courierguy wrote:One thing, is that VG's work on my S7-S, until they don't. Meaning, that if I push the plane to it's utter most limit (high AOA, low airspeed) and it finally gives it up, it will bite. Like right now! Probably more then the stock wing without VG's, as I recall (it's been 3 thousand plus hours since I've flown an S-7 without VG's) BUT, I wouldn't really call it a bad thing, as when it does this, bites, it is at a speed so slow one would have to be sound asleep not to be aware that something was going to happen. I believe this phenomenon has been addressed on this thread, and given a more technical name. It is a small price to pay for the increased low speed/high AOA performance and hasn't proven to be a significant drawback to having them. They seem to make the wing "work harder, longer", but like a friendly dog pushed to it's limit, it will for sure let you know when you have finally reached the limit. I do know that when it happens, the vary sharp break, I for sure have wrung every bit of performance out of it, there ain't any more to give.

Tom, Put Some Slats on that puppy and it’ll take the bite out completely!

VG's work. Pretty well. In a wind tunnel. With large studies to optimize criteria perfectly. With perfectly straight airflow over the wing.

They don't work as well, or at all, under more real life conditions, without real optimizing, and while crabbing at all, etc.

Lots of papers show 20% or more gains in Cl(max). Those gains disappear without really careful matching of the geometry of the vanes to the wing, airspeeds of interest, amount of bugs n the leading edge (really important, interestingly), etc. It is really unclear t me how much expensive and careful work is put in to really optimizing these things for the small segment of bug smashing plane owners. Particularly the smashed bugs/leading edge thing. But yes, I totally get that the determined person can feel comfortable and be safer in the low nether regions of usable airspeed with appropriate VG's. I'm not sure they would make a place I'd ant to land at more landable for me, but i get that many people think and act differently.

People who say they can reduce airspeeds by 10% are claiming a usable Cl(max) increase of over 20%, which is really hard to see outside of a carefully designed wind tunnel experiment with VG's. But I think the key word is "usable"...elevator and aileron response, etc. All of those things can be more significant than actual measured critical angle of attack improvements. VG's can marginally maintain attachment (and better control) longer into the critical angle of attack territory. Doing twin training in an Aztec before and after VG installation on the vertical stab was pretty much an eye opener for me. My foot met the floor a few mph lower when playing close to Vmc after the install of the little plastic vanes. It's no joke.

One thing that is never addressed with these mods is that the "New and improved" Cl(max) is, to my knowledge, never used to modify a placarded maneuvering speed.

If people are claiming to get a 20% bump on their Cl(max) (roughly a 10% reduction in stall speed, for example), the maneuvering speed and possibly Vne should be adjusted accordingly (by 10%, the square root of 21%). That would be a minimum of 13mph in my plane, for example. That would be a factor for the Sportsman kit and others like it. But this structural limit is never addressed in the STOL kits or other wing mods that I've seen.

lesuther wrote:VG's work. Pretty well. In a wind tunnel. With large studies to optimize criteria perfectly. With perfectly straight airflow over the wing.

They don't work as well, or at all, under more real life conditions, without real optimizing, and while crabbing at all, etc.

Lots of papers show 20% or more gains in Cl(max). Those gains disappear without really careful matching of the geometry of the vanes to the wing, airspeeds of interest, amount of bugs n the leading edge (really important, interestingly), etc. It is really unclear t me how much expensive and careful work is put in to really optimizing these things for the small segment of bug smashing plane owners. Particularly the smashed bugs/leading edge thing. But yes, I totally get that the determined person can feel comfortable and be safer in the low nether regions of usable airspeed with appropriate VG's. I'm not sure they would make a place I'd ant to land at more landable for me, but i get that many people think and act differently.

People who say they can reduce airspeeds by 10% are claiming a usable Cl(max) increase of over 20%, which is really hard to see outside of a carefully designed wind tunnel experiment with VG's. But I think the key word is "usable"...elevator and aileron response, etc. All of those things can be more significant than actual measured critical angle of attack improvements. VG's can marginally maintain attachment (and better control) longer into the critical angle of attack territory. Doing twin training in an Aztec before and after VG installation on the vertical stab was pretty much an eye opener for me. My foot met the floor a few mph lower when playing close to Vmc after the install of the little plastic vanes. It's no joke.

One thing that is never addressed with these mods is that the "New and improved" Cl(max) is, to my knowledge, never used to modify a placarded maneuvering speed.

If people are claiming to get a 20% bump on their Cl(max) (roughly a 10% reduction in stall speed, for example), the maneuvering speed and possibly Vne should be adjusted accordingly (by 10%, the square root of 21%). That would be a minimum of 13mph in my plane, for example. That would be a factor for the Sportsman kit and others like it. But this structural limit is never addressed in the STOL kits or other wing mods that I've seen.

That’s because when they certificate these things all they claim to the FAA (and prove) is that the installation does not create any negative flight characteristics. If they were to claim to the FAA that their kit reduces stall speed by XX knots, they would have to conduct much more testing and provide an AFM with the information you noted.

Now, look at the AFM for a Robertson STOL Kit.....which includes actual, documented stall speed reductions, and changes to a bunch of other data. As I recall, the reduction in stall speed for the Cessna 185 F was from about 56 knots to 37 knots in landing configuration.

I’d bet that if one were to conduct actual full out flight test on a Cessna VG installation, using true flight test methodology, you’d be lucky to see a change of a few knots, if that.

But, when advertising.....Katie bar the door, the FAA doesn’t prohibit false advertising.

All of which is not to suggest that VGs do not provide notable positive changes on some installations.

MTV

This video was kind of neat to watch on the subject.

pilotryan wrote:This video was kind of neat to watch on the subject.

First of all, there is no such thing as absolutely identical airplanes. Did they verify identical weights/CG, wing rigging, etc, etc.

MTV

Pretty intense background music.

G44 wrote:Pretty intense background music.

No kidding. I thought someone was about to be voted off the island.

mtv wrote:Now, look at the AFM for a Robertson STOL Kit.....which includes actual, documented stall speed reductions, and changes to a bunch of other data. As I recall, the reduction in stall speed for the Cessna 185 F was from about 56 knots to 37 knots in landing configuration.

I’d bet that if one were to conduct actual full out flight test on a Cessna VG installation, using true flight test methodology, you’d be lucky to see a change of a few knots, if that.

But, when advertising.....Katie bar the door, the FAA doesn’t prohibit false advertising.

All of which is not to suggest that VGs do not provide notable positive changes on some installations.

MTV

Not too many people around here refer to the Robertson kits with such fondness. As a young teen I used to ride the bus out the the airport in Bellevue, WA (where Robertson was based at the time) to take pictures and drool on airplanes. A C210 with drooped leading edge, stall fences and ailerons that deployed with the flaps was a bad ass. Fast forward all these years and people tend to recall those features less fondly. Seems to me Robertson paved the way for most of the mods we see now.

I am particularly fond of my Robertson STOL modification.

I am exceedingly fond of my Robertson STOL modification.

And, yes, I am very fond of Robertson kits on Cessna airplanes. Virtually all the Cessna 185/206 airplanes I flew for work were so equipped.

I know there are a lot of people who make noise about the RSTOL kits to the effect that they reduce roll effectiveness because they droop the ailerons. And, that is a fact. How many of those folks have actually worked a RSTOL equipped Cessna, I don't know. But, I never really found the kits limiting.

I've spent a couple of nights out somewhere when the crosswind gusts got too sporty for me to accomplish what I needed to. But, frankly, those conditions were sporty enough that I probably wouldn't have tried it with a straight wing Cessna.

Now, that said, it's worthy of note that I've never heard a single pilot claim the same of the venerable deHavilland Beaver, which droops it's ailerons with flap deflection.....a very similar system to the RSTOL system, and likely where Robertson first got the idea.

Finally, add a Sportsman kit to that RSTOL equipped airplane, and the aileron gap seals in THAT kit will pretty much give you back the roll authority you lost with the RSTOL kit. And, to me, that is the ultimate setup for a Cessna wing.

MTV

Anyone remember the adage, "steer towards the ditch"?

Aside from the fact that ailerons often create adverse yaw and can point the nose in the opposite direction of the bank, I suspect that pilots not accustomed to tailwheel aircraft and Robertson STOL aircraft are not using their feet enough for directional control and to lift a wing when necessary.

Squash wrote:Anyone remember the adage, "steer towards the ditch"?

Aside from the fact that ailerons often create adverse yaw and can point the nose in the opposite direction of the bank, I suspect that pilots not accustomed to tailwheel aircraft and Robertson STOL aircraft are not using their feet enough for directional control and to lift a wing when necessary.

Yep, the C-46 guy that gave me check rides many times called it "Drive it into the ditch", but same message. If it works on a 46, it'll work on most anything.

There's no doubt that the deflection of ailerons with flap does reduce aileron effectiveness some, but again, the Beaver does almost exactly the same thing, with one exception: In the Cessnas with RSTOL, the ailerons droop more with each flap deflection till you go to 40 flaps.....when you go to 40, the ailerons actually retract a little. I used to know the actual degrees of aileron deflection at each flap setting, but it's been a while.

But, the Beaver ailerons just keep on deflecting more, the more flaps you deploy......and the Beaver can go to 50 plus degrees of flap deflection.....not recommended for routine ops. I seem to recall the manual said any flap setting over 50 was for "emergency crash landings only" or words to that effect.

But, the Beaver ailerons get some serious deflection with flaps down.

MTV

Soooooooo..... I've had my Pacer for 2 years now and still can't figure out if VGs would actually help me in a real, practical way. If I can already land it slow enough and high enough angle of attack to touch tailwheel first, what will they do for me? Allow me to come crashing down onto the mains from even higher? I have 8.00x6 and plan to go to 8.50s next time I need tires. Probably won't go bigger than that because I don't want to pay the speed penalty. Or the huge price jump between sizes! So does that decision say VGs wouldn't help me in a real world way?

I live in Kansas where it can be very windy, and have also been "caught out" several times while going cross country by winds that I wouldn't necessarily choose to fly in. Will VGs have a negative effect in those situations?

I understand the safety benefits some airplanes can get from them, and think it's pretty cool how they use them to correct little design issues some aircraft have. But on my airplane, with its already well-mannered mush and stall characteristics....? At ~0.6AMU, it's an inexpensive mod and looks cool as hell, and to me that would be enough to justify it. I just don't know if I'll be making my airplane "worse" by putting them on. Shortwingpipers.org reading is also inconclusive, at least to me.

They’ll give you more aileron authority at low airspeed. I’m a big proponent for VGs on the Piper Shortwings.

Flyrite wrote:

courierguy wrote:One thing, is that VG's work on my S7-S, until they don't. Meaning, that if I push the plane to it's utter most limit (high AOA, low airspeed) and it finally gives it up, it will bite. Like right now! Probably more then the stock wing without VG's, as I recall (it's been 3 thousand plus hours since I've flown an S-7 without VG's) BUT, I wouldn't really call it a bad thing, as when it does this, bites, it is at a speed so slow one would have to be sound asleep not to be aware that something was going to happen. I believe this phenomenon has been addressed on this thread, and given a more technical name. It is a small price to pay for the increased low speed/high AOA performance and hasn't proven to be a significant drawback to having them. They seem to make the wing "work harder, longer", but like a friendly dog pushed to it's limit, it will for sure let you know when you have finally reached the limit. I do know that when it happens, the vary sharp break, I for sure have wrung every bit of performance out of it, there ain't any more to give.

Tom, Put Some Slats on that puppy and it’ll take the bite out completely!

Only on uphill landings, with lot's of throttle, and purposely dragging it in, really pushing it to the max, have I experienced this. Not a factor at all in "normal" off airport play, and nothing I'd call a problem, BUT, you got me thinking! I need to make a run over to Douglas Wyoming and pick Bruce's mind at Back Country Cub on his slats install on his S-7. Here's a several year old video of what the 7 can do with just VG's. The good part is at :40. https://www.youtube.com/watch?v=Va-DtQn64Xg

Just a repost from my past experience of installing those VG’s on a “shortwing” Cessna.

“I added VG’s during our restoration of a C-140 with an O-200. The plane behaves much different than before. During slow flight the plane has a very high nose high attitude up to stall. The stall itself has a much harder break than it did before, This goes for both power off and on. I’ve also done cross controlled stalls and spin entry’s and while the plane does seem to fly 2-3 mph slower. Once the wing lets go, it lets go pretty aggressively. But all planes are different and I can only report on how ours behaves. The roll control at slow speeds is better on takeoff and landing. Even with 8.50x6.00 tires if you tried to 3 point it the tail would touch WAY before the mains. We have 29” Bushwheel tires now and it’s almost perfect but even at low speed on rollout even if you think the tail is done and ready to be down for good you hold full aft wheel and the mains will get light or come off ground (BTW I wheel land 99.9% of the time).

Thanks for the insight guys. I'm pretty low time at ~400tt, last 300 of it in the Pacer. Perhaps with my current equipment and skills I wouldn't see the benefits of VGs, only what I traded for them. The anecdote of the 140 with 29s is one I have seen before and is the reason I haven't gone for them. Seems like they may be a poor choice for my airplane, its overall setup, and how I use it. Thanks again from a "long time listener, first time caller"

I think you’re missing the point. A three point landing does not require stalling the wing. If VGs do give the wing a little more usable AoA it doesn’t mean you can’t 3-pt without 35” bush wheels.

What VGs do give is increased aileron authority at low speed - something that I think the Pacer benefits from tremendously.

It’s seriously the best mod you can do for the Piper Shortwing. And it’s nice that it’s not too much $$, too.

I guess due to my inexperience I have trouble understanding how AoA beyond what you have while sitting on the ground can be considered useable or useful. Do VGs make you fly slower at the same AoA as before or something? As someone that has owned a shortwing with VGs I appreciate your sharing that the aileron response is what makes it worth it. The stall speed numbers and landing aspect of it are what never made sense to me.

Plvssr wrote:I guess due to my inexperience I have trouble understanding how AoA beyond what you have while sitting on the ground can be considered useable or useful. Do VGs make you fly slower at the same AoA as before or something? As someone that has owned a shortwing with VGs I appreciate your sharing that the aileron response is what makes it worth it. The stall speed numbers and landing aspect of it are what never made sense to me.

This is specifically why it’s a great mod on a Shortwing Piper - gusty crosswinds. You’ve got more aileron control to help you land straight with roll control in these situations:

Plvssr wrote:I live in Kansas where it can be very windy, and have also been "caught out" several times while going cross country by winds that I wouldn't necessarily choose to fly in.

And also, any extra padding you can give your wing’s performance is goodness in my opinion.

My plane stalls in the low 40 MPH range, but I don’t approach that slow. I fly an airspeed that allows me to tail-low wheel land most of the time. Occasionally I use a 3-pt, depending on the conditions. Neither of those landing types see my wing stall at touchdown - every MPH difference between my landing speed and wing stall I consider a safety factor.

I absolutely can drag it in and touch my tailwheel first, but that’s not good for the airplane. So I don’t. (At least not on purpose.)