Air flow measurement - again...

[Stephen Dubovsky]

  Just had a curious idea.  Im going to spit out every pro/con I can think
of just to get the idea out of the table for discussion.

  Instead of using a MAF w/ its flow reversion problems, why not use a
strain gauge?  Put a small object, like a sphere, in the airstream connected
to an aerodynamic shaft to a strain gauge oriented to measure force in the
direction of flow.  Should be able to read drag on the object quite
precisely and quickly.  There could be non-linearities due to the shaft and
object shape, but a look-up-table/linerization-circuit could correct these.
After linerization, there should be no problems w/ flow reversion (it would
measure reverse flow) or non-symetric operation.  It should measure
something very similar to a MAF (and could probably be made to replace one.)
It may also have difficulties at low flow rates like the MAF due to very
small drag force, but...  If the object is something nice like a sphere, one
could even find the drag vs diameter equation in any good text.  There would
be a tradeoff of object size vs low speed sensitivity, but I think that it
would be MUCH less restrictive than a flap type meter.

  Ive had a bit of practical experience w/ strain guages (in a small wind
tunnel even - to measure lift and drag) and could cook up something to stick
in a throttle body, but I dont have any way to test it yet.  

  Any thoughts/problems/opinions out here?

SMD
--
Stephen Dubovsky
dubovsky at vt.edu

95 Yamaha FZR600
83 Porsche 911SC
84 Jeep Cherokee