Originally Posted by FinnFlyer
Possibly slightly more drag. I understand that the air under the fuselage is already more turbulent than under the wing?
This might be true for a small transponder or ADS-B antenna (that an underwing location has more drag vs. on the belly) if
your belly antenna is mounted directly aft of the cowl exit area where on most RV's the exit airflow is relatively slow (unless you're name is Dan Horton or Dave Anders, or you have a P-51). But for Com antennas which are quite a bit bigger, I've always assumed that getting the antenna out of the prop blast would reduce drag...in other words under the wing far enough outboard that the local airflow is slower, there should be less drag. Also anything in the swirling, turbulent air behind the prop may have separated airflow which increases drag vs. smooth airflow like you have outside of the prop blast. But I don't have any data to prove these assumptions...maybe there's a NACA report somewhere on antenna locations??
As far as antenna/radio performance goes, I installed my COM2 antenna about halfway out along the right wing on my RV-8A and it worked just fine there. What I didn't like about it in that location is it's easier for little kids at a pancake breakfast or fly-in to run under the wing and I worried about somebody poking their eye on it. If you put it under the wing, I recommend locating it a little inboard of the flap/aileron junction. Then if you park the airplane with the flaps down, it helps keep the kiddos from running under that part of the wing. If you have a sissy trigear model like me, don't put it too far inboard or it'll get in your way when you're trying to add air or change a tire on the main gear.