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airspeed disagreement between two EFISs

prkaye

Well Known Member
I installed a backup EFIS (Garmin G5) and flew with it today. I noticed the airspeed reading on my G5 differs from that reported by my Dynon D-180 by about 2kts (pretty much consistently about 2kt difference at any airspeed). Does this sound like a reasonable difference?
 
A difference in airspeed begs the question, which one is right (or less wrong)?

End the pain and find out. A few minutes of work will produce an amazingly accurate Manometer to verify airspeed indication - and by extension airspeed indication calibration.

PM me your email address and I’ll send the PDF file that converts water column height to knots. Just make sure you print it out full scale.

Note - spent yesterday helping a neighbor with pitot/static leaks on his Archer. This Manometer is a perfect tool for the job.

Note#2 - no need to remove the instrument from the plane. Just connect to the pitot tube using appropriate size tubing and electrical tape.

Carl
498-A870-F-FDE1-4572-A3-CB-70551129-FE8-D.jpg
 
A difference in airspeed begs the question, which one is right (or less wrong)?

End the pain and find out. A few minutes of work will produce an amazingly accurate Manometer to verify airspeed indication - and by extension airspeed indication calibration.

PM me your email address and I’ll send the PDF file that converts water column height to knots. Just make sure you print it out full scale.

Note - spent yesterday helping a neighbor with pitot/static leaks on his Archer. This Manometer is a perfect tool for the job.

Note#2 - no need to remove the instrument from the plane. Just connect to the pitot tube using appropriate size tubing and electrical tape.

Carl
498-A870-F-FDE1-4572-A3-CB-70551129-FE8-D.jpg

Thanks Carl! I've PM'd you. That looks like a pretty slick testing rig, and worth doing for the educational value alone. I would guess that the error/precision range of that kind of setup exceeds 2 knots though :)
 
SNIP I would guess that the error/precision range of that kind of setup exceeds 2 knots though :)

My experience is it is as accurate as your ability to read the scale.

I used this to fix two analog airspeed indicators that read more than 5 knots off of actual (the standard ones you get from Van's), and nowhere near linear.

I note that doing the same checks on the SkyView the airspeed readout was dead on across the operating range.

Here is a shot of the SkyView and the post calibration analog airspeed meter.
Carl
1-EFB4-C04-8-BBE-47-E0-BB29-CC75425-E03-EB.jpg
 
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How do you know if you printed it out at the correct scale? Is there a calibration in the PDF (a line or mark that says "This line is 1 inch") or something to reference to?

See the numbers on the left side, next to the lines? Those ARE inches. Put a ruler on them and check, if you don’t trust your printer.
 
In case anyone cares, my P-S test box accuracy is .2k@100 and .1k@200
Pretty hard to get that with a tape measure :D

Of course, most EFIS's don't have a way to calibrate airspeed anyway.
 
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My digital ASI reads in 1.000 increments. Anything more accurate is a waste of time and money......:D

I paid $3.75 for my tape measure.
 
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