Twin Engines. Front and back.

[Dass.Kapital]

Just a question.

So...other than inter war flying boat designs. One fighter from the WW II that comes to mind and a Cesna.

Why hasn't pusher/puller piston engined aircraft seen more use/development in a 'twin' or tandem' setting?
Much cheers to all.

 

[BAROBA]

The main problem with pushers is that the propeller can hit the ground during landing and take-off, which would wreck the pusher engine. So it has to have high rear-legs,and its nose low(er) to the ground. but with two engines you need also a high frontwheel to keep the front-propeller from hitting the ground.That could be one reason.
Another one could be vibrations and shaking of the plane. Every plane vibrates and shakes when the engine is running, 2 engines would add more trouble or less. Because vibrations could strengthen eachother or cancel eachother, there is no way of knowing, also engines can run on different speeds and powersettings. Some settings give a smooth ride, others will shake the plane into pieces.
There could be other reasons too, I am not a aeroplane builder

Still I like pusher-puller designs, they look powerful and fast.

Cheers,

Rob

 

[Sundog]

Another reason, to add to what BAROBA said, is the rear pusher propeller is also more likely to be hit by FOD/Debris kicked up by the tires.

Some other reasons are packaging. Such a configuration typically limits fuselage size due to having to maintain the cg location. Also, most of these configurations are of a twin boom type to carry the tail loads, which generally leads to more drag and more weight when compared to a conventional twin. That means more cost, and when you consider many twin engine aircraft are just variants of single engine aircraft, you would be entering the market at a much higher price margin than your competition.

I would say you usually don't see such configurations because they aren't cost competitive, except in the off chance that they are designed for a specific mission for which a standard configuration won't meet the mission requirements.

 

[AeroFranz]

all of the above plus cooling. The pusher engine is harder to cool effectively.

 

[Jemiba]

The main problem with pushers is that the propeller can hit the ground during landing and take-off, which would wreck the pusher engine.

Tandem engines not necessarily means, that the thrust lines are exactly the same, but that of the pusher engine
often is a bit higher, than of the tractor engine, so alleviating the problems with the landing gear.
Biggest problem, I think is efficient cooling for the rear engine, as Franz said.

 

[Dass.Kapital]

*Bows*

Thank you al for the replies.

So...what causes the cooling problems? The fact that there's 'heat' being washed into them from the front engine?

Much cheers to all.

 

[Jemiba]

I think, it's more difficult to bring enough cooling air to the rear, than to the front engine, where you can simply
use the pressure on the frontal area.

 

[LowObservable]

You need some kind of cooling scoop, and you also lose the effect of slipstream immediately behind the propeller, assuming that you have an air-cooled engine. The Do335 was liquid-cooled, with the neat annular radiator on the front engine and a P-51-type arrangement for the aft one.

In a non-twin-boom design, CG concerns tend to result in a short tail arm and hence larger surfaces.

For the Do355, emergency escape was a bit of an issue since the rear prop could act as a Cuisinart. It had an ejection seat plus det cord to blow off the tail and the aft propeller.

Nonetheless, the 335 was one of the fastest propeller aircraft of the war, and certainly held the record for speed with one engine inoperative.

Rutan considered push-pull for the Pond Racer (having been a big advocate of that configuration, with the Defiant and Voyager) but realized that many Reno accidents had started with an engine failure that coated the windshield with oil and made a safe landing impossible.

I wonder how many engine-out recoveries have been made by NG-IAI Hunter UAVs? More OEI recoveries than with Predators, I would guess...

 

[pathology_doc]

For the Do355, emergency escape was a bit of an issue since the rear prop could act as a Cuisinart.

Whrrrrr, sliced bratwurst. "Oh he got out, Mein Frau, but..."


Mind you, it's not just the pusher prop that could kill you. Didn't Hans-Joachim Marseille die as a result of whacking into the tail of his (conventional) fighter as he egressed?

 

[GTX]

I think it was in Captain Eric Brown's book 'Wings on my sleeve' that the Do335 ejection system was described as a 5 stage process. The first stage blew the rear propellor of the plane, the second blew off the upper verticle stabiliser. The seat was then 'primed', then the canopy was ejected. Brown also wrote that he heard a story that when the system was first used the pilot who had ejected was found dead with both arms ripped off. The second pilot to eject was also found dead with one arm ripped off. It turned out that when the pilot grabbed the two handles to eject the canopy and pulled back the canopy was ripped off by the wind so fast the pilot couldn't let go and lost his arms!!