Stall Speed increase?

[BenCharvet]

A few days ago I went up to 3000 to practice stalls, and was surprised that my indicated airspeed at clean stall was over 60 mph. I tried another with flaps and it wasn't much different. This airplane has always stalled at around 45 mph like they should. Was carrying about 12 gal of fuel, and I weigh about 175. I went up again with a friend who has flown the plane before and we got the same result. Today I redid the weight and balance, and it looks fine.

The airspeed at cruise seems to pretty much match the GPS. I didn't think to check the groundspeed via GPS when we were doing the stalls. Several of my buddies seemed to think it was just instrumentation, but the same instruments used to read 45 at stall. Other than this complaint it flies great.
Ben Charvet
Sonex 809SX legacy, Jab3300

[gammaxy]

I suspect it's instrumentation. Probably not the actual instrument, but something in the pitot/static system. Is it possible the static line has a leak or has become disconnected?

I'm curious whether you've noticed a difference in sight-picture as you approach a power off stall in level flight. In my experience, the nose is quite high with no horizon visible over the nose for quite a while as you decelerate into the stall. 70mph is still pretty level. I'd expect 60mph to be somewhat nose high, but still quite some margin left before feeling close to the stall.

If your nose is really very high at 60mph as the stall breaks, then you're either extremely over weight or something has happened to significantly affect the wings--like missing a large portion of them :-) ~75% more lift should be available at 60mph than 45mph. IMHO, either case would be pretty obvious just looking at the airplane on the ground.

[GraemeSmith]

Indicating high as you describe is indicative of a possibly blocked or partially blocked static line or static port.

Make sure your pitot static system is in good shape - everything is lined up the way it used to be. If you are using the stock two aluminum tubes tack welded together under the wing set up - it's easily knocked slightly out alignment.

Did you just wash the plane or was it sitting in big rain? Consider blowing out the system to get rid of any tiny drops of water that might be in it. That same two tube set up is a water trap sometimes. If blowing out - disconnect at instruments and blow from the instrument end towards outside world. NEVER blow towards the instruments from outside with the line connected - you will destroy them. When washing the plane - tape over the static port to prevent water getting in. REMOVE TAPE AFTER!! :-)

Is there a low point in your Pitot and static lines that might hold water? If it is not a straight uphill run to the instruments - the low point can hold water. Static sides seem prone to this. Some systems fit a small catch bottle at the low point so any water that gets in the lines drops into the catch bottle - leaving the line clear. Bottle requires inspection and emptying regularly.

If that doesn't do it - when was your last Pitot Static check? The Avionics techs have very sensitive tools that will apply pressures representing airspeeds and which you can use to calibrate the instruments.

[BenCharvet]

Today I inspected all my static line plumbing and found that it had come loose from the altimeter. I have it reinstalled and am waiting for the weather to improve to test fly it for results. I am confident that will fix the problem. Thanks for your input,
Ben