Calculating Thrust from Propellers for Model Airplane

[reg]

can anyone tell me how to calculate thrust for a model airplane. i know the propeller size and pitch and also the engine power and RPM.

Any help would be much appreciated

regards reg_ram

 

[russ_watters]

Well, the simplest way would be if you know the rpm, you can multiply pitch by rpm to find the velocity of the air, then use bernoulli's equation to find the pressure (and multiply by surface area traced out by the prop to find thrust).

The reality is probably a little tougher: rpm will vary with the speed of the plane - the faster the plane goes, the easier it is for the prop to spin. What ends up happening is that the horsepower generated remains roughly constant while rpm changes.