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Vortex Generators - Flight test report.

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JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Wed Jul 11, 2007 8:21 am Post subject: Vortex Generators - Flight test report.

I put Vortex Generators on my Kolb MK III Xtra.  I did not want to post just a first impression so I have flown with them for about a months so that I had a chance to really try them out in a lot of different conditions.  The VG's have made a different airplane out of the MK III, not just in terms of reducing the stall speed, but in the feel of the plane at lower speeds.   It used to feel like an approach speed of 60 MPH was needed to have a good margain of safety and control.  Now, 40 on approach feels fine, although I use 50 minimum as a safety factor.



Stalls occour at 26 indicated, the plane is not really going this slow, as the GPS shows mid 30's stall with no flaps.  I have the traditional seperate flaps and ailerons, and Stalling with flaps seems to be at the same speed as stalling without them, mid 30's.  The stall is really a non event, the plane shakes 1/2 second before the nose falls a few degrees nose down,  Its so mild that I have a hard time calling it a stall.  Full aileron control is maintained throughout the stall, if a wing starts to drop anytime in the stall, a medium amout of aileron input immidately corrects it.  I was teaching my wife stalls and of course her first reaction was to jerk the stick back as soon as the nose fell, she abruptly pulled the plane level at 33 indicated a couple times and never got a secondary stall.



Yesterday evening, I wanted to see if I could really fly an approach at a very low airspeed, so I went to 2000 feet, went to idle power slowed down to 35 MPH indicated, and put in a huge amount of aileron, banked 45 degrees and roughly jerked the plane around like an idiot, but was not able to get an accelerated stall or felt like I was about to lose it.



Landings were a real problem at first, I was in the habbit of landing with no flaps, and with the VG's the plane started to bounce badly on every landing no matter how smooth the touchdown.  The airplane would touch down, but there was still enough lift being generated that it would fly again, even with a perfect three point landing... It was worse with a wheels landing.  Landing with one notch of flaps totally cured this, im guessing that it pitches the nose down enough that it does not tend to pitch up on a wheels landing, and its going slow enough on a 3 point landing not to fly again.  Now I land with flaps every time.



The down side is that it cost me some speed, im not sure exactly how much as a changed props at the same time I added the VG's, I lost 8 MPH in cruise with the prop change and VG installation.  Im guessing at least 5 of that is VG related.   I put the VG 's on with double sided automotive trim tape so that I could take them off if I ever wanted to.  Overall im so happy with the way the MK-III flys and feels at slow speeds with VG's, I am more than happy to cruise a bit slower.  



I used 140 VG's spaced at 2.5 inches apart from the center out to the wingtips.  The VG's are in pairs and centered in the valleys of the ribs and face the airstream at a 15 degree angle, and placed at 10 % of the chord of the wing.   Attached is a picture of the VG's on the wing, and my panel flying level with 3500 RPM just above stall.



Mike Bigelow



MK III Xtra 912-S

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

Kolb MK-III Xtra, 912-S

1planeguy(at)kilocharlie.
Guest

Posted: Wed Jul 11, 2007 9:15 am Post subject: Vortex Generators - Flight test report.

Might want to rethink the prop change...having flown 2 different RANS

S7's with and without VG's and communicating with several that had flown

them on Challengers, you're the first I've heard of actually losing

cruise speed.  A couple of folks thought "maybe a MPH or 2" but really

hard to tell.  Personally I could not tell any lose of cruise speed.

Read an article in Sport Aviation long time ago about a guy that tested

VG's on an RV-6 with an articulating pitot-static test boom and

everything and got somewhere around 4-5MPH loss...but that was on a

200MPH airplane, so go figure.



Your still a good advocate for the VG's...even thinking that the VG's

cost you that much cruise speed you were impressed enough with the slow

end improvement to leave them on...that says it all.  I'd bet a crisp $5

bill that swapping back to the original prop will show the VG's to not

have cost you much (if any) on the cruise end...



Jeremy Casey



<snip>

The down side is that it cost me some speed, im not sure exactly how

much as a changed props at the same time I added the VG's, I lost 8 MPH

in cruise with the prop change and VG installation.  Im guessing at

least 5 of that is VG related.   I put the VG 's on with double sided

automotive trim tape so that I could take them off if I ever wanted to.

Overall im so happy with the way the MK-III flys and feels at slow

speeds with VG's, I am more than happy to cruise a bit slower.  



I used 140 VG's spaced at 2.5 inches apart from the center out to the

wingtips.  The VG's are in pairs and centered in the valleys of the ribs

and face the airstream at a 15 degree angle, and placed at 10 % of the

chord of the wing.   Attached is a picture of the VG's on the wing, and

my panel flying level with 3500 RPM just above stall.



Mike Bigelow

Richard Pike

Joined: 09 Jan 2006
Posts: 1670
Location: Blountville, Tennessee

Posted: Wed Jul 11, 2007 9:25 am Post subject: Vortex Generators - Flight test report.

I'll see your five and raise you five...

$10 says it's not the VG's.

(Bad Preacher, No, No!)



Richard Pike

MKIII N420P (420ldPoops)

do not archive

---

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

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

George Myers

Joined: 10 Jan 2006
Posts: 76
Location: San Marcos, Texas

Posted: Wed Jul 11, 2007 10:01 am Post subject: Vortex Generators - Flight test report.

Did anybody see any vortez generators??? 



[quote] --

mdnanwelch7(at)hotmail.co
Guest

Posted: Wed Jul 11, 2007 10:49 am Post subject: Vortex Generators - Flight test report.

Very funny, George.   Yeah, what airplane??    Also, notice how Mike 

mentioned in his email how he had his lovely wife in the plane with him, 

teaching her stalls, no less!!!!   Gosh, should we be so lucky to have our 

wives support us so!!  I think it was a sly way for him to brag about having 

a real sweetheart of a wife.



  In case Mr. Mike reads this email,  do you have any specs/details of the 

VG's?  Where did you get the design, and how far back from the leading edge 

are they mounted?



                                                         Appreciate the 

info,   Mike in SW Utah

[quote]From: "George Myers" <gmyers(at)grandecom.net>

Reply-To: kolb-list(at)matronics.com

To: <kolb-list(at)matronics.com>

Subject: RE: Vortex Generators - Flight test report.

Date: Wed, 11 Jul 2007 13:00:55 -0500






Did anybody see any vortez generators??? 



 > --

Russ Kinne

Joined: 27 Jan 2006
Posts: 182

Posted: Wed Jul 11, 2007 12:16 pm Post subject: Vortex Generators - Flight test report.

If you hold a magazine over the left half of the image, you'll see  

the VG's!

do not archive



On Jul 11, 2007, at 2:00 PM, George Myers wrote:



[quote] 



 Did anybody see any vortez generators??? 



> --

jimhefner

Joined: 11 Jan 2006
Posts: 91
Location: Tucson, AZ

Posted: Thu Jul 12, 2007 6:22 am Post subject: Re: Vortex Generators - Flight test report.

Mike, did you put any VG's on the underside of the horizontal stabilizers?  You might want to consider that if not.  It might not be a big deal on the Mk III X but it will help keep the tail from stalling before the main wing on slow landings.  You might consider relocating the VG's from the outer wing sections to under the Vert Stab if you don't have enough.... you will not notice anything different and it will look better IMHO.



I agree with the others about the loss of speed being related to the prop change more than the VG's.  Any chance of putting the old prop back on to know for sure?



I'm glad, but not surprised, to see VG's made such a nice difference in a MK III X!

_________________
Jim Hefner
Tucson, AZ
Do Not Archive

lcottrell

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

Posted: Thu Jul 12, 2007 8:58 am Post subject: Vortex Generators - Flight test report.

---

jimhefner

Joined: 11 Jan 2006
Posts: 91
Location: Tucson, AZ

Posted: Thu Jul 12, 2007 9:54 am Post subject: Re: Vortex Generators - Flight test report.

Just what happens when the tail stalls?



Larry C 



Larry, my experience (and I know Jack Hart experienced this) is based on VG's on the main wing of a Firefly.  The tail would tend to sink faster than the main wing at slow speed, making a 3 pt landing difficult.  Usually the tail sink quicker than the main wing and the tailwheel would touch down and then the mains would come down quickly and not as gently as I wanted, due to the higher pitch angle created by the early tail stall.  I put VG's under the hor stab's and the problem was cured.  Jack experimented with this long before me so I was able to follow his lead and experienced the same things he did.  I think the same thing applies to all Kolbs with VG's

_________________
Jim Hefner
Tucson, AZ
Do Not Archive

d-m-hague(at)comcast.net
Guest

Posted: Thu Jul 12, 2007 12:34 pm Post subject: Vortex Generators - Flight test report.

At 12:57 PM 7/12/2007, Larry Cottrell wrote:

 	  Quote: 	
		  Just what happens when the tail stalls?


	


Since the tail normally is pushing down, when it stalls it goes up, the 

plane noses down, the tail starts flying again, and the plane recovers.



This assumes you're not pushing the stick forward and doing negative g's...



                         -Dana

--

--

The only correct outcome to an armed robbery attempt is a dead armed robber.

Richard Pike

Joined: 09 Jan 2006
Posts: 1670
Location: Blountville, Tennessee

Posted: Thu Jul 12, 2007 12:48 pm Post subject: Vortex Generators - Flight test report.

Maybe I am missing something here but...  Relocating/removing the VG's from 

the outer wing sections - and leaving them on the inner wing sections? Would 

that not give you tips that stall first? That doesn't sound like anything I 

would want.

Richard Pike

MKIII N420P (420ldPoops)



---

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

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

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Thu Jul 12, 2007 7:31 pm Post subject: Re: Vortex Generators - Flight test report.

Its very possible that the entire speed difference in my Kolb could be related to my prop change, more on this in a differnt post...



You definately want the VG's on the wingtips, so that they dont stall before the inner portion.  With the vortex generators on the wingtips, better aileron control is maintaned at slow speed and in stalls, which is a huge safety advantege.  Having VG's along the entire leingth of the wing is the best thing, I would not want to take some VG's off the wing and reduce the performance I have gained.  I would just buy more before I would do that.



I did not put VG's on the tail.   The tail generates downforce, so when the tail stalls, it goes up...  I have not seen any evidence of the tail stalling, I can touch the tailwheel first if I want, which tells me the tail is pushing down (not stalled) at my slowest speeds.  VG's on the tail could change its handling though, so if I ever wanted to change the way the plane feels, VG's could make landings easier, or harder.   The only way to know this would be flight testing with VG's on the tail... In my case im very happy and dont need VG's on my tail.  Every plane is different, so I can definately see that others might benefit from VG's on the tail.



I got the VG 's from www.landshorter.com and installed them exactly to their specs  10 % wing chord,  2.5 inches apart, and a very important and critical specification is that they be angled at a 15 degree angle to the airstream.   The land shorter Vortex Generators have been optimized in both shape and size, so its well worth spending the 100 bucks to buy 100 of them that are perfect aerodynamically rather than try to make them.  Extra VG's are only 1.50 each, so if I ever want to try them on the tail I will just spend 40 bucks and buy more.  The VG's are wonderful, and there is absolutely nothing else that one could do to add this much more performance to a Kolb for 100 bucks.



Mike Bigelow



MK III Xtra  Rotax 912-S

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

Kolb MK-III Xtra, 912-S

Ed in JXN

Joined: 24 Mar 2006
Posts: 122

Posted: Fri Jul 13, 2007 6:52 am Post subject: Vortex Generators - Flight test report.

Hi Larry,



        A very uncomfortable porpoising at least, if you're lucky.  Elevator 

control reversal and departure from controlled flight, if you're having a 

real bad day.



        VG's on the tail may be a bit of overkill, but they wouldn't hurt 

IMHO.



        The 2.5-inch spacing seems way overkill, compared to the GA aircraft 

I've flown with STC'd VGs.



Ed in JXN

MkII/503



---

jimhefner

Joined: 11 Jan 2006
Posts: 91
Location: Tucson, AZ

Posted: Fri Jul 13, 2007 1:22 pm Post subject: Re: Vortex Generators - Flight test report.

I stand corrected about the reason the tail dropped being due to stall.  I knew that and misspoke.   Actually,  I don't know what technically was going on but I know by adding VG's under the hor stab, it generated extra (negative) lift or some other technical phenomena  that eliminated the problem with the tail dropping too early during flare doing stall landings with full flaperons.  The Mk III X is a much bigger and heavier plane and may not have the same characteristics, so I was only mentioning this in case it does show a similar tendency that was experienced with the Firefly.  If it's good without them, don't change it.



Regarding potential removal of VG's I was only referring to the outermost 6 VG's on the wingtip area beyond the last half rib where the airfoil shape tapers down to the outer tube, top and bottom.  I didn't install VG's in that area and had all the same benefits everyone else has enjoyed with VG's.

_________________
Jim Hefner
Tucson, AZ
Do Not Archive

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