X-Mozilla-Keys:                                                                                 
Chuck Dunlap wrote:

     So I came up with the idea of using those cheap little cooling fans
     on Pentium processors as air flow sensors to gather
     data under real world conditions while one is flying around.

     One can get plug in cards for a PC that has counters on it.
     You then need an LED and photo transistor to detect the blade RPM
     which should (after calibration with the Omega air speed meter) be
     proportional to air exit velocity from the back side of the rad.

    Paul, some of those CPU cooling fans have a tachometer built in. I
used one and tied the output to a freqency counter to measure airflow
at only one point behind the radiator. The problem is that these
permanent magnet motors have to overcome the magnetism holding the
rotor inline with the stator to begin turning and requires air speed
of at least ~20 MPH. I took one of these apart and removed the coil
and iron stator so it would spin freely while keeping the tach
function intacked. Then it would start spinning at about 5 MPH. I
calibrated it by holding it out the window and driving at different
speeds noting the frequency on the counter.

    I think this would have provided better information if I had used
four or more as you suggested. I was trying to optimize ducting but
with only one point of reference, results were inconclusive. I may try
it again when I get my radiator relocated.
Chuck Dunlap
chuck@zekes.com

Great work Chuck. Do you remember the brand name?
I will pop over to Fry's and buy half a dozen.

I could make a little switch box to use one counter and look
at each tach in turn like some EGT/CHT gauges work.

Wonderful news Chuck. Thanks.

Paul Lamar
 
The Aircraft Rotary Engine Newsletter.              Powered by Linux.

http://home.earthlink.net/~rotaryeng/            http://www.linux.org