Important remarks: The propeller's pitch has a significant effect on the required engine power! Therefore any results in the calculated engine power field should be monitored carefully! As the propeller (with high-pitch) rotates faster and faster it is stalling more and more. It does generate higher inducted turbulent-resistance which takes engine power, preventing to produce enough thrust instead. In the real world the engine cannot rotate a stalled prop as fast as a lower-pitch prop would be rotated! By entering higher pitch with leaving other details the same, the calculator can NOT update the entered RPM but it will increase the required power (or vica versa)! In the real world by increasing the load (diameter or pich) the maximum RPM will be decreased, and by decreasing the load the maximum RPM will increase as the [load] and [maxRPM] are inversely proportional to each other.

Above all, counting with propeller's "high-pitch stalling" is important when the airplane is standing on the ground. If the airplane is flying then the propeller's pitch becomes more important, since the air that the propeller uses is "arriving" to the blades with the same speed the aircraft is flying. The perimeter speed of the propeller blades also very important! It should never be higher than the standard supersonic limit (approx. 320 m/s). The supersonic speed causes the blades to take a very high load due to the special airflow waves generated by the subsonic and supersonic changes! And finally, the Estimated flying speed field gives only an estimated information about the expected horizontal flying speed at full throttle. (The real speed may vary in extreme situations like acrobatic flying.)

Try to find the optimal propeller configuration that uses the maximum engine power AND the perimeter speed is not faster than 230 m/s AND gives enough thrust AND produces enough flying speed. The electric-powered small propellers are making difference as their optimal rotation speed is connected with the motor's RPM/V value. For the maximum power output see your engine's manual. The calculator can not check the reliability of the entered data therefore all inputs have to meet life-like value ranges. Real measurements should be made in order to check if the engine can rotate the given propeller at the given RPM, or the engine can produce the given output performance shown in the documentation by using the propeller you choose! The calculator is not "fool-proof" as you must enter valid data by fully understand what you are doing. Regarding to these facts the data calculated in the Required engine power field should be always in proportion with reality!

Note!  You may manually edit the CF (propeller's effectiveness coefficient) and Air density fields. When editing take care about the computer's regional settings: all Windows versions should use decimal point (not comma) between integer and fraction!

It's worth using the calculator by managing the Required engine power field mostly constant and in line with your engine's real (measured) power. If you feel that a configuration can be used, you have to test it and measure the real maximum RPM. You have to take care about the suitable prop sizes because: The engine is not loaded properly as it will overspeed with the too small propeller, OR the engine can be overloaded and cannot rotate the too big prop optimally, OR the given data is not possible in the real world.

Hint: Is it too hard to maintain the engine power constant with too many calculations? You may try the Optimal Propeller Calculator where the above calculations are "achieved from the opposite way."