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  #1  
Old 01-22-2005, 05:59 PM
Kevin Horton's Avatar
Kevin Horton Kevin Horton is offline
 
Join Date: Jan 2005
Location: Green Bay, WI, USA
Posts: 2,369
Default Pitot-Static System Errors - How to measure them

Every aircraft with an airspeed indicator and an altimeter has errors in those systems. The errors are due to many factors:
  • Instrument error,
  • Leaks in the plumbing,
  • Position errors in the static system, and
  • Position errors in the pitot system.
Instrument error in the airspeed indicator (ASI) can easily be measured using a water manometer. Instrument error in the altimeter cannot be easily be measured by the builder, but an avionics shop can test it with a pitot-static test set.

Leaks in the plumbing can be easily checked.

Position errors in the static system are caused by the fact that the air flowing around the aircraft has to accelerate and decelerate as it wends its way over the shape of the airplane. The air pressure changes as it accelerates and decelerates, so the pressure at the static port is quite likely different than the free stream static pressure well away from the aircraft. This difference between the sensed static pressure and the free stream static pressure is position error, and it accounts for most of the error in the ASI (assuming the instrument error is small, all leaks are fixed, and the pitot tube is not too poorly located).

The pitot tube is relatively immune to position errors, as it measures total pressure, not static pressure, and the total pressure isn?t changed as the air moves around the aircraft. If your pitot tube is reasonably well aligned into the airflow, and it is well clear of the prop wash, and it is not in the wake of something else, it should be quite accurate. Pitot tubes should provide reasonable accuracy if the local airflow is aligned within 15 degrees of the pitot tube. So, it might become inaccurate as you approach the stall.

I have put together a guide on how to measure ASI instrument error using a water manometer and how to determine static system position error via flight testing. This guide is located at http://www.kilohotel.com/rv8/rvlinks/ssec.html.
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RV-8 (Sold)
Green Bay, WI, USA
http://www.kilohotel.com/rv8/

Last edited by Kevin Horton : 06-22-2022 at 07:11 AM. Reason: Corrected link
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  #2  
Old 07-09-2015, 11:47 AM
kai kai is offline
 
Join Date: May 2011
Location: Berlin, Germany
Posts: 84
Default

Hi Kevin, is that guide still available somewhere? I would appreciate to get a copy of that!

Thanks,

Kai
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  #3  
Old 07-09-2015, 01:11 PM
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GalinHdz GalinHdz is offline
 
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Location: KSGJ / TJBQ
Posts: 2,339
Default

Quote:
Originally Posted by kai View Post
Hi Kevin, is that guide still available somewhere? I would appreciate to get a copy of that!

Thanks,

Kai
Here is a corrected link:

http://www.kilohotel.com/rv8/rvlinks/ssec.html

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  #4  
Old 07-10-2015, 03:47 AM
kai kai is offline
 
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Default

Great, thanks!
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  #5  
Old 03-10-2022, 07:26 AM
wawrzynskivp wawrzynskivp is offline
 
Join Date: Feb 2018
Location: Incline Village Nv
Posts: 317
Default

Going to try this, thanks!
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  #6  
Old 06-21-2022, 08:36 AM
prkaye prkaye is offline
 
Join Date: Jun 2006
Location: Ottawa, Ontario, Canada
Posts: 2,149
Default EAA1000 link broken

Within Kevin's guide he has a link to the EAA Chapter 1000 website for specific instructions on pitot-static instrument calibration:
http://www.eaa1000.av.org/technicl/instcal/instcal.htm
This link appear to be broken.
Does anybody know where this article, or alternative instructions for doing a pitot-static leak check, can be found?
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  #7  
Old 06-21-2022, 01:20 PM
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Kevin Horton Kevin Horton is offline
 
Join Date: Jan 2005
Location: Green Bay, WI, USA
Posts: 2,369
Default

Quote:
Originally Posted by prkaye View Post
Within Kevin's guide he has a link to the EAA Chapter 1000 website for specific instructions on pitot-static instrument calibration:
http://www.eaa1000.av.org/technicl/instcal/instcal.htm
This link appear to be broken.
Does anybody know where this article, or alternative instructions for doing a pitot-static leak check, can be found?
The Internet Archive is useful to find sites that have died or moved. See:
https://web.archive.org/web/20210125...al/instcal.htm

I retrieved a copy of the last version of the page from the Internet Archive, and saved it on my web site. It can be found at https://www.kilohotel.com/rv8/rvlink...libration.html
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http://www.kilohotel.com/rv8/

Last edited by Kevin Horton : 06-21-2022 at 06:05 PM.
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  #8  
Old 06-22-2022, 05:57 AM
Tim Lewis Tim Lewis is offline
 
Join Date: Aug 2006
Location: Bristow, VA
Posts: 193
Default

Kevin's VERY helpful airspeed/static system error flight test page link in his original 2005 post (above) doesn't seem to work (clicking the VAF link in the 2005 post, that is). Here's a link that works:

https://www.kilohotel.com/rv8/rvlinks/ssec.html
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