I am somewhat new to RC helicopter, so this might seem a bit ambushes.
I would like to design my own propeller, however while I am vary good at math and a fair sculptor (mostly carbon fiber). I cannot find sufficient equations on the internet to complete my design. I know that the angle of the blade changes as the radius changes from the hub moving outward, keeping the pitch constant. The equation I am using,
Angle = Tan^-1(pitch / (2*pi *r)) where 2*pi*r = the circumference. My question is, how do I know what pitch to use? This should be based on the rpm of the engine right? Do you have formula for it? Even recommending a book would be vary helpful. Any response is greatly appreciated, thank you for taking the time to read this.

ambushes? No ambitious ... probably.
vary .. very?

Anyway ... since you posted in the heli forum and not the airplane forum ... I assume you are referring to the rotor blades (main and/or tail) ... what you called a propeller. Do you need fixed pitch blades (lift determined by RPM changes) or do you need Collective pitch blades (blade AOA determines lift as RPM remains constant).

With fixed pitch helis ... the blades do seem to take a likeness to airplane propellors, however, collective pitch blades are generally the same shape (pitch wise) from root to tip.

So either you are in the wrong forum or your math just got very simple.

Good Luck,
d.tipton

If you are referring to the main blades, the only time you'd need to work out the shape of the blade is, as tippy said, you're working with fixed pitch blades. In a collective pitch bird, the blades simply use an airfoil shape and have no AOA, you've got semi-symmetrical and symmetrical airfoils and the rotorhead determines AOA.
*EDIT: I should note that on SOME larger helicopters that aren't designed for agressive flying, the blades do have a small ammount of AOA, but this is for very big birds like the yamaha rmax and others (I think?).

If you're working with fixed pitch, the ammount of pitch you build into the rotor is entirely dependent on the motor, the voltage, and the overall headspeed you wish to achieve. Less pitch = more speed required to produce the same ammount of lift and you get a more stable (but less responsive, elevation wise) helicopter. More pitch will result in generating more lift at slower headspeeds, but it will load the motor more and the helicopter will become less stable due to a lack of gyroscopic force.

In most cases, it's a matter of finding the happy medium between the two extremes. I believe most heli manufacturers that produce fixed pitch blades have already accomplished this, so it may be worth while to just use the stock blades as a reference for initial measurements and then make any small alterations you need to from there. Less pitch is probably more desireable than more, but it will require either a larger pinion gear or faster motor to produce the right ammount of lift.

Another thing to consider is staying within the operation range of the physical mechanics of the helicopter. You could make a fixed pitch helicopter ultra stable by removing much of the pitch in the main blades to achieve very high headspeeds. But now you risk damaging the mechanics (plastic hubs, bearings, etc.) that aren't designed to operate at high rotational speeds like that.

I'm not a math whiz, as such I can't offer any numbers for you, but these are some general ideas you can consider in the future from someone who has messed extensively (to my own cost! ) with different rotor setups in fixed pitch helicopters.

Yes tippy I did mean ambitious, thank you for the correction. Also I am referring to the blades on the main rotor, sorry for the confusion. I would like “lift determined by RPM changes”, I am a little confused though, am I using the wrong formula to design the blades altogether. Should I be mostly concerned with the airfoil and not the pitch?

What helicopter is it? It's not a matter of choosing which one you want to use, it's which one does your helicopter use.

In a fixed pitch helicopter, the blade grips and blades never move. The blades are built with a certain ammount of pitch much like an airplane propeller, and thus, the faster the main motor and the rotorhead spin, the more lift is generated.

A collective pitch helicopter is more complex, however, as these are how real helicopters operate, and is the "true" mechanics of a helicopter. These helicopters use blades that have no area of attack (pitch). Instead, the motor typically runs at a steady RPM, and the blade grips and blades them selves rotate in flight to produce the area of attack and subsequently, lift.

If it's a fixed pitch helicopter, then you need to build pitch into the blade, or atleast produce a flat bottom airfoil (semi symmetrical) with a twisted root, in order to produce the lift to get the helicopter off the ground.

If it's collective pitch, then it's just a matter of finding an efficent airfoil design, and then deciding on the type of flight you're interested in. Flat bottom blades (semi-symmetrical) produce good lift and stability in normal upright flight, but don't work well if you flip the helicopter or try very fast forward flight. Symmetrical blades use the same airfoil shape on both sides of the blade, which makes it well suited in both upright and inverted flight and thus better for aerobatics, but not as efficient as flat bottom blades would be if you just want to hover around.

Ok Credence thank you for your vary detail response, I understand now. Is there some formula(s) that I can use to design my airfoil (for collective pitch), based on RPM, weight or any other factors I should be concerned with. I have to be honest I have not done much searching the net with the new info you’ve given me, but both you and Tippy seem vary knowledgeable so I was hopping I could get one last little nudge.

Thank you, you’ve been vary helpful

Have a look here:
http://www.nasg.com/afdb/list-airfoil-e.phtml

Its a ginormic database of all kinds of airfoils used in both planes and rotary aircraft. The mathmatics are over my head, but I understand the pictures! .

They've got registered airfoils from the AH-1 attack helicopters and a bunch of others too, cool stuff .

WOW!!!!!!! thank you.