REFLECTOR: Static port calibration

[Laurence Coen]

Al,

Your altimeter and your transponder encoder are connected to the same static port and will always agree no matter who far off the static pressure is.  Not only that but your ground speed and your TAS not the IAS should agree.  In general, the IAS will be less than the TAS which would indicate that both your AS and altitude are both off in the same direction indicating that your static port is in a low pressure area.

Low Pass Safety Rules:
1. Always wear a cowboy hat.
2. Holler "YEE-HAW" at mid field.
3. Focus 100% of your attention on flying the plane.
4. Have someone else look at the altimeter.

The problem here is that there isn't enough headroom in a Velocity to wear a cowboy hat.  I, therefore, would like to describe the method I used to calibrate my static port.  GPS altitude.  Before folks get excited and say that GPS altitude can be +- 100 feet remember "can be" but rarely is.  Every time I fly as part of my instrument check I do a three way altitude check.  At the hold short line for runway 18 at OJC my altitude is exactly 1100 feet.  I check my aneroid altimeter and GPS altitude against this benchmark.  I almost never see a difference of more than 20 feet on either altitude.  The aneroid and GPS also track on cross country flights.  When I notice a difference I check a local ATIS or AWOS and reset my colesman to the local barometer and they again sync up.  A WAAS enabled GPS will typically show altitude to within 3 meters with a clear sky view.

Try it, you'll like it.

Larry Coen
N136LC


From: Al Gietzen 
Sent: Wednesday, March 04, 2009 9:40 AM
To: reflector 
Subject: REFLECTOR: Static port calibration


Out playing in the sky yesterday, I decided to do checks on altitude and speed readings.  I had never done the 'low pass over the runway' test.  150 KIAS, est 80 ft over the runway, altimeter readout on the GRT EFIS was maybe 100 ft too high.  Hum-m-m.  



Went out and flew the orthogonal square about the same speed; recording GPS ground speed and IAS in each direction, then took the average of each.  The speeds agreed within 1.2 knots.



I've always found my altitudes consistent with where ATC says I am - so I don't think I need to change anything.



Al



--------------------------------------------------------------------------------


_______________________________________________
To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector

Visit the gallery!  www.tvbf.org/gallery
user:pw = tvbf:jamaicangoose
Check new archives: www.tvbf.org/pipermail
Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.tvbf.org/mailman/private/reflector/attachments/20090304/60f0d75e/attachment.htm>