Pitch of Rotors

[isaysroar]

Should helicopters be effecient or powerful?

[jander14indoor]

The goal is the longest flight time possible, tends to point to efficiency to me. I mean, on any flight you have a fixed amount of fuel (rubber). If someone builds a more efficient copter than you and puts on the same amount of rubber, they will fly longer and win. More power just means whatever fuel you carry gets burned faster, meaning shorter flights.

Hope that makes sense. Not sure how that relates to rotor pitch...

Jeff Anderson
Livonia, MI

[Itsanthonguise]

what do you mean by the pitch of the rotors?

Because right now my rotors are like 1 inch tall and 29 inches in length.

[jander14indoor]

Pitch. At its simplest, think of your rotor as a giant screw. Again, at its simplest, the pitch of your rotor is the distance it would travel through a solid in one turn if it were a screw.

Propellor designers talk about pitch as if it were the real way the propellor (rotor) behaved because its easy to visualize and describe the physical rotor. In reality it doesn't move like a screw through a solid, there's a lot of 'slip' and the rotor doesn't move through the air as far as its geometrical pitch says. But it does describe the blade phsyically and allow comparisons. And when detailed analysis is done, all that slip stuff is taken into account.

See some of the following sites:
http://www.pilotfriend.com/training/fli ... /props.htm
http://www.allstar.fiu.edu/aero/flight63.htm
http://members.eaa.org/home/homebuilder ... lemma.html

Note, I sent you to sites about propellors as they were quicker for me to find. There is NO difference between a propellor and a rotor from a how they work point of view. Just how they are used.

Jeff Anderson
Livonia, MI

[isaysroar]

okay maybe if I rephrase it? Best angle for the helicopters blades? (ex: 18 degrees)

[talicoa]

For the highest efficiency, they should be flatter at the tip and steeper towards the center. The rotor spins faster at the tip. Look at a real aircraft propeller. It seems like this would be hard to build, but it pretty much comes naturally when you make blades with the leading and trailing edges running through the center of the propeller shaft.