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VG's, tail stall, angle of attack

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ceengland7(at)gmail.com
Guest

Posted: Mon Apr 03, 2017 7:52 pm Post subject: VG's, tail stall, angle of attack

Don't know about Kolbs (yet) but tail stall isn't that uncommon in other 

a/c. The early Cessna Cardinal required a stabilator redesign due to 

tail stall.



If answers are desired about whether there's a tail stall problem with a 

particular plane, why not install an angle of attack meter? Doesn't have 

to be high dollar; just an indicator that has consistent, repeatable 

readings.



The wing always stalls at the same angle of attack. If the plane stalls 

at some arbitrary angle indication ('x') on your AOA when the plane is 

lightly loaded, and it stalls at some lower angle (y?) on the same 

indicator when heavily loaded and/or at a more forward CG, then the tail 

has stalled instead of the wing. If the plane stalls at the same AOA 

indication but a higher airspeed, then it's the wing that's stalling.



Charlie

lcottrell

Joined: 29 May 2006
Posts: 1494
Location: Jordan Valley, Or

Posted: Mon Apr 03, 2017 8:53 pm Post subject: VG's, tail stall, angle of attack

This whole thing is getting blown out of proportion. Boyd's and John's

problem concerned weight and CG change, caused by weight. I believe

that the original beginning of this thread came about concerning VG's

on the wing, but none on the elevator. Perhaps the language or

description of the reasoning for why one should also put them on the

elevator was inadequate.



The "tail stall" that did or did not occur during landing was not a

problem in any other configuration other than landings. Even when it

did occur upon landing, it was in no way any more than a Hmmm factor

of about 1. It was just that I like others before me had learned, that

the wing still had lift, with VG's, long after the tail had dropped to

the ground. Since this was occurring at 2 feet above the ground, it

was not Scary! It certainly is not a design flaw.  Merely that you

now had a lot more usable lift than you had before the installation of

VG's, and you could even out the lift between the wing and the

elevator by adding some of the little thingys on the elevator.



There! I hope that clears things up a bit.



Larry



On Mon, Apr 3, 2017 at 9:53 PM, Charlie England <ceengland7(at)gmail.com> wrote:

 	  Quote: 	
		   



 Don't know about Kolbs (yet) but tail stall isn't that uncommon in other

 a/c. The early Cessna Cardinal required a stabilator redesign due to tail

 stall.



 If answers are desired about whether there's a tail stall problem with a

 particular plane, why not install an angle of attack meter? Doesn't have to

 be high dollar; just an indicator that has consistent, repeatable readings.



 The wing always stalls at the same angle of attack. If the plane stalls at

 some arbitrary angle indication ('x') on your AOA when the plane is lightly

 loaded, and it stalls at some lower angle (y?) on the same indicator when

 heavily loaded and/or at a more forward CG, then the tail has stalled

 instead of the wing. If the plane stalls at the same AOA indication but a

 higher airspeed, then it's the wing that's stalling.



 Charlie




	


-- 

The older I get, the less tolerant I am of those who are intolerant of others.



If you forward this email, or any part of it, please remove my email

address before sending.

_________________
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John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Tue Apr 04, 2017 4:38 am Post subject: VG's, tail stall, angle of attack

Larry C/Kolbers:



I didn't fly yesterday, and I forgot what I did day before yesterday.  Think I put VGs on the horizontal stabilizer.  



My job for many, many years was to fly prospective customers in the MKIII at Lakeland and Oshkosh.  I flew all kinds of shapes and sizes in a difficult environment at best, lots of traffic, confined airstrip, wind, and turbulence.  Never had a elevator problem.  On several occasions I did use extreme vigilance and care flying a few super heavy passengers.  Something I should not have done at the time, and something I would not do in the future.  One situation the customer would not buy the airplane without a ride first.  It was not the best flying MKIII I had ever flown.  I was pretty apprehensive about the flight.  I agreed to fly him out of Lakeland South where I had a lot more airstrip and less traffic.  This guy was what I called a "lopper".  When he got in the right seat he lopped over the aileron torque tube in the center of the aircraft.  Made it difficult for me to get my hand on the center mounted throttle.  This was a short flight, full throttle from take off to landing, one circuit around the pattern.  I was not going to take a chance of becoming a lawn dart.



I've never flown a Kolb that had an elevator problem, but when I was carrying large passengers I always carried a little extra airspeed until I was back on the ground.



john h

mkIII

Titus, Alabama





--

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

phcpilot

Joined: 24 May 2016
Posts: 16

Posted: Tue Apr 04, 2017 6:26 am Post subject: Re: VG's, tail stall, angle of attack

We shouldn't get upset because some people like to use correct and accurate terminology when talking about a phenomenon.



Charlie, I think your response is brilliant. For those of us who do want to use the correct term to describe what is happening I applaud your insight

and I can help with that. I make (and sell) an inexpensive Angle of Attack indicator that dozens of people love. After my last batch of probes and gauges ran out I haven't pushed it but am redesigning the probe for it and can offer it again. There is a link to it on my site  ranss7.com  New faces will have the needle more or less horizontal with red at the top (high angle) and green at the bottom.



And on the subject of VG s on stab, aren't they usually placed just ahead of the hinge line where the air is going to break as it goes over the elevator not up near the leading edge???



If answers are desired about whether there's a tail stall problem with a 

particular plane, why not install an angle of attack meter? Doesn't have 

to be high dollar; just an indicator that has consistent, repeatable 

readings.



The wing always stalls at the same angle of attack. If the plane stalls 

at some arbitrary angle indication ('x') on your AOA when the plane is 

lightly loaded, and it stalls at some lower angle (y?) on the same 

indicator when heavily loaded and/or at a more forward CG, then the tail 

has stalled instead of the wing. If the plane stalls at the same AOA 

indication but a higher airspeed, then it's the wing that's stalling.



Charlie[/quote]

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neilsenrm(at)gmail.com
Guest

Posted: Tue Apr 04, 2017 7:11 am Post subject: VG's, tail stall, angle of attack

I'm shocked!!! John H has put VGs on his airplane! I'm expecting some cataclysmic event to follow!!!!

Years ago I witnessed and reported on the great VG fly off between John and Richard Pike at a Kolb flyin. It should be in the archives so I won't go back into the details here. But it was a tie.

I have some VGs on the sides of my fuselage at the wide point on my doors and they do reduce the noise coming from the rear fuselage. I have plans to someday put VGs on my wings and under my tail but it is a low priority. I have a heavy engine and have put some major beef in the passenger compartment including myself, I don't think anyone lapped but I can't say that the old MKIIIC was ever less than capable of safely committing flight.

Also I saw the post about missing Buford, has something happened to him??? 

Rick Neilsen

Redrive VW Powered MKIIIC

lcottrell

Joined: 29 May 2006
Posts: 1494
Location: Jordan Valley, Or

Posted: Tue Apr 04, 2017 8:38 am Post subject: VG's, tail stall, angle of attack

We shouldn't get upset because some people like to use correct and

accurate terminology when talking about a phenomenon.

And on the subject of VG s on stab, aren't they usually placed just

ahead of the hinge line where the air is going to break as it goes

over the elevator not up near the leading edge???

---------------------------------------------------------------------------------------------------------------------



I suppose that I shouldn't feel a bit chapped, as I volunteered to

take the blame for the wandering of this thread.----This is the

original:



Larry Cottrell <lcottrell1020(at)gmail.com>



Mar 31 (4 days ago)

to kolb-list

I have to admit that I am quite proud of you. Whether you believe it

or not, the ones on the elevator do help t keep the tail flying and

will also improve the landings. As I mentioned earlier,  without them

the tail feathers stall before the wing.

---------------------------------------------------------------------------------------------



As far as the VG's are concerned they, to the best of my knowledge,

should be placed in front of the hinge line. Apparently they still do

quite well in other spots as well.



Inaccurately yours,

 Larry

_________________
do not archive

victorbravo(at)sbcglobal.
Guest

Posted: Tue Apr 04, 2017 9:22 am Post subject: VG's, tail stall, angle of attack

What some folks might think of as a "tail stall" may just be air separating from the elevator itself. So the entire tail is not technically stalled, but if the air separates from the bottom of the elevator you would very likely see a reduction in control authority. So maybe "elevator stall" is the better way to describe it. 



The flat cross section tails (no airfoil) would likely be more prone to this, because the airflow forward of the hinge line is not as smooth or organized as it would be on a properly airfoiled tail. But as we know, tens of thousands of Cubs, Taylorcrafts, Aeroncas, Porterfields, and Kolbs are flying safely without an airfoiled tail. The "flat" tail is simply a compromise to make the airplanes easier and/or less costly to build. On a 70-90 MPH airplane it is an easy and worthwhile compromise to make.



As a non-Kolb point of reference, I have an old Cessna 172 (1956, first year). Anyone with Cessna 172 time will verify that the airplanes are kind of nose-heavy with the rear seats empty, and that you basically "run out of elevator" when you are trying to do a minimum speed landing with one or two people in the front seats. What happens is that you feel the yoke (stick) hit the control stop, and you can't raise the nose any more, even though you can feel the airplane was willing to slow down a little more. 



But then I woke up one Christmas morning (in August), and in the middle of the night Santa Claus had installed little plastic VG's on the bottom of my horizontal stabilizer. As I was flying the aircraft directly to the Oklahoma City FAA office to report Santa for breaking the rules, I noticed that I was able to raise the nose of the Cessna just a little bit higher when I wanted to slow the airplane down that last mile an hour on landing. I didn't have any numerical way to measure it, but it was clear that there was a small improvement. By the time I hit the control stop with the yoke all the way back, the nose was a tad higher.



Another trick that works in the Cessna is adding a small touch of power at the last 2 or 3 seconds of the flare. This puts a little more prop blast on the elevator and allows you to raise the nose another degree or two higher before "tail stall" / "elevator stall" / "no more control authority". I have not done this on a Kolb, but perhaps some Kolb pilots have tried this. I'd  be interested to see if a little prop blast solves or delays the loss of elevator authority at the flare.



Bill Berle

www.ezflaphandle.com  - safety & performance upgrade for light aircraft

www.grantstar.net           - winning proposals for non-profit and for-profit entities

neilsenrm(at)gmail.com
Guest

Posted: Tue Apr 04, 2017 10:11 am Post subject: VG's, tail stall, angle of attack

Bill

With the high thrust line in our Kolbs I don't think adding power while flaring is going to help you raise the nose. The normal advice is to approach with a bit of power then cut the power to assist with flare.

As a side note, years ago when I was sorting out my VW I had a reduction drive failure when I was at about 1,000 AGL. My normal landing procedure is approaching with just a bit of power with one notch of flaps cutting power after I settle in. I practiced ahead of time landing with no power with no flaps and found the landing just about the same as some power with one notch. So using what I had practiced I used my flaps like a negative throttle to get me where I wanted to land then raised the flaps for landing. No big deal. The added bonus was that nice landing spot turned out to be a bean field and with no flaps I was able to get the tail down in the beans first. The beans grabbed the tail wires like a carrier arresting cable and I landed with no damage what so ever.

Rick Neilsen

Redrive VW powered MKIIIC

On Tue, Apr 4, 2017 at 1:22 PM, Bill Berle <victorbravo(at)sbcglobal.net (victorbravo(at)sbcglobal.net)> wrote:

 	  Quote: 	
		  --> Kolb-List message posted by: Bill Berle <victorbravo(at)sbcglobal.net (victorbravo(at)sbcglobal.net)>

 

 What some folks might think of as a "tail stall" may just be air separating from the elevator itself. So the entire tail is not technically stalled, but if the air separates from the bottom of the elevator you would very likely see a reduction in control authority. So maybe "elevator stall" is the better way to describe it.

 

 The flat cross section tails (no airfoil) would likely be more prone to this, because the airflow forward of the hinge line is not as smooth or organized as it would be on a properly airfoiled tail. But as we know, tens of thousands of Cubs, Taylorcrafts, Aeroncas, Porterfields, and Kolbs are flying safely without an airfoiled tail. The "flat" tail is simply a compromise to make the airplanes easier and/or less costly to build. On a 70-90 MPH airplane it is an easy and worthwhile compromise to make.

 

 As a non-Kolb point of reference, I have an old Cessna 172 (1956, first year). Anyone with Cessna 172 time will verify that the airplanes are kind of nose-heavy with the rear seats empty, and that you basically "run out of elevator" when you are trying to do a minimum speed landing with one or two people in the front seats. What happens is that you feel the yoke (stick) hit the control stop, and you can't raise the nose any more, even though you can feel the airplane was willing to slow down a little more.

 

 But then I woke up one Christmas morning (in August), and in the middle of the night Santa Claus had installed little plastic VG's on the bottom of my horizontal stabilizer. As I was flying the aircraft directly to the Oklahoma City FAA office to report Santa for breaking the rules, I noticed that I was able to raise the nose of the Cessna just a little bit higher when I wanted to slow the airplane down that last mile an hour on landing. I didn't have any numerical way to measure it, but it was clear that there was a small improvement. By the time I hit the control stop with the yoke all the way back, the nose was a tad higher.

 

 Another trick that works in the Cessna is adding a small touch of power at the last 2 or 3 seconds of the flare. This puts a little more prop blast on the elevator and allows you to raise the nose another degree or two higher before "tail stall" / "elevator stall" / "no more control authority". I have not done this on a Kolb, but perhaps some Kolb pilots have tried this. I'd  be interested to see if a little prop blast solves or delays the loss of elevator authority at the flare.

 

 Bill Berle

 www.ezflaphandle.com  - safety & performance upgrade for light aircraft

 www.grantstar.net           - winning proposals for non-profit and for-profit entities

 

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John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Tue Apr 04, 2017 10:12 am Post subject: VG's, tail stall, angle of attack

Rick N/Kolbers:

 

It'll be alright.  Miracles happen every day.  The cataclysmic event to follow was my dead battery.  Not much of an event, but enough to change my plans.

 

Yes, Richard P and I had a little slow flight competition between our two birds.  His with VGs and mine naked as a J-

Bird.  Rick thinks we tied.  Richard claims radio problems.  What's that got to do with slow flight?  I think I beat him.  We'll have to do it again now that I have VGs.

 

Buford has some medical problems.  Don't know what, but it is enough to keep him off the List.  Yes, I miss ole Buford too.

 

john h

mkIII

Titus, Alabama

 

 

 

 

From: owner-kolb-list-server(at)matronics.com [mailto:owner-kolb-list-server(at)matronics.com] On Behalf Of Rick Neilsen

Sent: Tuesday, April 04, 2017 10:12 AM

To: kolb-list(at)matronics.com

Subject: Re: VG's, tail stall, angle of attack



 

I'm shocked!!! John H has put VGs on his airplane! I'm expecting some cataclysmic event to follow!!!!



 



Years ago I witnessed and reported on the great VG fly off between John and Richard Pike at a Kolb flyin. It should be in the archives so I won't go back into the details here. But it was a tie.



 



I have some VGs on the sides of my fuselage at the wide point on my doors and they do reduce the noise coming from the rear fuselage. I have plans to someday put VGs on my wings and under my tail but it is a low priority. I have a heavy engine and have put some major beef in the passenger compartment including myself, I don't think anyone lapped but I can't say that the old MKIIIC was ever less than capable of safely committing flight.



 



Also I saw the post about missing Buford, has something happened to him??? 



 



Rick Neilsen



Redrive VW Powered MKIIIC

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Wed Apr 05, 2017 8:08 am Post subject: Re: VG's, tail stall, angle of attack

 	  John Hauck wrote: 	
		  Rick N/Kolbers:

 

It'll be alright.  Miracles happen every day.  The cataclysmic event to follow was my dead battery.  Not much of an event, but enough to change my plans.

 

Yes, Richard P and I had a little slow flight competition between our two birds.  His with VGs and mine naked as a J-

Bird.  Rick thinks we tied.  Richard claims radio problems.  What's that got to do with slow flight?  I think I beat him.  We'll have to do it again now that I have VGs.

 

Buford has some medical problems.  Don't know what, but it is enough to keep him off the List.  Yes, I miss ole Buford too.

 

john h

mkIII

Titus, Alabama 

 

 

	




Yes, it was pretty much a tie. When the radio quit (I had knocked one of the plugs loose from the comm box behind the seat where it was plugged in) there was no way for us to coordinate how we were going to do things. 

I was uncomfortable with getting side by side with even a highly skilled pilot like yourself when we are having a slow fly competition where we are flying side by side as slow as possible, and by definition on the edge of a stall, and not being able to communicate or coordinate with each other. At times I was lower than you and could not see you, and flying next to somebody I can't see or talk to had me thinking "This is insane." Maybe you could see me, and were watching me close, but how could I know that?  If I could have known that you were going to stay in a position to watch me and be responsible for any eventuality, that would have sufficed, & I could have focused on flying, but nothing had been arranged. So I was really distracted, & IMO it had a lot to do with everything.

It would be fun to do it again, but I suspect that next time you would win hands down. I think the reason for the tie last time is that both of us were using a lot of power and a 100hp MKIII w/o vg's ought to hang on the prop to the point that it can fly just as slow as a lighter 65hp MKIII with vg's. 

A better test would be two MKIII's of equal engine and prop, one with VG's, one w/o.

Hate that you missed S & F, you have always been a fixture at the Kolb tent.

_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Wed Apr 05, 2017 8:25 am Post subject: VG's, tail stall, angle of attack

Nope.  100 hp had nothing to do with the competition except increase the

weight of my already fat MKIII, which still had half my gear on board.

Wonder how much heavier it was than yours.  I was probably turning 3000,

nibbling on the stall.  As an added note:  My 912ULS only produces 95 hp on

my airplane because it is propped for 5500 WOT straight and level.  To get

100 hp I'd have to prop for 5800 WOT straight and level flight.



I can assure you I had you in sight constantly.  A little something I

learned about flying formation in helicopters many years ago.



Besides, I made it clear on the ground I would fly the right side, south, of

the airstrip and you would fly the north side.  I believe you also suggested

this slow flight competition to prove you could whip my ass with your VGs.





There is no better test than the test between me and you, my airplane and

your airplane, to see which one could fly the slowest.  I beat.  



john h

mkIII

Titus, Alabama - Fly like a butter fly, float like a feather.  



--

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

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