Twin-engined aircraft
 

Here's a completely idle and probably futile question that just popped into my mind.

It's sort of natural to assume that on twin-engined aircraft, both engines are of the same type. Symmetry and all that.

But have there ever been any twins designed from the start -- rather than under some testing regime -- to have two significantly different kinds of engines for some weird reason? Maybe some strange push-pull arrangement?

The Rutan Boomerang might qualify, one engine was a Lycoming TIO-360-C1A6D (left hand) rated at 210 horsepower, the other a Lycoming TIO-360-A1B (right hand) rated at 200 horsepower.


https://cimg7.ibsrv.net/gimg/pprune....547534a73.jpeg

AJI Hustler business aircraft, TPE331 turboprop in the nose, P&W JT-15 turbofan in the rear.

https://en.m.wikipedia.org/wiki/Gulf...erican_Hustler

Never made it beyond prototype stage but was developed into the Peregrine 600 jet trainer sans TPE331, then the Peregrine single engine business jet, neither of which developed beyond prototypes. Thought the Peregine looked great but it had a pretty tiny cabin I think. Predated the Eclipse and so on by some 30 years.

Also Rutan's World circling Voyager had different engines fore and aft.

Piston in the nose, jet in tail.

Curtiss XF15C-1, only three built

https://cimg0.ibsrv.net/gimg/pprune....6504269cc2.jpg

Ryan FR Fireball, 71 built, entered service March 1945 but never saw combat.

https://cimg1.ibsrv.net/gimg/pprune....cc2c515002.jpg

Saunders Roe SR 53. Turbojet ( Armstrong Siddeley Viper) plus rocket motor (de Havilland Spectre) Also the SR 177 although this was not completed.
Not "techie" enough to be able to post a photo !!!

I suppose that technically the counter rotating Twin Coms and Navajos have different engines! :}

You should have mentioned the Mosquito before that.
I mentioned it once but I thnk I got away with it.

Chevv, Mosquito didn`t have c/rot. engines...but the Hornet did....

Though possibly not satisfying the OP's "significantly different" criterion ...

But if we're allowing C/R props, the A400M is another candidate.

The Shackleton MR3 had 2 RR Vipers as well as the 4 Griffons....

The OP did say "Twin Engined".

Well we've already drifted to counter-rotating engines, so who's counting how many ? :O

In that case:
Lockheed P2 Neptune Twin piston & twin jet

Are the engines not the same, rotating the same way, but it's the gearbox that reverses the rotation of one of them (rather like having one half of a contra-rotating gearbox) ?

If we've wandered off from the original twin idea, I'll see your Shackleton MR3 and raise you the Convair B36, Six Turning and Four Burning.

You may well be right. I seem to recall hearing that the handed Allisons in the P-38 were made to rotate in opposite directions,

Wasn't there also a Fairchild Packet which had a jet engine on a pylon above the fuselage roof?

I seem to recall seeing a TWA one years ago in Nairobi. I think it was used for shipping engines about.

That's right, based in Europe. It's now preserved at Hagerstown.

To make a left hand engine from a right hand engine, you have to reverse the crankshaft, replace a regular gear with an "H" gear (this is a gear that skips over a gear that was used), and add a standard gear to reverse the prop rotation after you skip with the "H" gear. Every Allison engine has the ability to be reversed if you have an "H" gear and the added gear.

The right hand bank as viewed from the distributor end (rear of the engine) must have several spark plug leads interchanged because the cam lobes are backwards. It works out the same for the left-hand bank, somehow ... no left bank changes to the firing order

Basically, to make a left from a right, the engine must be almost disassembled because you must be able to get to the gearcase in front and must split the case and disconnect all the rods to reverse the crankshaft.

However, if you are BUILDING a left or right from parts, the difference in build up is trivial, assuming you have an "H" gear, the new gear, and you know the plugs to interchange (this means rewiring the ignition harness on one side ... so it is MUCH easier to simply build a left or right wiring harness than it is to change one that is already wired).

The "H" gear:

A Standard gear is just a gear with a keyed center. An "H" gear looks like two standard gears joined by a small cylinder in the middle to skip over the gear that was formerly meshed by the standard gear. The new gear you add is to turn the skipped gear in the other direction. All gearcases have the ability to turn either way ... the gear bosses are in all of them, internally.

For both left and right engines, the cams turn the same direction and the crankshaft is reversed and turns backwards.

There is no other engine I know of from WWII that as so easy to make turn in either direction when being built up ... two gears, turn the crankshaft around, and change the right bank firing order ... that's it.

You need a starter that turns the other way, and you need an idler type gear to reverse the direction of the cam towers.

You can see the difference below.


https://cimg3.ibsrv.net/gimg/pprune....60656cabd3.jpg
https://cimg6.ibsrv.net/gimg/pprune....332ae6d444.jpg

The He177 was a four engine, twin prop aircraft.