Perimeter speed =
Required engine power =
Estimated flying speed =
9.1 - Developed by
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.
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!
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
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.
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"
and you may also read about the used calculation formulas.