Question about engine placement

[fdiron]

The P39, with its engine behind the pilot, had a very streamlined shape.  This also allowed the P39 to have a 37mm cannon mounted in the nose.  Why didnt other U.S. fighters have their engines placed behind the pilot?  It seems this would have many advantages such as lower drag and better aiming for weapons.  It could also possibly protect the engine for hostile fire. If the engine was mounted over the center of gravity I dont see any negative effects of this arrangement.

[mrsid2]

Well the P39 was reported to have a very poor stability just because of the problems that were introduced with placing the engine in the back.

Combined with underpowered engine and very unreliable 37mm cannon it made the airacobra a deathtrap for many pilots.

Finns fought succesfully against P39's in brewsters (you know, the ones that were put to training use by U.S. navy after first encounter with a6m and 13 out of 16 lost..)

I've read that the pilots respected the awesome firepower but didn't consider the plane much of a threat because it could be outmanouvered easily.

Strangely the same was said about hurricane and spitfire - the top finnish ace described them as 'clumsy, stiff and horribly slow below 3km altitudes.'
and
'hurricane is the easyest to kill in a turnfight, try to fool him into turning so he is easy to kill. Just a short spray in the front of the plane usually sets it to fire from the first hit.'

That doesn't sound at all like the spits and hurri we have here (except the slow part..) I wonder what kind of beast the brewster was..

[Hortlund]

Actually I suspect the issue is more pilot related than anything else hehe.

Did the commies have any good pilots btw?

[mrsid2]

Of course they had a few aces also but mostly the pilot quality was low. Judging from what I read anyway..

Uncle Stalin was kind enough to execute most of the talent of the military before the war so there were many newbies both in leadership and crew.

They had nice numbers though, about 10:1 I think. Sometimes the bombers came in near thousand figures while we had maybe 20 fighters to protect

That ofcourse lead to amazing stories, like one that happened over my home city. A finnish pilot made the worldrecord of shooting down 6 enemies in about 30 seconds (bombers.)

He then had to rtb because he had spent all his ammo.

[fats]

And that was with a Fokker D.XXI if I recall right?



// fats

[mrsid2]

That might have been, I don't recall any more details of that.
I do recall of the pilot saying he used crude caliber mg's so it might have been fokker.

[gripen]

Rolls Royce planned to make a experimental Mustang version with a  RR Griffon mounted like in the P-39. The project reached mock up stage. Estimated performance was something like near 800km/h at high altitude.

IIRC Sarvanto's case was 6 DB-3s in  4 minutes with the D.XXI. There might have been other similar cases later.

gripen

[Staga]

http://www.elknet.pl/acestory/sarvan/sarvan.htm

[funkedup]

Why didnt other U.S. fighters have their engines placed behind the pilot?

Putting the engine behind the pilot is not a good thing by itself.

- It moves the CG of the aircraft towards the rear which reduces stability.  The only way to restore stabiity is to put a bunch of weight in the nose.

- The aft engine location increases weight and cost and complexity.  A drive shaft system is required, which in the case of the P-39 was quite heavy, took a lot of time and money to develop, added one more critical system that could fail and would require time and money for maintenance.

So if a rear engine sucks, why did they put the engine in the rear on the P-39?  Because the plane was designed around the huge 37 mm cannon.  It was too big to fit in the wings and the only way to fit it into the nose of such a small fighter was by moving the engine somewhere else.

[Smut]

Originally posted by funkedup

So if a rear engine sucks, why did they put the engine in the rear on the P-39?  Because the plane was designed around the huge 37 mm cannon.  It was too big to fit in the wings and the only way to fit it into the nose of such a small fighter was by moving the engine somewhere else.

Not exactly:

"The Bell P-39 Airacobra had its origin in June 1936 when the Buffalo, New York-based Bell Aircraft Corporation's design team, headed by Robert J. Woods and Harland M. Poyer, began the design of a single- seat fighter. The Bell corporation was responding to a 1936 Army Air Corps request for a new single-seat fighter design, one which would be equal to the new European fighters just then beginning to undergo flight test.

Woods and Poyer conceived the idea of mounting the engine in mid-fuselage, driving the propeller via a ten-foot extension shaft. Such an arrangement was not exactly new, having been tried earlier by the experimental Westland F.7/30 biplane and by the Dutch Koolhoven F.K.55 monoplane. Among the potential advantages offered by such an arrangement was the possibility of superior maneuverability, since the weight of the plane would be more nearly concentrated at the center of gravity. In addition, it would facilitate the installation of a heavy nose armament, since the armament could be mounted near the centerline, minimizing the effects of recoil forces. It would also offer good visibility for the pilot, and would permit the installation of a tricycle undercarriage.

Bell's original proposal was to place the pilot behind the engine, forcing the cockpit very far to the rear and making the proposed aircraft look a lot like the Curtiss XP-37. A mockup with this configuration was built with this configuration and was given the company designation Bell Model 3. However, the problem of visibility over the engine eventually forced Bell engineers to move the pilot ahead of the engine, and a revised mockup, given the company designation Bell Model 4, was used as the basis of a formal submission to the USAAC on May 18, 1937. The Bell submission promised a top speed of 400 mph at 20,000 feet and a gross weight of only 5500 pounds."

- from Joe Baugher's P-39 article

Full article at http://home.att.net/~jbaugher1/p39.html

-Smut

[mrsid2]

P39 versus 109G2 story and more at http://www.elknet.pl/acestory/juuti/juuti2.htm

[ergRTC]

It excelled in the low-altitude strike role and the 37-mm nose cannon made the Airacobra an excellent tank buster. When operating at low altitudes, the Airacobra was often able to hold its own against German fighters.

Some Soviet pilots felt that the P-39 outclassed even the Messerschmitt Bf 109 and Focke Wulf FW 190 at altitudes below 10,000 feet. Several Soviet Airacobra aces are known. Lieutenant Colonel of the Guards Alexander I. Pokryshin, a Soviet ace with 59 kills to his credit, scored 48 of these in a P-39. He was awarded the Distinguished Flying Cross by President Roosevelt. There are eight other P-39 pilots with at least 20 kills. The four after Pokryshin were Captain G. A. Rechkalov with 44 kills, Captain N. G. Guliav with 36 kills, and the Klinka brothers Major G. P. Klinka with (text lost)


http://home.att.net/~jbaugher1/p39_19.html

[fdiron]

I bet the P39 would have been a good fighter had it had a merlin engine and a supercharger.

[kreighund]

You guys give the merlin toooooo much credit compared to the allison...the problem with the allison was the US Army...
I you look at time lines the allison has many firsts...
A few wing commanders cited the 1942 P-51A's allison with remarkable ability to come home on ruined bearings whilst the merlins were too sensitive and prone to seizing more often..the allison could be coaxed beyond its safe limits and be forgiving...
I the boys had Shaw's book they would have cleaned up against the zeros in 1942....

I'd love to have the P-39 with the turbo in 1942....so about 375 to 380 at 20000ft..low altitude performance would suffer though....

[fdiron]

I read in some book, I have forgotten the title, that the Allison engines never did catch up with the Merlin engines for high altitude performance.