Vortex Generator Installation

[JohnAJohnson]

I'm installing Micro AeroDynamics VGs on my Cardinal, and one of the wing VGs will sit right on top of a skin seam. The manual says to move the problem VG inboard or outboard the minimum amount needed to clear the seam. I called and asked if I could shift the whole lot (all of the VGs) outboard by 1/4", and the lady said no, I must shift the one VG only.

I understand the company stance - The STC was approved with the VGs at precise locations, but I'd rather not move just one if their response was purely CYA. Couple reasons... The template would have to be cut and realigned for the one VG. And, there would be a lack of uniformity - this one pair would be wider spaced than the other pairs.

My question... Is it possible for a 1/4" shift (side to side of course) of the entire wing's VGs (both wings) to make any difference aerodynamically? And have any of you or any A&Ps installed VGs and shifted them to clear obstacles such as skin seams or protruding rivets?

 

[denverpilot]

If they're being installed under STC, the company's opinion reigns, right?

If you want to move them that'd be a 337, and you're in uncharted territory. Better make sure the FSDO is on board before you go there.

 

[upstateny]

I don't see the problem. Who besides you is going to notice than one VG is off-center by 1/4"?

 

[bbchien]

Cut the template. don't ask a question if you are not prepared for the answer, John.

 

[Sleepingsquirrel]

My question... Is it possible for a 1/4" shift (side to side of course) of the entire wing's VGs (both wings) to make any difference aerodynamically?

Is putting them on going to make any difference aerodynamically?

 

[JohnAJohnson]

Template will be cut per STC. Thanks all.

 

[Ted]

Is putting them on going to make any difference aerodynamically?

Depends on the airplane. They do seem to help with twins, especially in the stall and Vmc realm.

On a Cardinal? Probably not much.

 

[wabower]

Don't sneeze while you're aligning it to the plane. It could easily move 1/4" and you'd never know it.

Template will be cut per STC. Thanks all.

 

[Sleepingsquirrel]

Depends on the airplane. They do seem to help with twins, especially in the stall and Vmc realm.

On a Cardinal? Probably not much.

I especially think the ones on the rudder are the best idea for critical engine out operations.

 

[flyingcheesehead]

Don't sneeze while you're aligning it to the plane. It could easily move 1/4" and you'd never know it.

The FAA probably wouldn't either...

 

[ElPaso Pilot]

The FAA probably wouldn't either...

Until the thread was posted on a publicly accessible site with the N-number of his plane in his signature.

 

[Piloto]

For a good bonding remove the paint to bare metal in the area to be installed. Otherwise they are going to start falling off as the paint ages.

José

 

[richas]

For a good bonding remove the paint to bare metal in the area to be installed. Otherwise they are going to start falling off as the paint ages.

José

Not True.

Mine have been on 40 year old paint on forty year old fabric for many years.

Rich

 

[Piloto]

Not True.

Mine have been on 40 year old paint on forty year old fabric for many years.

Rich

When you are going for a new paint job the paint remover chemical will remove the old paint thus also removing the Vortex fins. Depending on paint application and exposure paint can flake with time. I see this every day even on planes with 5 years old paint jobs. To do job the right way just lay the fin on the wing surface and mark with a pencil the foot print. Using a Dremel tool with a brush tip or sand paper wheel just remove the paint within the marked perimeter. Apply the glue and stick the fin.

José

 

[flyingcheesehead]

Mine have been on 40 year old paint on forty year old fabric for many years.

You replace your fabric with another set of 40-year-old fabric every year?

 

[greghughes]

I have the same VG's (Microaerodynamics) on my Warrior. Move the one per the STC instructions. They spent a lot of time finding just the right layout, so I would definitely not shift them all. You can count on insurance companies and the FAA conveniently blaming a 1/4" shift in all VGs, not in accordance with the STC, as a contributing factor in an accident. Which would - of course - not be good.

My experience is that he 1/4" move looks perfectly normal when done.

And do they make an aerodynamic difference. In my experience -- absolutely, yes. In several ways: Responsiveness in all phases/speeds, substantially lower stall speed, increased rate of climb, and in my case slightly higher cruise speed as well. Each plan is a little different, but big difference in my case.

 

[JohnAJohnson]

Well, they are installed, and per the STC templates/instructions with the exception of the two that were moved 1/4", and you can't even tell by looking at them. I've been flight checking it for two days and have some detailed numbers, and some subjective touchy-feely stuff. Bottom line is that I can slow-fly the aircraft 5 MPH slower than I could Pre VGs. There is no top end penalty, and IAS remains the same for stall breaks, etc. The breaks are a tad harsher, whereas Pre VGs, the break was very docile. Otherwise, I can't tell any difference in flyability.

My numbers were a result of flying the aircraft in the same environment before and after VGs and at exactly 65%, and flying it at minimum controllable speed before and after, over three nav legs recording GS and Track (from the GNS430), then computing TAS back at home. Net net = 5 MPH on the bottom, and no speed loss at 65% cruise, and no relearning the plane.

 

[Piloto]

Well, they are installed, and per the STC templates/instructions with the exception of the two that were moved 1/4", and you can't even tell by looking at them. I've been flight checking it for two days and have some detailed numbers, and some subjective touchy-feely stuff. Bottom line is that I can slow-fly the aircraft 5 MPH slower than I could Pre VGs. There is no top end penalty, and IAS remains the same for stall breaks, etc. The breaks are a tad harsher, whereas Pre VGs, the break was very docile. Otherwise, I can't tell any difference in flyability.

My numbers were a result of flying the aircraft in the same environment before and after VGs and at exactly 65%, and flying it at minimum controllable speed before and after, over three nav legs recording GS and Track (from the GNS430), then computing TAS back at home. Net net = 5 MPH on the bottom, and no speed loss at 65% cruise, and no relearning the plane.

What is it worth it?

 

[denverpilot]

What is it worth it?

I was going to ask the same thing.

 

[JohnAJohnson]

What is it worth it?

I was going to ask the same thing.

Good question, and one I really can't answer for anyone but me. I'm in the process of doing two things to get my plane a bit safer; adding VGs, and adding an AOA indicator. Both combined should give me a bit more confidence on base -> final going into short fields, which is what I'm looking to do. All told, the VGs were $1,700 in materials, $0 labor, and the AOA will be $1,000 complete.

So to me, at this point, for the VGs, I'd say yes, but only because it was a fun project that was relatively affordable.

 

[Ted]

Curious - for base/final, why not just make a longer final if you've got concerns? I'd typically want VGs for making the plane more comfortable at low speeds for helping me fly slower on short final.

The 310 has VGs on it. It's very nice at slow speeds, which is important for coming into the home drone (2800 ft).

 

[JohnAJohnson]

Curious - for base/final, why not just make a longer final if you've got concerns? I'd typically want VGs for making the plane more comfortable at low speeds for helping me fly slower on short final.

Sometimes you can't because of hills. But the big thing for me is a nice, slow, usually steep final. Sometimes to get to that, the base has to be a bit slower too.

The 310 has VGs on it. It's very nice at slow speeds, which is important for coming into the home drone (2800 ft).

Don't VGs all but eliminate or severely reduce the blue line speed?

 

[Ted]

Sometimes you can't because of hills. But the big thing for me is a nice, slow, usually steep final. Sometimes to get to that, the base has to be a bit slower too.

Understood there are variables, but I've found there are typically ways to maintain decent speed for most of the pattern in the majority of birds we fly. Especially something like a Cardinal, which is still in the relatively draggy stage. Just a comment.

Don't VGs all but eliminate or severely reduce the blue line speed?

I think you're thinking of red line speed (Vmc), which is the minimum speed at which the aircraft remains controllable. If you want to test this in X-Plane, load up any piston twin, set it to max gross with an aft CG, then feather one engine and fly the plane slower and slower until it flips over. You can do the same in a real plane, too, except X-Plane is cheaper. VGs do typically reduce Vmc speed.

Vyse (blue line) I think typically goes down a bit with VGs, but not a ton.

On the 310 as an example, the VGs make it so the plane pretty much won't Vmc roll (of course I also don't try it with a full load, aft CG, etc.), and low-speed handling is very nice.

 

[greghughes]

Good question, and one I really can't answer for anyone but me. I'm in the process of doing two things to get my plane a bit safer; adding VGs, and adding an AOA indicator. Both combined should give me a bit more confidence on base -> final going into short fields, which is what I'm looking to do. All told, the VGs were $1,700 in materials, $0 labor, and the AOA will be $1,000 complete.

So to me, at this point, for the VGs, I'd say yes, but only because it was a fun project that was relatively affordable.

Curious what your experience is in terms of control authority improvements near and at landing speeds with the VGs. On my Warrior that was an area of substantial and noticeable improvement. Much better authority even while landing 5+ mph slower.

I also had a lot of fun doing the project on mine.

And regarding the glue vs. paint question: I've had one VG come off, and it was because the paint let go, not the glue. Sure, if you get a brand new pain job and it's perfect you shouldn't have to worry about paint detaching, but the people at Microaerodynamics told me that when one comes off, it's always the paint that fails. My experience agrees. I didn't sand down to the metal, but for the one I am replacing that's what I'll effectively do.

 

[JohnAJohnson]

Curious what your experience is in terms of control authority improvements near and at landing speeds with the VGs.

The VGs on my friend's Musketeer noticeably improved control authority at slow speeds, especially during the flare. I cannot say I've noticed any improvement on my Cardinal, but I have to say, the plane had always handled nicely and had great flight control effectivity all the way to the stall and beyond.

Thinking about this further... If the plane is actually slower at landing speeds (I always try for full aft yoke right before the mains touch) and the pitch authority appears to be is the same, that must mean the VGs on the underside of the stabilator are giving me more at lower speeds, and if the rudder appears as effective, it must mean the VGs on the sides of the fin are giving me more rudder at lower speeds. Same for the ailerons. So to answer your question, I can't say that I'm experiencing any control authority improvements, but logic tells me that I am, and not realizing it tells me the VG kit for my plane was well engineered.

 

[LDJones]

Flew a Duke today wit VGs. The Duke expert I was with said that STC made a significant improvement on the low end.

 

[denverpilot]

Wow. A second Duke moving under its own power. David White will be impressed.

 

[timwinters]

Both combined should give me a bit more confidence on base -> final going into short fields, which is what I'm looking to do.

Curious, how much do VGs help the take-off performance on a typical bird? Is the length shortened proportionately to the landing length?

My stock 1957 172 would get into places that you'd never get back out of. So if VGs don't also significantly reduce the take-off run then they wouldn't be useful because, after all, one does have to get back out.

My 1958 182 is the opposite...if you can get her down and stopped, she WILL get back out.

How does a Cardinal compare?

 

[JohnAJohnson]

Curious, how much do VGs help the take-off performance on a typical bird? Is the length shortened proportionately to the landing length?

My stock 1957 172 would get into places that you'd never get back out of. So if VGs don't also significantly reduce the take-off run then they wouldn't be useful because, after all, one does have to get back out.

My 1958 182 is the opposite...if you can get her down and stopped, she WILL get back out.

How does a Cardinal compare?

Don't know Tim. I haven't been able to measure takeoff performance due to all the variables. Subjectively: My first takeoff after VG installation... With pitch trim set where I always set it (neutral), at rotation (60 mph, same as always), the airplane acted as if it wanted to fly, whereas before, it took some persuading to get it to leave he runway. On the second flight I did a soft field takeoff with 15 degrees flaps, and it seemed like it definitely got the mains up quicker, and then it was very difficult to hold in ground effect. The three or four flights since, with various weights and weather, seem to confirm that takeoffs are happening quicker and with a better initial climb rate. But again, I haven't figured out a valid way to measure it.