Fox 35 Horsepower Curves


The Fox 35 has the Classic 4-2 break stunt run.  In level flight the motor runs rich, purring a long in a 4 stroke at around 8500-9000 rpm.  When the plane starts to maneuver the motor switches to a 2 stroke run and picks up a significant amount of power.  Most people use a 10/5 or 10/6 propellor to do this.  It nicely matches many of the old Classic planes like the Nobler, Smoothie, and Chief.

Note that the peak torque, which accellerates the plane in maneuvers, occurs at around 6500-7000 rpm.  Nomal takeoff rpm is around 9000.  It settles into a 4 stroke running pretty much the same rpm once in the air.  A 4 stroke at 9000 rpm produces less horsepower than the 2 stroke power shown in the graph.  The motor is putting out maybe .2-.3 hp. in level flight.  When the plane maneuvers the change in load and change in fuel head combine to make it start to fire on every stroke and usually speed up some too.  Exactly what happens depends exactly how things are trimmed- fuel, prop, glow plug, size of plane, compression ratio. The power goes up significantly, maybe to as much as .4-.5 hp.  The extra horsepower counteracts the extra drag induced from the lift needed to turn and the extra drag of the flaps.