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Vortex Generators
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Watkinsdw

Joined: 15 Mar 2009
Posts: 138
Location: Deerfield Beach, FL

Posted: Thu Sep 17, 2009 8:23 am Post subject: Re: Vortex Generators

Hi, Jason, 

I elected not to place them beyond the last full rib. This was on the recommendation of Joa Harrison, the designer. I see Mike Bigelow has his all the way out to the wingtip bow, and someday, we'll hook up and try some side-by-side comparisons.



My reported figures were at max gross weight, about 1050. 

They were ridiculous with only one occupant.  My memory is fuzzy, but I think I was stalling clean at about 25. With one notch of flaps, it was in the teens. I felt like I could have got out and walked and measured the true airspeed with a pedometer. Of course there was significant instrument error at those high angles of attack, so this is clearly subjective. 



Have fun -- that's what this is all about as near as I can tell.



Dave

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Thu Sep 17, 2009 11:04 am Post subject: Re: Vortex Generators

My VG's go all the way to the bow tip, although I think Joe Harrison was correct that they probably don't do any good there.   There is really no airfoil for the last  1.5 feet of the wingtip, and I doubt a VG will work where there is no airfoil.  I stuck them on because I had them, and I figured they would not do any harm there.   



This will change when I put the Hornier style wingtips on the MK III Xtra, I will have a true airfoil all the way out to the tip, not wasting 3 feet of wingspan on a flat board that provides no benefit.



My Stall speed is not as low as Dave's,  I am looking forward to getting a look at his plane very well to see what he did !   I also don't have Vortex Generators under my horizontal stabilizer, just for the reason of being lazy , I need to put them on soon.



Mike

_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!

Kolb MK-III Xtra, 912-S

jbhart(at)onlyinternet.ne
Guest

Posted: Thu Sep 17, 2009 11:58 am Post subject: Vortex Generators

At 12:04 PM 9/17/09 -0700, you wrote:

 	  Quote: 	
		  

This will change when I put the Hornier style wingtips on the MK III Xtra, 
	


I will have a true airfoil all the way out to the tip, not wasting 3 feet of 

wingspan on a flat board that provides no benefit.

 	  Quote: 	
		  


	


Mike



That flat three feet outboard may not generate lift, but it does show benefit 

in that it pushes the tip vortex outward, increases wing aspect ratio which 

reduces induced drag. 



Jack B. Hart FF004

Winchester,

capedavis(at)yahoo.com
Guest

Posted: Thu Sep 17, 2009 2:53 pm Post subject: Vortex Generators

Jack thank you for your last you said it finer than I am capable  of saying it ! Chris

 

Chris Davis

KXP 503 492 hrs

Glider Pilot

Disabled from crash building Firefly 



 

   From: Jack B. Hart <jbhart(at)onlyinternet.net>

To: kolb-list(at)matronics.com

Sent: Thursday, September 17, 2009 5:08:56 PM

Subject: Re: Re: Vortex Generators



--> Kolb-List message posted by: "Jack B. Hart" <jbhart(at)onlyinternet.net (jbhart(at)onlyinternet.net)>



At 12:04 PM 9/17/09 -0700, you wrote:

 	  Quote: 	
		  --> Kolb-List message posted by: "JetPilot" <orcabonita(at)hotmail.com (orcabonita(at)hotmail.com)>

This will change when I put the Hornier style wingtips on the MK III Xtra, 
	


I will have a true airfoil all the way out to the tip, not wasting 3 feet of 

wingspan on a flat board  that provides no benefit.

 	  Quote: 	
		  


	


Mike



That flat three feet outboard may not generate lift, but it does show benefit 

in that it pushes the tip vortex outward, increases wing aspect ratio which 

reduces inbsp;                    =======================



           [quote][b]

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Thu Sep 17, 2009 4:43 pm Post subject: Re: Vortex Generators

 	  jbhart(at)onlyinternet.ne wrote: 	
		  



That flat three feet outboard may not generate lift, but it does show benefit in that it pushes the tip vortex outward, increases wing aspect ratio which reduces induced drag. 



Jack B. Hart FF004

Winchester, 	




Jack,



The wingtip vortex may be outward of the airfoil on the current design wing, but it still flows around the tip, and hits the top of the wing.   If you remember John H Test flights of the factory MK III Xtra, its stall numbers were much lower with pure wing out to the end of the aileron even though it had no tip at all.   The same span new Kolb wing without any span wasted on the useless flat wingtips has more lift than the old Kolb wing, and LESS induced drag.  The wing with the current flat wingtips actually INCREASE induced drag because of all the area wasted where there is no airfoil, the opposite of what you claim.



The tests have been done and the results are in...  The new wing design on the factory Kolb MK III Xtra stalls at a significantly lower airspeed with no wingtip at all,  The old design wing that we all have now has less lift due to wasting several feet of its span, and has higher induced drag.



http://forums.matronics.com/viewtopic.php?t=41264



Kolb changed the design for a reason, its been tested, and proven.   Some can theorize and talk about how great the current wingtip is all they want, its not going to change the facts.



Mike

_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!

Kolb MK-III Xtra, 912-S

gliderx5

Joined: 30 Jun 2008
Posts: 203

Posted: Thu Sep 17, 2009 5:54 pm Post subject: Vortex Generators

Mike



I'm not familiar with the MKIII tests, but I did look at the link that you posted.  Do I understand that the test wing had a constant airfoil out to a flat tip, and later a new tip was added, extending the wingspan?  And, was there an original bowed, flat bottomed wing tip that also extended the wingspan, and was tested, but gave higher stall than the shorter flat tip?   I would have expected the results that Jack mentioned, being lower stall with more wing span.  The additional "flat" bottom area on the original design is not actually a "no lift" waste.  It is an airfoil, although not a great one for sure, and would likely generate a lot of drag to accompany the lift that it generates.  Also, dosen't the new wing have a different airfoil?  



Malcolm Morrison

MKII

---

jbhart(at)onlyinternet.ne
Guest

Posted: Thu Sep 17, 2009 7:06 pm Post subject: Vortex Generators

At 05:43 PM 9/17/09 -0700, you wrote:

 	  Quote: 	
		  



Jack,



The wingtip vortex may be outward of the airfoil on the current design 

wing, but it still flows around the tip, and hits the top of the wing.   If 
	


you remember John H Test flights of the factory MK III Xtra, its stall 

numbers were much lower with pure wing out to the end of the aileron even 

though it had no tip at all.   The same span new Kolb wing without any span 

wasted on the useless flat wingtips has more lift than the old Kolb wing, 

and LESS induced drag.  The wing with the current flat wingtips actually 

INCREASE induced drag because of all the area wasted where there is no 

airfoil, the opposite of what you claim.

 	  Quote: 	
		  


	


Mike,



Just for the record, every wing has a tip.  With a wing being of constant 

profile, it has a flat, non rounded tip.  I agree that a constant profile 

wing with a flat tip will generate more lift than the same length wing with 

Homer's tip design.  But the non rounded tip will suffer from flow 

separation drag.  Adding droop tips corrects this tendency and further 

enhances aspect ratio and reduces induced drag.  Rounding the tip will get 

rid of the separation drag.



Jack B. Hart FF004

Winchester, IN

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Fri Sep 18, 2009 3:26 am Post subject: Re: Vortex Generators

From JetPilot:



"...when I put the Hornier style wingtips on the MK III Xtra..."



Is that the comparative form of Horny, or did you mean Hoerner?



do not archive

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Sat Sep 19, 2009 10:01 am Post subject: Re: Vortex Generators

This morning I was going to install VGs under the HS to see if I could get more nose up pitch to enable an actual stall. As you may recall, with the VGs installed I was able to get down to 42 mph IAS (no flaps) but ran out of elevator and the SS wing was not stalled, just mushing with good roll control.



However, before doing this I decided to test the stall speed with 1/2 flaperons, which is as deep as I ever lower them since the SS sinks at 900 fpm at idle power and approach speed of 65 mph and no flaps. Before the VGs stall with 1/2 flaps was 42-43 mph IAS. I was astonished to learn today that with 1/2 flaps and VGs, I had enough elevator to get an actual stall break at.... 34-35 mph IAS. Since I can get a stall break at such a low speed with 1/2 flaps (my normal landing and take-off configuration) I decided I didn't need to have a stall break without flaps. Therefore, I'm not adding the HS VGs.



I am one very happy VG Kolber!

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

pj.ladd(at)btinternet.com
Guest

Posted: Sun Sep 20, 2009 1:14 pm Post subject: Vortex Generators

Before the VGs stall with 1/2 flaps was 42-43 mph IAS.>>



Hi Thom,

been to a battle of Britain airshow today. Spitfire, Hurricane, Lancaster 

etc.  Among the rest of the show was the Antonov Biplane. The biggest single 

engined biplane in the world and it featured a very slow fly past.

The commentator read from the pilots handling notes which said. In case of 

engine failure at night or in bad visib ility pull the stick right back and 

keep the wings level. The speed will reduce to 20 mph and the plane will 

descend in a level position at the speed of a personal parachute.  Who needs 

VG`s?



Incidentally another item was a glider airobatic show. The glider was tugged 

up by a Pawnee, which is much used here for tugging but it did a straight 

and level fly past while the glider did 10 rolls WHILE STILL ON TOW.. 

Incredible bit of flying.



Cheers



Pat

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Sun Sep 20, 2009 1:31 pm Post subject: Re: Vortex Generators

Pat,



I've seen the Anotov Biplane fly too but not as slow as you mentioned. It is an oddball airplane for sure but great at its intended mission. 



Funny you should mention the bit about poor visibility. After doing the most recent stall speed tests with VGs, one of the reasons I decided not to install VGs under the horizontal stabilizer is that I realized that in just such a situation, I could use the non-stalled full up elevator to get down slowly and relatively safely, virtually blind. I hope to never need that but its a nice tool to have in the bag. Of course I have a ballistic recovery chute too but once you commit to the chute you are no longer a pilot. In the slow controlled descent, say through an undercast, once you break out you can resume flying normally. Can't do that with a BRS.



do not archive

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

John Hauck

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

Posted: Sun Sep 20, 2009 3:54 pm Post subject: Vortex Generators

I could use the non-stalled full up elevator to get down slowly and 

relatively safely, virtually blind.



In the slow controlled descent, say through an undercast, once you break out 

you can resume flying normally. Can't do that with a BRS.

 	  Quote: 	
		  

 > Thom Riddle
	


Thom R/Gang:



That is a wonderful idea.



How do you intend to keep the wings level once you lose the horizon?



The decent rate in a mush in my mkIII is about 2,000 fpm.  Not slow by any 

means when the standard rate of climb and decent during instrument flight in 

an Army rotary wing aircraft was 500 fpm, when I was still flying them.



I think I'll keep out of clouds and decend visually.  I haven't been 

instrument rated in over 33 years and my Kolb doesn't do well partial panel.



john h

mkIII

Rock House, Oregon

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

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Mon Sep 21, 2009 3:14 am Post subject: Re: Vortex Generators

John H.



You are correct, of course. My Kolb doesn't have an artificial horizon either so staying out of the clouds is always the better choice.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

pj.ladd(at)btinternet.com
Guest

Posted: Mon Sep 21, 2009 6:14 am Post subject: Vortex Generators

The decent rate in a mush in my mkIII is about 2,000 fpm.>>



Grief ! Thats about twice the climb out speed.  Not an experiment I want to 

try.



Cheers



Pat

pj.ladd(at)btinternet.com
Guest

Posted: Mon Sep 21, 2009 6:18 am Post subject: Vortex Generators

use the non-stalled full up elevator to get down slowly and relatively 

safely,>>



Hmm!  I dont think I would like to try it.



The AN2 didn`t actually carry out the procedure. I assume that it wouldn`t 

do the undercart much good, but you could probably walk away. which in that 

position is the best you can hope for.



Cheers



Pat

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Mon Sep 21, 2009 6:34 am Post subject: Re: Vortex Generators

Now you have me wondering what my sink rate is at idle power at MCA. I know it is about 900 fpm (no flaps) at 65 mph, my normal approach speed. I will find out next time I fly. 



do not archive

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

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