Hello P-39 Expert,
In trying to gather some information about the P-39C, I am coming up with some different conclusions.
From what I have been able to find, the Gross Weight of P-39C was 7180 pounds. Maximum Take-Off Weight was 7300 pounds.
There was no provision for external fuel or stores.
The interesting thing about Bell's "Gross Weight" is that they had a tendency not to list full fuel loads there. Full internal fuel loads were considered "Overload". In this case, it seems to fit with the 120 pound difference being explained by 20 Gallons less fuel.
Your addition of 15 rounds of 37 mm ammunition would only bring the total ammunition load to 30 rounds, not 60.
The P-39C only carried 15 rounds and the P-39D only increased that to 30 rounds total.
The big problem comes with the other changes you are proposing.
The changes in fuel load would not affect CG by much, but they are located a couple inches ahead of the empty CG of the aircraft, so it WOULD have some effect.
All the other major deletions are at the nose very far ahead of the CG.
The two .30 cal MG with their ammunition is probably a bit over 100 pounds but about 50 pounds was permanent.
The guns would not have been removed in flight.
The additional 15 rounds of 37 mm ammunition adds back 30 pounds of weight but that was likely to be expended in flight.
The 95 pound gear box armor was there probably as permanent ballast and removing that without something compensating would have been "interesting".
So, although the modified P-39C you are suggesting would certainly be light, it would also be pretty badly out of balance.
The idea that nose armour was permanent ballast is supported by the fact that the weight of this armour was reduced to 70 pounds in some models of Airacobra. I believe armour weights were used to balance the aircraft which explains all the different thicknesses for the same basic pieces of armour plate.
From a flying and handling standpoint, the best piece of armour to delete would be the 29 pound plate behind the oil tank.
The Soviets definitely did that in testing but I am not quite sure if they did that on their operational Airacobra. They also increased the ammunition load for their P-39D up to 270 rounds per gun to push the CG even further forward.
- Ivan.
