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Archive for October, 2011
Posted by Herb | Oct 13, 2011 @ 05:29 PM | 36,771 Views
Once in a while an EDF fan comes along where there's plenty of measured data to evaluate how good it is ...

Here's some nice and complete systematic data for the new 90mm JetFan :

Of great relevance of the overall fan efficiency, defined as

efficiency = (mechanical work done per unit time) / (input power) , in e.g. (N.m/sec)/Watts

A good substitute for the above quantity is, based on simple formulas relating work to fan thrust and fan efflux:

efficiency = (const.) x thrust^(3/2) / (input power)

You would imagine that if somebody is really serious about designing an efficient fan they would take the time to actually do relative measurements of different designs, in order to figure out which rotor/stator design in the end is best.

Indeed that is how serious fan designers (eg WeMoTec, Daniel Schuebeler etc.) indeed do it ...

But then often a new design comes up (nowadays every other week, in some cases a copy of somebody else's rotor, with one blade added or subtracted so it don't look like a copy ) - without any clear measurements of anything.

If it is a clear shameless copy of a DS-51 fan, then it has to be as good as the DS-51, right ?

Then the relentless overhype follows ("20% more efficient than anybody elses fan'" - to the point that now the overall efficieny adds up to 110% ), and more adverts such as "best fan I ever tried in my xx" etc.

Now, the Jetfan 90 data is interesting and accurate enough to pull out :

1) the relative efficiencies of different motors in the JF

2) the very slow rise of efficiency with power/voltage

3) the large errors inherent in all these measurements

4) the wide spread in motor efficiencies (up to 31%).

Posted by Herb | Oct 02, 2011 @ 12:29 PM | 27,441 Views
Last month I had a chance, while spending some extended time in Paris for work, to visit the Air and Space Museum in Le Bourget.

The museum is located within a large airport in the Bourget suburb of Paris, and is the site the Paris Airshow (which takes place usually in June).

It has an amazing collection of - what else - French (mostly Dassault) jet aircraft, including some weird looking experimental aircraft, but also Montgolfieres, some very early 20-th century planes (Bleriot), some very nice WWII warbirds (including a FW-190A and a Spitfire Mk. IX) and two Concorde.

A Visit to Le Bourget Air and Space Museum (2011) (3 min 14 sec)

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