Sail area vs. servo size
Um - drum servo or arm? HiTec drums are stronger than Futabas at the expense of more battery drain and a lot lesszs oney than the Futaba.(I have 3 HiTec's). 670 squares is what the one-meter and 36/600 guys use. A Futaba S125 or whatever its equivalent is now would work OK. Tower has a hugemongous servo now - 60 degrees.....but over 300 oz of torque. That'll pull in anything......