Gap Seals Anyone?

Searching VAF (& other venues) on gap seals (ailerons, flaps, elevator, & rudder) yields spotty commentary on their usage.
Anecdotal comments suggest there's potential gain in drag reduction and control surface responsiveness.
And, these gains far outweigh their cost and effort.

So, what's been the experience (& evidence) of those who've tried them?

Control surfaces:

What's the effect of gap seals on operation in the flight envelope?
There have been a couple of thread comments indicating they change the handling characteristics.

Do they? If so how?

Speed:

Do gap seals increase, decrease, or have no effect on performance?
Some have suggested gap seals yield as much as 2 knots of improved speed.

Any empirical results available?

Other gaps:

What's the effect from gap taping on areas other than control surfaces?
For instance taping the gaps on the cowling.
Some use only for racing.
Or, taping the gap(s) on the wing to fuselage connectors?

Types of tape:

Mylar, tape, ??
Most effective in flight? Some users indicate the tape can detach during flight.
Some suggest that partial detachment has caused some hair-raising moments.

Cautions:

What are the cautions? Gotchas?

Where to buy?

Sail plane sites? Auto racing?

Installation process:

What's the most productive installation process? On control surfaces: Cover the hinges? Cover the hinges & the gap?

Double sided tape, mylar to the double side, & tape over the leading edge of the Mylar. What works?

Size of seal? 1 inch, 1.5 inch, 2 inch, over 2 inches?

RV Models:

What RV models have tried gap seals? Do results vary by model? How?

Regards,

Gap seals

While somewhat anecdotal, my primary experience with gap seals has been on models. The most noticeable difference with seals is they increase the effectiveness of the control surface. I have always been doubtful of the performance claims on full size aircraft.

If I were adding them on a full size airplane, my number one priority would be to make 110% certain that the seals could not cause any binding of the surfaces.

I would also be interested in knowing what effect they have on an RV.

Anecdotal:

My full size soaring / glider flying experience says that gap seals are indeed a performance enhancer and improve flight control effectiveness

My miniature radio controlled model airplane experience also shows that racing aircraft performance improves with gap seals. Aerobatic aircraft benefit from improvements in flight control effectiveness and that improves general handling with less flight control deflection required for roll rate, etc. Furthermore I have also put gap seals on higher speed and large RC airplanes but there have been times where the gap seals were not stiff enough and some mylar gap seal buzzing occurred from about 180mph upwards on one aircraft. I'm sure when this happens any sort of benefit is erased and there may even be some reduction in flight control effectiveness though I did not specifically "feel it" in my case and certainly not at slower speeds as any buzzing was gone below 120 or so.

For a full size aircraft I would proceed cautiously and most likely try to talk to the glider guys who use a thin plastic gap seal material. Trouble is, glider guys are rarely going more than 150mph so for an RV more research will probably be warranted. Maybe talk to the Reno Race / and Open Course race guys on the forum, maybe some of them are doing it already. http://sportairrace.org/sarl/

Gap seals

We have gap seals on our RV6A. All tail gaps are covered and the space between the aileron and wing tip has felt in it. We are located in Texas where there isn't much chance of any ice. I could see that as a potential problem. Our gaps are installed with glue and one inch tape, they cover the entire Gap on elevators and rudder. I have only flown a RV 8 besides the 6 and I think the performance is about the same. We have a 0-360 and the 8 was IO-360, 162 kts. True at 9500 ft. On the 6 all the time. I can't tell much difference in handling qualities, but it looks great. It doesn't seem detrimental at all, but you do not want them to come loose.

Investigate the 'Frise' type aileron before installing gap seals. Also if you are using a slotted flap (RV-9/10/14) the same rules apply. Gap seals will essentially prevent airflow over these control surfaces reducing their efficiency. Not sure what other effects (detrimental or not) that they might also have.

Maybe Steve Smith will chime in...

http://en.wikipedia.org/wiki/Aileron#Frise_ailerons

Thanks Joe. Here's a quick blurb from a google search:

Frise Aileron: A type of aileron that has a beveled leading edge projecting beyond its inset hinges. When lowered, it forms an extension of the wing surface: when raised, its nose protrudes below the wing, increasing DRAG and reducing YAW. Named for its inventor, British engineer Leslie George Frise.

Gap seals would appear to negate the positive effects of the Frise aileron.

Next time you're at the airport, go find a Mooney and look at the fit between the control surfaces and the wings/tail. On a properly rigged one you can't fit a business card in there, which is where a lot of the speed is derived (amongst other things).

I can't imagine gap seals wouldn't increase speed, however the way the control surfaces are hinged I'm not sure how you would do it properly without creating a potential risk for interferance.

Best thing I can think of us taping over the gaps on the top and bottom of the flaps, and making no flap takeoff/landing while they're taped.

Time for Bob Mills to chime in, that dudes plane has more tape than a Home Depot.

Aileron gap seals...

I was speaking to a friend of mine about this thread. He has built an RV-4, three Glassairs, and some others. He is also a retired USAF test pilot and instructor.

He said that for the RV ailerons to work properly there has to be a gap between the skin and the aileron. Something to do with the front of the aileron dropping below the bottom of the wing when deflected and proper airflow over the aileron in that position.

He said that he flew an RV-6 one time where there was no gap when the aileron was deflected upward. He said that because of no airflow over the aileron that the roll control was compromised. He also says that this interruption of airflow is one of the causes of the RV bump. I know that my RV-4 has that bump when I use full deflection for a fast roll. On his plane he has at least a 1/2" gap and he says that he has no bump at all, at any speed, or at any deflection.

Food for thought, YMMV...

When I was younger I worked for an FBO that did a lot of Mooney work. I remember they had a mod to cover the gaps at the hinge points on the tail surfaces. I thought it was interesting when I saw this at Vans Homecoming:


And this one on the HS/elevator:

Speed Tape

Any one know where we can buy that ''Speed Tape'' ??

I had Gap Seals on my Piper Arrow years ago and they did increase the speed quite a bit...

I feel a need, a need for speed..( So tomorrow I will have a look at a Rocket

Thanks

Bruno
[email protected]

RV-4 said:

Any one know where we can buy that ''Speed Tape'' ??

I had Gap Seals on my Piper Arrow years ago and they did increase the speed quite a bit...

I feel a need, a need for speed..( So tomorrow I will have a look at a Rocket

Thanks

Bruno
[email protected]

Click to expand...

PM rvmills. he can point you in the right direction.

Chaz, et al:

I wouldn't consider myself a tape expert, but I have gone few a few rolls. I once pulled off all the tape at one time after Reno so I could deep clean and prep for a condition inspection, and the resulting shmooshed-up tape ball turned out the size of a basketball!

We've had a lot of discussions among racers about what tape to use, where to tape, and what does and doesn't work. I will tell you that I do think it works. With everything taped, I have shown a repeatable 2-3 knot speed increase. By far the cheapest speed gain I've seen in my speed chase. I think Steve Christopher has seen similar in his RV-7

I did listen when told not to tape the ailerons. Never have tried it, so I have no data...but I did hear a couple harrowing tales...first and second hand. I've seen a few folks tape a mylar tab across the upper hole at the aileron hinges, and have heard no negative reports on that. I also have the lower aileron hinge bolt fairings, and there were no adverse effects from that. However, as Shadey Blank said, its best not to tape the spanwise gaps at the ailerons.

I've tried the Wings and Wheels tape system on the elevators and the rudder gaps (full span). I used the multi-layer, multi-step process, and it did not stay on during speed tests (twice...I'm a slow learner!). To be fair, I did apply it to a painted surface, and perhaps a little better "adhesion preparation", may have helped. However, the tape came off the rudder gap sides, and the elevator tops at just over 180-190 mph (rudder first each time). A short zzzzzzip sound, and my chase pilot said "there it goes". No damage, except to the pocketbook. The system stayed attached to the lower elevator gaps to full speed, and lasted for quite a while. No adverse control inputs with any of the product on, whether top and bottom, or bottom only. The W&W stuff is high quality, and used properly, and in the right locations, I'm sure it is a value-added product. I've seen lots of fast glass guys use their Turbulator tape (the V-shaped tape) in various locations. It supposedly acts as a miniature vortex generator...or some similar magic.

I've been using primarily 2" wide 3M 471 tape. Amazon occasionally has deals on it...but its pricey, as tape goes. It adheres well, stays put (usually), and conforms to curves well (takes some effort at times, and its easier to apply when its warm. Comes in lots of colors, and my experience is it can be left on quite a long time. One caution, the clear version yellows, and leaves more gummy residue than the colored tapes...I think its a sun thing.

I tape the upper and lower intersection fairings, parts of the wheel pants, the wingtip lights, the tail fairing, and various panels. I also tape the wingtips, wing root fairings and cowl halves, to cover the gaps, the screws and tinnermans. Gaps perpendicular to the airflow are primary targets, but there are for and aft gaps that I go after too. All of those tapings are ways to improve the fit and finish to the level that a Gold Lindy aircraft might have. I've also experimented with taping over the first sideways skin seam on the top and bottom of the wing. Mark (F1Boss) and I chatted about this, and he tried it and liked it. However, the RV wing's seam is further aft than the EVO wing's, and may be beyond where laminar flow has already stopped, so it may not help salvage or extend laminar flow (which is why Mark tried it).

On the rudder and elevator hinge openings, I first tried Wings and Wheels mylar, cut to fit the openings, and it worked pretty well. Then my racing buddy Jason Rovey shared his method of using a certain water bottle, cut to fit. It turns out various sizes of one brand of water bottle are just the right size for the various control surface curves. The brand is a trade secret...you'll need to be as smart as Jason to figure it out!

I doubt there is any particular place that adds more value than others. I think its one of those "sum of the parts" things, and its all additive, to the point where when you do it all, you see some results. Taping is just one gap control method too. Take a look at Formula and Unlimited racers at Reno...there are a lot of nuggets there. Pierre and I were looking at Strega and VooDoo one year, and saw that they have material that kinda looks like very thin carpet between control surface horn gaps. The material barely rubbed on each other, and looked to be there to just stop airflow bleed though those gaps.

Of course you have to watch those racers. I also heard an urban legend of a guy who had gained some significant speed from one year to the next, and everyone wanted to know how. He wouldn't tell, but he did add some of that turbulator tape to a random (and completely aerodynamic neutral) location, where everyone could see it. Sure enough, other race planes started sporting the same tape, in the same location, within a day or so during race week! Was good for a few chuckles during the awards ceremonies!

Cheers,
Bob

Tape cure for the "whistling 9As" ...

A few years ago, there was significant discussion about 9As having an audible whistling sound when doing low passes. They theorized the whistling noise had to mean unnecessary drag. The result was a number of builders taping the gaps at the elevator and rudder hinge points. The gap tape stopped the whistling, but I don't recall if any reported a speed increase. Certainly everybody felt better about their newfound stealth.

I'm sure miss the low pass wistle from my former RV9A plane...

Got some low rate roll on my new RV7A and buffet that I'm trying to solve...