Twin-engined aircraft

[AnotherFSO]

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?

[megan]

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.org-vbulletin/600x400/1700968951_b7bd8014f40f103d9927becf0049de6547534a73.jpeg

[treadigraph]

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

https://en.m.wikipedia.org/wiki/Gulfstream_American_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.

[megan]

Piston in the nose, jet in tail.

Curtiss XF15C-1, only three built

https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/300x164/curtiss_xf15c_1_730330b01492a28f336599a611980b6504269cc2.jpg

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

https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/300x233/ryan_fr_1_fireball_vf_66_north_island_1945_f6ca402498dd27d0e 56192ea1cc2c0cc2c515002.jpg

[Planemike]

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 !!!

[treadigraph]

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

[chevvron]

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.

[sycamore]

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

[DaveReidUK]

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

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

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

[sycamore]

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

[dixi188]

The OP did say "Twin Engined".

[DaveReidUK]

The OP did say "Twin Engined".

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

[Self loading bear]

The OP did say "Twin Engined".
In that case:
Lockheed P2 Neptune Twin piston & twin jet

[WHBM]

I suppose that technically the counter rotating Twin Coms and Navajos have different engines!
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) ?

[dixi188]

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.

[treadigraph]

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) ?
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,

[BSD]

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.

[treadigraph]

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.

[megan]

I seem to recall hearing that the handed Allisons in the P-38 were made to rotate in opposite directionTo 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.org-vbulletin/1200x975/allisonv_42e62308489d0ef4cead2beab958d560656cabd3.jpg
https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/1200x951/allisonv1_9b08d58c99b089809ad284dae33ba9332ae6d444.jpg

[DogTailRed2]

The He177 was a four engine, twin prop aircraft.

[DuncanDoenitz]

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) ?
Nope. The TIO-540 series powering the NavajoCR/Chieftain is a direct-drive engine without a reduction gearbox, so the whole engine, and its magneto and accessories, rotate the opposite way, and the redesigned engine becomes an LTIO-xxx (Left-hand rotation, Turbocharged, fuel Injection, horizontally Opposed.

The standard engine, like most American powerplants, has what is termed Right-Hand Rotation (clockwise, upper propeller blade moving to the right, as seen from behind). Of course, when the airframe designer decides to equip contra-rotating engines, usually to address the problems of "critical" engine failure, it is the right-installed engine which undergoes the change. Hence, the left-side engine of a Chieftain has right-hand rotation, and the right-side engine has left rotation, and a left-hand prop.

[AnotherFSO]

Thank you very much to all responders. And thread drifts are welcome -- they're what bring forth other interesting topics and tidbits.

[DaveReidUK]

Of course, when the airframe designer decides to equip contra-rotating engines, usually to address the problems of "critical" engine failure, it is the right-installed engine which undergoes the change. Hence, the left-side engine of a Chieftain has right-hand rotation, and the right-side engine has left rotation, and a left-hand prop.

With the exception (sole, I think) of the 700P variant of the Aerostar, which had outward-rotating props and so the LTSIO-540 is the left engine.

[DHfan]

Using criteria previously mentioned, the Westland Whirlwind must count.
The Rolls-Royce Peregrines were designed from the outset to be handed. Not just with an idler gear, the whole engine rotated in the opposite direction.

Having it tried with the Peregrine, Rolls-Royce concluded it was a b***** stupid idea and never did it again.

[treadigraph]

With the A400 isn't it something like the inboard props rotate top blade outwards and the outboard props rotate top blade inwards? Noisy bugger whatever...

Good thread indeed and educational!

[dixi188]

A400M props are "CACA" ie. Clockwise, Anticlockwise, Clockwise, Anticlockwise, when viewed from behind.
In French caca means pooh!

[Sue Vêtements]

If you can include the B36, then you can also include The Avro Lancastrian

https://planehistoria.com/wp-content/uploads/2022/11/8812225299_66018a6ef1_o.jpg

[Sue Vêtements]

Of course, when the airframe designer decides to equip contra-rotating engines, usually to address the problems of "critical" engine failure, it is the right-installed engine which undergoes the change.

Didn't the P38 have two critical engines?

[B2N2]

Didn't the P38 have two critical engines?

Yes and no.
Both engines turning outward gives the stronger “P-factor” slipstream on the side of the rudder deflection in case of an engine out.
As far as I recall.

[Allan Lupton]

If you can include the B36, then you can also include The Avro Lancastrian


The B36 was a production aeroplane but the mixed-power Lancastrian was a one-off conversion, to be an FTB for the Ghost engine

[EXDAC]

Didn't the P38 have two critical engines?

What definiition of "critical engine" would allow that to be true?

FAA definition - "Critical engine means the engine whose failure would most adversely affect the performance or handling qualities of an aircraft."

The definintion requires loss of one engine to have a more adverse effect than loss of the other.

[treadigraph]

The C-123K and KC-97L also carried a pair of turbojets to boost take off performance.

[Discorde]

There's a piccie of an Indian Air Force C-119G sporting a dorsal Orpheus (https://www.steemrok.com/airpic/6308/aug63.html) on the cover of Air Pictorial, August '63.

[Self loading bear]

Medic 022 and Nord 1500 Griffon II both powered with turbo jet and ram jet.

[DaveReidUK]

No end of types with auxiliary jets, and then there's JATO/RATO ...

[pax britanica]

Trident 3
3 proper engines and an oversize and unbelievably noisy APU boost engine or must t be a mix of jet and prop.


Also from the real past the Fairey Rotadyne, another fuel to noise unit
Two RR Tynes on the wings-such as theywere- and ducted air sinning the monster rotor

[DaveReidUK]

Trident 3
3 proper engines and an oversize and unbelievably noisy APU boost engine

If you're going to count APUs as well, then the T3 had 5 engines (as did most 4-holers).

[dixi188]

If you're going to count APUs as well, then the T3 had 5 engines (as did most 4-holers).
Not sure about the 4 holers.
B707/720, DC-8, CV880/990, VC-10, DH Comet, didn't have APUs.
4 holers with APUs - B747, A340, any others?
OK, the RAF VC-10s did and I saw a VIP 707 with one.
There was a 5 engined Vulcan.

[eckhard]

I believe the TWA Fairchild was called “Ontos”.

[Captain Dart]

I flew the A340-200 and -300. These aircraft were considered to have four hair driers and one APU.

[rigpiggy]

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) ?
Same engine block, different camshaft and other accessories to allow it to tur. Backswards

[WHBM]

Same engine block, different camshaft and other accessories to allow it to turn. backwards
Thank you, I've learned something there (you'll be glad to know I'm not a licenced powerplant engineer for the relevant types !). It does seem however the more surprising and complex approach, different spares needed for each side, ever the risk of some procedure being applied wrongly, etc.

[Jhieminga]

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?
Surprised no-one has mentioned the Rutan Model 76 Voyager yet. Push-pull design with an O-240 at the front and an IOL-200 aft. It was initially flown with two O-235s that had received a 'dirty rag overhaul' as in, a quick wipe before bolting them on. For the world flight they needed two slightly different designs. The IOL-200 was supposed to run for the entire flight, with the O-240 only used for take-off and the first couple of days until the weight had gone down enough to shut it down and maintain altitude on the rear engine only.

[treadigraph]

Surprised no-one has mentioned the Rutan Model

Post #3 ;). Only in passing though...

[dixi188]

Just remembered, BAe 146/RJ, 4 APUs and a Hair drier.

[sycamore]

I remember seeing a 4 engined Catalina parked on the `civvy` terminal at Albuquerque..Looked like big Lycoming 6`s outboard of each P& W....

[treadigraph]

I remember seeing a 4 engined Catalina parked on the `civvy` terminal at Albuquerque..Looked like big Lycoming 6`s outboard of each P& W....
That was the Bird Innovator, recall seeing it at Titusville 40 years ago. Must have sounded great taking off!

[Jhieminga]

Post #3 ;). Only in passing though...
My apologies!

[dduxbury310]

DHfan (post 24, 27th November) states that the RR Peregrine was designed to have "handed" versions for the Westland Whirlwind fighter. This may well have been the case, but by the time these aircraft entered front-line service in about mid-1940, Peregrines were all of one kind, with all engines rotating in same direction - see the close up views in the Pathe movie "Whirlwind Fighter Squadron" (1943). Pilots' notes make no mention of handed engines/propellers. Don't know how authentic the sound on latter part of this movie is, but it is very exciting!

[treadigraph]

My apologies!
none needed! :)

[Jhieminga]

That was the Bird Innovator, recall seeing it at Titusville 40 years ago. Must have sounded great taking off!
Currently undergoing long-term restoration, it has been converted back into a two-engined flying boat: Consolidated Catalina/Canso Registry - A Warbirds Resource Group Site (http://www.warbirdregistry.org/pbyregistry/pby-rcaf9746.html) and https://en.wikipedia.org/wiki/Bird_Innovator

The interesting answers to the original question are types where the two different engines have two differing specifications because of a quirk in operation or the role envisioned for it. Mixed-powerplant types such as the Ryan Fireball and Saunders-Roe SR.53 have been mentioned before. Most of the times, having more than one powerplant is because you want redundancy and in that case having two similar engines makes sense from a spares/handling/economy point of view. Having 'handed' engines is just a way of dealing with less-than-ideal one engine out performance and is not related to the mission or role if you ask me.

Looking at civil types, the two Rutan models discussed are the only ones I can think of that started with two different engine types. Looking a bit beyond that, the airshow performers such as the Screaming Sasquatch (https://eaavintage.org/the-screamin-sasquatch/), the Yak-110 (https://www.fargoairsho.com/yak-110) and the Rich Goodwin Pitts (https://www.richgoodwinairshows.com/) are conversions (the last two are three-engined types if we're being picky) that use two different engine types.

[DHfan]

DHfan (post 24, 27th November) states that the RR Peregrine was designed to have "handed" versions for the Westland Whirlwind fighter. This may well have been the case, but by the time these aircraft entered front-line service in about mid-1940, Peregrines were all of one kind, with all engines rotating in same direction - see the close up views in the Pathe movie "Whirlwind Fighter Squadron" (1943). Pilots' notes make no mention of handed engines/propellers. Don't know how authentic the sound on latter part of this movie is, but it is very exciting!

Putnam's Westland Aircraft since 1915 states that two early prototypes were flown for comparison, one with handed engines and one with both rotating the same way. There was no noticeable difference in handling, which I'm sure delighted R-R, but it doesn't say when the handed engines were officially cancelled.

[dduxbury310]

Thanks for clarrification DHfan.

[megan]

The reason I often see mentioned for the cancellation of the handed Peregrine was the doubling up of some spares, no doubt the handling issue noted by DHfan, was the prime reason, the Whirlwind being the engines only application.

The handed Peregrines were installed in one of the two Gloster F9/37 (https://en.wikipedia.org/wiki/Gloster_F9/37)prototypes.


https://cimg3.ibsrv.net/gimg/pprune.org-vbulletin/1196x320/pere_d15fa92f89d7fcfcc0c76846f9be5ca26310826f.png

[megan]

Originally Posted by Sue Vêtements
Didn't the P38 have two critical engines?Yes and no.
Both engines turning outward gives the stronger “P-factor” slipstream on the side of the rudder deflection in case of an engine out.
As far as I recall.The reason the P-38 had the prop rotation it did was to reduce the pitching moment variation with power variation, aim being to provide better gun aiming.

As with many of the high powered twins of the day (Mosquito) the safety speed was far higher than the take off speed so an engine failure during the period of airborne acceleration to the safety speed required a power reduction on the good engine in order to maintain directional control.


https://cimg4.ibsrv.net/gimg/pprune.org-vbulletin/1304x1678/p_38001_4b9dec1414524d46ea1ae2f7a8b354415cd7e439.jpg

[tdracer]

Back when Pratt was developing the PW4000/94" (767/747-400), they used the very first 767 (VA001) as a flying test bed - PW4000 on one side, JT9D-7R4 on the other.
Very nearly ended in tears during an early test flight - at about 50 ft. during TO, the PW4000 surged big time - the PF calmly reached over and pulled both thrust levers to idle :eek:
The other pilot quickly slammed the levers back up - the JT9D slowly pulling the aircraft skyward while the PW4000 kept surging away.
The PF is question was later removed from "Experimental Flight Test"...

[Self loading bear]

Bristol Brabazon did have all the same engines but twinned in an unusual setup of 4x 2 engine each under 32degree angle of the axle of the counter rotating propellers.
https://cimg4.ibsrv.net/gimg/pprune.org-vbulletin/960x640/img_9130_f89d9e5727fb570256a120354b7240a984dcd96f.jpeg