P-39 Cannon Rounds

[Randy1]

The most notable other handicap was probably the lack of range, but I also don't think the armament was ever entirely satisfactory.   The 37mm had a really low ROF and low muzzle velocity, and the combination of cannon, .50 cal, and .30 cal weapons meant you had 3 different ballistic properties to contend with.  The 37mm was also plagued by jamming in combat (at least in the south and southwest pacific).
 

There could have been political or even board member pressure to use the 37mm.  The specs should have said bad canon before it was incorporated.  Just another example of bad engineering and or bad management.  I strongly suspect bad management either at the executive level or project level or both.

The P39 for the time  it was first designed could have been top fighter with more development.

[Soulyss]

Larry Bell was a strong advocate of the 37mm gun, although he did argue with the USAAF to remove the 4 .30 cal machine guns from the wings to save on weight.

[Blinder]

Larry Bell was a strong advocate of the 37mm gun, although he did argue with the USAAF to remove the 4 .30 cal machine guns from the wings to save on weight.

There is documentation out there that the Soviets removed the wing machine guns to improve roll rate by reducing rotational inertia. But they also did this and then installed 12.7mm gun pods so go figure. 

[Saxman]

The most notable other handicap was probably the lack of range, but I also don't think the armament was ever entirely satisfactory.   The 37mm had a really low ROF and low muzzle velocity, and the combination of cannon, .50 cal, and .30 cal weapons meant you had 3 different ballistic properties to contend with.

Whenever I'm in a P-39 (which isn't often) I find I prefer the "P-400" package in the D model. The 20mm in the hub is a much better A2A weapon, and a good bit lighter, too.

[bustr]

Tested the M4 37mm offline NDisles A16 over the 5000ft drop-off.

Needed to squeak the front wheel down the slope a tad to the level the gun. Maximum range is 1800 yards, and dispersion is crappy. Eventually I settled on aim marks for 1, 1.5 and 1.8 to test active shooting. As long as you are shooting ground targets starting at 1k, it's not too bad of a gun. 1.5 and 1.8 is just throwing Hail Mary's for the end zone.

I did a similar test for the NS-37 in the Yak 9T. Maximum range is 2400 yards. Until 1000, shooting was throwing Hail Mary's for the end zone again.

[Ack-Ack]

I often wonder what stunted the P39, and latter the P63 development programs.  Bad management, back room politics, poor engineers or all four. Loosing both P63 prototypes suggest bad design and bad management.

If you look at the P-39's development history, it was under continuous development testing but a lot of those didn't pan out like the XP-39E and P-76 and I also think that the airframe itself was at its limits, any significant developments would have probably also included major changes to the airframe.

I will say though that the removal of the super-turbocharger was a bad idea and there are some conflicting stories behind the reasons why.  Some state that Bell and other members of the designed team felt that a turbocharger would clutter the P-39 aerodynamically and without providing any advantages.  Other stories say that the Bell was hungry for cash flow and didn't have an active production program.  There is also a story about how the USAAC ordered the removal of the super-turbocharger because of the vast distances of the Pacific and Atlantic oceans, an attack on the continental US by high altitude bombers was unlikely.  

In my opinion, the P-39 was a result of pre-war philosophies and it shows in the design.  For a plane designed to counter existing threats at the time, it was a good design but war has a way of changing things and the reality of the air war made the P-39 almost obsolete out of the gate.

As for the 37mm Oldsmobile cannon, the original design called for a smaller cannon, but as someone mentioned, Bell wanted a higher caliber main weapon and the only one that was suitable was the 37mm Oldsmobile cannon.

ack-ack

[Randy1]

Super reply Ack-ack.   

So interesting trying to understand how history turned out the way it does.

[Sabre]

I also recall reading somewhere that there was considerable discussion among the design team about whether or not to use a laminar-flow wing in the Cobra's design, like the P-51 eventually got.  This would have dramatically improved both range and speed, at the expense of sustained turn-rate.  However, it was still considered unproven, and Bell decided to go with what they knew.  There was also talk mid-war about replacing the engine with the Merlin, but by that time the plane had already developed a tarnished reputation; AF brass had pinned their hopes on the P-51, and would not split the Merlin production.  Even with the Merlin, the P-51 would have the edge in range and speed over the Cobra without laminar flow wings, or so I recall.

[bustr]

Finished some reading from a translated interview with a VVS P39 pilot.

The wing guns were removed. The Russians received both P400 and P39. In both cases the gunsight was an early N2 with either a basic cross reticle or "Christmas Tree" reticle, vertical line with range ticks for the 37mm. The 37mm was considered inadequate for long range shooting due to the drop and horrid dispersion. It was appreciated for it's close range one shot kill on aircraft and destructive ability on ground targets.

The Russian tactical doctrine for air to air gunnery was maximum 200m(218yds). Because dispersion, maneuvering and drop effected being able to land enough rounds on the target to destroy it. The PBP-1 reticle describes this with it's two rings. The inner ring is the average wingspan of 109 and 190 at 200m. The outer ring accounts for the equivalent of 100mph as the radius like the allied 100mph ring. Ground attack distances are at most 500m-600m, but, when you look into their rockets and bombs description of use, 400m max unless steep dive bombing.

200m had another significance in the choice of the UB 12.7 and ShVAK 20mm or NS-37 combination in Yak fighters. To 200m the rounds had similar ballistics with all shooting straight forward. After that the 20mm\37mm which was bolted level with the engine began dropping off sooner than the UB 12.7. That's why yak fighters have a 200m mark on the back of the prop to adjust the center of the PBP1 reticle for 200m before takeoff. This would mean adjusting the center of the reticle to pass down through the bullet trajectories at 200m. Depending on the number of guns, including caliber, all guns were mounted to shoot strait ahead. The PBP1 reticle had enough view width to allow for the drop of the NS-37 to 600m even though the round was about a 4000m round.

I have wasted about 8 hours using Russian language searches looking for bore sighting pictures of Yaks and Lavochkins. The factory mounted the guns in level, shooting straight out, is all I have ever found as a description.

Since I can hardstand tail draggers offline in the TA arena over the deep slope towards the town due north. I think I will static test our motor cannons to see how close to specs the drops are by accounting for the slight up-tilt at 150. The artificial horizon level will allow me to squeak the planes forward just past level on the slope to level the motor cannon. If I don't set any azimuth to the target, the red horizontal line will be even with the engine line before I squeeked the nose down slope to level the cannon. Probably something like 2.5Mil down at 150 yards.

[catdaddy]

I have read that there were three types of rounds for the 37MM on the 39, HE, AP, and tracer and most of the time they were loaded with all three types. The Russians loved the 37mm. the P-39 was oddly well balanced but experienced inertial coupling, if over controlled it would tumble end over end which made for some hairy combat maneuvers for the ham handed. there were more than a few losses in training and early combat.