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edf tube

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john davidson 102/12/2019 21:30:27
69 forum posts

I am installing an edf fan in an F16 foamy, is it good practice to make a tube the same diameter to connect the fan assembly to the exit of the fuse? I imagine this might help efficiency by limiting turbulence in the duct

Stuphedd02/12/2019 22:52:39
721 forum posts
376 photos

Hi not quite sure what you mean? But lately I have been "playing " with fan exit tubes , jet tubes, to see what effect it might have on my Mig 29.

I assumed the tube should reduce in diameter to about 80% at the end , as this would be the same area as the Fan ring , and gives about 7 deg included angle to the jet pipe , I machined various tapered tubes and shrunk pop bottles onto them so to get a good smooth surface ,light and easy to do.

I already had a static thrust test rig so it was only a few hours work .

the results were NOT what I expected and were somewhat puzzling , .

The best Static thrust was the parrallel tube with no convergence ??!! and the proof was in the flying , cos it was the best too .

The main thing to do is make sure the wires to the motor , which normally clutter up the jet tube are suitably streamlined./


Steven S02/12/2019 23:28:16
369 forum posts
193 photos

When I built my Sabre Jet I came across this duct calculator. It is best to have the duct taper to the calculated dia at the exit.  I made my tube out of some old X-ray film.

Duct calculator

Edited By Steven Shaw on 02/12/2019 23:29:50

Steve Balaam03/12/2019 09:38:07
137 forum posts

I've used this program successfully to produce a thrust tube template, very useful.


john davidson 103/12/2019 21:00:26
69 forum posts

thanks for the interesting replies, I have previously made a twin fin delta with a bare fan unit mounted , flew it then added a cut down polystyrene cup which narrowed the exit, and it flew appreciably faster and was then referred to as the Dyson, The F16 kit was a bargain discontinued HK. kit bought at Barkston bring and buy and came with no info as to setting up so might try the same approach after the maiden to see if it goes faster.

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