Airflow measurement - again...

[Stephen Dubovsky]

  First of all, thanks for all of the replies/ideas.  Seems to have
generated quite a stir.  As for the problems mentioned:
  1) I had not thought of the cars acceleration affecting the sensor...  It
could be conteracted like in a MAF sensor by using 2 sensors, one in the
airflow, and one not, and use the differential forces to null the 'common
mode' acceleration.
  2) someone mentioned that a flap type meter does not measure density,
which I disagree with.  (Moving in a vacuum produces less drag - the old
physics class trick of dropping a feather and a hammer...) Drag is a
function of density as some kind person dug up the equation:
Drag=Coeff_drag*.5*air_density*air_velocity^2*projected_area
  3) humidity.  I agree humidity affects the density also and would create
measurement errors, but this also affects the MAF (which doesn't REALLY
measure MAF).  I brought up this point a while ago and I believe Todd
Knighton of Promotive Engineering (I hope I got this right;) says from 0-99%
RH the density changes <2%.  I have not rerun the numbers (haven't had a
chance to find some of my materials handbooks) to verify this, but Ill take
someones word for now (he seems to know alot about other stuff, so I dont
doubt him).

  As for LDA or other types of doppler anemometry (sp?), this also seems
quite interesting.  Will have to look into it...

Thanks, SMD
--
Stephen Dubovsky
dubovsky at vt.edu

95 Yamaha FZR600
83 Porsche 911SC
84 Jeep Cherokee