Thread: Article Sky Angel 50mm EDFs Review
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Old Jan 21, 2013, 02:45 PM
chas650r is offline
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santa barbara, CA
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Originally Posted by mopetista View Post
...well, you know the discussions on the threads: as soon as you bring up this topic you get overly simplistic formulas thrown on the head which all assume that the speed of the exiting air is uniform - then, it is correct, you can infer the efflux speed solely from the thrust and the outlet area (and therefore, diameter).
This might hold in good approximation for longer thrust tubes where the air molecules had more opportunity to exchange energy with a resulting flattening of the velocity distribution.
However I have yet to read about when and where and why the approximation of uniform air efflux speed is working, and to what extent. People are just proclaiming that in a pretty dogmatic fashion which I find puzzling.
What has become clear is that the multiblade fans do accelerate air in a more uniform manner and therefore thrust is not suffering when running completely without thrust tubes - whereas for fans with lower blade count it seems better to mix the air more and possibly have some diameter reduction (air with uniform speed has higher thrust because higher velocity means a quadratic rise in energy needed whereas thrust rises just with momentum change, i.e., proportional to the efflux speed...)
Seems like it's still best to "fly" the differences between fans and combos...
agreed! the in flight test takes into account all the variables and puts them to the real test.

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