NOOB ALERT - I'm not trying to design a helicopter or a space ship or something ridiculous, I just want to design a little hovercraft with a computer fan, so don't get all indignant and righteous at me.(adsbygoogle = window.adsbygoogle || []).push({});

Anyhoo, I found this Lift equation and tried experimenting with some numbers, just to get a hang of it. I used specs from a 21,000 RPM RC heli engine and a .5 ft blade.

Here's the engy:

http://www.rcplanet.com/ProductDeta...click=109537&gclid=CLWdw925-LMCFYN_QgodngcAUQ

L = .5 * ρ * V^2 * CL * Sref

p = .002377 slugs/ft^3

CL = 2 * pi * angle of attack (I assumed a 1° (pi/180) angle of attack)

My problem, though is with the velocity. I assumed it was rad/sec and converted 21,000 RPM to 2199 rad/sec, and plugged it in. (Some website said it was right.)

However, I got 316.8255 lbs of lift with that velocity, which means that little RC heli engine could lift the combined weights of me, my mom and my dog (a really messed up answer.)

Some site suggested the velocity was the airspeed over airfoil, another said it was the change of velocity over time. After hours of searching I became flummoxed, so I decided to ask the experts.

The question, stated bluntly: What is the velocity measured in (ft/sec, rad/sec, etc.) for fans in this lift equation? Did I do anything else wrong? And if anyone has experience in hovercraft build-age, how did you go about calculating lift and motor/engine selection?

Thanks in advance for your gratuitous and gracious answers :3

Note: My unrealistic dream is to make a human-sized hovercraft large enough to fit my fat arse on it, so if you can help me with that too, please do :) I have taken electronics classes and 1 basic physics class, so hopefully my basic understanding of stuff is enough (likely not)

**Physics Forums - The Fusion of Science and Community**

# HELP ME - Lift equation for Helicopter Fan

Know someone interested in this topic? Share a link to this question via email,
Google+,
Twitter, or
Facebook

Have something to add?

- Similar discussions for: HELP ME - Lift equation for Helicopter Fan

Loading...

**Physics Forums - The Fusion of Science and Community**