An interesting idea
On a purely qualitative basis, I am not sure that improving the airflow over the fins (if you could even do such a thing) would give you much of a benefit, at least in regard to increasing the consistency of flight profiles.
I think you would gain more consistency from improving the quality of your fin airfoils and especially from improving the alignment of fins with respect to the body axis. I think you would gain far more drag reduction from exposing that boattail and losing (removing) that last section of full-diam body tube. (BTW, keep the transition/corner from BT to boattail smooth and, if possible, rounded.)
On a side note, remember that the motors you are using also tend to have a small amount of performance variation, motor to motor, due to manufacturing tolerances. You are worrying about something relatively small (fin drag variations) while seemingly accepting other relatively large variations (in motor thrust).
Your idea to reduce fin turbulence (and drag?) might make for an interesting subject for a smoke-tunnel model; this would allow you to see whether the flow behaves the way you are hoping or whether it does something worse/completely different. My SOTP estimate of the levels of drag reduction is that even with a finely made wind tunnel model set up with pressure taps for force measurements and wake rakes to survey momentum losses behind the model, your potential drag reductions will be in the "noise level" of the measurement capabilities of your experimental test hardware.
My two cents
(what is that in British coin?)
Last edited by powderburner; 29th August 2013 at 06:11 AM.
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