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Old Mar 17, 2013, 08:21 PM
Punch it, Chewie.
RPM314's Avatar
United States, NY, Brooklyn
Joined Apr 2012
721 Posts
Question
Lift fan placement

Hi, all. I'm currently drawing up plans for a hovercraft, and there is one detail I have not found much on.
I've seen the lift fan mounted either vertical in the center of the craft or tilted slightly forward and closer to the nose, but no info regarding how much of an impact this makes. I assume that it is to keep the air flowing well at high speed.
Does anyone have any experience with this? If so, is it worthwhile to complicate the ducting and build by tilting the lift fan?
Thanks in advance, -RPM.
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Old Mar 18, 2013, 03:10 AM
MHA webmaster
United Kingdom, England, Reading
Joined Mar 2011
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AFAIK, the inclination of a front mounted fan is to do with the geometry of the hull to accommodate the motor and makes no difference to air flow. At model scale you can take advantage of the small size of electric motors relative to the fan/ prop so you shouldn't need to incline it unless it is very far forward. Unless of course you are building a scale model in which case it's more about the look.
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Old Mar 18, 2013, 02:58 PM
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Alrighty then. Good to know.
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Old Mar 21, 2013, 08:21 PM
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United States, MI, Kalamazoo
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Mounting in the front will make it easier for the air to inflate the skirt at higher speeds. The air wont have to travel to the front of the craft against the flow of water.
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Old Mar 22, 2013, 06:45 AM
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Australia, VIC, Bass
Joined Jan 2013
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if using a full flow bag skirt an angled fan won't really make any difference but if it's a no flow bag there could be some forward thrust produced depending on the design of the duct and the angle - some of the earliest hovercraft designs used this layout
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Old Mar 23, 2013, 05:41 AM
MHA webmaster
United Kingdom, England, Reading
Joined Mar 2011
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I don't think we're talking about those early style craft here, if we were, the fan would need to be at an angle greater than 45 degrees, and in any case angled fans for thrust have been shown to be inefficient and more difficult to control compared to when mounted perpendicular to the craft with skirt takeoff. I really don't think it makes any noticeable difference to the forward thrust if you have a separate thrust fan, or to the performance over water.
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Old Mar 23, 2013, 06:02 PM
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Portugal/Ovar/Válega
Joined Mar 2007
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The best advantage you have by using a single angled fan/prop to provide trust anf lift (real life or scale model) is that you can lower the center of gravity of the craft by lowering the engine in the hull, without using any transmission (no extra mechanical parts nor extra spent money, no extra parts to break nor to inspect and maintain, no power losses...). I did it several years ago (1997/1998) with a nitro powered model and I will soon remake it with electric power.



bisonte terra (0 min 6 sec)


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Carlos

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