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Shorting the bow tips

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mustangsally(at)semo.net
Guest

Posted: Thu Apr 20, 2006 6:19 pm Post subject: Shorting the bow tips

Has anyone shortened the bow tips on the wings of Firestar? Seems to be a lot of drag out there. Doing some measuring, 6" could be done pretty easy. That would be 12" less of nonlift producing drag gone.

Jerry

biglar

Joined: 14 Jan 2006
Posts: 457

Posted: Thu Apr 20, 2006 6:46 pm Post subject: Shorting the bow tips

Not sure about the FireStar, but a few years ago, Ron Christensen built a 

much modified Kolb that he called the Mk III 1/2.  It gave me several ideas 

for Vamoose.  There's a couple of pics of it on one of my Vamoose webpages. 

He originally tried just what you're asking, and lost performance.  Then he 

built several variations of wingtips, including drooped, out of fiberglass. 

He did a beautiful job, but finally wound up with stock wingtips, and said 

they performed best.                       Lar.



Larry Bourne

Palm Springs, CA

Building Kolb Mk III

N78LB  Vamoose

www.gogittum.com



---

_________________
Larry Bourne
Palm Springs, CA
Building Kolb Mk IIIC
"Vamoose"

John Jung

Joined: 10 Jan 2006
Posts: 108
Location: Surprise, AZ, USA

Posted: Thu Apr 20, 2006 8:41 pm Post subject: Re: Shorting the bow tips

 	  mustangsally(at)semo.net wrote: 	
		  Has anyone shortened the bow tips on the wings of Firestar? Seems to be a lot of drag out there. Doing some measuring, 6" could be done pretty easy. That would be 12" less of nonlift producing drag gone.

Jerry 	




Jerry, 



I'm not so sure that the tips don't produce lift. My original Firestar had stock tips and my Firestar II has shorter tips. I suspect that they do. If I ever build new Kolb wings they will have stock tips.



do not archive

_________________
John Jung
Firestar II N6163J
Surprise, AZ

Denny Rowe

Joined: 10 Jan 2006
Posts: 89
Location: Leechburg, PA

Posted: Fri Apr 21, 2006 5:20 am Post subject: Shorting the bow tips

Remember the tips are at an incline to the relitive wind, same as the rest 

of the wing, they are producing plenty of lift by deflecting air downward.



Denny

---

jindoguy(at)gmail.com
Guest

Posted: Fri Apr 21, 2006 6:28 am Post subject: Shorting the bow tips

As I have stated before, I'm not an engineer and this is worth exactly what

you paid for it.

All Kolb aircraft have a straight, rectangular planeform wing. For the

purposes of lift distribution in high speed cruise, it is the worst

planeform to use. For the purposes of lift distribution at stall it is the

best.

Discussing the Kolb wing tip as a lift producing device is, well, quite

frankly, the back assward view. If we could look at the airflow over the

wing starting at the root and working outboard we would see that somewhere

around 75 to 80 per cent of the way to the tip the air begins to turn, drawn

by the difference in pressure between the top and bottom of the wing, and

run spanwise down the wing. This effect becomes more pronounced as the wing

angle of attack increases. So it comes down to an inescapable conclusion.

Wing tips don't produce lift,  wing tips reduce loses due to spanwise flow.

Now what is you want to do?

Do you want to land slower and shorter? Take a look at the work done by the

STOL speciality shops. To inhibit spanwise flow, they add wing fences and

wingtips with a down ward curl along the trailing edge. The benefits are

that you get to go slower AND maintain an unstalled flow over the ailerons

so they remain effective at the lower airspeed.

Do you want to go faster with very low induced drag in cruise? I hate to

break it to you, but you bought the wrong airplane. The Kolb has a boatload

of parasitic drag at all airspeeds and that is far more effective at

inhibiting its cruise performance than anything going on at the wing tips.

Even if you could clean up most of it, the Kolb would still be Vne limited.

I have no trouble at all reaching red line airspeed in my Mk III while

trying to maintain altitude in the grips of even a mild Kansas thermal.

My suggestion would be this, concentrate on the areas that will get you the

biggest bang for the buck. Streamline the lift struts, gear legs and control

tubes. Make a good sealed gap cover. Seal the gaps around all the

stabilizers and the gaps at the control hinge lines. These things can be

done very cheaply, will get you immediate benefits, and most important,

won't compromise the structure of the wing.

You will, of course, do exactly as you please.

On 4/20/06, John Jung <jrjungjr(at)yahoo.com> wrote:

 	  Quote: 	

 mustangsally(at)semo.net wrote:

 > Has anyone shortened the bow tips on the wings of Firestar? Seems to be

 a lot of drag out there. Doing some measuring, 6" could be done pretty easy.

 That would be 12" less of nonlift producing drag gone.

 > Jerry

 Jerry,

 I'm not so sure that the tips don't produce lift. My original Firestar had

 stock tips and my Firestar II has shorter tips. I suspect that they do. If I

 ever build new Kolb wings they will have stock tips.

 do not archive

 --------

 John Jung

 Firestar II N6163J

 Surprise, AZ

 Read this topic online here:

 http://forums.matronics.com/viewtopic.php?p=3D29801#29801

--

Rick Girard

"Pining for a home on the Range"

slyck(at)frontiernet.net
Guest

Posted: Fri Apr 21, 2006 6:58 am Post subject: Shorting the bow tips

 	  Quote: 	
		   Do you want to go faster with very low induced drag in cruise? I hate 

 to

 break it to you, but you bought the wrong airplane.


	


funny

 	  Quote: 	
		  

   Guess I knew that when I first saw a Kolb.
	


  58 hp/65 mph ,    90 hp/85 mph  + a lot more petrol.



But then I'm a slow guy, happy with a slow plane.



Buy a Sonex if you want a fast, simple airplane.

I like feeling like I'm riding around the sky on a barcalounger

instead of in a sardine can.

-BB,  MkIII, REALLY inefficient wingtips.

 	  Quote:

gtb(at)commspeed.net
Guest

Posted: Fri Apr 21, 2006 7:50 am Post subject: Shorting the bow tips

My apologies to the group.



I failed to add the authors name to my last post.



It was Richard R. Ryburn <ric(at)srclink.net>



George

Kirk Smith

Joined: 10 Jan 2006
Posts: 78
Location: SE Michigan

Posted: Fri Apr 21, 2006 10:09 am Post subject: Shorting the bow tips

I remember a Kolb Mark3 at Oskosh that had lengthened the wings 

to slow it even more so they could do hang glider tows. Now that 

was neato. I'd like to see leading edge slats on one also, slow it 

down to about a 15 mph flight.  



Do not

archive

eagle1(at)commspeed.net
Guest

Posted: Fri Apr 21, 2006 10:37 am Post subject: Shorting the bow tips

Been there, done that, on my Firestar II. I would not recommend it. I 

thought that I would gain some speed but I could not see that it did that 

but slowed the take off a bit ( Not that that hurt anything). I shortened 

the bow about 8 inches on each side. In my opinion, you will not gain 

anything worthwhile.

     Az Bald Eagle

---

Possum

Joined: 12 Jan 2006
Posts: 112
Location: Georgia

Posted: Fri Apr 21, 2006 12:50 pm Post subject: Re: Shorting the bow tips

 	  mustangsally(at)semo.net wrote: 	
		  Has anyone shortened the bow tips on the wings of Firestar? Seems to be a lot of drag out there. Doing some measuring, 6" could be done pretty easy. That would be 12" less of nonlift producing drag gone.

Jerry 	




I did  - to 26'9" - I'll send some pictures. I think it works fine. I have standard Kolb Ribs (built on a wooden jig - the old fashion way) - different wing bow  ...a few other things different but not with the wings though - execpt VGs.

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Thom Riddle

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

Posted: Sat Apr 22, 2006 3:50 am Post subject: Shorting the bow tips

If that Hoerner Style wing tip does to a Kolb what they do for a 

Cherokee, the results must be wonderful. Of course the original shape 

of the Hershey bar wing tip on the Cherokee is not as good as the 

original Kolb wing tip.



Thom in Buffalo

_________________
Thom Riddle
Buffalo, NY (9G0)

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

Dennis.Kirby(at)kirtland.
Guest

Posted: Mon Apr 24, 2006 12:59 pm Post subject: Shorting the bow tips

<< Been there, done that, on my Firestar II. I would not recommend it. I 

thought that I would gain some speed but I could not see that it did that 

but slowed the take off a bit ( Not that that hurt anything). I shortened 

the bow about 8 inches on each side. In my opinion, you will not gain 

anything worthwhile.  Az Bald Eagle  >>



Here's another story that corroborates this exact point:



In the mid-90s, at the little airport I fly out of near Albuquerque, a

fellow arrived with a newly-purchased Mark-III that he bought from someone

in Arizona who built it with shortened wingtips.  In the attempt to "make it

a little more agile," the builder truncated the wing at the end of the spar,

essentially eliminating the tip bow altogether.



Our hapless buyer had no Kolb experience, so he talked one of the local

ultralight instructors into doing a few test flights in the Kolb, to better

evaluate how the plane flew.  This instructor was experienced, including

time in Kolbs, but he was not prepared for the drastic decrease in available

lift at low speeds in this modified Mark-3.



On the first test flight, the engine quit just after departure, at about

300' AGL.  At this altitude, most normal light sport airplanes in this

weight class are able to execute a 90 degree turn and glide safely to a

landing on this airport's crossing runway.  My instructor friend tells us

that, while trying to do this, it stalled at nearly 60 mph in a slight turn.

Spun it in from nearly 80 feet.  Totaled the Mark-3, but he survived with

only a charley horse in his thigh.



Aside from taking away the message that you should leave Homer's wings

alone, this story speaks volumes about the crash worthiness of these Kolb

airplanes!



Dennis Kirby

Mark-3, 912ul

Cedar Crest, NM

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