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Vortex Generator suggestions

R

reliableflyer

Registered User
Seldovia, Alaska
VG’s come with recommended placement. We have all seen or had aircraft with variations from supplier recommended placement. Has anybody had experience or knowledge about deviation from suppliers recommended placement. These VG’s will be on a standard 18 wing with original flaps and round tips. It will be flown by experienced cub pilots only.

I would appreciate knowledgeable input and discussion. Thanks. Stu
 
Their chordwise placement is a result of testing and ultimately is a compromise of several values like stall behavior, control response, and cruise speed. Another variable is their height into the boundary layer of flow above the wing for the same reasons. One thing I'd be cautious about is placing them too far back from the LE or made from too low a design without some tuft testing of the airflow during high AOA. If their vortices suddenly reduce or stop due disturbed flow above the stall can become abrupt. My opinion and experience FWIW.

Some are mounted on a straight line along the LE and others are offset to the rear inboard to let that part of the wing go first. I've wondered how a tapered straight line further to the rear inboard would work.

Here's some reading material: https://stolspeed.com and http://fly-fbi.com/html/vortex_generators.html

Gary
 
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Another interesting factoid is Micro chose short height VG's for the PA-18 and then tall (like the tail VG's on some) for the PA-20-22. Same airfoil. What aerodynamic mystery created that?

Gary
 
Eddie Foy said:
Why would you not put them where the manufacturer dictates?
Click to expand...

because the manufacturer used to send kits with double sided sticky tape so you could try them in different configurations and provide feedback as what worked best (micro, for 185 in the 1990's)
 
I'm fixing to put VGs on my Cub in a day or two. When considering VGs I consulted the best VG expert I could think of, and Jerry Burr told me to do what my supplier advised since they'd done the testing and already had the position figured out.

I don't need to know how, I need to know who to ask!

IMG_5171.JPG


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stewartb said:
I'm fixing to put VGs on my Cub in a day or two. When considering VGs I consulted the best VG expert I could think of, and Jerry Burr told me to do what my supplier advised since they'd done the testing and already had the position figured out.
Click to expand...
FWIW, I followed Jerry's advice for application with Crosswinds leading edge cuff, and am very happy with the result.
 
Next time down, tell me about that. I suspect the Crosswinds cuff needs VGs.

As to experience with non-standard placement - yes. I flew a C-180 with Sportsman + Micro, where they used the stock wing placement template. Not dangerous, but I was not impressed at all. I was more comfortable at low speeds with the stock wing/Horton and no VGs.

But that was gut feel - I did not experiment or take any data.
 
VG's and Crosswinds cuff - Charly recommends them together on his webpage.

I've flown the cuff on three planes. I owned his cuff w/o VG's on a 7GCBC and liked the improvement in slow flight. I also owned a PA-12 with his cuff and no VG's that had extended wings with Sullivan tips. After some years I had the cuff removed and enjoyed the difference both slow and fast. Gordon Mandell who was involved in the design when working for Crosswinds told me the cuff "reduced the LE pressure peak at the stall".

I guess that's good. Maybe VG's make it even better.

Gary
 
"When we are at cruise speed the AOA is zero" Alex left me in his wake with that while me is looking for a snack. Maybe his is. Some aren't. Ask Boeing. Flying at +25 degrees AOA? Why?

Gary
 
Jerry Burr is/was pretty much the authority from experience on VG's. There is some interesting tables and info if you search for it. Most interesting to me was the sweet spot was much further forward than I expected. If you find the thread(s) that this chart was saved from, you'll get some good explanations as well.

1.1%, that's less than 1" back in a 63" chord... but I like that data profile.

Jerry Burr VG placement.jpg
 

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Determining the best position for VG's that yields the lowest TAS stall is interesting but is it a practical application in normal flight? By practical I mean what angle relative to earth can be used for takeoff or landing especially on floats or skis? For 3-point there's a limit unless we're willing to roll the tail on takeoff or land tail first and drop like Storch. For slow flight it has more application.

For Jerry's chart adding that deck angle versus TAS for all configurations would be a bonus. I'd guess the lowest airspeeds with flaps were determined in a nose high AOA at altitude.

My Micro AeroDynamics prints for the PA-12 and 18 indicate the forward edge of the small VG's are located 0.75" behind the wing leading edge, or about 1.1% chord #4 in the chart.

Gary
 
Yep, and furthermore that 3/4" remains valid with the Crosswinds leading edge cuff.

In my opinion the value isn't so much being able to use a high AOA for touchdown. It's the "safety margin" that's provided in situations such as gusty conditions or landing in a turn (or my sloppy flying). I don't have any knowledge of how cruise speed is affected by the combination, but overall I'm happy with the arrangement.
 
Yes Gordon safety margin for sure especially on a sharp LE wing Taylorcraft that's prone to an abrupt loss of lift and nose down stall.

For my Cubs and 12 the benefit was mainly on floats and somewhat skis in deep snow. In any wind the float planes with power would fly directly from plowing mode to takeoff (in the 30's mph GPS) via wave bounce and prop blast on the flapped portion of the inboard wing with little planing and then maintain flight just above the water while speed built. On landing I could touch the rear of the floats easy (same 30's mph with power) then plop down in a very short arrival. The 12 had a Crosswinds cuff and I never added VG's but now wished I had retained it and put them on. The cuff without VG's stalled like the Taylorcraft when it was pushed at altitude and was all done flying, the stock wing not as much. On normal landing (less than ~15*) it never let go unexpectedly.

Gary
 
BC12D-4-85 said:
Determining the best position for VG's that yields the lowest TAS stall is interesting but is it a practical application in normal flight? By practical I mean what angle relative to earth can be used for takeoff or landing especially on floats or skis? For 3-point there's a limit unless we're willing to roll the tail on takeoff or land tail first and drop like Storch. For slow flight it has more application.

For Jerry's chart adding that deck angle versus TAS for all configurations would be a bonus. I'd guess the lowest airspeeds with flaps were determined in a nose high AOA at altitude.

My Micro AeroDynamics prints for the PA-12 and 18 indicate the forward edge of the small VG's are located 0.75" behind the wing leading edge, or about 1.1% chord #4 in the chart.

Gary
Click to expand...

Gordon Misch said:
In my opinion the value isn't so much being able to use a high AOA for touchdown. It's the "safety margin" that's provided in situations such as gusty conditions or landing in a turn (or my sloppy flying). I don't have any knowledge of how cruise speed is affected by the combination, but overall I'm happy with the arrangement.
Click to expand...

I agree 100% with Gordon on this. If there’s no meaningful effect to cruise speed, I don’t know why I’d consciously turn down a slower stall speed.

I’ve never landed in a full stall. And I don’t think I’d ever start to do that just because my airplane could fly slower after a mod.

Safety margin is where it’s at. Still land within the limits of your landing gear, regardless of stall speed.
 
I've thought about these VG's off and on over the years. They are fun to play with at odd AOA and control can be improved during slow flight. For the Cubs, Cessnas, Aeroncas, and Beaver I've flown without them I never felt the absolute need as I never unintentionally stalled or spun those planes. I've done lots of slow flight and same in turbulence apparently safely but perhaps marginally so. As mentioned in #17 there were certain ops that they outperformed a standard wing for me. If they save a life then of course that's good.

To quote Stu the thread's originator "Has anybody had experience or knowledge about deviation from suppliers recommended placement. These VG’s will be on a standard 18 wing with original flaps and round tips. It will be flown by experienced cub pilots only". I guess #13 and #!5 answers that for short height Micro-style VG's. I wondered in #4 why the PA-20/22 has the higher units installed from Micro. And Cub Crafters further chooses a different method of placement and style to compound the questions.

Hopefully when Stu tests them he'll take this to another level we'll get feedback on their experience with and without.

Gary
 
I recall a comment Jerry Burr made in a thread about Micro and BLR's different VG placements about 14 years ago. He said BLR was better for power off landings and Micros were better for power on. I assumed that meant Micros were better at a higher AOA. I haven't kept up with BLR/Cubcrafters/VG STOL and have no idea what their locations are these days. When I think VGs I think Micro.

Any comments about VGs with slats? I'm a few minutes from sticking mine on. Here's a pic of BCSC's VG template. CNC milled aluminum. That's different!

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Yes, Boundary Layer Research applied larger VGs to the Piper wing, and in a somewhat different location and they’re staggered, in an attempt to keep flow energized over the ailerons at high Alpha. That design and STC is now owned by Cub Crafters, and installed on the Top Cub and perhaps others?

Years ago, I discussed this kit with Bob DeRuesh (and I’m sure I butchered his name) the owner of BLR. Bob worked for Robertson STOL back when. He now has a number of mods for various aircraft involving VGs, including some spray planes.

With regard to the different height of the VGs between the BLR and Micro kits for the Cub, I have to wonder......why Micro uses the same taller VGs that BLR/CC uses on the Cub in its kits for the Cessnas? Intuitively, I would think that the boundary layer on a Cub wing would be thicker than that of a Cessna, not the other way around. So why does Micro use shorter, smaller VGs on there Cub kits and taller, larger VGs on their Cessna kits?

MTV
 
MTV: "So why does Micro use shorter, smaller VGs on there Cub kits and taller, larger VGs on their Cessna kits?" And tall VG's on PA-20/22's? I confirmed that today.

Also short on my Taylorcraft. I feel puny and insecure with my small VG's but I'd never leave Earth now without them. Oh, and run them across the upper windshield to keep the fuselage flying.

Gary
 

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mvivion said:
...With regard to the different height of the VGs between the BLR and Micro kits for the Cub, I have to wonder......why Micro uses the same taller VGs that BLR/CC uses on the Cub in its kits for the Cessnas? Intuitively, I would think that the boundary layer on a Cub wing would be thicker than that of a Cessna, not the other way around. So why does Micro use shorter, smaller VGs on there Cub kits and taller, larger VGs on their Cessna kits?
Click to expand...

Charlie White at Micro would be the one to ask.
 
BC12D-4-85 said:
Yes Gordon safety margin for sure especially on a sharp LE wing Taylorcraft that's prone to an abrupt loss of lift and nose down stall.

For my Cubs and 12 the benefit was mainly on floats and somewhat skis in deep snow. In any wind the float planes with power would fly directly from plowing mode to takeoff (in the 30's mph GPS) via wave bounce and prop blast on the flapped portion of the inboard wing with little planing and then maintain flight just above the water while speed built. On landing I could touch the rear of the floats easy (same 30's mph with power) then plop down in a very short arrival. The 12 had a Crosswinds cuff and I never added VG's but now wished I had retained it and put them on. The cuff without VG's stalled like the Taylorcraft when it was pushed at altitude and was all done flying, the stock wing not as much. On normal landing (less than ~15*) it never let go unexpectedly.

Gary
Click to expand...

As a past T-Craft flier, I still find any comments on it's flight characteristics interesting. Mine didn't have VG's though, and I didn't do any off airport with it. It wasn't until I bought my first RANS S-7 25 years ago that I got interested in all that, and I started noticing Micro's ads for certified aircraft VG's. I remember Chuck White referencing Jerry Burr when we talked about where to put them on my 7, ( the same as on a Champ it turned out, wing and the hor stab) and after 3 different placements (with double sided tape) I settled on the first, which is quite far forward. I set my second 7 up the exact same way, if it was good enough for Jerry Burr, it's good enough for me! It's when landing steeper slopes that I get my slowest landing, the slope kinda matching the high AOA on touchdown.

I can safely venture much closer to the "all done flying, ain't no more" area on landings and even low level maneuvering, and often do. BUT, when I really push it right to the edge, it can bite. Like a friendly dog, friendly, right up until it snaps at you! But it is nothing I worry about doing accidental, as the stick pressure and AOA gives me plenty of warning, in fact I have played with it, at 6" height.....just to get more familiar with it. I like to keep some power in on very short landings, and the vg;s placement seems to really help this be safe and keep it flying.

On this recent video Jonas shot (he of landing in the snow on tires/getting stuck fame/infamy, his idea, don't drag me into his decision making process) I finally got visual affirmation of how slow I can land the thing when it all comes together, damn slow. Upslope, about 6500' about 35-40 degrees, no wind. Cut to the good part= 10:32 in. https://www.youtube.com/watch?v=nmTK-fdqe_M&t=16s
 
courierguy said:
On this recent video Jonas shot (he of landing in the snow on tires/getting stuck fame/infamy, his idea, don't drag me into his decision making process) I finally got visual affirmation of how slow I can land the thing when it all comes together, damn slow. Upslope, about 6500' about 35-40 degrees, no wind. Cut to the good part= 10:32 in. https://www.youtube.com/watch?v=nmTK-fdqe_M&t=16s
Click to expand...

I have no need to comment on his decision to land there and not to simply fly off the side hill as he eventually did.
BUT how can someone be so damn stupid to wear his seatbelts as he does. Why does he even put them on? It is clear he has never work belts in a car or truck.
 
hotrod180 said:
Charlie White at Micro would be the one to ask.
Click to expand...

Actually, Bob would be the one to answer that question. He explained the strake on the tail to me, complete with video of a tufted tail, and made me a believer in those devices on a Cub.

MTV
 
CharlieN said:
I have no need to comment on his decision to land there and not to simply fly off the side hill as he eventually did.
BUT how can someone be so damn stupid to wear his seatbelts as he does. Why does he even put them on? It is clear he has never work belts in a car or truck.
Click to expand...

I think he got distracted a bit, (!) next time I see him I will for sure point it out, and jam him on it. The other errors made are self evident. To be fair: seatbelts in cars/trucks auto adjust for proper position, so someone used to that feature would maybe still not have a habit of using plane type harnesses correctly, I know my passengers always need to be taught, and it's something I remind them on before landing. Least of his problems on that day, but good catch.
 
mvivion said:
Actually, Bob would be the one to answer that question. He explained the strake on the tail to me, complete with video of a tufted tail, and made me a believer in those devices on a Cub. MTV
Click to expand...

If you had posed a question about BLR VG's, I'd agree -- ask Bob.
But y
ou posed a question about Micro's choice of VGs, that's why I suggested asking Charlie.​
 
Does Micro include VGs on the fin of a Cub? I can't remember. They do on my Cessna. No fin VGs in my exp VG kit.


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