a quick look at your score shows you have a hit percentage of 1.24 in fighters, and 1.16 in GVs. Most of your kills are in GVs, where one hit....if well aimed... can kill a vehicle. Planes on the other hand, need a few more hits to down due to the smaller rounds you are throwing at it.
You seem to fly a number of different planes. While the ballistic for the cannons on the Nik and Las are close, the 50 cals on the P47, TBM, and FM2 are a bit different. Also, you have to set the convergence...or use the default.... but either way you have to know "where" the bullet streams from your guns converge, and only fire when the target is at that range.
You may be seeing hits, but not nearly enough to do the damage you need to down a plane.