# Upthrust calculations for hovercraft (1 Viewer)

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#### nuttall86

Hi,
usually don't ask for help but this is bugging me now!
I am working on a r/c model hovercraft, i have been trying to work out the upthrust but can not get a formula to do so.
I know the air cushion pressure is a factor, i am using a ducted fan for upthrust with attatched 9 v motor.

Any help would be very much appreciated.

cheers
nuttall86

#### 3trQN

An estimate could be made from the cushion pressure, and the pressure from the mass of air that the fan can shift ( its usually stated with the fan/motor if its a complete assembly ).

Pressure = Force/Area

Upthrust (F) = Pressure x Area

Your hover craft skirt dimensions and its weight will be factors also.

Weight = mass x 9.81

Youll want a nice balence between weight and upthrust and skirt area.

If you know the mass of air your fan can shift, you can calculate the skirt pressure. Though if you make sure its over rated and you can vary the speed, you can just find it experimentally.

The pressure will depend on the skirt design, so you can play about with that.

You could make more detailed estimates if needed, sorry if this isnt enough, my level of physics is poor.

#### arthuritus

Yeah, I'm trying to figure out the same thing, but I have no idea how to work out the pressure. If my engine output is 780m^3/h, where do I go from there? I can do the velocity pressure, which works out to about 2 kg, but im stumped when it comes to the static pressure. Anybody know?

#### Cyrus

If you are trying to calculate this analytically, good luck. Get yourself an electronic scale and try to measure the thrust with your model.

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