Lycoming, supplier of engines to Auburn, Cord, and Duesenberg, has an additional claim to fame: builder of the XR7755, the largest U.S. aircraft engine of World War II.
As part of E.L. Cord’s vast corporate empire, Lycoming Aircraft Engines of Williamsport, Pennsylvania manufactured the engines for Auburn, Cord, and Duesenberg, Cord’s three famed automobile brands. By the time the USA entered the Second World War, the three carmakers had gone of business, but Lycoming carried on, participating in the Allied war effort. Its contributions were many, but the most memorable must be the XR-7755, the largest piston aircraft engine ever built in the USA.
The U.S. military’s naming conventions provide some info about the XR-7755: X stands for experimental; R indicates a radial cylinder configuration; and 7755 is the approximate displacement in cubic inches. That’s not a typo: 7755 cubic inches, 127 liters. There were 36 cylinders laid out in four rows of nine, each one with a 6.375-in bore and a 6.75-in stroke, displacing 215 cubic inches per cylinder.
The engine was conceived as part of the USA’s European Bomber project, in which the U.S. armed forces proposed to strike targets in Germany directly from airfields in North America. Lycoming’s leviathan was 10 feet long, more than five feet in diameter, and weighed 6,050 lbs. It nearly dwarfed the U.S. military’s next-largest piston aircraft engine, the 28-cylinder Pratt & Whitney R-4360 Wasp Major.
Unlike most radial aircraft engines, the giant Lycoming was liquid-cooled, due in part to its giant size. Another distinctive feature was its sliding, dual-lobed camshaft design, in which the camshafts could be shifted forward and back to alter the valve timing for full takeoff power or cruising. Two complete engines were constructed, and 5,000 horsepower was easily achieved in dynamometer testing before the project was cancelled in 1946. The war was won, the American military establishment could see that the future in large aircraft engines was in jet turbines, and thus the enormous engine never powered an aircraft. The lone surviving example is on display at the Smithsonian National Air and Space Museum in Washington, DC.
I saw the XR7755 not long after it was restored at the National Air and Space Museum. It is indeed a giant. I remember thinking it was nearly the size of the Mercury space capsule.
I wonder how much fuel it consumed per hour?
rated at 580 gallons per hour.
The article is incorrect when it states the engine was arrayed in four rows of nine cylinders; as you can plainly see, it should be nine rows of four cylinders.
In a radial engine, the rows are regarded vertically. (Most radials are single row.) Each vertical row is connected to a common crankshaft throw with a master connecting rod and link or slave rods. In a true radial, there is always an odd number of cylinders in each row, 9 for example, and the firing order goes 1-3-5-7-9-2-4-6-8, alternating the odd and even cylinders to provide balance.
My Dads crop duster had a Pratt & whittney 1340? On it, he clocked 1000’s of hrs on those radials .
The master rod broke at 4’ above a muddy field , stuffed engine into mud 👀 he got the rod to keep as a trophy, I kept it for yrs until it disappeared 🙁
It is 4 rows of 9 cylinders a radial needs odd numbers to get the correct firing sequence ie 9 cylinders firing in 720°
When you view a radial engine from the front, you’re looking at the “front row” of cylinders. Look at the PW R-985 – single row, 9 cylinder engine. 1 row of 9 cylincers, not 9 rows of 1 cylinder.
A 3 ton engine using 580 gallons per hour. By at least two. Would need a very big plane to carry all this plus a payload of bombs.
As a matter of interest how much fuel did a Lancaster or B17 use?
B-17 was 200+ gph for all four engines.
Quite the contrast to their other products, judging by the ad! There was also a Lycoming factory in Stratford, CT which built Wright engines under contract to power Corsair fighter planes in WWII.
Amazing engineering that never got used,still stunning statistics on power of engine!
Another interesting piece that never flew was the CHRYSLER HEMI inverted V16 aircraft engine. Built for a modified version of the P 47 but the war ended . I saw one at the CHRYSLER MUSEUM in MI>