|Posted: Sun Jun 10, 2012 2:09 am Post subject: Glasair-List: Indicated stall speed question
Mike, I get the stall suddenly at 73
Mph on my G1 TD. Robin
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----- Reply message -----
Date: Sun, Jun 10, 2012 12:08 am
Subject: Glasair-List: Indicated stall speed question
I was wondering what you GI FT and GII FT pilots (but not stretch or SS) see for an indicated stall speed?
Our airspeed will drift down to about 65 KIAS and stay there throughout the stall. (Power off, flaps up, for example.) I know that can't be correct because it takes a while for the stall to occur and I can hear the wind noise decreasing during that time. The airspeed should continually be decreasing, but that's not the indication I get.
Apparently we have some kind of installation problem.
We have a combination pitot/static tube, as used on the old Viking aircraft, that's mounted behind the main spar shear web. (I'm told this is a $1000 part now. Sure doesn't work like it.) The static port never did work right on the Glasair - you would take off and watch the altimeter go below the runway as the static air wasn't! More critically, I was never at Glide Slope crossing altitude on ILS approaches. And that bothered me when it was for real.
So I moved the static ports to the aft fuselage, per a newsletter article by John Levy. That pretty much solved the false altimeter problem. But now I'm wondering if I'm getting a low pressure area behind the rear windows in the stall configuration that causes the airspeed in stall to read artificially high?
Last week I extended the pitot tube away from the wing a few inches so that the tip is now 6 inches below the wing. I've only done one stall in Phx thermal conditions. It didn't seem to make much difference in the stall speed behavior.
I'm thinking of temporarily hooking the static side of the system to the old hose that's hanging open inside the wing as an experiment. Surely inside the wing ought to be a big lazy pool of static air?
In the meantime, I thought I'd ask the group if you're seeing any bizarre stall speed behavior? Or had to do anything to solve this problem?
I beta tested a Rite Angle AOA for Elbie Mendenhall years ago, and installed it also about 6 inches below the wing on a streamlined tube coming out of an inspection cover. We also got bizarre results. The AOA would begin to increase a little as I would slow down but then hold the same into the stall. We figured there was too much bow wave and we had to move the probe about 10 inches away from the wing. But I never tried that so we don't know.
Mike Palmer <><
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