Air flow measurement - again...

[David Kraft]

Just a few half assed ideas...

What is the relationship between Air density, and drag?
Don't you need density measurements? If the air is moist, and contains 
h2o, therefore is less dense, how does that combust compared to dry air
under high pressure (more dense)?

The hot wire measures this, but a dragged object wouldn't be able to
calculate
true combustible related properties.

What are the reverse flow problems, and how do they affect the hotwire?

David


Stephen Dubovsky wrote:
> 
>   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