Why did mixing engine types never take off ?

Im wondering why the idea of a mixed engine plane was never used in combat ? I would have thought with jets being so new at the end of war that more countries would have made either a mixed fighter like the Ryan fireball or a bomber like the B-36 something combing early jet tech with high HP piston engines to increase speed and payload curious to see what people say

Now for WW II we can 'claim' that the piston engines were close to the turbo prop curve.
The orange and green curves didn't exist (n service engines).
We will go with the red turbojet curve, adjust a bit if needed.

Basically a mixed propulsion aircraft could not use both propulsion systems to very food efficiency at the same time.

Altitude will have some effect on this which is why the B-36 worked, kind of.

What complicates things is that the turbo jet had a much better power to weight ratio than the piston engine so it could provide a useful "booster" engine function.
However the turbo jet engines of the time got truly horrendous fuel consumption so you wanted to use them for very short periods of time.

For bombers or transport planes perhaps the "booster" engines did make sense. Even a B-29 could use between 400-800 gallons of fuel just climbing to cruise attitude depending on weight and perhaps a couple of "booster" engines and the fuel for them might have weighed less than running the piston engines for required time.
Most piston planes climbed at around 200mph (or less) where the turbo jet was horribly inefficient.
In single seat fighters the weight penalty of the "booster" engine gets harder to put up with since the proportion of aircraft weight for the power plant/s is a much higher percentage than the with percentage in a bomber or transport.
Any once the fighter is doing much over 500mph the prop is just slowing the airplane down.

VA5124 said:

Im wondering why the idea of a mixed engine plane was never used in combat ? I would have thought with jets being so new at the end of war that more countries would have made either a mixed fighter like the Ryan fireball or a bomber like the B-36 something combing early jet tech with high HP piston engines to increase speed and payload curious to see what people say

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I would point out the B-36 started with only piston engines. It wasn't until the B-36D that jet engines were added.

There was also the dual propulsion Lockheed PV-2 Neptune and the Fairchild C-123 Provider. C-123Ks were used in Vietnam.

There were jet pods used on C-119s. I believe in India.
But I think this was to help with hot and high air fields.

The Martin Mercator, though a low production aircraft, did have integral jet engines behind the radial engines, as I believe a version of the Shackleton. The Mercator had the highest loss rate per airframe manufactured during the cold war. 22% if I remember correctly. Tell those guys they weren't in combat, snooping along the borders and such of communist countries.

The Martin P4M Mercator was designed from the start for two recips and two jets in the same nacelles.

I'd imagine logistics and budget would have something to do with it as well. Different engines on one airframe would require two supply-chains, etc.

The Afro Shackleton MR3 had two2,500lb thrust Viper engine in addition to the Griffons.

Quite a few of the combo jet/piston types were "jet-assisted" for take-off performance or for enhanced performance in attack phase of flight for some bombers. The low-ish extra weight of the of the jet engines was a penalty worth carrying if they enabled a certain enhancement in a corner of the flight envelope. This was still true for quite a few piston aircraft that operated well into the "jet-age".

Eng

muskeg13 said:

There was also the dual propulsion Lockheed PV-2 Neptune and the Fairchild C-123 Provider. C-123Ks were used in Vietnam.

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I made my first parachute jump out of a C-123, I seem to remember it was the very last C-123 in USAF inventory at the time (May 1978). While I was wound up about making my first parachute jump, I was never so glad to get out of an aircraft as I was that raggedy-ass C-123. I made a lot of jumps aftewards (C-130s and C-141s, Hueys and Chinooks), but those things were crap. Everything else was a better ride.

When talking about combining powerplant to achieve a faster outcome, i.e. adding rocket engines to jet powered aircraft, such as the Saunders Roe SR.53, or jet engines to piston powered aircraft, such as the Ryan Fireball, the answer is simple, but for a few different reasons. In both cases better performance was required from what was the status quo, or what conventional i.e. what was in general use at the time, engines could produce. Adding rocket power to jet powered aircraft was experimented with by many companies during the late 1940s and 50s simply because the jet engines at the time couldn't produce the climb rates and thrust to reach altitudes required for expected successful interception of bomber aircraft. Two views of the Saunders Roe SR.53, note the stepped rear showing the different exhaust ports for its jet and rocket motor, an Armstrong Siddeley Viper and de Havilland Spectre respectively.

DSC_0331

DSC_0332

The problem was that to power your aircraft with two types of engine requires two disparate types of propellant, which means that your aircraft is carrying a given volume (and weight) of fuel but without the benefits of adding any extra endurance to its flight profile. Rocket motors were at the time fuelled by exotic chemicals in some cases, that didn't mix particularly well with normal methods of storage, which required special materials, which added weight and complexity to the designs. Okay if your aircraft is a bomber or big transport, a bit of a problem if you're developing a single-seat fighter.

The advance of technology eventually ended the age of mixed propulsion; the aforementioned SR.53 and its in service derivation the SR.177 which was never built, were overtaken in performance by the brute force of jets like the English Electric Lightning, which didn't need mixed propulsion to achieve the kind of performance expected of mixed propulsion aircraft. A model of the cancelled SR.177. The Luftwaffe was interested in this aircraft at one stage, but eventually bought F-104s instead.

SR.177 ii

The British developed a range of added thrust rocket engines, such as the de Havilland Sprite, fitted to de Havilland Comet airliners to improve take-off thrust in hot and high conditions, and the Napier Double Scorpion, fitted to a Canberra to achieve a record altitude at the time. Another project was the Avro 720 mixed propulsion interceptor that was developed based on German research into the Me 163 and the Rocket Research Establishment's development of HTP as a rocket oxidiser based on Helmut Walther's work in Hamburg.

Napier Double Scorpion rocket motor powered by HTP and kerosene.

RAFM 100

glennasher said:

I made my first parachute jump out of a C-123, I seem to remember it was the very last C-123 in USAF inventory at the time (May 1978). While I was wound up about making my first parachute jump, I was never so glad to get out of an aircraft as I was that raggedy-ass C-123. I made a lot of jumps aftewards (C-130s and C-141s, Hueys and Chinooks), but those things were crap. Everything else was a better ride.

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Just pointing out historical dual propulsion combat use per the thread, never said I was a C-123 fan, which I always thought was a poor excuse for a C-130. The USAF used C-123s for mosquito control in the vicinity of Langley AFB, locally known as Langley Field, in the 1960s and 1970s, soon after their Agent Orange mission was completed.

For a good indicator of why the mixed engine types didn't really take off compare the Ryan Fireball with a Grumman F8F-1.
Both carried four .50 cal guns. The combined weight of the Fireball's engines was very close to the the Bearcat.
The Fireball actually had no performance advantage, in large part due to the compromises made for the dual engines.

Many of the 2/4 engine types listed here were late model conversions of twin engine planes.
The C-123 didn't get jets until the J model (10 built)

and the much more common K model
The Lockheed Neptune didn't get jets until the P2V-7 version

only a few were designed to use mixed propulsion.

VA5124 said:

Im wondering why the idea of a mixed engine plane was never used in combat ?

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The Avro Lancaster had two engine types.

4 x Rolls Royce Merlin
1 x Triumph 500cc Square Barrel APU

Thank you everyone it was just something i was curious about. Now i understand not only was performence not changed enough to make it worth it . But now i also understand the fuel and parts probelms you would have.

Shortround6 said:

The C-123 didn't get jets until the J model (10 built)

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It's interesting to note the two different jet engine configs on the C-123. Two different examples in Seoul modelling the engine location...

C-123J with the Fairchild J-44 jets

DSC_8579

C-123K with the GE J-85 jets.

C-123 i

Admiral Beez said:

The Avro Lancaster had two engine types.

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The list of aircraft with APUs is massive... And let's be clear, APUs are not a means of propulsion. They are there to generate power for auxiliary systems on the ground. Not many APUs can be/were used in the air. The majority of modern airliners have APUs that only work on the ground when the main engines are not generating AC power.

DSC_8107

Mixed power-plant warplanes.
Post-war there are many but the one that immediately springs to mind is the North American Savage.