I've got four planes with 91 four strokes. Two TF warbirds one 10.5 lbs one 11.5 lbs both fly well with Graupner 14-7 props. A Citabria @ 9 lbs flys with a APC 14-6. A CAP232 @ 8 LBS. with an APC 15-4W. Very good vertical, the W is for wide, not the thin sharp typical APC it actually resembles the Graupners.