How much weight were the Soviets able to strip out of the P39?

[Shortround6]

Or crashed a bunch of planes.

I am wondering how much of the reason for the 100lbs of armor right behind the propeller was ballast for CG reasons as much as for actual "protection".
trying to mount vacuum tube radios in the nose to help compensate is asking for trouble. British found that firing the nose guns knocked the compass out of action. Having the vibration of the nose guns break one or more vacuum tubes in the radio doesn't sound like a good result either. I wonder if radios got shoved into the rear of the planes to get them away from engine vibrations in addition to weight balance and ease of access for service.

radio access through hatch in the side? Radio techs idea of good access may differ??

Not sure what deleting the wing guns really gets you in actual numbers.
P-39D was tested at 7529lbs in Dec of 1941. AS noted before that is several hundred pounds lighter than full internal fuel and full ammo.
Cutting the .30 cal ammo to 300 rpg saves 168Lbs.
Weight and balance charts for P-39L and K show 300 rounds per gun as a standard load.
A P-39K could get to 7648lbs with full internal fuel and 300rpg for the wing guns.
Since WEP power settings weren't officially approved until Dec 1942 any estimates of performance for early P-39s during 1942 have to take this into consideration. Yes individual squadrons did over boost their engines in service before this but the practice may not have been universal and availability of spare engines and spare parts has to be taken into consideration.

 

[P-39 Expert]

Or crashed a bunch of planes.

I am wondering how much of the reason for the 100lbs of armor right behind the propeller was ballast for CG reasons as much as for actual "protection".
trying to mount vacuum tube radios in the nose to help compensate is asking for trouble. British found that firing the nose guns knocked the compass out of action. Having the vibration of the nose guns break one or more vacuum tubes in the radio doesn't sound like a good result either. I wonder if radios got shoved into the rear of the planes to get them away from engine vibrations in addition to weight balance and ease of access for service.
View attachment 486429
radio access through hatch in the side? Radio techs idea of good access may differ??

Not sure what deleting the wing guns really gets you in actual numbers.
P-39D was tested at 7529lbs in Dec of 1941. AS noted before that is several hundred pounds lighter than full internal fuel and full ammo.
Cutting the .30 cal ammo to 300 rpg saves 168Lbs.
Weight and balance charts for P-39L and K show 300 rounds per gun as a standard load.
A P-39K could get to 7648lbs with full internal fuel and 300rpg for the wing guns.
Since WEP power settings weren't officially approved until Dec 1942 any estimates of performance for early P-39s during 1942 have to take this into consideration. Yes individual squadrons did over boost their engines in service before this but the practice may not have been universal and availability of spare engines and spare parts has to be taken into consideration.

The 100# of armor plate in the nose may have been for ballast as Bell planned for larger propellers which would have weighed more. These actually appeared in the P-39N. I didn't recommend moving the radios up into the nose to compensate, I recommended moving the radios over the engine just behind the pilot to compensate for removing the 100# in the nose. Lots of P-39s in service had the radios there, they can clearly be seen in photos.
Regarding the wing guns, I rounded the 168# to 200#, my error. Standard load was actually 1000rounds per gun, but by the time the K and L came out the Army had realized that they needed the increase in performance (lower weight) more than the extra 700rpg. 300rpg gave about 15 seconds firing time.
Regarding WEP, it was approved in late 1942 and retroactively covered the V-1710-35, so from 1943 on it was available.
One last thing about the P-39D weight in wwiiaircraftperformance, the Army quoted gross weight (sometimes gross weight at takeoff) as half fuel or mean fuel. The P-39D actually weighed 7889# less half fuel 360# = 7529#. I believed they used this mean weight figure for their calculations, since the weight of the plane reduced from 7889# at takeoff (when you couldn't fight anybody) to 7169# empty on landing (couldn't fight anybody then either). So they used mean or average fuel for their ratios (power/weight, wing loading etc.). Just my opinion.