircraft Engine

John,
According to many accounts that I read back in the old days, the reversible props that were used for braking, had a bad habit of going into reverse pitch at full throttle during takeoff! The engines consumed oil at an alarming rate, and it was not unusual for an engine to go through it's entire 150 gallons of oil during one flight. The engines tended to overheat, especially the rear cylinders, and would regularly eat a set of sparkplugs in less than 20 flying hours due to the oils consumption! It was an enormous plane with a huge appetite for maintenance. The generally accepted number back then was that it took over 600 people to support and fly one B-36. Talk about stretching the limits of an old technology! When you contrast it's short life with the B-52, which has now been in continous service for almost 50 years, it is amazing.

Regards, John McGraw

[Klaus Friedrich #33362]

Re: some radials the crank stood still

Hello together,

did you know that there was a motorcyle called "MEGOLA" that had a radial engine in the front wheel? It was built in the 20th and 30th of the last century. You can find picture in the internet. Really interessting and rare!

Klaus Friedrich
#33362