Detecting Airspeed Indicator Inaccuracies

kontiki

kontiki

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Kontiki
The PA-28 I've been training in lately was just grounded for an inaccurate airspeed indicator. It explains a few things about what we've been seeing.

In general, anybody know of a quick and dirty accuracy check, suitable for a rental?

I'm not sure I could have caught it by working out density altitude and trying to gauge performance.

Thanks,
 
Broken aileron cable and now this! Must be the Cherokee from hell.

I don't know of any test other than 'feeling' the airplane, but you can guard against following an inaccurate ASI into a stall by practicing them (Cherokee I fly gives a lot of control buffeting before stall) as well as ensuring the stall warning is operative during your preflight.

Of course you can check ground speed w gps..

Usually intermittent problems are caused by water in the system, IIRC
 
kontiki said:
In general, anybody know of a quick and dirty accuracy check, suitable for a rental?

Thanks,
Click to expand...
How about flying parallel to another plane for a while at a pre-set and agreed on air speed. Then see if either plane opens up a lead. Of course, if there is a difference it could be that either one of them is wrong or both. The closer you are the better, but you may need permission from ATC,and you should both have experience in formation flying. I have never done it, but I understand it can be harder that you might think.
 
fly opposite direction legs at a fixed indicated air speed. compare to gps ground speed. assumes the wind stays constant for that period of time.
 
Who the hell is inspecting that thing. Does it have a current IFR pitot/static test?
 
Thanks for the useful info. It gives me me something to think about. This ship is an Arrow. We've done quite a bit of slow flight in it over the past few months. It's very noticeable. Don't know when the IAS problems started.

We really saw performance issues that didn't add up practicing power off 180 landings. I'd be at best glide (maybe in a bank) and it would want to sink just before touchdown.
 
FWIW at high AOA there can be large errors in the ASI. I can fly a 182 at 0 IAS...
 
kontiki said:
We really saw performance issues that didn't add up practicing power off 180 landings. I'd be at best glide (maybe in a bank) and it would want to sink just before touchdown.
Click to expand...
Best glide in a bank is faster than best glide wings level. I'm guessing it goes up with the square root of load factor -- I'd have to do some digging in my aero books when I get home to confirm that. If that is correct, then in a 30 degree bank, best glide would go up about 7% -- like 5-6 knots in most light singles.
 
Look at the calibrated vs. indicated airspeed curve in your POH. As above, the error can get quite large at high angles of attack.
 
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