DIY ducted fan

Goedendag Terence,

Tread carefully, computerfans or not designed for DF speeds.

Prettig weekend ;-) Ron van Sommeren

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The message from "Ron van Sommeren" contains these words:

Hi Ron, they tend to be made from high impact engineering plastics these days so may stand up to it OK but may need fine balancing as most of them only run at 1500 rpm or thereabouts, not so bad as it will be in a duct with extension tube on the back and if it goes bang then tough luck, got a nice ittle plan for a Vampire free with RCM&E this week March issue) that should have a i/c engine in the nose which makes it look nothing like a Vamp so was thinking on converting it to ducted fan. Many years ago when I was with Cosford Aerospace Museum Society I tried to find spares to rebuild a Venom FB4 that had been sent back from Kai Tak as deck cargo and was in a pitiful state when it arrived, serial was WR539 as I recall and I saw this serial again a while back on a model of a Venom in one of the magazines. During my search for spars I approached the Swiss Air Force who still flew them and we ended up giving 539 away and swapping a Bristol Hercules radial for one of the Swiss AF Venoms which is now at Cosford, we were very pleased to get a flyable Venom for the collection but I wasnt aso happy to get a £4000 bill for flying it in to Greenham Common,

regards, Terry

Terry, running at 1200 rpm is not a problem, but running at 10-30 times that speed is, balancing aside. The plastic may be strong but it may be too elastic and stretch or break.

DF work (either slimer, electric or even turbine) needs solid engineering and materials science to make it work. Unless you're qualified in that field, I'd stick with the commercial products that have been tested and do work.

Most EDF's are running at 20-30,000 rpm, so you're talking serious levels of inertia.

Years ago I took the center part of a computer power supply fan and mounted it on an 11 turn triple motor I had lying around and created an air-powered RC10. It sure sounded mean, and I never had a problem with the fan blowing up. Feeling pretty good about how well it went, I made a second one and apparently the plastic had a flaw in it because it DID blow up, and it embedded plastic blades into the ceiling, drywall, etc. Very nasty. And it was way out of balance after it threw a few blades off ;-)

If you do it, best advice is to Be Careful.

Chris

from "byrocat" contains these words:

Must admit looking at the cost of a ducted fan unit it hardly seems worth the effort of building your own, just wondered if anyone had tried it on an aircraft as I know a couple of people who have built r/c airboats using computer fans but pushing something over water as against getting it into the air and keeping it there is a different matter.

I have hit these things with a hammer and they didnt break but have no idea what pitch the blades are at or even if the through-put of air would be sufficient, it may be a case of 'light blue touch-paper - stand well back' and see what happens,

regards, Terry

The message from "Hal" contains these words:

Hi Chris, had these fingers a long time and found them quite useful, also I am ugly enough without altering my features so care will be Nr 1 priority as with any experimenting, one of the fans I have laying around I tried twisting a blade off but only managed to cut myself on the edge so they are pretty tough but as already mentioned elasticity is something else and if the blades 'grow' in the duct it could be a case of molten plastic flying around,

regards, Terry