4298Views2Replies

# How much thrust usally does a 9 inch fan give out ?

How much thrust does a 9 inch fan give out? Also how about a 1.5 feet R/C helicopter. How much horsepower is required to lift a human. How much thrust. If you had a 100lb man and had 101lb thrust how far up in the air would the 100lb person go. Sorry really dont want to do the calculations right now.

## Discussions

You generally just need to know the pitch of the propellor and the RPM.

propellors are generally marked, and an rpm meter is easy to obtain.

there are lots of online thrust calculators once you have this info.

You don't provide enough information for anyone else to "do the calculations," so you're going to have to do some more work yourself. Too bad.

The thrust from a fan depends on the rate at which it pushes air through. If you check the data sheet for your specific "9 inch fan" (they're all different), it should give you a flow rate in cubic feet per minute (CFM).

a) The density of air (according to Wikipedia) is 0.074887 lb(m)/ft

^{3}, so you can convert the flow rate into a mass flow directly (CFM * 1.2481x10^{-3}lb(m)/s).b) The area swept out by a "9 inch fan" is pi*(4.5 in)

^{2}/144 = 0.44179 ft^{2}. You can convert the flow rate into a velocity in ft/s: CFM / 0.44179 / 60.c) Now you can compute the thrust T = v * dm/dt in pounds of your fan by multiplying the results of (a) and (b), and identifying lb(m) with lb(f).

Repeat calculations (a) and (b) for your 1.5 f RC helicopter fan. You might even be able to skip directly to (c) in that case by reading the data sheet.

Using 101 lb of thrust on a 100 lb person, you're effectively lifting them at 0.01 g (100 lb of thrust makes them "weightless", the extra 1 lb / 100 lb weight is the upward acceleration). Assuming there's no air resistance or instability, they'll just keep going upward, very slowly. In real life, I suspect they won't go very far before falling off.