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Dennis.Kirby(at)kirtland.
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 Posted: Wed Feb 01, 2012 1:22 pm Post subject: VGs - Flight Report |
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Kolb Friends –
Here’s another data point to the on-going discussion (argument?) about the relative benefit of installing Vortex Generators on our Kolbs. I installed JG’s “StolSpeed” clear polycarbonate VGs on my Mark-3 last November, and here are my findings.
I have flown 8 times with them so far, and I collected flight data for a variety of power settings – everything from minimum power for level flight to WOT.
BOTTOM LINE: For my Kolb, the VGs allow me to fly at lower power settings than before, without sinking.
At speeds just above stall, the airplane feels noticeably more solid (smooth). Previously, I could detect the air separating from the top of the wing by these two effects: I could feel the airplane shudder as the airflow would separate & reattach in rapid succession, and I could hear the prop cavitate (rum-rum) as the separated (and highly turbulent) flow was coming off the wing and into the prop. Now, it flies solidly, right up to the stall. No shaking or rum-rum. And, when the stall finally happens, it’s still the signature Kolb gentle stall, where the nose just drops straight ahead. My power-off stall (now about 38 mph) decreased by 5 mph.
I often fly at low power settings – within ten mph of the stall speed. This is because most of my flying is local sightseeing, exploring the mountains and valleys around my area of central New Mexico. No need to go anywhere fast, so might as well burn as little fuel per hour as possible. And so, I was especially interested in seeing how the VGs affected my minimum level flight power settings.
Previously, when flying solo, the lowest I could throttle my 912 back to and still maintain level flight was 4000 rpm (48 mph IAS). Now with VGs, I can go as low as 3800 rpm (40 mph) and still fly level with no sink. For local flying, I usually putter around at 7500 feet MSL at 4400 rpm, get 55 mph IAS (63 mph TAS at this altitude), and burn about 3.2 gph.
Cruise speeds and top speed are unchanged.
My takeoff and landing distances are about the same - testament that Homer optimized the design of his airfoil for STOL performance from the beginning.
I also put VGs on the underside of my horizontal stabilizer, in pairs, about 4 inches ahead of the elevator hinge line. 10 per side. This supposedly increases elevator effectiveness at low speeds by minimizing flow separation when flying near max elevator “up” deflection. My landings appear to have improved a little bit – am more consistently making smooth landings – because I seem to have a little more elevator authority at the slow landing speed. (But maybe I was just being sloppy previously – time will tell.)
I installed the VGs per the standard advice we’ve seen offered so often on this List – about ten percent chord aft of the leading edge (approx six inches). I placed two VGs per valley, evenly spaced between the ribs. Stuck them on with double-sided carpet tape. The tape was thin, and very sticky. No way these will come off unless I intentionally pull them off. And if I do, it’s an easy job, as the sticky tape just rolls up into a little rubber ball when you rub it back and forth with your finger.
Overall, I’m happy with the VGs – I think I’ll leave ‘em on! My thanks to John Gilpin for providing the StolSpeed VGs, and Richard Pike for his detailed discussion on his website of his experimentation with optimal placement of VGs on Kolbs.
So … anybody here think we can talk ol’ John Hauck into trying these one day? (hehehe)
Dennis Kirby
Mark-3, 912ul, “Magic Bike”
Sandia Park, NM
[quote][b]
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Wed Feb 01, 2012 3:17 pm Post subject: VGs - Flight Report |
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So … anybody here think we can talk ol’ John Hauck into trying these one
day? (hehehe)
Dennis Kirby
Dennis K/Gang:
Since my name was mentioned I will make one comment.
Your numbers are impressive. Undoubtedly, the VG's have made it a better
airplane and you a better pilot.
However, I have a MKIII that is probably well over 100 lbs heavier than your
MKIII. It does what your MKIII does, only better without VG's. Wonder why?
Chubby Miss P'fer (don't tell her I said that) flies at 3,000 rpm without
falling out of the sky. In ground effect she breaks as the ASI needle is
coming through 30 mph. I have complete control of my MKIII no matter how
she is configured or at whatever flying speed above stall, which is between
30 and 35 mph with full flaps depending on how she is loaded, altitude,
temp, etc.
There were a couple occasions during the life of Miss P'fer that she decided
not to fly. At those times it would have taken more than VG's and an act of
God to keep her in the air. A flying crane might have helped.
In Sep 1993, powered with a 582 I lost the engine coming out of a confined
area with full flaps low airspeed and about 30 or 40 above the ground.
Pilot error. Bent airplane.
May 2009, coming out of Grants, NM, (your neck of the woods) a combination
of high altitude, high density altitude, cross wind, and dust devils, put me
into a position of coming back down instead of going up from about 30 or so
feet. I kept full power, crashed into the sand on the left side of the
runway, bounced back up and flew out of it in ground effect, being very
gentle on the controls, nursed it through ground effect to altitude. Two
other MKIII's took off ahead of me experiencing the same problems, but they
were lucky enough to stay in the air.
Come to think of it, I had two other take off problems at high altitude.
One at Leadville, CO, 9,927 feet ASL, MKIII max gross. Forgot where I was
and tried to do a sea level take off. Never got out of ground effect.
Double Eagle, Albuquerque, NM, two up, 250 lb passenger. Screwed up and
topped off the fuel tank, 25 gal/150 lbs, before I realized my nephew wanted
to fly. Took off, flew through ground effect and right back down to the run
way. After I got it back together again, took a deep breath, nursed the
little MKIII off the tarmac, got a lot of airspeed in ground effect and
eventually climbed to 10,000+ near the summit of Sandia Mountain. Dennis K
is very familiar with this mountain.
All the above situations were way beyond VG salvation. Would they have
helped? Maybe. I don't really know. Would have helped had the pilot had
his head out of his hind end though.
Had a fly off with a Kolb List member a few years ago at the Kolb
Homecoming. He had VGs. I don't. My MKIII is much heavier than his. How
much I do not know. I might add I forgot to unload my MKIII. It had a
dozen (case) of MRE rations, tool bag, other assorted gear on board and
about 100 lbs of fuel. At low altitude we flew side by side at slowest
possible speed. I'll call it a draw although my competitor called it off
because he was afraid I would fly into him. He wasn't supposed to see me
because I was flying his right wing.
No. I am not ready for VGs. I have flown a FS with VGs and saw some
improvement in landing just prior to touch down. Seemed to soften things up
a bit. Other than that, I personally did not see enough improvement to buy
and attach them to my wings or horizontal stabs.
I have nothing against VGs. Simply do not need them on my MKIII.
Well...that was more than a comment. Sorry about that.
john h
mkIII
Titus, Alabama
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John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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Richard Pike
Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee
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| Posted: Wed Feb 01, 2012 4:11 pm Post subject: Re: VGs - Flight Report |
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| John Hauck wrote: |
<snip>
Had a fly off with a Kolb List member a few years ago at the Kolb
Homecoming. He had VGs. I don't. My MKIII is much heavier than his. How much I do not know. I might add I forgot to unload my MKIII. It had a dozen (case) of MRE rations, tool bag, other assorted gear on board and about 100 lbs of fuel. At low altitude we flew side by side at slowest possible speed. I'll call it a draw although my competitor called it off because he was afraid I would fly into him. He wasn't supposed to see me because I was flying his right wing.
<snip>
john h
mkIII
Titus, Alabama |
Let me hijack the thread for a minute and talk about something other than VG's. That was a classic example of going flying when you shouldn't.
I failed to discuss in detail with John ahead of time how we were going to do things. Then the airplane refused to start because of a low battery. Finally got it started but by then I was annoyed at myself - it really stinks to come to the Kolb Fly-In and then have your airplane not start. Kind of like going to the Prom and your date stands you up...
Taxied out and discovered that the radio was not working. I had made up a set of ear buds to replace the headset jacks, and while getting in and out of the airplane had somehow managed to disable the jack box that they plugged into. So I taxied out and discovered I had no radio, and by this time I am somewhat flustered.
Did 2 or 3 fly-bys (don't remember exactly how many) and since we had not coordinated ahead of time exactly how we were going to do it, most of the time I couldn't see John. Meanwhile I am flying my airplane behind the power curve, knowing that I am in close proximity to another airplane. I am assuming that probably he is watching me, but since we didn't coordinate ahead of time, I am also aware that this whole operation flies in the face of everything we get taught about formation flying.
Ever been flying while you were overwhelmed by the idea that you are doing something really dumb? That was me.
Moral to the story: never go flying because of a perceived need to prove anything to anybody. Never go flying if the airplane is not functioning the way it ought to be functioning, especially since we were in a situation where a radio was vital to coordinate. Yeah, all the systems that made it airworthy were functioning, but the mission-specific systems were not, so it should have been scrubbed.
Bottom line - failed to plan & coordinate properly, failed to require all the necessary systems to function properly, failed to fly worth a poot because of anxiety over the previous two failures. Not making excuses, perhaps a rematch would turn out the same way.
But don't ever fly because you think you need to. That's really stupid and that was definitely my day for stupid.
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Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0
Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing. |
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Dennis.Kirby(at)kirtland.
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| Posted: Thu Feb 02, 2012 9:00 am Post subject: VGs - Flight Report |
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John Hauck wrote:
<< Chubby Miss P'fer (don't tell her I said that) flies at 3,000 rpm without
falling out of the sky. >>
===============
??!! 3000 RPM?
You sure that’s not a typo, and do you really mean 4000?
I wonder if my Mark-3 performance numbers are a result of the high elevations I fly at. My home airfield is 6500 feet MSL. So the majority of my flying is at 7000 feet and higher. These are the altitudes my flight report numbers came from – somewhere between 7000 and 8000 feet. The lowest my Kolb has ever been was when I landed at Mid Valley airport in Los Lunas, New Mexico (elev 4830’). When I departed that airport, I could tell my Mark-3 had better climbout performance that what I was used to.
I believe that all airplanes are able to fly at lower power settings at lower altitudes, due to the “thicker” (more dense) air. (Another way of saying the same thing is, airplanes perform better on the same power settings at lower elevations.) One of my goals is to fly my Kolb to the coast, and experience flying at near sea-level. I’ll probably be amazed at the apparent performance improvement!
Dennis Kirby
New Mexico
do not archive
[quote][b]
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Vic Peters
Joined: 30 Oct 2009
Posts: 54
Location: Millinocket, Maine
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| Posted: Thu Feb 02, 2012 1:12 pm Post subject: VGs - Flight Report |
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Mine also stays in the air at 3000 400ft alt though.
Vic
[quote] ---
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Vic
912ul Xtra
Maine
Too old to cut the mustard but not the cheese. |
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lcottrell
Joined: 29 May 2006
Posts: 1494
Location: Jordan Valley, Or
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| Posted: Thu Feb 02, 2012 7:28 pm Post subject: VGs - Flight Report |
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On Thu, Feb 2, 2012 at 9:56 AM, Kirby, Dennis Civ USAF AFMC AFNWC/ENS <Dennis.Kirby(at)kirtland.af.mil (Dennis.Kirby(at)kirtland.af.mil)> wrote:
Dennis, and the rest of you intending to install VG's. My Firestar II ( heavy) has two sets of VG's on the wings. The first ones were installed on the ribs ( 7 ) at 11 inches. That gave me a 6 MPH reduction in stall. There was some talk on the list that was too far back, so I installed another 7 at 10 inches in the false rib bay, and that gave me another 5 MPH hour reduction. Which means that at gross weight my plane stalls at 32 to 36 MPH.
Roger Hankins has a KXP and he installed VG's at 10 inches and promptly took them off as it made the planes performance worse. On one of his trips over here to the Rock house we decided to try again and test them to see where his best position would be. Since he had already tried 10 or 11 inches we set the first try at 9 inches. He then took off and did several stalls, and different flights. It was better, but still not what he wanted. We next tried 7 inches and the results were very much better. Flight stability and stall was much improved.
The primary findings to me are that each model may respond differently at the same settings, and each model or plane should be tested to obtain the best results. (If they were all built by the same company as is the spam cans are then each model would respond the same) Your results appear to be close to the norm for VG's, so I have no clue as to whether you could improve its performance by further testing. I have no explanation for why I seem to have obtained a larger reduction other than the fact that my final stall speed is in the ball park of where it should be. My original stall apparently was exceptionally high.
The point that I am trying to make is that one size does not fit all. For instance Roger's KXP actually landed slower with out VG's than my Firestar did with them. Now it flies much better than it did before.
I am glad that you are happy with the VG's. Give up on John, he is right in that Pfer does every thing he wants her to do and better than I can with mine with VG's. I doubt that skill has anything to do with it however, but like you I am convinced that VG's would make her even better. We will never know though.
We are having the Rockhouse Fly-in the 23rd to the 30th of June this year. It is on the way to the Oregon coast, so come on out and join us. You can go to the coast afterward.
Larry
[quote][b]
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