Any opinions on what is the best aileron and H stab/elevator gap seals? What's been working very well for you guys who have them on your LSA / home-built aircraft?


Also, what brand of VG (vortex generator) has been working exceptionally well for LSA / home-built STOL aircraft? Is any one better than the other in terms of performance?


Thanx,
RR

Ridge Runner wrote:Any opinions on what is the best aileron and H stab/elevator gap seals? What's been working very well for you guys who have them on your LSA / home-built aircraft?


Also, what brand of VG (vortex generator) has been working exceptionally well for LSA / home-built STOL aircraft? Is any one better than the other in terms of performance?


Thanx,
RR

I like Micro Aerodynamic vg's, just because they are anodized aluminum (they look great, I don't paint them, I like the contrast to my painted wing) and come with a stencil making it super quick and easy to lay them out and glue them down. Having said that, I gotta think they are ALL pretty much the same as in how they effect the airflow, whether plastic or metal. Where you put them chord wise seems to be the biggest difference between the different vendors who offer them. Different pilots and techniques pretty much make judging vg's a crap shoot, I would rather have ANY brand in ANY position then none at all, I'll never fly without them, too many benefits for few if any drawbacks, at least for what I fly.

Rans includes some plastic extrution that rivets to the spar for wing gap seals, works well and is permanent.
"Frost King" 2'" clear tape works on the hor stab gap, but it gets funky after a while.

Thanks for the good report. I went to Micro Aerodynamics web site and checked them out. They seem a bit expensive. I like the idea of pre-formed metal type though, if only for its greater adhesive surface area and that they are already formed at the right angle (I hope).


On the H stab/ elevator gap seal, since the wings and tailfeathers are fabric (but not the horiz stab), I'm not sure I want an aileron gap seal that would puncture the fabric in any way, nor do I want a tape that might become a sticky mess in a hot, tropical environment and possibly create an uneven surface and/or have an irregular shape. I'll keep looking around for ideas on it.

The best gap seal is a 3M surgical tape called "Blenderm". It comes in 1/2, 1 and 2 inch widths. It is a special order or eBay thing... you will not find it in your local retail pharmacy. You will need the 2 inch for best results. The advantage of this material is it is the most stretchy tape in existence, but it will not add any friction to your control system.

Put a thin film of light oil or vaseline on your actual hinges so the tape will not stick to the hinge. Make sure the control surface is extended all the way in the OPPOSITE direction from the side you are installing it on. Putting it on the top side of the elevator gap will keep water out of your hinges, and seal against air squirting through the gap.

A company in Australia called Stolspeed sells VG's that have an advantage over the Micro Aero aluminum ones. Wash your airplane and run your hand across the wing in the wrong direction, and the aluminum ones will slice your hand open. Stolspeed's VG's are soft plastic and have round edges. I think it is stolspeed.com and perhaps Aircraft Spruce sells them now.

Thanx guys. Well, I went with Hall vortex generators, allegedly "wind tunnel tested", pre-formed aluminum. It looked like a good set, curved at the bottom for the wing vgs, flat for the horizontal stab. If upon personal inspection they aren't that great, I'm only out $180 and will then look toward Stolspeed or Harrison.


EZ Flap, on the Blenderm tape....Does it get sticky in a hot environment? Also, do you have a close-up pic of a Blenderm tape installation on an airleron gap or a horizontal stab/elevator gap?

Check out the ones from Austrailia, 100 bucks and gives you everything you need to install.
Have used them on a couple of aircraft and they seem to work fine, polycarbonate, they don,t like gasoline tho.
Good luck GT

Ridge Runner wrote:

EZ Flap, on the Blenderm tape....Does it get sticky in a hot environment? Also, do you have a close-up pic of a Blenderm tape installation on an airleron gap or a horizontal stab/elevator gap?

I don't have any photos of it, but I can assure you it is nearly 100% transparent... think "satin finish clear shelf paper". From two feet away you will not see any color difference under the tape.

It is certainly less than .005 thick, you can barely feel it with your finger once it is burnished down.

I have used it on gliders out in the Mojave desert for years, and on fabric covered control surfaces in 110 degree F Los Angeles CA summers many times. Never saw it get sticky or fall apart.

When you go to peel it off, the tape itself comes off without too much effort but it does leave a sticky adhesive residue. The solvent for this is called "xylene" and is sold as "goo gone" and "goof-off" etc. But pure xylene when you find it works faster. So to remove the residue you cut little strips of paper towel or tissue, lay them down on the residue, and soak them with the Goof Off a couple of times, and you can wipe it off. I have used this on the Stits Poly-Tone paint without damaging the paint, and on fiberglass gel-coat. I have not tried it on any other type of fabric finish (Stewart).

What I can guarantee 100% is that the Blenderm is waterproof, air-tight, and very very flexible. For the best possible appearance, you can put it on both sides of your control surface gap. The reason for this is that if you only put it on one side of the gap, dirt and dust will accumulate on the exposed sticky strip opposite the gap and look dirty.

This stuff works miracles on sealing around skylight panels, windows, windshields, etc. You can keep rainwater out of your airplane structure, stop air leaks and whistles, etc.

I've used Blenderm on my glider too, works for attaching tape-on fairings and for covering gear door gaps etc. And while I haven't used it for elevator gap seals, I have seen the clear packaging tape used - - doesn't last too well. But, and I'm thinking this might work for the Blenderm too, the application I saw was different:

The application used two strips of tape, with sticky sides facing each other and bonded together overlapped part way lengthwise. This leaves you with a doubled tape strip the center doubled part no longer sticky, and the outer edges being sticky and facing one up and one down. This strip is then applied to the gap, one sticky edge attaching to the top of the control surface gap and the other sticky edge going on the bottom. The tape bridging the gap being the doubled up part.

Would this work as well as the "one strip on top and one strip on the bottom method?

One could also use the same sort of idea with 2" wide and 1" wide Blenderm. Center the 1" wide and bond it, sticky to sticky, in the center of the 2" wide. This would leave you with 1/2" sticky on each side to apply to the top or bottom. The center would no longer be a dirt magnet as EZ Flap mentioned.

Back to the VG's. I used to see some listed on Barnstormers that were trade named "Land-Shorter" If I remember correctly they sold for $99 a set.
Now back to the regularly scheduled discussion on Gap seal tape.

With no less than two very positive recommendations for Blenderm tape from a of couple experienced pilots who have used it first hand, well that's good enough for me. I found some available at Amazon.com, bought two rolls (2" and 1") and they are on their way to the Rocky Mountain Wing's shop in Idaho. Thanx a lot guys.

However, I won't use it right away. After the plane is finished being built (sometime in May I hope), it will be test flown and the performance measured before VGs and gap tape are installed, then after VGs and gap tape are installed.

Joa Harrision is the LandShorter VG guy, and is great to deal with, I felt bad I didn't give my vg biz to him, but Charles at Micro did me a huge favor in the past so I went with his again, even though they are pricey. Joa would be the best bang for the buck, but when it comes to flying stuff I get a what the hell attitude as to the cost and get what I REALLY want!

Another good all around tape I've been using is called pipe wrap tape, available at any plumbing wholesalers. Intended for securing your electrical cable to your well drop pipe, it is black, comes in wide 3" rolls, and very sticky but leaves no residue. I wouldn't use it for gap seals (good callout there EZ, that sounds like the best stuff for that) but I use it for places where I used to use duct tape, use your imagination there. It is like electrical tape, but wider, thicker, and stickier, I don't leave home without it.

Bumper said"

The application used two strips of tape, with sticky sides facing each other and bonded together overlapped part way lengthwise. This leaves you with a doubled tape strip the center doubled part no longer sticky, and the outer edges being sticky and facing one up and one down. This strip is then applied to the gap, one sticky edge attaching to the top of the control surface gap and the other sticky edge going on the bottom. The tape bridging the gap being the doubled up part.

Here's a couple pictures of that method. My kitfox is folded up in the shop right now so I can get a picture of just part of the elevator to horizontal gap seal. The stuff in the pictures is clear shelf paper. This brand is "Kittrich", but I use whatever brand the hardware store has at the time. It is very durable. This has been on for two years now and I heard a guy tell of his being ten years old with no problems. An 18 inch by 24 foot roll is about $8.

What has been mentioned by Bumper and TCJ is what we old broken down model airplane trash used to call the "Monokote Hinge", and the "Over and Under" hinge method. Goes way back to strips of cloth and dope or glue on control line models in the 1940's. But in these examples it is being used as a seal, not a hinge.

This method will certainly seal the hinge line almost as well as the Blenderm method. You would see 90-95% of the same seal effectiveness (less the openings at the hinge as shown in TCJ's photo). Some airplanes even use strips of the aircraft covering fabric instead of back-to-back tape.

In my opinion, FWIW, the over and under method takes more time and loses one big advantage of the Blenderm method. With one layer of Blenderm on the top surface of the stabilizer/elevator hings, in a grand total of five or ten minutes, you can make a 100% air seal AND and keep rain water or falling snow off of the hinges, and keep that water from seeping in under the fabric where the fabric is cut around the hinge tubes. I would thus expect the Blenderm to provide much more protection against corrosion than the method in the photo. I would think that the method in the photo would actually create a little trap or trough for water to sit in if it rained. Most of the water would drain off the ends, but due to surface tension and any dirt/mud present there would be moisture trapped against one of the surfaces.

Adding the second layer from underneath is only a cosmetic option to keep the dirt out of the tape, but now that I think of it it would keep splashed water, mud, etc from getting onto your hinges from underneath.

TCJ thanx for posting the pix, and it looks like a nice and clean install. How wide is the gap tape just before you stuck it on? Also, I assume the pic is taken with your elevator relaxed, down. Your gap tape appears to not have any slack amount in it when the elevator is down like that. What does the tape do when your elevator is equal with the horizontal stabilizer, or when pulled back (up) all the way?



EZFLAP, does the Blenderm method involve a single piece of the Blenderm tape going across the entire edge surface and across to the leading edge of the elevator, including covering the hinges? Or maybe two pieces with a middle piece stuck to the sticky side in the middle like Bumper was describing and also covering the hinges?

Pix would be very helpful from anyone who uses the Blenderm method.


This gap tape thing might seem more complicated than it needs to be, but I just want to know what's been working well for you guys who use it. For me, I'm just looking for a good way to seal off the air that slips out the gap and hopefully increase the air flow against the elevator when in the stick-back position. Likewise for the ailerons.

The tape method I am suggesting is the easiest and fastest, as well as providing the most protection against rainwater. It will take less time to install it than it will to read the lurid instructions below. Sorry for the filibuster-length post...

Here is how you would do it on an elevator:

1) Put a drop of thin penetrant oil on the hinge pins and work the elevator back and forth to make sure your pins are not stuck or galling.
2) Clean the elevator and stabilizer surface with rubbing alcohol to remove any dirt, grease, oil, etc.
3) Using a small "acid brush", put a very thin coat of vaseline over the top surfaces of the actual hinge tubes (both the elevator and stabilizer hinge sections).
4) Move the elevator into the full down position (stick forward). Put a weight on it or bungee the stick forward all the way.
5) Apply the 2 inch wide Blenderm centered halfway on the elevator and halfway on the stabilizer. As you apply the Blenderm, use your little finger to push the Blenderm down into the gap, as opposed to stretching the tape taut over the gap. You do NOT want the tape stretched taut, because it could restrict elevator movement. (So to answer your question directly, the Blenderm does not go from top to bottom or bottom to top, it's on the top of both stab and elevator.)
6) Burnish the tape down (and down into the gap) using your fingers. Burnish it down until the tape turns the same color as the paint, meaning it is all stuck down good.
7)Verify that the Blenderm does not "shear" because it stuck to the two parts of the chinge that move relative to each other.
8 ) Verify that the tape does not get so taut that it tries to prevent the elevator from reaching the full "down" position. Verify you have full, free, unrestricted movement with no resistance, rough spots, etc.
9) if you wish, bungee the stick fully back (up elevator) and do the bottom of the gap the same way. If you choose to do the bottom, attempt to stick the two layers of Blenderm together in the middle of the gap if you can. This is absolutely NOT necessary but it will serve to prevent an ugly strip of dirt from sticking to the underside of the upper tape.
10) On an annual inspection or every few pre-flights if you like, check to make sure the tape is not ripped, and not "shearing" where the hinge sections move relative to each other.

BTW the only way you can do this on an aileron is if you have the same type hinge (welded tube hinge or piano hinge) as you have on an elevator. But the standard "Frise" type aileron hinge method (offset hinge, as seen on Taylorcraft, Cub, etc.) will not allow this type of tape seal. For that, we have to use a different seal called a "wiper seal", which has its own quirks and procedures to work correctly... but alas, that is the subject of next semester's course in control and gap seals

Since this thread is about VG's and gap seals, be aware that you may still need VG's on the bottom of your stabilizer to get the maximum control authority (to match the extra AOA capability that your wing VG's give you). That's not a bad thing, but it certainly will give you more elevator power, which like all power, can be abused. With VG's on the bottom of your stabilizer you will be able to exert more elevator power, meaning more wing bending loads. Please check with the Ridge Runner's designer to make sure you have the structural reserve for this. Your life genuinely does depend on it.

Has anyone here ever tried to seal ailerons or stablizer on a Champ? I have thought of doing it several times but really couldn't find anyone to be the guinea pig before me.
WW

Ridge Runner asked:

TCJ thanx for posting the pix, and it looks like a nice and clean install. How wide is the gap tape just before you stuck it on? Also, I assume the pic is taken with your elevator relaxed, down. Your gap tape appears to not have any slack amount in it when the elevator is down like that. What does the tape do when your elevator is equal with the horizontal stabilizer, or when pulled back (up) all the way?

Heres some pictures of up, neutral and down elevator.

On this application each piece of tape is 2 inches wide. The overlap is 1 inch for a total tape width of 3 inches with 1 inch of sticky side exposed on each side to attach to the surfaces. The width of the overlap will depend on the width of the gap being sealed and the thickness of the control surfaces.

Notice a pencil line on the tape at the trailing edge of the horizontal stab. That is the line I used to line up the two tapes when I stuck them together and shows the area the overlap covers so the tape does not stick to the surfaces there.

With the S shape of this application and the design of the hinge being centered on the control surface tubing there is no slack regardless of elevator position.

Elevator Up


Elevator neutral


Elevator down

TCJ... it looks good. Thanx for taking the time to post those pix. It looks like either the tape is tight when first installed and just has enough flex to stay fairly tight, or there just isn't much movement to create much excess to bunch up. It looks good.

Also, EZFLAP, thanx for the detailed step by step.


I might just experiment with different methods and see what I can do that turns out well. They both sound good and both will provide sufficient reduction in air leakage.

Thanx and noted on the extra tailfeather lift by having VGs on the H stab. I will put VGs on the H stab to provide increased control at the slower speeds the VGs on the main wing are expected to provide. Some RRs are already flying with them without issues.

WWhunter wrote:Has anyone here ever tried to seal ailerons or stablizer on a Champ? I have thought of doing it several times but really couldn't find anyone to be the guinea pig before me.
WW

Can't speak directly for the Champ, but if it has the same type of hinge as the T-craft, seals can cause some problems. The T-craft has a slotted aileron which essentially functions as a Fowler Flap in some cases, or as a flow acceleration slot in other cases. It is widely accepted in the T-craft community that sealing off the slots creates problems with roll rate and adverse yaw.

Bill,
Thanks for that tidbit of info. I seem to remember something I had read similar to what you said about it disturbing the flow. I am thinking I could try it on the stabilizer and wouldn't have any issues.
Thanks,
WW