Pattern Help

[John Ferrell]

Some of the slower full scale experimental craft use a venturi arrangement to measure airspeed. The ram air pressure get pretty small. 

The nice part about this kind of experiment is that you can hang it all out a car window...

John Ferrell    
http://DixieNC.US

  ----- Original Message ----- 
  From: Bob Richards 
  To: discussion at nsrca.org 
  Sent: Friday, January 14, 2005 10:30 PM
  Subject: Re: Pattern Help


  Earl,

  The 3/8" distance may not be enough. I suspect that in a stall/snap situation that there is enough air "spilling" around the LE to disrupt the operation of the pitot tube. (That's an over simplification, maybe)  I would try sticking it out maybe 2" or more just to try it out. Also, have you tried snapping in both directions to see if you get the same readings?

  On most aircraft the pitot tube is fixed, but on some test/experimental aircraft the pitot is mounted on a vane so it always points directly into the airflow.

  I'm very interested in this. Keep us posted!!

  Bob R.


  Earl Haury <ehaury at houston.rr.com> wrote:
    Bob

    Correct on instrument methodology. You may be correct regarding observed readings also. 

    However, very high roll rates seem not to generate the same speed reading effect. The pitot extends about 3/8" forward the center of the wing LE in my installation. I've not seen any difference in normal speed data with it varied 1/4" or so from that position.

    Pressure anomalies will definitely affect the altitude sensor, however I don't see the same "signature" on downline snaps. I've not been specifically looking at snaps to this point, the data were generated flying the P-05 sequence. I plan to look at this further in a different (more expendable) airplane with a G sensor also. Possibly that sensor can be oriented to provide pitch load and thrust (longitudinal) accel / decel info. (Should receive sensor in the next couple of days.) BTW, data rate is 10x/sec.

    Earl
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