The transponder antenna should be on the bottom of the aircraft, in the center of a ground plane, the dimensions of which I do not remember. So, mounting your ADAHRS, on a shelf that spans the longerons, should work perfectly because that puts it on the same plane as the flight of the aircraft.
My Panther Building Documentation at PantherBuilder Web Site Daniel R. Heath -?Lexington, SC -----Original Message----- After some thought, I could mount it on a small platform (3/32 ply) glued to the upper aft fuselage horizontal braces behind the left seat. I'll have to relocate the transponder antenna which is presently located there.
