Largest Piston Engine for Aircraft

[GregP]

I was poking around and found a blurb on the Lycoming XR-7755. This behemoth was the largest piston aircraft engine ever built in the free world. From 7,755 cubic inches (bore of 6.375", stroke of 6.75") and 7,050 lbs it gave 5,000 horsepower under test in 1944; 7,000 horsepower was the development target. Nine liquid cooled inline four cylinder engines about a common crankshaft. Two contra-rotating prop shafts. The camshafts each consisted of two sets of lobes. One set of lobes for takeoff, the other for economy cruise. The camshafts were shifted axially to switch lobe sets. 580 gallons of fuel per hour at takeoff power, BSFC of 0.43 at cruise. Paul McBride of Lycoming says it was for the B-36 but political pressures caused the B-36 to be fitted with the Pratt & Whitney R-4360 instead. Awesome. A survivor still exists at the Smithsonian's Garber facility. See it if you can. Circa 1944.

[tenmmike]

here you go http://www.aviation-history.com/engines/xr-7755.jpgThis 36 cylinder engine was destined to be the largest reciprocating engine ever built. The displacement was 7,755 cubic inches. When compared to Lycoming's largest production engine in production today which displaces 720 cubic inches, it was more than 10 times larger!

This huge engine was 10 feet long, 5 feet in diameter and weighed 6,050 pounds. It produced 5,000 HP at 2,600 RPM, and the target was 7,000. It used 580 GPH of av gas at the 5,000 HP rating.

There were nine overhead camshafts which could be shifted axially for METO power in one position and cruise at the other. Two great shafts emerged for coaxial propellers, and there was a two speed gear-change box between the crankshaft and the propeller shafts.

Development of the XR-7755 began at Lycoming in Williamsport in the summer of 1943. With the end of World War II in 1945, the military no longer had a need for an engine of this size, and development of the XR-7755 stopped at the prototype stage.

During those years, Lycoming put together a team, under the leadership of VP Engineering Clarence Wiegman, to develop this super-size engine.

The engine now resides at Silver Hill of the Smithsonian Institute.EDIT this is certainly not the largest reciprocating engine there are many much much larger but as a aircraft engine yes it was

[GregP]

Thanks tenmike. Maybe you can show me how to get pics on the forum!

[Paolo Tagliaferri]

Easy.
If the pic is online already, just (IE) click on them with your right mouse button, copy the URL of the photo, then place it in the post with the [IMG] code (look in the reply panel buttons)

If the pic is not online, you need first to put it online on a webspace ... then do the same way. Maybe a free webhosting space is what you need.
The problem is, many webspaces have an anti-leech policy so that you can't view the photo from a third party website ... but only if the photo is displayed on a webpage on the same free space (TRIPOD (http://www.tripod.lycos.com/) for example).
As always I can host photos for you if you need to ...

[Burunduk]

But it seems XR-7755 never fly.

In this case the candidate for the most powerful "flying" piston engine is Soviet VD-4K.

4 such engines were installed on strategic bomber Tu-85 (first flight 09/01/1951).

The power of the engine is 4300 hp.

[GregP]

Hi Burdunduk,

Welcome to the forum.

I believe you are correct, the Soviet VD-4K WAS probably the most powerful piston engine to actually fly on an aircraft. The Soviet Union also designed the largest radial engine ever to be made, the Zvezda 42-cylinder, 7-row engine that was designed to be used for tractor pulls. It dispalced 8,760 cubic inches or 143.6 liters and made 6,035 HP / 4,500 kW, but was NOT an aviation engine.

We claim the Lycoming 7755 was the largest aviation radial engine ever built and I believe it WAS. I do not believe any claim was made that it flew, but it DID run well. It WOULD have flown had not jet engines spelled the doom for pistons in the US military. Once the relaibility of turbines was established, the piston engine days were bound to be short-lived.

For your reference, the largest piston engine of any sort ever made is the Wartsile-Sulzer RTA96-C, water-cooled, inline Marine Engine. It has 14 cylinders with a bore and stroke of 37.9 inches (98.5 cm) x 96.3 inches (250.2 cm), displaces 1,556,002 cubic inches (25,500 liters), and produces 108,920 HP (81,222 kW) at 102 RPM. Torque is 5,608,312 pound-feet (7,603,839 m-N). Quite the little beastie!

Weight is 4,600,000 pounds or 2,086,514 kg! It is 3-stories tall! ... and, best of all, it is still in production!

[Wuzak]

I believe that the XR-7755 was destined for use in a variant of the B-36. But it didn't quite make it. It did have some impressive features, like camshaft phase shifting.

Was the Zvezda really designed for tractor pulls, or did it have some more mundane purpose before being adapted for the tractor pulls?

[Red Admiral]

The Zvezda was used for various marine applications in patrol craft in the Soviet Navy. I believe it was originally designed with an aircraft role in mind though, in case the NK-12 was a failure.

[Burunduk]

GregP, thank you for very interesting and informative post. 108+K HP piston engine - it's amazing.

RedAdmiral, radial engine ASh-4K (Zvezda means just "Radial" in Russia when you speak about engines and "Star" in other cases) was really planned as second canditate not for Tu-95, but for Tu-85.

But it was not ready to fly test time and never fly.

The reserve variant for Tu-95 was duplex TV-2F (4 installation, each installation consists of 2 engines + 2 co-axial props), based on German design. But it is turboprop, not piston engine.

First Tu-95 was made with TV-2F, only the second (and all next) with NK-12.

[Red Admiral]

http://www.enginehistory.org/phpbb/viewforum.php?f=2

Another forum all about engines that I've just found. Look to be some knowledgeable people there.

[Kutscha]

That is a great site Red. Visited many times but didn't know they had a forum. Thanks.

[Trexx]

http://img.villagephotos.com/p/2007-10/1283790/xr-7755motor.jpg

GOOD GAWD, CRIMANY SAKES! HUMONGOUS MUTHA!

----> BUT,


QUESTION:

Are we sure those just aren't very tiny people and a regular sized engine? [:I]

[Wuzak]

quote:Originally posted by Trexx

http://img.villagephotos.com/p/2007-10/1283790/xr-7755motor.jpg

GOOD GAWD, CRIMANY SAKES! HUMONGOUS MUTHA!

----> BUT,


QUESTION:

Are we sure those just aren't very tiny people and a regular sized engine? [:I]


In terms of size, I think that the XR-7755 would be similar in diameter to an R-2800 or R-3350. Of course it is much longer.

And yes...it is humungous!