S/E lightweight Pusher Do 335.

[Shortround6]

Problems with a single engine pusher of the type of the Do 335.

1. the extension shaft adds weight and complication.
2. as part of the above the rear fuselage has to be stiff enough to to keep the propeller in line, adding weight. P-39 was about 100lb heavier than a front engine fighter would have been.
3. cooling, a problem on the real Do 335, engines need more than just radiators and oil coolers. Many engines needed cool airflow over the spark plugs, ignition components and accessories.
4. The CG issue. And part of the reason behind the configuration of the US planes. XP-54 has the engine AND prop near the CG but has the guns and nose balanced by the booms and tail surfaces. XP-55:

Is not only a canard but uses a swept wing to keep the engine weight near the center of lift of the wing. Armament is also four .50 cal guns with just 200rpg. P-39s were not to flown without guns/ammo unless ballasted.

XP-56 used a short extension shaft, note exhaust outlets.

to keep engine near the center of lift.

4a. the above mentioned P-39 problem with guns/ammo. increasing the gun/ammo load may work as long as the ammo tanks are full. Firing off hundreds of pounds of ammo located a number of feet from the CG could lead to a dangerous handling airplane. Same with using the nose space for fuel.

5. the bail out problem.

Now some or all of these problems can be fixed with enough time and effort but what have you got at the end? anything really better than a tractor prop plane?

 

[l'Omnivore Sobriquet]

Take out the front engine and the nose will rise up and the tail will sit on the ground. Add armament to balance it out and you have half the power it had when it went fast and you're back to the same empty weight if the CG is in the same place.

Well no, the idea is to optain a lighter plane than the twin Do-335 of course. So let's repeat : Remove the front engine and replace it with front armour, pilot, and, somewhat more centered, big gun (most of it being behind the pilot), AND move the attachment of the wing accordingly ("and hopefully easely.")
THEN one has a balanced craft, lighter than the original twin.
With a different wing, lighter weight then yes I think that aeroplane contrary to the Do-335 would indeed have good rought field capacity. Especially if it keeps the original undercarriage, becoming oversized (though heavy.) (but that'd no obligation, something built with other serial produced parts would do. However height has to be maintained.)
Of course there remain the little space available between ground and the lower fin. The latter for rought employs has perhaps (?) to be strengthened. Take offs initially at low angle of attack, landings at low angle of attack. But different wing, different flaps... So why not ? [We are - at least I am - aiming at a lower but decent performer, for ground attack tank busting employ.]
Yes I think it can work. Let us remember also that tricycle configuration does NOT impair rough field operation, but actually eases it. The P-39 amply proved, at minimum to the French in North Africa (they used roads at times certainly, with P-63 I think.)
We get a plane that while being heavier than a Ta-152 is of course lighter than Do-335 with dedicated wing + armor + heavy gun. Should work within decent performances and overall behaviour.
Real drawback is ease of maintenance/change of the engine in that configuration. How did they do with the P-39 and P-63 ?

 

[wuzak]

The Do 335 had a tail bumper with strut in the lower tail fin. For landing it was recommended to touch down with this, before lowering the nose.

 

[Shortround6]

Well no, the idea is to optain a lighter plane than the twin Do-335 of course. So let's repeat : Remove the front engine and replace it with front armour, pilot, and, somewhat more centered, big gun (most of it being behind the pilot), AND move the attachment of the wing accordingly ("and hopefully easely.")
THEN one has a balanced craft, lighter than the original twin.
With a different wing, lighter weight then yes I think that aeroplane contrary to the Do-335 would indeed have good rought field capacity. Especially if it keeps the original undercarriage, becoming oversized (though heavy.) (but that'd no obligation, something built with other serial produced parts would do. However height has to be maintained.)
Of course there remain the little space available between ground and the lower fin. The latter for rought employs has perhaps (?) to be strengthened. Take offs initially at low angle of attack, landings at low angle of attack. But different wing, different flaps... So why not ? [We are - at least I am - aiming at a lower but decent performer, for ground attack tank busting employ.]
Yes I think it can work. Let us remember also that tricycle configuration does NOT impair rough field operation, but actually eases it. The P-39 amply proved, at minimum to the French in North Africa (they used roads at times certainly, with P-63 I think.)
We get a plane that while being heavier than a Ta-152 is of course lighter than Do-335 with dedicated wing + armor + heavy gun. Should work within decent performances and overall behaviour.
Real drawback is ease of maintenance/change of the engine in that configuration. How did they do with the P-39 and P-63 ?

Trying to save anything from the original Do 335 is probably more trouble than it is worth.

Trike gear works pretty well on rough fields because you have a wheel either just under the prop or the props between the wheels. Having a nose wheel and tail prop maybe asking for prop strikes. Or tail fin strikes.

Engine maintenance may be easier, you can sit/stand on the wing if it is moved back far enough. Changing is a little tougher as it has to come out the top rather than "off" the front but since you need a crane in either case the difference is?????

1750hp just isn't enough unless you shrink the plane considerably.

 

[swampyankee]

Why is the rear mounted (liquid-cooled) engine any more of a challenge to cool than a front mounted engine?

The engine compartment still has to be cooled.

 

[GrauGeist]

For what it's worth, the rear engine of the Do335 did have an arrangement for cooling via an air duct and there were no more prop-strikes with the existing model than there would be with a proposed single-engined airframe if the reinforced ventral tail assembly were left in place.

With the existing armament being relocated to the nose and additional armament being added, you'll probably have a good chance of keeping the CoG but without the benefit of the second engine, you're going to have a heck of a time moving all that mass.

 

[swampyankee]

To do a "single-engine" Do335, you start with a clean sheet of paper, and design a single-engined aircraft. I'm not a big fan of pushers, especially pushers where the engine is in the extreme tail, but, yes, it could be done. Doing that, Dornier would probably not elect a pusher design: putting the engine in front would make the entire design process much more straightforward.

 

[l'Omnivore Sobriquet]

Well my idea is precisely not to start with a clean sheet of paper, but make use of whatever is available in serie production (planned for 1945, if there's any worth.)
I'm not the author of this thread, just jumped on the opportunity to submit an old idea, as it fit the topic rather well.

Given an hypothetical large scale production of Do-335 (one cannot get around it in any 1945 lasting scenario), given the unique opportunity offered by the aft design of the 335 to mount forward of it one big gun of some kind and forward still an armoured cockpit to optain a 'cheap' single engined 'flying cannon' recip aircraft, given the probable need to replace the Henschel 129 by something somewhat better, given, whatever the 'lasting' scenario may be, dire urgency to act against ennemy troops and directly on battlefields, excluding any other revolutionnary wunderwaffe and restricting 'clean sheet design' to a minimum, we're having this.
In fact after some discussion here I pretend it is still a viable concept : but I reckonn I did not too well realise how heavy the thing would have to be for the power available, due to the size of the mendatory rear half of the Pfeil...
So, a lot of wing, so too small a top speed, not enought punch from the Db605 and weak general behaviour ?
Perhaps. Perhaps not.

I won't argue anymore than this anyway, being sure by know that I am not misunderstood. Interesting to submit see criticts rapidly focusing on the true weakness of the concept.

 

[GregP]

I think it is possible but extremely unlikely. As stated above, there haven't been any successful propeller pushers other than the SSAB J-21, which wasn't all that successful to start with.

Sounds like championing the layout just for the sake of doing it, not for any good reason for it. Sometimes I have done that with a radio control aircraft ... just for the sake of it. But those efforts only took maybe a week and some balsa wood, not thousands of man hours. Building a flying circular disk was fun, but I would not have pursued it if I had to come up with a reason that recommended it over a conventional layout.

For the pusher, the pros include centerline armament. The cons include CG issues, explosives on the rear of the aircraft, the penaly of an ejection seat, and no clear reason to DO it. And I seriously doubt the ability of the landing gear configuration on rough fields.

So while you may be able to build it, I see no reason to do so until the jet engine came along with sufficient thrust.

But it MIGHT work, who can say? I CAN say it never DID work in real life and was only adopted once, by SAAB, noted as being unconventional.

The only one that looked promising to me was the 1949 French Sud Ouest SO.8000 Narval, of which they built two that had a top speed of 454 mph. At the time jets were well pushing 700 mph and it never had a chance. It had a SNECMA 12H 02, which was a French copy of the Junkers Jumo 213. Again, not successful and not adopted.

 

[l'Omnivore Sobriquet]

The Narval was a distinguished failure. Very bad flight behaviour.

 

[GrauGeist]

The Japanese had a pusher that was in development late in the war. Late enough that hostilities ceased before it could start production.

It was the Kyushu J7W "Shinden" and was a canard designed pusher with a top speed of 469mph (750kph) and armed with four 30mm Type 5 cannon. It tested favorably, though it still had a few development issues such as a shaft vibration and prop flutter. Interestingly enough, it was powered by a Ha-43 radial engine.

While certainly nothing like the Do335, it did show quite a bit of promise for a pusher.

 

[GregP]

I have read that it was not proceded with, but never why. I figured it had more to do with the relative performance of jets than the airframe.

Thanks for the update on that.

It is possible the flight behavior could have been corrected, but it still would be 200+ mph slower than the jets. Once the Dassault Ouragan came out in 1952, it would have been tough for a propeller FIGHTER to gain any support. Maybe a COIN or ASW platform with a turboprop, but not a piston fighter. The Breguet 1050 Alize and the Morane-Saulnier MS 1500 come to mind. They were never inteded to compete with jet fighters, but rather to fill a specific role for which propellers were suited.

As far as I know, the J7W Shinden only flew twice or three times and the only pilot who flew it was glad to have gotten up and down without being killed. The vibrations were severe, though I'm also sure they COULD have been corrected given time and resources for it. The layout didn't really ever show any promise in real life since it never got out of the traffic patttern, but it DID get built and flown. It would have been interesting to continue the development post-war, but that was never going to happen.

I believe the only surviving J7W Shinden in in storage at the Smithsonian Museum in Building 7 of the Garber facility in Maryland.

 

[tyrodtom]

From what Wiki says, the Shinden had a total of 45 minutes flight time, and first flew on the 3rd of August 1945.
I was ordered into production before it's first test flight. But none were produced.
That's just a indication of how desperate the Japanese were, not how good the aircraft was.

 

[GregP]

It would be interesting to do a wind tunnel test today with what we know about aircraft behavior and see how well designed it was. I wonder about the general stability, spiral stability, behavior in a stall, and other flight characteristics of the J7W, particularly high speed behavior and behavior at altitude, say ... 35,000 feet, assuming the engine could get there. According to the data I have it had a planned ceiling of 40,570 feet (12 km).

And there was a rocket verison on the drawing board, the Mizuno Shinryu, intended as a suicide glider after the rockets burned out, but it was abandoned in favor of the Shinryu 2, which was intended as an interceptor and ground attack aircraft. None were built since hostilities ended before that happened.

 

[jim]

The configuration of 335 may have been useless to America and england but it was very interesting for germany.
Germany , because of lack of raw materials,was doomed to lose the engine power race. So it had to use other means to achieve aircrafts with competitive performance. The 335 configuration was an interesting idea for low drag
I believe it could have been developed to a useful trouble free design IF
a) development was concentrated on specific variants (night fighter,mosquito and rec interceptor ,high speed/attack bpmber,) with specific goals
b) RLM could decide in time what it wanted and could control the uncontrolled designers with all their endless new fantasy designs so development efforts and resources concentrate on 335
c) faster availability of 1750hp class engines

I dont believe Do 335A was too heavy. F7f tigercat was heavier , with only slightly more wing area and with no internal bomb bay as 335.
If less weight loss was needed, a good start would be the replacement of the 140kgr Mk103 30mm cannon with a third 40kgr Mg151/20
A better wing may also had helped

 

[GrauGeist]

Burt Rutan proved the Shinden's design was along the right track

 

[Shortround6]

The Do 335 may be an interesting design for a twin, one large fuselage but NO separate engine nacelles. Going back to one engine leaves it with no clear cut advantage over a traditional single engine aircraft and a number of engineering problems the tractor engine doesn't have.

By 1945 even the 37mm AA guns without tungsten cored ammo are of diminishing capability against Russian tanks and the 75mm is really too big for a 1750hp airplane leaving the 50mm gun as the only real choice and it may ( or may not?) have problems dealing with armor. Remember these gun armed planes are NOT diving at the tops of the tanks but firing only a little above horizontal.

 

[GregP]

Hi Jim,

The Do 335 was not too heavy. But is certainly was if you wanted to make that airframe into a single engine pusher with the same engine in the rear and replace the front engine with armament. The Tigercat was NEVER going to be a single engine anything. I daresay the Hornet wouldn't have performed veryw ell with only one engine either.

GrauGiest,

You won't find any fans of Burt Rutan's canards at the Planes of Fame among the volunteers. We've had 3 people killed in Rutan designs, one of which was a Long EZ. In the Acccident the canard departed from the plane in mid-air and it lawn darted. Turns out it is held on by two bolts. The other accident was the Pond Racer that had an engine failure with one of out best friends in it and the stopped prop could not be feathered. Might not be the fault of the Pond Racer ... might be the Electramotive Nissan V-6 engines, but the Pond Racer had so many issues it wasn't funny.

Friends don't let friends fly in planes with wings that can come off in-flight. These did. The design is such that is can happen to ANY EZ. Why take that risk?

 

[Shortround6]

Burt Rutan proved the Shinden's design was along the right track

Most of Rutan's designs use rather light engines in the rear with NO extended propshafts.

even the Beech Starship used a pair of engines that weigh considerable less than a single DB 603.

And the Starship had a few problems with the pusher configuration.

 

[FLYBOYJ]

. We've had 3 people killed in Rutan designs, one of which was a Long EZ. In the Acccident the canard departed from the plane in mid-air and it lawn darted. Turns out it is held on by two bolts.

Greg, sorry to hear about the death of your friends but I think its more to it than that. I know many people who have owned (and still own) Long EZs with no issues. Not to comment on the incident you describe but I know many accidents on homebuilts attributed to the builder, rather then the basic design of the aircraft.