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Old Feb 12, 2012, 12:34 PM
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Finland, Espoo
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Originally Posted by lhb009 View Post
I am in the process of building a 5' EDF flying wing(EPP foam). I have built about 30 pusher flying wings, but I have never built or flown EDF models. What key differences would you point out? In addition to my flying wings I have built, more than a dozen balsa buildup, gas/Electric/sailplanes.

I plan to make it 5' span, weigh less than 4 lb, dual EDF units on the top rear where the prop normally would be. How big of EDF units should I start with? I was considering 60-90mm units. I will be flying it with a DX6i, with HS 82mg servos. Is there anything else I should know prior to buying electronics?
I have to first admit that I am less experienced than you, especially about flying wings. I have only assembled couple of Multiplex Xenos. However, I have tried this:
- I have flown Xeno with similar than the stock motor and prop
- I have flown the Xeno with an insane motor (it achieves flutter speed in level flight)
- And I have flown the Xeno also with 68mm EDF with 4S battery

The difference between the prop flying and EDF flying is mainly that the EDF does not have that bad P-factor and the tendency to roll on launch does not exist with EDF. The EDF version goes straight and the flying qualities are very pleasant.
Launching the EDF-version was a little bit harder because less static thrust available. However, taking this in account, the EDF-Xeno can be hand-launched almost identically than the prop Xeno (the more normal motor version with reasonable thrust).

I am flying now also some EDF jets and in general I think they are easier to fly than the prop planes because they go straight and do not suffer from the P-factor nor from the prop wash over the wing and tail. EDF is a bit like pusher propeller but with less static thrust. Electric Ducted Fan does not take much time to spool up, it is not like turbine. Instead it is a small diameter propeller in a duct really and there is no magic. The prop efficiency of a typical EDF is lower than that of a prop without the duct around it largely due to the fact that typically the EDFs have small diameter and the basic rule is that it is better to increase the speed of greater air mass a little than increasing the speed of a little air mass a lot. EDF does the latter.

EDF plane is easier to fly if there is enough thrust on the EDF system. That usually means that the EDF diameter is as large as possible.
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