Hi all,

Just to put some perspective here, VGs are dependent on three factors, their size (are they acting inside or outside the boundary layer), their shape (High energy or low energy vortex) and their placement.

The placement if the VG is the relevan to the intent for their usage, in the case of the wing, their placement near the LE is based on the airfoil shape and the wing type (rectangular, tapered, elliptical, ect.) and what you are trying to resolve. In the case of the stall speed (or delaying boundary layer separation) you need H-Vortex to exit the air and keep it on the wing. The most effective way to do this is inseparable the bounds layer... but outside the boundary layer works well, similar to pressing down on it as it starts to separate sort of speak. If you look at what can be achieved, you are looking at sub 10% improvements, so if you sell speed is 37mph (really light cub, tight fabric and good paint job) you are impacting this by, well 10% or 3.7 MPH (give or take in a best case scenario.)

This considered, it varies from aircraft to aircraft and I'l be darn if someone can tell the difference at that speed... it can be measured, but its really had to notice it.

I guess what happens to most pilots is that the happens to most golfers, when you sped $5K on a new set of club, they sure as hell improve your game, no mater what the scorecard say...

SpainCub wrote:I guess what happens to most pilots is that the happens to most golfers, when you sped $5K on a new set of club, they sure as hell improve your game, no mater what the scorecard say...

This is the argument used by the nay-sayers against things like the Sportsman, VGs, etc, and often tossed around by folks with no personal experience. I would be really really interested to know if you have actually flown a Cessna wing in slow flight at 40-45 mph with VGs? Tested aileron authority with and without VGs? My bet is no.

Yeah, soooo, interesting read. To clear up a couple of mis-assumptions. I'm not going to be putting 31s on. I am not trying to compensate for a lack of skill. I am, however a terrible golfer, but that's more due to my back and a lack of practice than not having the latest graphite titanium nano driver.

The 195 is a tricky plane to land. There's a lot reasons why, but one of the big ones is a lack of airflow over the tail in the 3 point attitude. What most folks do, myself included is approach power on at about 80mph (1.3Vso), touch down in a tail low wheel landing, then raise the tail until directional control is assured, then gently lower the tail, at which time you can get on the brakes. The result is a nice straight, but long landing.

Most of us, if we don't have the crosswind gear, are running 310 wheels and brakes (double puck). If you happen to get on the brakes too soon, it looks like this:


What I've found, is that if I approach at 70mph, I can still touch down as before, but I can get on the brakes a lot earlier as there is a lot less momentum. The result is a much, much shorter landing roll.

The down side to this is that there is very little elevator and rudder authority in that tail low attitude with the power near idle, thus making it a calm wind or very wide runway technique, because if there is any wind at all, it's about to get exciting.

So my thinking is VGs, which are on Hawkers and 737s and all manner of GA airplanes that don't run 31s or 84" inch props (mine is 93" but who's keeping score? ) would keep what little airflow I have attached to the elevator and rudder a little longer and give me a little more control authority at touch down. At the wing root, maybe by keeping some of that air attached it would make its way to the tail?

PilotMikeTx wrote:Yeah, soooo, interesting read. To clear up a couple of mis-assumptions. I'm not going to be putting 31s on. I am not trying to compensate for a lack of skill. I am, however a terrible golfer, but that's more due to my back and a lack of practice than not having the latest graphite titanium nano driver.

The 195 is a tricky plane to land. There's a lot reasons why, but one of the big ones is a lack of airflow over the tail in the 3 point attitude. What most folks do, myself included is approach power on at about 80mph (1.3Vso), touch down in a tail low wheel landing, then raise the tail until directional control is assured, then gently lower the tail, at which time you can get on the brakes. The result is a nice straight, but long landing.

Most of us, if we don't have the crosswind gear, are running 310 wheels and brakes (double puck). If you happen to get on the brakes too soon, it looks like this:


What I've found, is that if I approach at 70mph, I can still touch down as before, but I can get on the brakes a lot earlier as there is a lot less momentum. The result is a much, much shorter landing roll.

The down side to this is that there is very little elevator and rudder authority in that tail low attitude with the power near idle, thus making it a calm wind or very wide runway technique, because if there is any wind at all, it's about to get exciting.

So my thinking is VGs, which are on Hawkers and 737s and all manner of GA airplanes that don't run 31s or 84" inch props (mine is 93" but who's keeping score? ) would keep what little airflow I have attached to the elevator and rudder a little longer and give me a little more control authority at touch down. At the wing root, maybe by keeping some of that air attached it would make its way to the tail?

Buy some VGs (they’re readily available online), attach them to tail surfaces with double sided carpet tape, and try them out. If they work, you have a decision to make. If not, peel em off and move on.

MTV

Bigrenna wrote:

SpainCub wrote:I guess what happens to most pilots is that the happens to most golfers, when you sped $5K on a new set of club, they sure as hell improve your game, no mater what the scorecard say...

This is the argument used by the nay-sayers against things like the Sportsman, VGs, etc, and often tossed around by folks with no personal experience. I would be really really interested to know if you have actually flown a Cessna wing in slow flight at 40-45 mph with VGs? Tested aileron authority with and without VGs? My bet is no.

Well, I can’t speak for Spain Cub, but I think if you’ll read his WHOLE comment, you may agree with him, at least on the aerodynamics.....if not the golf club analogy.

I have flown Cessna wings, and I have flown them before and after installation of Micro Aerodynamics VGs. In my experience, they do in fact mellow out the stall a bit, particularly in an aggressive stall, such as power, bank angle, etc. But this is on a wing which actually has a very mellow stall to begin with. Not a bad thing, mind, but a sea change? Not in my experience.

And, indeed, there is a bit better aileron authority with the VGs. That said, I never felt that aileron authority was particularly lacking in the stock wing Cessnas. Maybe that’s because I learned a long time ago that RUDDER is the primary flight control for roll at high Alpha—not aileron.

As Spain Cub noted, there may in fact be some reduction in stall speed with these VGs, but in my experience, it would be so small as to be quite difficult to detect. And, yes, I have driven these airplanes around at high Alpha a fair bit.

You bring up the Sportsman kit in your argument, but that is an entirely different kettle of fish. In my experience, the Sportsman does what the advertising claims, including a notable reduction in stall speed, better roll Control, etc., but again, this thread is about Micro VGs, not cuffs.

VGs as used on jets are there to fix problems with local area flow...you won’t see them arrayed along the leading edge of jets......but rather to reduce interference drag around cowlings, for example. I certainly wouldn’t compare that to a wing installation.

And, yes, they do some seriously good work on a few light to medium twins. Well documented.

Which brings up the point that some GA wings benefit more than others from the addition of VGs. Most everyone agrees that the Cub wing does. But, different airfoils May or may not benefit equally from their installation.

Finally, the distance that VGs are mounted from the leading edge makes a significant difference in their effectiveness, AND in the amount of drag they create at cruise. As does the size (height) of the VGs. Unfortunately, or perhaps fortunately, with certificated Aircraft, those parameters are dictated by the STC holder.

FWIW.

MTV

I posted a while back about when I put some left over Micro vg's (I've used them on my last two S-7's, which seems to have one of those planforms that respond very favorably to their addition) on the roof of my Toyota Yaris sub compact, right before where the roof line ends, and becomes the hatchback.

I had noticed a high speed bit of wandering and a bit of a wobble at times, nothing bad but there none the less. I had top of the line tires, at the proper pressure, and the front end checked out. Being on a Yaris owners forum back them (moved on, now I'm a Prius geek) I picked up on the fact that the sedan model of the Yaris, with the same exact front end, got better MPG, as it had less drag, the trunk being better then the chopped off hatchback aero wise. This gave me the idea of the vg's, so I ran a line across the rear roofline, with a vague idea that the car's wandering was caused by the turbulent airflow of the hatchbacks abrupt shape. Same pairing and angles, using the same template. Bottom line, it tested out great, it tracked like a much bigger vehicle, like it was on rails, it was a noticable improvement.

The punch line is, when I sold it, the guy looking it over noticed them and I launched into my "I'm a pilot and blah blah blah" proceeded to educate him on what vg's were, what they do, etc., that's when he told me he was a working corporate jet pilot and had a passing knowledge of what they did, we both had a good laugh and a minute later he wrote the check out. What are the odds of that, that a car with vg's on it would be bought by another pilot?

mtv wrote:... there may in fact be some reduction in stall speed with these VGs, but in my experience, it would be so small as to be quite difficult to detect.

The common misconception of the VG is that it slows your stall speed down. Folks often ask if they should install a Sportsman OR VGs. VGs assist in aileron and rudder authority at slow speeds. They are a safety mod, not a STOL mod which just so happens to be beneficial when we are trying to get in and out short. I wasn't disagreeing with his math, but taking offense to the comment that just because someone spends a bunch of money on a mod they cant be objective. At least in my case, I have always been completely honest when reporting every mod I have tried, no matter what the cost.

In the case of VGs on a Cessna wing (only experience I have) there is no doubt that the increased safety margin is well worth the cost. It's my feeling that anyone who says different either has not flown the aircraft with the mod, or has not flown it slow enough to actually feel the benefit.

The funny thing about safety mods like this is most folks would never know if it saved them from the edge or not... Maybe like flea/tick protection on the dog? The guy who puts it on every month might say that the stuff isnt needed because he has never seen a tick near the dog, when in reality he has no idea just how many tried to hitch a ride and were thwarted.

If there is a 1% chance that they might save me in the wrong moment, I'm a customer. Just my .02

Anyway, good discussion and I appreciate the different opinions...

I wish George M would comment on his experience of VG's on a Husky. I know George is not the type to give a thumbs up to a mod if it does not deserve it just because he laid out the cash for it, he will give an honest report on his findings.

Kurt

I park next to two Federally owned and flown floatplanes. The C-185 has VG's on a Sportsman cuff and the PA-18 has them on stock wings. They must have a reason for them being added.

Gary

PA1195 wrote:I park next to two Federally owned and flown floatplanes. The C-185 has VG's on a Sportsman cuff and the PA-18 has them on stock wings. They must have a reason for them being added.

Gary

Sure. The end of the fiscal year was drawing near, and the current budget had to be spent, or there was fear that next year's budget wouldn't be approved due to the current year's "surplus".

Kidding a little, but just because Uncle Sugar spends money doesn't mean that it's justified. It may or may not be justified operationally.

Cary

I installed a set of Micro VGs on my old C150/150TD.
I was underwhelmed by the results.
I wont ever bother putting them on another stock Cessna wing.

Hi all, I was not trying to discredit any product, but I'm sure some would appreciate a real honest science driven outlook to set the right expectations on VG's as far as lowering the stall speed is concern. Like Sir. Adrian Newey once said, you don't need a lot of calculations to gestimate your design, your can only impact it by the amount of air (surface change) in comparison to the entire system. In the case of the LE VG's, just look at the surface exposed to the air vs the entire wing. You can't expect to get more out of it proportionally- Like everything, there are exceptions, like Gurney Flaps, they give you the most bang for surface our there to give an example.

All I can say in my pursuit of ultimate STOL, VG's seemed like the best bang for the bucks, I bought a 3d printer, a bunch of anemometers, go-pro camera, and enough flow viz to pain a solid line a meter thick from here (Madrid) to Anchorage... So I have flow with out them, with them, and any other iteration you can consider... my take is, in the end, the noise from my measuring equipment ( and I did not go cheap) was too great to find the improvement of VG's. in the LAB, they work, within that margin of <10%... dependent on placement, shape or airfoil, and build of wing... if you got 7% out of them your are high fiveing everyone around you, most of the time, it was below that. Now I never had the privilege of running any test on pressure stable wind tunnel, and we mostly saw variance of changed conditions.

I have a saying, some of these technologies just work at the ovo-pedic nerve level (that's the never directly attach to your b4lls and your feet) it loosens it up.

My observations on Micro VG's:

PA-18A before vs after installation: Offered a bit of AOA reserve before mush or stall during steep descents and flare. Held AOA on floats during rough water takeoffs with nose held high. Stall behavior didn't change much.

PA-11 with flaps after vs before installation: Same as SC gave a bit more AOA before mush/stall but that attitude was fairly unusable in normal flight for me. I left them off after a rebuild. After rebuild added flaps helped on landing; not enough power to really use them over the added drag on takeoff.

Pre-WW2 Taylorcraft with shorter vert stabilizer but longer rudder before and after: I'd not fly one without VG's. The 23012 airfoil likes to head directly to home on Earth at stall; with them installed it's a shaking mush well controlled by rudder. Sudden down aileron can precipitate a tip stall with both configurations but the break is softer with VG's and doesn't exceed rudder authority.

Gary

Bigrenna wrote:

mtv wrote:... there may in fact be some reduction in stall speed with these VGs, but in my experience, it would be so small as to be quite difficult to detect.

The common misconception of the VG is that it slows your stall speed down. Folks often ask if they should install a Sportsman OR VGs. VGs assist in aileron and rudder authority at slow speeds. They are a safety mod, not a STOL mod which just so happens to be beneficial when we are trying to get in and out short. I wasn't disagreeing with his math, but taking offense to the comment that just because someone spends a bunch of money on a mod they cant be objective. At least in my case, I have always been completely honest when reporting every mod I have tried, no matter what the cost.

In the case of VGs on a Cessna wing (only experience I have) there is no doubt that the increased safety margin is well worth the cost. It's my feeling that anyone who says different either has not flown the aircraft with the mod, or has not flown it slow enough to actually feel the benefit.

The funny thing about safety mods like this is most folks would never know if it saved them from the edge or not... Maybe like flea/tick protection on the dog? The guy who puts it on every month might say that the stuff isnt needed because he has never seen a tick near the dog, when in reality he has no idea just how many tried to hitch a ride and were thwarted.

If there is a 1% chance that they might save me in the wrong moment, I'm a customer. Just my .02

Anyway, good discussion and I appreciate the different opinions...

Greg,

A couple points:

First, the reason for the “common misconception of the VG that it slows your stall speed down” is actually quite simple: Read Micro Aerodynamics’ advertising hype, where they claim significant stall speed reduction.

Second, your assertion that VGs improve rudder efficacy is only true for Aircraft with VGs installed on the vertical tail. The Cessna 170, Super Cub, and many others don’t have those. In fact, the early Micro kits didnt install VGs under the horizontal stab either.

Which again reinforces the point that you can’t make broad generalizations about the benefits of VGs (or many other mods, for that matter).

In fact some knowledgeable pilots have argued that on some wings, the addition of VGs makes stalls more aggressive, rather than the opposite.

In any case, operating any aircraft near the edge of its envelope has risks. Modifications MAY modify those risks slightly, but there’s no “magic” involved, and it’s still incumbent on the pilot to avoid stepping over that edge, wherever it be.

If you RELY on these mods to save your bacon, I fear at some point you’ll be sorely disappointed.

MTV

Well said MTV. Flying low all my life, I avoided giving up kinetic energy (airspeed) except on short final and landing and to zoom up to jump obstructions or begin an energy management turn. I didn't make level steep turns. I got the down wing up with rudder. I didn't get close enough to stall to have noticed any difference had I had Vgs. Stall was not a maneuver. Stall was a fatality.

Some good some bad results are probably a function of wing design (airfoil), VG height, and placement. If too far forward it takes lots of AOA to get them to fluxulate the air (hah!). Nobody can see the ground or runway but hey we're still flying.

If in the airflow over the wing at stall AOA they may help keep it attached some for lift. If too far aft they suddenly quit their benefits and a quick loss of lift and stall occur.

That's maybe what happened on Arctic Tern when they were tested if placed too far back. Like the Taylorcraft that wing tends to form a detached layer forward as well as from the rear over 12* AOA. If the VG's are in that forward layer as it separates strange things may occur.

Offset VG's - back at wing root and forward in front of aileron is a better compromise for gradual stall like CC's setup. May be the same for height above wing of some outboard vs others shorter inboard but nobody has done that AFAIK.

For me if I can see the runway on landing and keep it in sight I doubt they do much. Maybe on takeoff if thrown airborne like on rough water with floats they help. Doing lots of turns at slow airspeeds - they might help certain wings keep the leading edge flying.

Gary

...

"Finally, the distance that VGs are mounted from the leading edge makes a significant difference in their effectiveness, AND in the amount of drag they create at cruise. As does the size (height) of the VGs. Unfortunately, or perhaps fortunately, with certificated Aircraft, those parameters are dictated by the STC holder."

So, I am wondering if I should get some management tape and try several different locations on my Pacer before I make a permanent installation.

VGs comibined with the Angle of attack indicator does wonders in my Cessna, yes when you are using the wing , elevator and rudder to its full performance and you have that AoA indicator telling you exactly how much lift you got, those VGs are being put to work, and they perform.

Not only on aileron, also rudder and elevator, more authority and control in everything, very crisp in the controls at 50mph or less in my 182.
One of the first things I noticed was not running out of elevator at very slow landings.


So in the end are they for everyone? if you want to squeeze the full performance of your airplane yes.

I think on twin engines they are easier to notice their benefit.

buck_justice wrote:"Finally, the distance that VGs are mounted from the leading edge makes a significant difference in their effectiveness, AND in the amount of drag they create at cruise. As does the size (height) of the VGs. Unfortunately, or perhaps fortunately, with certificated Aircraft, those parameters are dictated by the STC holder."

So, I am wondering if I should get some management tape and try several different locations on my Pacer before I make a permanent installation.

Per the STC they can only be in one place. So if you want to stay legal then you need to follow where they say to put them. If you dont care about being legal, then just buy some VGs from aircraft spruce and try them in different locations...