Matronics Email Lists :: View topic - Indicated stall speed question

Matronics Email Lists
Web Forum Interface to the Matronics Email Lists

Get Email Distribution Too! FAQ Search Memberlist Usergroups Register

Profile Log in to check your private messages Log in

Indicated stall speed question

Matronics Email Lists Forum Index -> Glasair-List

View previous topic :: View next topic

Author Message

mppalmer(at)aol.com
Guest

Posted: Sat Jun 09, 2012 8:09 pm Post subject: 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 <><

- The Matronics Glasair-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?Glasair-List

Craymondw(at)aol.com
Guest

Posted: Sat Jun 09, 2012 8:59 pm Post subject: Indicated stall speed question

I built a Glasair2S FT and Cliff advised me to place my static ports near  the middle of the fuselage and half way between the end of the rear window and  the leading edge of the stabilizer. That was twenty years ago and now you have  me wondering and will take measurements to be sure. My static ports consist of a  plate on the  out side that is connected to the fuse by three small  bolts. I purchased them from AC Spruce. I added a three inch extension to my  pitot and it is about five inches below the wing. I attached my pitot  to the outer inspection plate. I am a little on the thick side and  have never been able to understand what a knot is and have everything calibrated  in MPH. With that in mind, my indicated flaps down stall speed is 63 mph and  around 66 flaps up. I do show a discrepancy between my indicated air speed and  GPS ground speed at cruise with my GPS showing a 10 mph faster speed than  my indicated. I should add that my empty weight with seven quarts of oil is  around 1,375 pounds and I weight 147 pounds. During my test flights I tried  coming over the fence at 75 mph and found that I didn't have enough speed  to flare with and the plane fell out of the air and I made a hard landing.  So I increased the speed to 85 mph and that smoothed it out.  

                                                                      Chuck Raymond N16CD 

 In a message dated 6/10/2012 12:09:38 A.M. Eastern Daylight Time,  mppalmer(at)aol.com writes:

   	  Quote: 	
		  -->    Glasair-List message posted by: mppalmer(at)aol.com



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      the  ies  ay                 - MATRONICS WEB FORUMS               - List Contribution Web Site  p;                             



	


 [quote][b]

- The Matronics Glasair-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

http://www.matronics.com/Navigator?Glasair-List

Display posts from previous:

	Matronics Email Lists Forum Index -> Glasair-List	All times are GMT - 8 Hours
Page 1 of 1

Jump to:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum