View Full Version : New comer in Oz Multiple fans for lift?

michael30.06 - n/a
28-Feb-08, 06:02 AM
http://hovercraft.org.uk/images/icons/smiley_icons/icon_rolleyes.gif Has anyone used fans in series one after the other sort of like the concentric propellers used on some swamp boats. Or the multiple sets of blades in a turbine? think ultimate performance. http://hovercraft.org.uk/images/icons/smiley_icons/icon_twisted.gif

profqwerty - n/a
28-Feb-08, 01:12 PM
concentric...do you mean like the "contra-rotating" props?

I've seen them on boats...

I imagine they'd be better for high pressure / low velocity...?

Turbines are the other way round I think...very high air velocity, but small blades wouldn't generate much pressure.

jar2 - n/a
28-Feb-08, 02:15 PM
Do you mean a multi-stage axial fan? In theory, they should perform well in a hoverrcaft lift system. But, like all things mechanical they have a downside - cost and mechanical complexity!

michael30.06 - n/a
28-Feb-08, 07:39 PM
http://hovercraft.org.uk/images/icons/smiley_icons/icon_cool.gif I suppose I am thinking of more than one fan rotating in the same direction both in the same duct, even on the same axle as an improvement in lift or increase in pressure in the Plenum?

Paul Fitz - n/a
1-Mar-08, 04:46 PM
multi-stage axial fans work ok, but why do you think you need one? Determine the size and laden weight of the craft first and then design the lift system to suit. It is quite unusual to need a multi-stage fan whether 2-fans on one shaft or Contra-rotating.

The more fans the greater the power consumption. 2 similar fans on one shaft would give almost twice the total pressure (note: not static pressure) of a single fan of the same size, but absorb twice the power.

Note: you cannot "increase the pressure in the plenum" with a change of fan. This is determined by the cushion footprint and the weight of the craft. The pressure at the fan outlet will be slightly higher due to losses (resistance) in the distribution system regardles of fan type.

See this artical for more info on multiple fans-

http://www.greenheck.com/technical/tech_detail.php?display=f (http://www.greenheck.com/technical/tech_detail.php?display=files/Product_guide/multfansystems) iles/Product_guide/multfansystems

michael30.06 - n/a
2-Mar-08, 09:25 AM
Thanks for the article link. Fairly involved stuff. I was just wondering, about the multi fan idea to try and understand all my options. More than one way to skin a cat so to speak. At times I seem to have available some smaller diameter fans than are called for in the UH18 plan. Ive been told I will need a 30inch lift fan. If that becomes a problem here in far north queensland I wanted to know if I could achieve the same result with 2 smaller fans in series.

But this is all just a fishing expedition until I commit and buy the plans, I'm sorting out what resources I have available that will suit the build and what I should sell or trade to get what I don't yet have. I have a thrust prop from a light aircraft and a light 4cyl engine. But I must weigh the engine and see if it is roughly the same as the recommended subaru unit. It's no easy task to weigh an engine on your own.

I have been offered a supply of foam boards at a good price but still have to confirm exactly what the foam is. ie PVC PU or some other set of letters.

Thanks very much for your patience with my questions.