Choosing A Prop for best performance

Tools needed 

To prop for speed

 Choose a prop with a pitch between 6 and 8 that produces at least a 1:1 thrust to weight ratio and runs at the bottom of the RPM range on the ground.  

 To prop for aerobatic performance

Choose a prop between 4 and 6 pitch that produces maximum thrust and runs near the upper RPM limit.  

Prop for a speed of 65 MPH - 80 MPH. 

. 

Diameter and pitch

Diameter is the first number = the overall length of the prop

Pitch is the second number = the theoretical distance a prop will move forward with one revolution in inches.

Ex. A 12x9 prop, will move forward 9” with one revolution assuming 100% effeiciency.

More Diameter = more thrust (torque)

More pitch = more speed

Too much dia or pitch for a given engine will overload the engine, and cause overheating.

Prop size and pitch are determined by the particular model and desired flying style with the additional requirement that the maximum rpm should not exceed the manufacturers recommended maximum rpm.  

     Each engine has a range of propellers appropriate for it. Be safe.  It is best to follow the manufacturers recommendations for proper prop sizes.

     Some models fly better with bigger diameter and lower pitch  and other models are better with more pitch and less diameter.

     Props with pitches of 8 or more is for SPEED. The high pitch and short diameter prop would try to pull the airplane very fast. 

     Takeoffs are less difficult using a larger diameter prop with a lower pitch and can maintain lower speeds for landing than a high pitch prop.

A 10X6 prop turning at 10,000 rpm will try to pull a plane about 80 mph.  This is not a good choice for a trainer that is typically designed to fly closer to 50 mph.

The 11X4 or 12X3 will produce good static thrust and efficient  take-off performance and aerobatics performance.

If the plane is designed to fly slow use a long prop with low pitch. If the plane is designed for speed use a shorter prop with a high pitch.

Match the prop to the engine AND the airplane. 

      It is extremely important to balance the propeller prior to installation of the engine.  
Failure to do so may cause  damage to the  engine and/or the airframe.

     Discard any propeller that is nicked, scratched, cracked or damaged in any way.

A 3 blade has 1 more blade than a 2 blade, so it will move 1.5 times the volume of air,

A 4 blade will move 2 times the volume