# HELP ME - Lift equation for Helicopter Fan

by iwannafly
Tags: helicopter, hover, hovercraft, lift, noob
 Mentor P: 11,925 To get matching units, your velocity should be calculated in ft/s. 2200 rad/s should correspond to 1100ft/s at .5 ft radius (assuming that value is the radius). Depending on your definition of Sref, you might have to use a smaller value, as not the whole rotor has this velocity. SI-units would make that easier. 1° angle of attack looks a bit small.
 P: 3 I was also unsure about the angle of attack. I though it was the angle between where the wind hits the airfoil and the chord line of the airfoil, but I didn't know what to plug in for the lift formula. Is that something I randomly approximate the range (like from 0° to 15°)? It's weird because at 0° the lift equation becomes 0. That's just weird to me. Doesn't the heli hover at a 0° angle of attack...? It can't do that with 0 lift, soo... -__-" Magical force of God lifts at hover? I am so confused :(
 Mentor P: 11,925 HELP ME - Lift equation for Helicopter Fan It depends on the blades and their angle relative to their direction of motion.
 P: 546 You may want to take a look at a tool called Javaprop. It uses simple blade element theory (Basically you divide your fan blades into sections and compute the local aerodynamic forces) to compute the lift (thrust), power requirements, RPMs for a blade geometry you create. Here is a link: http://www.mh-aerotools.de/airfoils/javaprop.htm Regarding your velocity question: Velocity, regardless of application, always has units of length/[unit time]. Angular velocity, on the other hand, is a measure of rotation rate and has units of angle/[unit time]. The latter has the same units of frequency.
P: 3
I looked at Javaprop - though I've done Java a long time ago, I don't feel like re-learning everything, for a propeller :-l

I made this spreadsheet for the Lift equation: can something PLEASE download it and check if it's alright? I'm getting a few outrageous answers (such as 1297.661361 lbs for a 12in radius prop, at 17,000RPM, pitch=1°) that don't feel right.
Attached Files
 heli_copy.xls (28.0 KB, 5 views)
 P: 546 You obviously didnt look at it hard enough because it doesn't require any programming. Give it a shot I assure you it will save you time in the long run.

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