P-39D (IMO) is for someone whose newer to it. The 39D turns well, but doesn't run well. With the 20mm package, you dont really have to worry about accuracy like with the P-39Q. With flaps, it can easily turn with most spits, dives well. And it's most efficient at 10-15k. Most like to fly this, it has the most American skins on it.
P-39Q is for someone whose more familiar to the 39. They know the 39's strengths and weaknesses and knows what to do during certain situations. It has an option of 4 .50s and 1 37mm, or 2 .50s and 1 37mm. Either option really depends on what you're doing. If you're base defending from a CV, up with 2 .50s and 1 37mm, only shoot with the 37. Learn to shoot well with it, that and turning are your best bets with it. Belive it or not, it's the best plan for the HO, you can easily pop a tater into the nose of a 110 or an A-20 and duck really quickly for an easy kill. (Need to be a good shot too)
With 4 .50s and 1 37mm, just shoot them all at once. That's your best bet.
For maneuvering with a P-39, it's hard to explain. The P-39 has it's own technique of fighting, and for the most part, is a GREAT plane to learn ACM from. If you can teach your 39 to fight nose to nose with a Spit 16 and win, you'll be very very VERY deadly in just about any other plane you up.
To best keep control of your 39, you wanna have good throttle and flap controls. A good reverse for the 39 is a chop throttle/rolling scissors. (if you do not know how to do a rolling scissors, then you should learn first) The big emphasis on the 39 is also keeping speed up as long as possible, it holds speed very well, but will take a long time to gain it back if you bleed it all off to fast. If you're only shooting the tater (Most reccomended for 2 .50s and 1 37mm, program a 2nd fire button into your joystick), then you should be making shots from 400 to 0. I always seem to lead way too much when I fire the tater, which always seems odd. When I go and look back at films, it'll show my bullets in front of them, so you have to learn the tater on it. The 37mm is nothing like the 109's 30mm.
You can also use the 37mm for tank busting. I've turreted/taken out up to shermans with the 37mm. Just watch your shooting and come in from a high back angle. (very hard to kill a sherman. It took me all 30 rounds on the only 3 I've ever killed)
