Good Morning

I wish to build a model Hovercraft and have bought a 12volt centrifugal fan for lift with the following characteristics

Voltage 12volts
Current 15amps
Electrical power 180 watts
Outlet exhaust velocity 16.7meters per sec
Outlet exhaust area 0.01square meters
Inlet area 0.01 square meters
Inlet velocity 5 meters/sec

Volumetric flow rate (no load) 0.17 cubic meters per second

From this data I would like to be able to calculate the following variables
In a relationship

Gross weight (GW), skirt foot print area(SFA), ride hide (RH)

In the form

Gross weight(GW) in Newtons = Constant K(from above data) times function of SFA & RH

I.e. GW= K(Func(SFA,RH))

I appreciate that I have not expressed this using normal mathematical convention but hope there is enough information for some help in getting an answer.

Many Thanks all

David Hills
davidhills@riverford.co.uk

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HOVERCRAFT DESIGN EQUATIONS

Design equations will have to be developed from the following 'rules of thumb'. Of necessity these rules are only approximations of any physical situation and will require iteration to achieve an optimum solution in any case.

(1)The total (lift plus thrust) power to weight ratio for a practical craft will be 100 hp per ton (73.4 kW/tonne) of all up weight for minimal performance and 200 hp per ton (146 kW/tonne) for good performance.
(2)Lift power is approximately1/3 of the total power for skirted craft.
(3)Cushion length should not exceed twice the cushion width.
(4)Cushion pressure in pounds per square foot not to exceed a numerical value equivalent to the cushion length in feet or the cushion pressure in kg per square meter not to exceed 1/7.2309 times the cushion length in meters.
(5)Cushion air flow rate will be 3 times the cushion length, for a 2:1 cushion width to length ratio, times the square root of 2P/d times factor f where P is cushion pressure, d is air density and f is the air gap factor equivalent to 0.0025 times cushion length for smooth surfaces and 0.004 times the cushion length for average surfaces. Note this applies to a 'skirted craft' an un-skirted craft will have an f factor at least 10 times higher.
(6)Total hard structural clearance or ride height (skirt height plus air gap) will not be more than 1/10 times the cushion width for simple open skirt systems without stability elements.

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