## Customer asks a good prop question with implications…..

Hi Dave,

Quick question about the APC props. I note that for multi-rotor the sizes seem to be with 4.5 pitch. Is there a reason why I should not use say, 9×6 with 9x6R for multi rotor craft?

Thanks
David

Hovering props or props that produce best thrust in static air tend to be pitched about 1/2 of diameter or less. As you add more pitch, they can fly faster, but have less bite in static air. They can actually be stalled and have less lifting force until the prop gets to moving forward. This is also why props which are the same otherwise make more noise with lots of pitch. Initially they are stalled or partially stalled. So, if you need more prop than a 9-4 to apply the power to the air you have available in your system, you go to 10-4, not a 9-6. Certainly a 9-7 would be such a bad choice as to be worthless.

All this is considering the model is essentially hovering all the time. Even forward flight isn’t quite as forward as an airplane. Other types of flying and machines can have other considerations that make higher pitch (relative to diameter) correct but this is unlikely in all multi-rotors except maybe a racer.

What we call these props is 1/2 square. Meaning pitch is about 1/2 the diameter. A pattern aircraft or war bird might use a 3/4 square (like a 10-7 or 11-8) or even a square prop (like 12-12) because hovering is not a required and speed is more desirable. These setups are poor on hole shot, but once they get moving they really go.

Dave
Hi Dave,

Quick question about the APC props. I note that for multi-rotor the sizes seem to be with 4.5 pitch. Is there a reason why I should not use say, 9×6 with 9x6R for multi rotor craft?

Thanks
David

## Handy Factors For Common Calculations

Calculating Pitch Speed:
RPM X Pitch Inches x .0009469 = MPH Pitch Speed

Convert wing area from square decimeters (dm) to Square Inches and back:
Sq dm x 15.5 = Square Inches
Square Inch x .064516 = Square dm

Servo Torque:
KG CM x 13.887 = Inch Ounces
Inch Ounces x .072 = KG CM

Ounces & Grams:
Grams X .03527 = Ounces
Ounces X 28.3495 = Grams