Single-engined pusher planes: any role for those?

[Elmas]

You may have some Swedes argue that fact...

From Wiki:

"The first of three J 21 prototypes flew on 30 July 1943 flown by SAAB test pilot Claes Smith. During the takeoff, the wrong flap setting resulted in the prototype running into a fence at the end of the runway, damaging one of the landing gears. The subsequent test flight ended with a successful landing on the undamaged undercarriage units.[4]
A total of 54 J 21A-1 fighters constructed at the main plant in Trollhättan were delivered from December 1945, followed by 124 and 119 examples respectively of the J 21A-2 with revised armament and the J 21A-3 fighter-bomber. Utilized mainly in the bomber role, the limitation of the design led to a proposed front-engine replacement, the J 23."

and from

SAAB aircraft that never were

"In March 1941 Saab was given the task to design a better fighter than the Seversky Republic P-35:s and Reggiane 2000:s we had been able to buy. (The Mitsubishi Zero had also been considered.) This resulted in the twin-boom pusher J 21 (which hardly was a fighter, but became a passable ground attack aircraft). This was a technological risk, with ejection seat and all, so a more conventional fall-back design with the same engine was needed. In December 1941 the fall-back design was cancelled, as it was considerably less manoueverable than the J 21. Both designs were to use the same engine, DB 603, and interestingly the J 23 was to have an ejection seat too! "

and from the same site:

http://www.x-plane.org/home/urf/aviation/text/21saab.htm

"The J 21A-1s were all retired at the beginning of 1949. It was never a success as a fighter, but those designated A 21 (A = Attack, ground attack) or even B 21 (B = Bomb) made good service. They had the same armament as the fighter version, but also provision for carrying rockets and bombs with a bomb aiming sight, as well as two RATO bottles."


The same old story: a poor fighter or interceptor becomes a"passable" ground attack aeroplane......

 

[FLYBOYJ]

From Wiki:

"The first of three J 21 prototypes flew on 30 July 1943 flown by SAAB test pilot Claes Smith. During the takeoff, the wrong flap setting resulted in the prototype running into a fence at the end of the runway, damaging one of the landing gears. The subsequent test flight ended with a successful landing on the undamaged undercarriage units.[4]
A total of 54 J 21A-1 fighters constructed at the main plant in Trollhättan were delivered from December 1945, followed by 124 and 119 examples respectively of the J 21A-2 with revised armament and the J 21A-3 fighter-bomber. Utilized mainly in the bomber role, the limitation of the design led to a proposed front-engine replacement, the J 23."

and from

SAAB aircraft that never were

"In March 1941 Saab was given the task to design a better fighter than the Seversky Republic P-35:s and Reggiane 2000:s we had been able to buy. (The Mitsubishi Zero had also been considered.) This resulted in the twin-boom pusher J 21 (which hardly was a fighter, but became a passable ground attack aircraft). This was a technological risk, with ejection seat and all, so a more conventional fall-back design with the same engine was needed. In December 1941 the fall-back design was cancelled, as it was considerably less manoueverable than the J 21. Both designs were to use the same engine, DB 603, and interestingly the J 23 was to have an ejection seat too! "

and from the same site:

Saab 21

"The J 21A-1s were all retired at the beginning of 1949. It was never a success as a fighter, but those designated A 21 (A = Attack, ground attack) or even B 21 (B = Bomb) made good service. They had the same armament as the fighter version, but also provision for carrying rockets and bombs with a bomb aiming sight, as well as two RATO bottles."


The same old story: a poor fighter or interceptor becomes a"passable" ground attack aeroplane......

It is recognized that this airframe design by far wasn't a record beater but it was utilized for several years by the SAF. Additionally the same airframe was converted into a jet. The basic design, considered poor did serve into the 1950s as the jet version was retired in 1956.

 

[tomo pauk]

When someone says:

which hardly was a fighter, but became a passable ground attack aircraft

such a comment smells as being an opinion, rather than a fact.

Then:

Utilized mainly in the bomber role, the limitation of the design led to a proposed front-engine replacement, the J 23

What was a limitation?

In December 1941 the fall-back design was cancelled, as it was considerably less manoueverable than the J 21. Both designs were to use the same engine, DB 603, and interestingly the J 23 was to have an ejection seat too!

So the fall-back design was canceled, not the pusher. And, then, DB-603 engines???

"The J 21A-1s were all retired at the beginning of 1949. It was never a success as a fighter, but those designated A 21 (A = Attack, ground attack) or even B 21 (B = Bomb) made good service. They had the same armament as the fighter version, but also provision for carrying rockets and bombs with a bomb aiming sight, as well as two RATO bottles."

How good/bad the combat record was for J-21, so we can judge the success?
Further, J-21 used the engine that was sub-standard for 1945 and on (under 1500 HP). Asking from such a plane to compete vs. what war-winning countries were fielding then would be too much.

 

[FLYBOYJ]

Don't know the source for this comment....

"The design foraged on and was reportedly quite the aircraft to fly - responsive, steady when firing her armament and robust."

Saab J 21 Fighter / Attack Aircraft - History, Specs and Pictures - Military Aircraft

"At any rate, the successful development and operation service of the Saab 21 series provided the nation of Sweden with an indigenous design that was quite capable in the tasks assigned to it. The platform served its purpose for a time and offered up much-needed experience in the field of aircraft engineering that would serve the country well in the coming decades, producing further stellar home-grown designs in the form of the Tunnen, Draken, Viggen and - ultimately - the Gripen."

Seems to be differences of opinion there........

 

[Elmas]

..................
offered up much-needed experience in the field of aircraft engineering that would serve the country well in the coming decades, producing further stellar home-grown designs in the form of the Tunnen, Draken, Viggen and - ultimately - the Gripen."

Seems to be differences of opinion there........

That were all jets, not piston pusher fighters.
A jet is a completely different thing than a piston propeller pusher : put a Napier Sabre with a Rotol propeller instead of a Goblin in a Vampire, and I will see if you can make it fly.......

The fact that, initially designed as a fighter, the J21 was very soon declassed to ground attack, and that the Sweden Air Force bougth and used Mustangs as fighters

ending the production of J21 " Originally 484 were ordered, but with the purchase of Mustang the number was reduced to 422, but in the end only 298 were made. (Same site)".

tells many things about how the Swedish Air Force considered the J21 as a fighter.

By my personal point of view, of course.

 

[tyrodtom]

Surplus P-51's costing a lot less than building new J-21's might have had some influence on their decision.

 

[FLYBOYJ]

You have a point but understand that Sweden never intended to procure the P-51, fate determined that. Had the Mustangs not been avainlable or WW2 lasted longer, be rest assured the 484 planned J21s "would have" been produced.

Bottom line this aircraft did work and if you take into account that it did serve at least 4 yesrs did show that a pusher design was developed during WW2 with limited success. Could it compete with aircraft like the P-51 or later model BF-109s? Never. But it did provide Sweden for what was needed at the time, an indigenous fighter that could at least ensure the country's neutrality.

I see nothing in any Internet sources about this aircraft that because of its configuration it was limited by CG issues during normal course of operation. If anything it seems that if it had a better engine it might of performed better, the latter of my statment being my opinion...

 

[FLYBOYJ]

Surplus P-51's costing a lot less than building new J-21's might have had some influence on their decision.

I believe these were "gifted" to the Swedish Government after hostilities, so yes, such a deal!

 

[Elmas]

I don't think that money was, and still is, a real concern for Swedish Air Forces, as they prefer to develop their own planes ( with the related costs ...) than to buy foreign material.
By my personal point of view, to buy a bunch of, say, Sabres or F 16s could have been much cheaper than to develop all their machines, excellent as they can be.

In a beautiful book by J. Quill, whose name you certainly know, almost a whole chapter is dedicated to longitudinal instability of the Spitfire, for a CG exceedingly backwards.....
The Spitfire! a machine that was loved by her pilots for the delightful handling.....

By my point of view, instead, a more powerful piston engine means also an heavier one and in a propeller pusher that means a CG more backwards that must be compensated by weight in the front etc.: have you ever heard about the Varignon's theorem, which states that the moment of a force about any point is equal to the sum of the moments of the components of the force about the same point, and about the equilibrium equations?
It's a dog chasing his tail.
That was easily solved by jet engines, much lighter than piston ones.

Et de hoc satis, as the ancient Romans used to say, at least for me.

Cheers

 

[tomo pauk]

Any plane that received a heavier engine in front (Spit IX -> Spit XIV, Bf-109D -> Bf-109E etc) was subject to what you say. Issues were solved, and nobody looked back at predecessors.

 

[FLYBOYJ]

I
By my point of view, instead, a more powerful piston engine means also an heavier one and in a propeller pusher that means a CG more backwards that must be compensated by weight in the front etc.: have you ever heard about the Varignon's theorem, which states that the moment of a force about any point is equal to the sum of the moments of the components of the force about the same point, and about the equilibrium equations?
It's a dog chasing his tail.
That was easily solved by jet engines, much lighter than piston ones.

Et de hoc satis, as the ancient Romans used to say, at least for me.

Cheers

The P-51 for the Sweeds was a winfall although they were bending the rules on their own arms policies. Be rest assured that aqusition affected and probably comdemed the J21 program. It did not prevent the Sweedes to continue to design and build indigenous fighters and still deploy the J21.

Varignon's theorem? Know it well - I've done weight and balance on dozens of aircraft of all classes for many years. Have you proven that any WW2 pusher fighter designs was plagued with the limitations stated in your original statement? Agree they did not live up to their tractor counterparts but I have yet to read or hear anything about any WW2 pusher aircraft that had CG/MAC problems because of expended payload issues. Most if not all of them did have stability issues that had nothing to do with expended payload, ie - ammunition. If you have data, please share!

What about the Dornier 335? - a combination of both pusher and tractor. Do you feel that same about that aircraft?

 

[Elmas]

As you probably know Decimomannu is ( or better, was, before 1991....) one of the most important Nato Airports in the world and it is few miles from my home.......
And for some reasons I had the possibility and the pleasure to have long talks with both Pilots and with my Colleagues Engineers, both Civil and Military, with a beer or a bottle of scotch in front of us....
I have seen the first flights of the Typhoon there, when one of the prototipes was performing the armament trials at the Capo Frasca firing range....... I could tell you some amusing little strories about, but I don't want to go O.T......

What about the Dornier 335? - a combination of both pusher and tractor. Do you feel that same about that aircraft?

Of course not. But I can't see any similarity in terms of static balancing among the J 21 ( wich had only one engine, behind the CG) and the Dornier 335 ( wich had two, one in the front and one behind).

So, no problems at all for the latter about static balancing ( centraggio, in Italian): all the consumables can be easily placed at, or near, the CG: look at the main fuel thank just behind the pilot's seat, on the leading edge of the wing, as the main armament, on the leading edge as well.

But, as aeroplanes are real life, and in real life noboy gives you something for nothing......... the distribution of the masses of two engines fore and aft of the CG and at distance from it, gave the Dornier a very high Moment of Inertia (rotational Inertia) in the longitudinal axis so a very careful handling of such an heavy plane was, I think, also needed.
But, of course the Pfeil was designed to be a powerful opponent to the B 17s, and not to make loopings and immelmans.....

 

[tomo pauk]

What a beauty, the Pfeil.
Wonder if a similar piece would do anything good for Allied cause. Or Axis, for that matter, with 601s (hallo, Dave )New what if topic...

 

[gjs238]

CAS. A rear prop normally provides superior forward visibility

We've had quite a bit of discussion regarding deflection shooting vs. view over the nose. A rear prop with the pilot far forward might be excellent for deflection shooting.