Air Speed Indicators

dodd · Post by **dodd** » Fri Jul 13, 2007 12:28 am

I have my first question for all you experienced 170 owners.
I have noticed my ASI sets a few ticks counterclockwise from 360.
I had my mechanic check it with some sort of thing he has that does that kind of readout.
Obviously I was not with him or I would know a little more.
Anyway, it seem to be way off. He game me a piece paper with the # on it.
He did qualify his work by saying his testing equipment had not been calibrated in a while.
At 60Knts indicated it is actually 74 knots.Now at high speeds it does not matter much, but at stall speeds it would matter somewhat more than a little.
It goes on like that. At 120 kts indicated it is 126 actual.
Anybody got any thoughts on this??

Dennis Dodd N8018A
Finally a tail wheel guy

robert.p.bowen · Post by **robert.p.bowen** » Fri Jul 13, 2007 2:09 am

Sounds like it's time to send that rascal to your favorite instrument shop. Include a note with it containing the data points in your post.

N2865C · Post by **N2865C** » Fri Jul 13, 2007 5:37 am

I really like these guys.....
http://www.trade-a-plane.com/unprotecte ... 690743.pdf
(the link is a PDF and takes a minute to download)
Good prices, great customer service and fast turnaround.

lowNslow · Post by **lowNslow** » Fri Jul 13, 2007 12:33 pm

N2865C wrote:I really like these guys.....
http://www.trade-a-plane.com/unprotecte ... 690743.pdf
(the link is a PDF and takes a minute to download)
Good prices, great customer service and fast turnaround.

Same here, I would also recommend them (Rudy Aircraft Instruments). Had two gyros overhauled by them and the service and turnaround time were very impressive. One of the gyros had some internal corrosion, they replaced all the effected parts including the case for no extra charge.

Post by **GAHorn** » Fri Jul 13, 2007 3:04 pm

Having an airspeed indicator that indicates accurately at low speeds in accordance with a calibrated air-pressure is a misleading matter. Example: 60 mpg air pressure = 60 mph IAS might lead one to believe in accuracy. But that does not take into consideration "position error" which is the high angle of attack of the pitot tube and how it relates to actual airspeed. That perfectly calibrated indicator might actually read 40 mph when the aircraft is making a true 60 mph.

But perfection is a nice goal. Your mechanic should not attempt to convince you of your indicator's actual accuracy by using a non-calibrated calibration device. You might be well advised to have an instrument shop not only bench-check your instrument, but also perform a complete pitot/static system check on your aircraft, if you truly want it all to be performing as intended.