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Old Feb 10, 2012, 06:55 PM
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... I had lengthy discussion on this topic with Daniel Schuebeler a few years ago.

EDF fan conditions are never static as the air enters the duct (say of a 90mm F-16) already at 70 m/sec, so that the description of it as "static" (whatever that means) is physics nonsense.

That is of course the reason why "static" fan measurements with a good sized intake lip or intake duct, albeit imperfect, correlate very well with "flight data" ( I found that out a few years ago).

The absence of any significant fan unloading in flight (which we measured by video and doppler, thus obtaing the fan rpm in flight vs static), also pointed to the validity of the static data.

Daniel himself described to me all he details of his wind tunnel setup at the Technische Fachhochschule Lippe, and how difficult it was to quantify efficiencies once you started the additional airflow.

In any case the present exercise is, for me, a way of avoiding costly and time-consuming mistakes of putting a junk fan in an otherwise quality airframe (eg AW Me-262). I install my fans, for a number of reasons, in such a way that I want to avoid as much as I can having to take them out if I can ...

Incidentally, compressibility effects can be estimated and are at (v/c)^2, where v is the airflow speed and c is the speed of sound.

For airflow at 70 m/sec that is a (70/330)^2 = 5% effect.

Here are a few more interesting comments related to fan efficiencies and relative tradeoffs :

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Last edited by Herb; Apr 03, 2012 at 02:11 PM.