WI: 'push-pull' aircraft introduced in ww2 airforces

There was several attempts to produce aircraft where half of the horsepower would've been pulling the aircraft, and other half was supposed to push it. Like the Fokker D.XXIII, Do 18/26/335, Marton XV, Short Singapore; the flying boats listed saw actual service.
So, for the sake of discussion, lets asume that some if not all of the major air forces introduce a 'push-pull' combat aircraft on large scale, from late 1930s on. What roles should've been tailored for, what to cancel instead, who should've benfitted the most? For what roles and/or countries it would've been a bad bet?
 

Driftless

Donor
Do.335 "Pfeil" should have been hot stuff, had it been available earlier AND in greater numbers. It had good performance characteristics from the layout: very high speed through big horsepower and limited drag; limited/no control impact from engine torque; decent control. They even put in an ejection seat to eliminate the fear of bailing out into a whirling prop.

That should have been a great interceptor.
 

Deleted member 1487

Do.335 "Pfeil" should have been hot stuff, had it been available earlier AND in greater numbers. It had good performance characteristics from the layout: very high speed through big horsepower and limited drag; limited/no control impact from engine torque; decent control. They even put in an ejection seat to eliminate the fear of bailing out into a whirling prop.

That should have been a great interceptor.
It has its own issues. The thing is the technical developments that made it possible were only available in 1945 after extensive development. According to Eric Brown, the famous British test pilot, it was a difficult aircraft to fly, had a nasty reputation among test pilots (the ejection system routinely tore both arms off the pilots, killing them in the process), and it had serviceability issues. While it looked great on paper, it wasn't exactly something that had promise; plus it was developed as a back up in case jet engine developments didn't pay off.

To answer OP the Germans could have made the Do26 as their primary naval long range recon aircraft instead of the Fw200, as it could even carry some bombs, had diesel engines, and was longer range than anything they had IOTL and very fuel efficient. It was pretty ideal for the role and didn't require expensive avgas.

Another option would be a push-pull version of the He177 for strategic bombing. That was suggested for the Me264. I don't see why it wouldn't have worked with either 4 Jumo 211s/213s or 4 DB601/5s or 603s. I don't really know about Allied projects, so I can't really comment on those options.

oxxygino-me-264-pp-3view.jpg
 
I've posted this on another board, a bomber/heavy fighter as a next-gen Dornier after the Do 17. Uses two Jumo 211 engines (though the intake is on the wrong side), wing area ~45 sq m. (parts for the pic are from Do 217 and Do 335)

dornierssss top 800 px.jpg
 
Does anybody knows if there has ever been a (more or less) proper evaluation on the efficiency of the 'push-pull' configuration, especially when combined in a common nacelle as shown in the 'what if' wiking has shown above ?

I would/could assume, that the turbulences of the pull-component might have quite some impact on the efficiency of the push-component of such a combination.

... as well as on the aerodynamics of the wing, as the airflow might also be altered.
 
I'm not sure for the 4-engined craft.
Two engined - single-seater Do 335 with DB 603A was much faster than Me 410 with same engines, by some 100-140 km/h; even the 'humpback' night-fighter two-seaters with 'antlers' and flame dampers were faster by 60-70 km/h than the day fighter Me 410.
 

Deleted member 1487

Does anybody knows if there has ever been a (more or less) proper evaluation on the efficiency of the 'push-pull' configuration, especially when combined in a common nacelle as shown in the 'what if' wiking has shown above ?

I would/could assume, that the turbulences of the pull-component might have quite some impact on the efficiency of the push-component of such a combination.

... as well as on the aerodynamics of the wing, as the airflow might also be altered.
The Do26 was a four engine aircraft that did fly and fly well for its role.
 
True, I just wonder, why this concept hasn't been used more widespread.

On paper it offers the possibility to double the power output by keeping the smaller airframe, smaller wing, aka without adding much of drag.

What - if there were/are any, beside 'common custom' - were the drawbacks ?
The only one I can think of right now :
danger of the 'pushing' airscrew hitting the ground, what could be countered by tripod landing gear and pilots training to start and land with lesser 'nose-up', more nose down as well as starting more level ground than hard pulling upwards.

... and ofc : 'if the others don't used it, it can't be of good. So I don't use it either:'
 
Quite a big one - engines in the wings mean that the airflow is blown over the wings, giving much better low speed characteristics. You can also get away with a much lighter wing structure - the wing is producing lift along it's length, if the engines are in the fuselage then the wing spar needs to be able to support the weight of engines and fuselage at the root. If in the wings, the root only needs to carry the fuselage.
load.jpg

The better you can balance lift and weight, the less weight you need to put into the structure.

The only real benefit from tandem engines is roll rate, which is critical in a fighter but not really of importance in a heavy aircraft.
 
Dornier J, 18 and 26 flying boats had push-me-pull-you propellers.
Their primary motive was mounting propellers above how waves. A secondary goal was minimizing control problems with only one engine running.
Most subsequent flying boats had tractor propellers.

As for criticisms of the Dornier 335 Pfeil'e ejection seat .... everyone's first attempt at ejection seats was crude .... everyone's Mark I ejection seats injured pilots. All the refinements (mortars, rockets, belt retractors, Spurs, face curtains, side curtains, pilot chutes, slug guns, reefing ropes, quarter bags, spreader guns, sliders, automatic activation devices, survival kits, automatically-inflating life-rafts, integral oxygen bottles, etc.) of ejection seats were written in blood.
 
To the original question: As push-pull aircraft are basically fast twin-engined aircraft, albeit with some aerodynamical tweaks, they would get the roles traditionally occupied by fast twins: heavy fighter, long-range fighter and light bomber. Although it may be interesting to speculate about a push-pull version of the Do-17 or Ju-88, there would be a lot of considerations making the design impractical, like the rear engine and driveshaft competing for space with the bomb bay and the gunners field of fire being impeded by the spinning props fore and aft.

Also word is still out about how two engines in push-pull configuration would fare compared to two engines coupled together like in the famous Heinkel 177, the infamous Koolhoven FK55 or the Douglass B-42. Or how they would fare against simply one very powerful engine.
 
Quite a big one - engines in the wings mean that the airflow is blown over the wings, giving much better low speed characteristics. You can also get away with a much lighter wing structure - the wing is producing lift along it's length, if the engines are in the fuselage then the wing spar needs to be able to support the weight of engines and fuselage at the root. If in the wings, the root only needs to carry the fuselage.
The better you can balance lift and weight, the less weight you need to put into the structure.

The only real benefit from tandem engines is roll rate, which is critical in a fighter but not really of importance in a heavy aircraft.

The airflow is still being pushed over the wings with a push-pull configuration, granted just by one prop instead of two. On the 'classic twin', there is a question of how much lift was lost due to the nacelles, not an issue for the push-pull.
One of the advantages is that there is no need to come out with handed engines to cancel out the torque. Engine-out situation is less problematic, there is no haste (= easy for the pilot to make mistake) to go through multi-item procedure when in enemy-held airspace or during take off and landing.
The weight of the wing for the push-pull is overblown, eg. the wing of P-47D-25 (lifting the fuselage containing the heavy R-2800, turbo, 370 gals of fuel, obvously the pilot, among other stuff) was lighter by 25% than of the P-38J, 35% lighter than of the DH Hornet I.
Real benefit is smaller drag, as seen in comparison between Me 410 and Do 335. The 'venturi effect' that accelerates the local airflow due to having fuselage and engines close by is avoided, a thing that plagued P-38:

38dive3.JPG



To the original question: As push-pull aircraft are basically fast twin-engined aircraft, albeit with some aerodynamical tweaks, they would get the roles traditionally occupied by fast twins: heavy fighter, long-range fighter and light bomber. Although it may be interesting to speculate about a push-pull version of the Do-17 or Ju-88, there would be a lot of considerations making the design impractical, like the rear engine and driveshaft competing for space with the bomb bay and the gunners field of fire being impeded by the spinning props fore and aft.

Also word is still out about how two engines in push-pull configuration would fare compared to two engines coupled together like in the famous Heinkel 177, the infamous Koolhoven FK55 or the Douglass B-42. Or how they would fare against simply one very powerful engine.

In case people are producing a push-pull bomber, rear field of fire is non-issue, do to the bomber having a speed of the current fighter. Frontal fire is same as with classic fighters, again no problems.
Quirk with many countries is that there was no very powerful engine around. Jumo 222, M-71, V-3420, R-3350, Vulture, a host of Japanese engines were plagued with smaller or bigger problems, and a push-pull can come in handy there. Eg. the fighter with 2 of the best Kestrels has alsmost as much of power of what early Sabre did at 15000 ft, some 5 years earlier, and on 87 oct fuel.
 

Deleted member 1487

In case people are producing a push-pull bomber, rear field of fire is non-issue, do to the bomber having a speed of the current fighter. Frontal fire is same as with classic fighters, again no problems.
Quirk with many countries is that there was no very powerful engine around. Jumo 222, M-71, V-3420, R-3350, Vulture, a host of Japanese engines were plagued with smaller or bigger problems, and a push-pull can come in handy there. Eg. the fighter with 2 of the best Kestrels has alsmost as much of power of what early Sabre did at 15000 ft, some 5 years earlier, and on 87 oct fuel.
With something like the strategic bombing with a push-pull layout, that would be on the wings, so there wouldn't be a field of fire issue, check the Me264 layout above.
 
DH Hornet was also with thinner wing, 14.37% root thickness, vs. 16% on the P-38. Thinner wing delays the onset of compressibility better than thick wing, in case simlar or same wing profiles' design is used. It would've been great if someone has more data about the Hornet's wing aerodynamic properties.
Hmm - perhaps the radiators helped a bit with situation, 'swallowing'/redirecting plenty of airflow that would've been going above the wing otherwise?
 
A quick glance at here brings 18% root thickness for both. Do 217 seems to be using NACA 22XX series of airfoils (like Spitfire or P-36/40, but obviously cosiderably thicker in relative and especially absolute terms), the Do 335 used modified NACA 23XXX series (not unlike plethora of ww2 aircraft).
We can recall that eg. F4U-4 and F8F-2 were good for ~450 mph (~725 km/h) with their thick, NACA 23018 wing, while experiencing far less of compressibility problems than P-38 with a bit thinner NACA 23016 profile. (all profiles in ths post are for root)
 
I can recall that the F8F Bearcat that goes by the name Rare Bear is listed as having a root thickness chord ratio of 15, and some sources list the Corsair as having a 2415 at the root. Still, a better comparison might be the F7F Tigercat, which also could suffer from venturi effect.
 
SAC for the F4U-4 lists NACA 23018 at root, thinning out to 9% at the tip (last page): link
Also: pic
SAC for XF4U-3: link
F8U-2 SAC (23018 thinning out to 9%): link

Unless someone engineered and produced a new set of wings for the Rare Bear, it will still have stock wing profile.

eta: F7F was with NACA 23015 (root): link
 
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