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Old May 22, 2006, 09:05 PM
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Thrust Tube for Wemotec Mini Fan


Hi all, want to put a small thrust tube on my Mini Fan 480, but only have about 4 inches to work with. I need to know how far I can choke down the thrust tube to get the most thrust. Any help appreciated. Rich
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Old May 22, 2006, 09:41 PM
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Rich,

Choking down the exhaust will decrease thrust, but increase efflux velocity. Wemotec recommends an exhaust diameter of 56mm for optimum thrust and efflux velocity. Although choking down to 56mm in only 4 ibches may be a bit abrupt.

You might try sending a PM to Herb or Haldor. They're both very knowledgeable in this area.

Rob
Old May 31, 2006, 07:51 AM
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If you go to www.pulserate.com and download their free software you will be able to print out a cone to suit your exact dimensions. IE 65mm from the back of the fan reducing to approx. 56mm at the end of the exhaust over a length of 4 inches in your case. I have the same WeMoTec mini fan and reduce over a length of 92mm to a 52mm outlet which gives me a large increase in Amps and exhaust velocity. A common reduction that you will hear quoted, however, is about 80% of the fan swept area. I know a 52mm outlet still works and gives me great results on a Typhoon 2W20 motor on 4S. 48A and I have measured 920g of thrust.
Old May 31, 2006, 09:16 AM
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4 inches is long enough.

If you taper down to 56 mm the efflux velocity rises, but the thrust does not go down (i.e. efficiency of fan rises as well).
If you go down further more, you start to trade in thrust for efflux velocity.
The minimum I saw was 48 mm.

This is for the original five bladed WeMoTec Mini Fan. Other 69 mm designs with less blades are more critical reg. the exhaust dia.

Oliver
Old May 31, 2006, 01:07 PM
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Does the shape of the tube matter? In other words if it gradually changes from "round" at the fan to "oval" at the end, will it have any adverse effects?
Old May 31, 2006, 01:23 PM
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Rich,

This should do the trick!

(Tapered down to 56mm)

Made with Cone 1.3 a VERY handy program for making all kinds of Cone shaped obejects!!

Have fun,

Cheers,

Appie
Old May 31, 2006, 04:57 PM
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If anyone is intersested I have this tool that I want to get rid of. It is a perfect fit for the minifan and was made on a CNC lathe. The lip on the front makes it so the thrust tube slides perfect over the fan and has a smooth transition on the inside.
Old May 31, 2006, 10:51 PM
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uh how much?
Old Jun 01, 2006, 02:12 AM
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$80 plus S+H. It is 9 inches long.
Old Jun 01, 2006, 02:22 AM
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Quote:
Originally Posted by danj31
$80 plus S+H. It is 9 inches long.
It's a good thing you included a picture, danj!
Old Jun 01, 2006, 02:45 AM
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The aluminum tool is 9 inches long also-
Old Jun 01, 2006, 03:07 AM
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Quote:
Originally Posted by danj31
The aluminum tool is 9 inches long also-
exactly why i said it's a good thing you posted a picture, so the buyer is knows what they're buyin'

Old Jun 01, 2006, 08:55 AM
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Quote:
Originally Posted by aireze
Hi all, want to put a small thrust tube on my Mini Fan 480, but only have about 4 inches to work with. I need to know how far I can choke down the thrust tube to get the most thrust. Any help appreciated. Rich
Optimum thrust/efflux velocity point depends on the airframe. Details please. Do you want max speed or max thrust?


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