REFLECTOR: TAS calibration?

[Laurence Coen]

Geoff,

If the airspeed indicator has been calibrated on the ground and is reading correctly the most likely source of the error is the static reference.  If the static port is being pressurized by forward motion it will cause the TAS to read low.  If you have a WASS enabled GPS it's altitude should be very close to your aneroid altitude.  If you find that the aneroid altitude is consistently lower than the GPS altitude then that would indicate that your static port is indeed pressurized.  Another test is to see if your altitude reading changes with speed.

Larry Coen
N136LC


From: Geoff Gerhardt 
Sent: Saturday, September 28, 2013 7:29 PM
To: Velocity Aircraft Owners and Builders list 
Subject: REFLECTOR: TAS calibration?


Guys, 


Flying today I realized that my ground speed seems to be always greater than my TAS.  I figured at least some of the time it should be less (i.e. into a headwind).  But it always seemed to be greater.  So, today, I flew in a box, E, W, N, S and recorded my TAS and GS.  My TAS was constant at 159ktas on each leg, and my GS (GPS) was 185, 179, 171, 175 for the W, N, E, S legs.  If I add all those up and divide by four, I get 177.5kts, yet my TAS registered 158ktas.  Am I missing something?  Is my airspeed indicator reading too low?


Thanks.


Geoff




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