P-39Q Airacobra (1 Viewer)

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carman1877

Airman
51
0
May 14, 2009
I just was wondering about the P-39Q and what you everybody thought of it? I read that the "Q" model had one 37mm with 34 rounds and 4 .50s two cowling mounted with 200 rounds and 2 wing mounted with 300 rounds. Along with a drop tank or (1) 500 pound bomb under the fuselage. As many people know this plane had the engine in the mid section of the aircraft for several reasons. One is that they wanted to be able to fire the 37mm through the propeller hub, so they needed space in the front. Second they thought that since this was going to be used as a ground attack plane that having the engine in the middle would protect it more from AA fire. And unlike many planes of its time it had doors instead of a moveable canopy. The doors opened forwards like a cars and the window could roll up or down with a crank. People sometimes think that it would be hard to eject from this plane but when you pulled a red lever near the hinges of the door, the door flew off the plane making it easy to get out of. It also had a decent speed and range which is why it was one of Russia's best planes of WW2. The tricycle landing gear was also very knew and inovative for the time. So write whta you think of the P-39Q.

Thanks
 
Hello
I cannot recall was there 30 or 34 37mm shells. And Russians usually removed the wing guns to lighten the plane and to improve the rate of roll. And against Finland AF's Bf 109G P-39 was more or less as dangerous opponent than Yak-9 but La-5/-5F/-5FN was more dangerous.

Juha
 
It was Chuck Yeager's favorite WW2 fighter. It could be a bit unstable, it had a lateral and vertical center of gravity.
 
It had the inherent drawbacks of all P39s, small internal fuel load, it was designed for a pilot who was no more than 5' 8" and there was a large CG shift when the nose guns ammo was used up.
 
Thanks for the effort to explain, but I'm still within confines of school phisycs that claim that one body has only one CoG.

What is a "water line" in an aircraft?
 
I love the P-39 / P-63. I don't think though, that the engine placement was in part for ground attack. The P-39 was designed as a bomber intercept pursuit. In the same realm as the P-38, all during the AAC fallacy of pursuits only being needed to shoot down enemy bombers attacking the U.S. coast.

The P-39 ended up being a decent ground attack aircraft after the orginal turbo installation never worked out and the plane ended up with the normal Allison we all know and love. However I cannot recall any wartime pilots talking about the love of the 37mm nose gun either.

And contrary to what has been repeated in literature, the Russians use of the plane was not primarily tank busting with the cannon. It was a low altitude interceptor. And since the plane performed best at low to medium altitudes, the Russians learned to exploit the true value of the Airacobra.

Now I have to change my avatar back to a P-39 again.8)
 
P-39 was not a decent ground attack plane any more then Spitfire or Me-109.
 
I was just trying to make the point that ground attack was not the design genisis, nor was it something into which it evolved.

I would rate a plane as either; Poor, Decent, Good, or Great, when speaking of ground attack. Poor would be a .30 caliber only fighter, like early Spitfires, and little to no bomb load. The Airacobra at least had a cannon and some .50's, and little to no bomb load. I personally would rank the Airacobra just above the Spit in that regards, so you can choose whatever terminology, but Decent works for me. And if I had my choice, I wouldn't chose to fly and fight in "Decent", I would much prefer Good or Great!

I really think we agree, just different verbage.
 
Thanks for the effort to explain, but I'm still within confines of school phisycs that claim that one body has only one CoG.

What is a "water line" in an aircraft?

Stations measured from the ground up...

Although technically correct that a body could have one CoC, you also have to consider where on that object the CoC exists, and in terms of aircraft, where it exists with regards to the Mean Aerodynamic Chord. In the case of the P-39, the designers came up with a fore and aft and "up and down" CoG that considered the large moment (the engine) that was well aft of the datum point (hopefully you know a little about aircraft weight and balance).

Here's a link that shows a P-39 weight and balance chart. Notice the chart "vertical and horizontal arm and moment."

http://www.zenoswarbirdvideos.com/Images/P-39/P39WBC.pdf

BTW, helicopters' CoG are calculated the same way.
 
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I was just trying to make the point that ground attack was not the design genisis, nor was it something into which it evolved.

I would rate a plane as either; Poor, Decent, Good, or Great, when speaking of ground attack. Poor would be a .30 caliber only fighter, like early Spitfires, and little to no bomb load. The Airacobra at least had a cannon and some .50's, and little to no bomb load. I personally would rank the Airacobra just above the Spit in that regards, so you can choose whatever terminology, but Decent works for me. And if I had my choice, I wouldn't chose to fly and fight in "Decent", I would much prefer Good or Great!

I really think we agree, just different verbage.

Yep, in the scale of 1-4 (4 being the top value), the P-39 could snatch 2.
 
Winkle Brown and Yeager loved the P39.
Yeager said no one could beat a P 39 at 100 feet but who wanted to fight there.
 
Q was almost exactly the same as the N except for the wing guns. Remove those wing guns from both and they are the same plane. Faster and much better climb than earlier P-39s they comprised over 7000 (N and Q) of the total 9500+ produced.
 
Thanks for the effort to explain, but I'm still within confines of school phisycs that claim that one body has only one CoG.

What is a "water line" in an aircraft?
Tomo - academic courses in physics (or Materials) rarely deviated from solid bodies when calculating CoG (ball, brick, I beam, Eccentric but solid body with multiple geometric features - each with definable CoG and solvable in tabular format.)

Aircraft are largely open space with some fixed masses in a fixed place with little change over time (engine, guns, pilot in s/e a.c, etc) as well as substantial masses which vary over time. Fuel in fixed volume changes over time (you know all this but I want to make a point), ditto ammunition.

Thrust line is constant in aircraft but DISTINCTLY variable in a helicopter/rotary wing a/c. Center of Pressure over a lifting surface is essentially constant in cruise/level flight in the incompressible flow regime. There are Lift and Drag components to wing and horizontal stabilizer which will plugged into stability calculations and applied to derive Static Margins in which the various CoG locations are examined based on take off position with load conditions as well as the change to CoG based on dM/dT mass changes over time. All must be taken into account to get the Neutral Point and Static Margin for Stability calculations.

(Note - not discussing variable geometry wings or thrust vectoring here)

Such stability derivatives are more complex when the change of mass over time has a more profound moment change due to Thrust line or CoG travel within the Static Margin (measured from CoG to the Neutral Point). The P-39 was an example of 'touchy' because it had more of the variable mass distributed along the water line as Joe pointed out

The helicopter is a whole new world because not only the CoG varies over flight envelope, but the Thrust line is Variable as mast head/rotor adjustments move the Vertical thrust line forward/aft/left/right of the CoG as the pilot is varying cyclic, collective and rudder/tail rotor controls. Pat your belly while scratching your head and whistling Dixie
 
Anyone have the weight and balance chart for the P-39?
 

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