Fan Forces

[Leo S]

Hey my name is Leo Saturday, i am trying to figure out exactly how to determine the amount of force a fan will produce given a certain fan angle, fan rpm, and fan blade radius. I would like to know this because im trying to determine what is the easiest way to lift a human off the ground using simple fan power. Thanks alot for whoever helps me out.

[Fuzzwood]

Look at basic helicopter design.

[swansont]

Aerodynamics is complicated. I don't think you will find a simple formula to find the thrust/lift.

[Leo S]

Thanks a lot. However knowing these 3 things is it not possible to use an integral to find the force the blades produce at every point along its span? I figured this could be done fairly easily by using the sin of the angle divided by the hypotenuse or would I have to take into account rotational physics. Sorry if I misspelled anything, im on my phone

[swansont]

The equations tend to be nonlinear. Bernoulli's equation will give you the pressure from the air speeding up, and with the fan area you can get the force, but I don't know how to tie that back to the propeller properties. Hovercraft design sites might be of help, since this is what they do.

[Enthalpy]

You could get some first impressions, but these are not figures usable in a design.

 

In a helicopter at fixed altitude, air's exit speed multiplied by the mass throughput is the lift. Throughput is the area multiplied by the exit speed and by air density. Though, air speed isn't really uniform...

 

Now, and this is imprecise as well, the inclination of the blades let them cut air more or less flat, so their speed and angle relate with the air exit speed. In fact, air accelerates before entering the rotor mostly. However, blades need some extra angle to accelerate the air.