WattFlyer RC Electric Flight Forums - Discuss radio control eflight - View Single Post - EDF for about 4kg thrust using low cost motors
Old 04-02-2020, 11:11 AM
  #7  
Shantz
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Join Date: Feb 2020
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Originally Posted by quorneng View Post
I fear that to produce 4 kg, or even 2.5 kg, of thrust within an 8 inch diameter body you would have to use a multi bladed fan. A prop will not create such thrust. Using two 4" (100 mm) diameter side by side I doubt even EDFs would achieve it.
Then there is the problem of getting the air into the fans efficiently and keeping the duct lengths as short as possible.
If it has electronic stability sufficient for it to hover then the launch acceleration is not really critical as long as it is up wards!

What you are attempting is quite a challenge so I strongly advise that you take it in gradual stages.
Your first task surely is to try to find what sort of thrust could be achieved from the biggest prop(s) your design can accommodate. 75% of this figure would give you a 'target' all up weight for your complete rocket.
Unless this looks a feasible then I am afraid it is "back to drawing board" to work out another way of doing it.

This was exactly how I approached my own EDF 'rocket'.
Having selected an EDF (I had already used similar in EDF planes) I built just the inlet and exhaust section and fitted it onto a test stand to see how much thrust was available.
From the result I judged it would be just feasible but only by using extremely light weigh construction. lightweight components and a very highly stressed battery with a full power duration of less than 1 minute.
Attachment 187923
It worked and took off vertically but the gyro controlled vanes in the exhaust were never sensitive enough to allow a hover. However once air born it flew very nicely as a normal RC plane at much reduced throttle.
If I reduce the amount of batteries to 2, it'll make the weight of electronics and batteries just under 1 kg. Foam frame would be the better option to reduce weight but I am not sure how I will mount everything on such a fragile frame. What frame did you use for your project?
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