Has a fixed-wing aircraft ever been conceived, prototyped or built that features multiple turbines powering a single propeller? The concept of a twin-engine aircraft with a single propeller is intriguing to me. Picturing something like a Pilatus PC-12 with two engines under the hood and a single prop might have some advantages. I come from a fixed-wing background and know little about helicopters, but if something exists I suspect it is a rotor wing.

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    Aircraft, yes, as in helicopter. Airplane I'm not so sure. The Osprey can power both propellers with a single engine (the other way around). The only one I know of that actually does this with a PT-6 is the Soloy Dual-Pac – Ron Beyer Jan 23 '17 at 2:46
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    Wow I have to look into how the Osprey does that. That's nuts. – ryan1618 Jan 23 '17 at 2:51
  • The obvious reliability problem with this is "what happens after a single engine shutdown". With a conventional twin aircraft, the answer is "usually, nothing very exciting". At least a helicopter can do an autorotation landing, unlike a plane. If you have to add a lot of complexity (and weight) to handle that scenario, the advantages may evaporate. – alephzero Jan 23 '17 at 5:07
  • There would also be the regulatory issue of whether this counts as "single engine operation over water," which in general is only permitted if the plane can reach land at a location suitable for a forced landing. – alephzero Jan 23 '17 at 5:17
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    Do you mean propeller or rotor? There's a non trivial difference. – KorvinStarmast Jan 23 '17 at 23:06
up vote 29 down vote accepted

The LearAvia LearFan 2100 used two separate PT-6B to drive a single pusher propeller through a common gearbox.

LearFan 2100 in flight
LeraFan 2100 in flight (picture source)

If you want to know why its official first flight date is December 32, 1980, read here.

LearFan 2100 engine arrangement
LearFan 2100 engine arrangement (picture source)

This engine arrangement was the LearFan's eventual undoing when the FAA denied it a proper certification because of concerns that the single gearbox constituted a single point of failure.

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    ... doesn't the propeller also constitute a single point of failure, then? – immibis Jan 24 '17 at 8:41
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    @immibis: Haha, good point. Yes, it does, but the FAA had more concerns with the gearbox. Propeller failure outside of ground contact is very rare; gearboxes, however, are a different story, especially when poorly maintained. – Peter Kämpf Jan 24 '17 at 9:22
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    From the source (article in Popular Mechanics) it seems more that with few test flights they had already demonstrated excessive wear on the gearbox. FAA denied certification because they've seen it as signs of imminent failure, the single point made it only slightly worse. – Agent_L Jan 24 '17 at 13:54

Well multi engine helicopters like the Bell 430 or the Westland EH101 do it all the time.

I don't recall any current production fixed wing aircraft using multiple engines to drive a single propeller, but the ill fated LearAvia LearFan used this propulsion arrangement, using two PT-6 engines to drive a gearbox connected to a pusher prop.

Yes, see Soloy's Dual-Pac concept.

enter image description here
Image courtesy of Soloy

The Soloy Pathfinder 21 is powered by the Dual Pac PT6D-114A. It is essentially an extended and redesigned Cessna 208 with exactly what you describe: two PT6 engines geared to one prop hub. I understand that the project has not progressed beyond the prototype built.

enter image description here
Image courtesy of Soloy

The Dual-Pac was also tested on a DeHaviland DHC3 Otter platform:

enter image description here
Image courtesy of Soloy

Quoting from the Dual-Pac page:

Soloy Dual Pac – Twin Engine reliability with single propeller symmetry. The Dual-Pac was designed, patented and Certified by Soloy to safely combine the output of two independently operating Pratt Whitney PT6D-114A engines for a single propeller output. The system was developed with extreme redundancy so that single engine operation is not only safe, but able to be done intentionally under certain conditions.

The Ayres LM200 Loadmaster was a similar design concept, though a clean sheet design using a different powerplant and also ultimately unsuccessful for economic reasons.

See also the rotorcraft applications of the P&WC PT6T Twin-Pac, such as those that Carlo Felicione mentions.

Well, there is the Armstrong Siddeley Double Mamba engine.

It powered the Fairey Gannet

It wasn't a true single prop, but rather a contra-rotating prop (which amaze me).

Found a few more, some being single contra-rotating, others......multi-multi-engine?

Aircraft powered by the Allison T40

There is one example of the twin turbine to single shaft Allison T40 powering a single propeller aircraft...the Republic XF-84H

The thing was apparently as loud as the Tu-95, due to having a prop that spun at supersonic speeds on its outer edges. And the prop created a continuous visible shockwave.. Personally, I am not sure if you would classify this as an aircraft, or more of a shock/awe weapon.

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    Well, the shockwave was much more audible than visible. Audible enough that people standing nearby got literally sick. – Peter Kämpf Jan 24 '17 at 11:46
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    @PeterKämpf And strong enough to knock people over if they weren't careful. – NZKshatriya Jan 24 '17 at 13:31

A similar concept was adopted on a bomber used by the German Luftwaffe in WWII. The bomber, named Heinkel 177 "Greif" was a four engine but had just two propellers since a pair of engines was mechanically coupled in each of the two nacelles. However coupling mechanically two engines on a single propeller revealed as a source of troubles (e.g. overheating occurred frequently on the rear engines) and the design proved to be unsuccessful. This probably explains why it has not been used any more since then.

  • Better use the He-119 - this one had two coupled piston engines driving a single propeller. But not turbines. – Peter Kämpf Jan 23 '17 at 18:38

Depending on how strict you are about "single rotor" The AH-64 Apache has 2 engines and one main rotor. From Wikipedia "American four-blade, twin-turboshaft attack helicopter"

  • As does the Black Hawk, both using the T-700. – KorvinStarmast Jan 23 '17 at 23:05
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    And the Russian Ka-50/52...though they have a coaxial rotor setup instead of having a tail rotor. And the Mi-28.....heck....how many military helicopters out there today don't use a dual turbine arrangement.. – NZKshatriya Jan 23 '17 at 23:11

Kamov Ka-26 (1969, 816 built) is powered by two 325 hp (239 kW) Vedeneyev M-14V-26 radial piston engines mounted in off-board nacelles, connected by a transverse shaft which drives the co-axial rotors.

image source: Wikipedia

According to Wikipedia, the reciprocating engines, although more responsive than modern turboshafts, are relatively maintenance intensive. The Ka-26 is underpowered with its two radial engines, especially when used in cropdusting role, where excess payload is common. No other helicopter exists in the world that runs at constant 95% engine power for most of its flight regime. This leaves the pilot with little power reserve for emergencies. Due to frequent overloads, the interconnect shaft which joins the two engines is prone to breakage and requires frequent inspection.

NOTE An edit to the question makes this answer nonresponsive.

  • Cut little thing. The wheel pants are a nice touch. I wonder how much of whatever's being crop-dusted the pilot ends up breathing? Wouldn't want to fly in it for anything, but, y'know, cute... – Bob Jarvis Jan 24 '17 at 12:22

The Fairey Rotodyne probably counts, depending on your definition of "single rotor".

In level flight it was essentially an autogyro, driven by twin turboprops on short wings, deriving a fraction of its lift from these and the rest from the undriven rotor.

To achieve vertical takeoff and landing, the rotors were spun by tip jets, fed from bleed air from the turboprops, augmented by fuel burnt in the tip jets.

Although it seems to have been technically successful both in lifting capability and speed records for rotorcraft, the tip jets made it unacceptably noisy at takeoff and low altitude, precisely where noise was most objectionable.

I wonder if bleed air alone could work nowadays (given higher pressure ratio turbines) to reduce the tip jet noise.

The CH-53 uses 2 jet engines to power one rotating wing.

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