i bet the fg 36 makes a bunch of torque to swing a big prop
http://shop.singahobby.com/?q=node/12900
Recommended propeller (and static thrust):
APC 17x10 - 5.7kg
APC 17x13 - 5.4kg
APC 19x8 - 6.5kg
APC 19x10 - 7kg
APC 20x8 - 7.5kg
APC 18x8 - 6.8kg
APC 19x8 - 7kg