Gap Sealing Elevators & FLAPS

[Frank Imbriaco]

I religiously gap seal elevator, ailerons and rudder on my R/C pattern aircraft. Haven't bothered with my ukie stunters because  I build with a tight hinge line.  I'm  also  mildly concerned that the seal would stiffen the movable surface.
After a summer's worth of flying in ridiculous N.E. turbulance, I'm inclined to ask others who   CURRENTLY FLY GAP SEALED  STUNTERS- Do you feel a difference?

[Tim Wescott]

I seemed to notice a difference, flying in a very turbulent spot in the northwest.  But I'm kind of a beginner...

Everything I've read convinces me that it should be done, and if you do it with Scotch tape you don't really stiffen things up noticeably at all.

[Randy Powell]

Over probably 30 stunters I've built over too many years, I can say I'm have had one or two instances where sealing the hingeline did not help and once where it actually made the plane fly worse (that was a way outside the envelope design). But that leaves 28 times where it helped. In several of those instances it helped enormously. I usually make the maiden flight with a plane without the hinges sealed then seal them for comparison. The seal usually, well, almost always stays in place.

[Howard Rush]

Having some dementia, I am able to do blind experiments: I have forgotten that I had removed seals, then wondered why a plane flew poorly.  Even when seals don't make much difference, it's hard to isolate trim anomalies when the surfaces aren't sealed.

It is probably possible to make flaps that don't need to be sealed or even that work better with gaps.  I suspect that the Yatsenkos know how.  We put gaps on full-scale-airplane flaps, but their wings typically are restricted to lifting in one direction.  Most stunt planes I've seen benefit from having sealed surfaces.  

[Peter Nevai]

I would'nt know as you would be hard pressed to pass a business card through the hinge lines on my birds. Actually, I cover the wing and the surfaces after assembly and threading even monokote between the parts is a challange.

[Randy Powell]

I have built planes with pocketed control surfaces that seal themselves when deflected. Worked OK, but was a pain to build and I saw no great benefit from it over standard construction.

I have certainly built planes with a very, very tight control surface gaps. Didn't make much difference since the air pressure still sent a certain amount of air through the gap and they they still benefited from sealing the gap up. As Howard notes, if nothing else, it make working out trim issues easier since the anomalies introduced by air leakage between surfaces is eliminated.

[Eric Viglione]

Here is an argument for not only sealing the gap, but also having a reasonably stiff flap... if they flex this much, a whole bunch of air is going to go through that expanded un-sealed gap at deflection.

This pic is at the pull-out of a square or something, can't remember... but I do remember looking at this pic after and saying "holy !@!@#". LOL!!

Too bad the camera back focused on the tree line, I would like to see a little clearer view of the flap hinge line, but I still think the picture is very telling.
EricV

[Steve Fitton]

There is no substitute for actually trying it and knowing.  On my Time Machine, taping elevators and flaps helped in some areas, but made others much worse, although I think I know why.  Generally speaking though, there is sufficient anecdotal evidence to support taping as a general rule.

[FLOYD CARTER]

I usually seal the hinge line with Moore's Crystal Clear tape.  Before trying that, I used ordinary cellophane tape, which was hard keeping it on.  Also, from time to time, I like continuous cloth hinges, which require no further seal.  F.C.

[Randy Powell]

Holy Flexiflap! Yea, the deformation of surfaces under pressure is a good argument to seal things up. At least you can eliminate leaking air as a contributor to the any problems.

[Dick Pacini]

What are we looking at, the bow of the inboard flap?

[Brett Buck]

I religiously gap seal elevator, ailerons and rudder on my R/C pattern aircraft. Haven't bothered with my ukie stunters because  I build with a tight hinge line.  I'm  also  mildly concerned that the seal would stiffen the movable surface.
After a summer's worth of flying in ridiculous N.E. turbulance, I'm inclined to ask others who   CURRENTLY FLY GAP SEALED  STUNTERS- Do you feel a difference?

  Always seal the hinge lines, it removes so many potential issues there is no reason not to. In some cases, it causes other problems, but in every case I have seen so far, it's because the hinge gaps were masking other problems that also needed to be fixed.

    Brett

[Howard Rush]

At which way to pull out
There may be a lapse,
But the Jive Combat Team
Has the stiffest of flaps.

[Ted Fancher]

Here is an argument for not only sealing the gap, but also having a reasonably stiff flap... if they flex this much, a whole bunch of air is going to go through that expanded un-sealed gap at deflection.

This pic is at the pull-out of a square or something, can't remember... but I do remember looking at this pic after and saying "holy !@!@#". LOL!!

Too bad the camera back focused on the tree line, I would like to see a little clearer view of the flap hinge line, but I still think the picture is very telling.
EricV

Holy Cow, Eric!

Forget the flaps.  The bloody wheels musta blown out the bottom of that square!

Ted

[Ted Fancher]

Gotta side with Brett on this one.  I'm a big fan of his comment from years ago when he stated (roughly) "I don't care how tight your hinge lines are the gap is still wider than a molecule of air."  The only way sealing hinge lines can make an airplane "worse" is if they are applied poorly and stiffen the freedom of movement of the surfaces.  "Nothing" bad can come from insuring the high pressure air on one side of a lifting surface doesn't sneak through to the low pressure side...nothing!

Those that feel sealing the hinge lines made their ships fly worse are missing the point.  Sealing the hinges allowed them to discover their ships weren't trimmed to their optimum capability and the lack of seals was disguising that inferior state of trim.  It would behoove those fliers to start their trimming process over again because now the airplane is capable of being trimmed better than it had been before.

The most basic value of sealing is increased efficiency of the lifting surface involved.  It can be instructive to seal just the elevators for instance and (most likely) discover on the next flight the ship is more sensitive because the same control input results in more lift from the tail and the ship turns quicker.  The opposite can often be detected if one seals just the flap hinge lines.  When the flaps become more effective the negative pitching moment from deflecting them requires more tail force to overcome and, thus, the airplane will be less responsive to control inputs.

An effect that people often don't consider shows up in the roll axis.  Even if your hinge lines are "really tight" the gap between the wing and the flaps will likely vary as the flaps go up and down.  Every variation in the gap results in greater or lesser lift production and, if one wing gets a tighter gap and the other a larger gap the tighter gap will produce more lift and cause the airplane to roll.  We don't want our stunters to roll so, if for no other reason, flap hinge lines should be sealed to prevent that issue.



After stealing the idea from Denny Adamisin a hundred or so years ago (it was one of those "Holy Cow, dumby!  Of course you've got to seal them" moments) I became sort of an evangelist for the idea and engaged in a lot of on-line discussions on the subject.  A search of the forums will bring up tons of copy on the subject going back many years.  I urge Frank to do so.

I also urge him to just have his wife read them to him go ahead and seal 'em while she does so! 

Ted Fancher
"

[Paul Walker]

At which way to pull out
There may be a lapse,
But the Jive Combat Team
Has the stiffest of flaps.

Er, HAD the stiffest flaps.

[Steve Fitton]

Er, HAD the stiffest flaps.

I have to ask.  Did the stiffest of flaps survive the accident?

[PJ Rowland]

What accident?

[Howard Rush]

I have to ask.  Did the stiffest of flaps survive the accident?

Old ones are retired
'Cause I won't match the checker.
The new ones are stiff
As a honeymoon ...

[Frank Imbriaco]

Man, speaking of waxing poetic... er, is that waxing and waning ?

[Randy Powell]

Howard's stiff flaps
Didn't keep him from crashing
Carbon fiber and resin
Didn't keep him from bashing

[Will Hinton]

Touche!

[PJ Rowland]

Sounds to me like nostalgia..

Missing the days of yore with Combat crashes..

We should keep notes of great models to be crashed and declare a winner at the end of the year.


I think its a 2 horse race ..

[Dick Pacini]

If your flippers and flaps got some big gaps
Throw some tape on that b--ch

If the airflow leaks and the horns you must tweak
Throw some tape on that b--ch

If your plane wants to hunt with the weight up in front
Throw some tape on that b--ch

If your best reason is a good flying season
Throw some tape on that b--ch

 

[Eric Viglione]

Hi Ted,

Never fear, landing gear is here! More like sucked up, not blown off...heh.

I have to admit, they let me fly this bird, and it was spooky flying a stunter with no gear showing after the retracts pull it up. Leaves you feel more like you are flying a combat ship...also, my vision is good enough to focus on the tail wheel still being down and found that rather incongruous to what my brain expects to see in flight. It also leaves you feeling that somehow your bottoms have gotten higher, since I guess we see the gear in our peripheral visualization of our bottoms. I also have some opinions on how the gear up affected the over all trim of the plane, but I don't want to totally hijack this thread and will leave it at that.

At it's current state of trim in this photo, I believe it was 80+ ounces... and those flaps were not helping the situation by flexing so much.

I would imagine that flap flex not only would be negative for loss of lift, but for many other reasons as well, like...

A overly flexible flap would:

1) let more air spill through an un-taped gap
2) add a springy feeling to the controls
3) allow you to be driven down in consecutive maneuvers in high winds, just like springy pushrods. Add an over-weight forward C/G plane to this mix, and splat.
4) potentially create an untrimable airplane, especially if only one of the flaps is flexible, and the other is stiff. Lesson here is make sure both are of similar wood and covering technique.
5) mess with your muscle memory when flying in varying conditions

I say overly flexible only because Howard seems to have found a way to take stiffness too far, at least thats what he posted once that Paul told him?
Maybe Howard / Paul can add more to the story and make a list of what the pitfalls of that was? My only guess is that it made them too efficient, and perhaps he didn't have adjustable controls available to dial out the ratio to suit?

EricV

Holy Cow, Eric!

Forget the flaps.  The bloody wheels musta blown out the bottom of that square!

Ted

[Howard Rush]

I say overly flexible only because Howard seems to have found a way to take stiffness too far, at least thats what he posted once that Paul told him?
Maybe Howard / Paul can add more to the story and make a list of what the pitfalls of that was? My only guess is that it made them too efficient, and perhaps he didn't have adjustable controls available to dial out the ratio to suit?

I think that airplane had flaps that were too big and a tail that was too small.  The bigger the tail, the wider the available CG range.  Even with flap/elevator ratio of .85 or less, the CG had to be farther back than one would have liked for stability with the small tail.  Not only were the flaps stiff, but they had more chord on the right tip than recommended and way more chord on the left tip than recommended. Both that flap configuration and that stabilizer configuration had been successfully used on past Impacts, but not together.  I built a new, larger stab for that airplane that I'd planned to install before this year's team trials.

I think it's nice to have the flaps do the same thing at different airspeeds, but the Beringers got away with really rubbery flap control horns.  I'll have to think about this some more, although it may not help.

[john e. holliday]

That looks awesome with the gear out of sight.   

[Randy Powell]

Howard,

You're not the only one thinking about it.

[Peter Nevai]

Here is an argument for not only sealing the gap, but also having a reasonably stiff flap... if they flex this much, a whole bunch of air is going to go through that expanded un-sealed gap at deflection.

This pic is at the pull-out of a square or something, can't remember... but I do remember looking at this pic after and saying "holy !@!@#". LOL!!

Too bad the camera back focused on the tree line, I would like to see a little clearer view of the flap hinge line, but I still think the picture is very telling.
EricV

Aah, where R the LG?

Never Mind

"At it's current state of trim in this photo, I believe it was 80+ ounces... and those flaps were not helping the situation by flexing so much."

Kind of explains the flaps 80 ozs makes for a heck of a wing loading.

BTW If taping hinge lines is so much in vogue, How come in the photos of front row CLPA models do you never see a taped hinge line?

[Tim Wescott]

BTW If taping hinge lines is so much in vogue, How come in the photos of front row CLPA models do you never see a taped hinge line?

Because those folks are very good at not letting the tape show.  I had to get within four feet of Paul Walker's Impact to see the tape on his -- I think he must replace it before each contest, so you don't get treated to all of his collected dirt and crud.

[Mark Scarborough]

Taping hinge lines occurs on the bottom of the wing. My Avenger has been taped ONCE and it still has the same tape on it. It still looks pretty invisible even from the bottom. Not sure a picture would show it actually.
Of course my Avenger SELDOM gets close enough to the ground to collect dirt and grime in the hinge line,, sigh, some day I will get below 8 foot bottoms,, some day,,

[Randy Powell]

Hmm, 8 foot? Ah yea, right.

[Brett Buck]

BTW If taping hinge lines is so much in vogue, How come in the photos of front row CLPA models do you never see a taped hinge line?

    I think they were. I know Uncle Jimby's got 20 points, hinge seals in place. I am pretty sure that all of this years front row models were sealed.  Done correctly it's essentially invisible. Jim even has a way to make it immune to fingerprints getting in the adhesive.

   I would guess at least 80% of the Top 20 for the last 10-15 years had sealed hinge lines.

     Brett

[Howard Rush]

...some day I will get below 8 foot bottoms,, some day,,

My most recent bottom was below 8 feet.

[scott matthews]

I'm assuming that you seal the gaps between the hinges on the bottom of the elevator with tape and you do not go over the hinges? Also what type of tape is preferred to do this, and is there any tricks to not make your controls get stiff?

[Brett Buck]

I'm assuming that you seal the gaps between the hinges on the bottom of the elevator with tape and you do not go over the hinges? Also what type of tape is preferred to do this, and is there any tricks to not make your controls get stiff?

   "Search" is your friend.

http://stunthanger.com/smf/index.php?topic=11355.msg99465#msg99465

    Brett

[scott matthews]

Thanks Bret your advise is always right to the point and very informative. I will definitely give this a try.

[Howard Rush]

I put Windex on one of the surfaces.  it makes the stickum slippery for about 20 minutes.  I stick the tape to the other surface and get it tucked nicely into the crack by the time the Windex starts to wear off. 

[PJ Rowland]

My most recent bottom was below 8 feet.


Another ode....

We have the new technology
We fly with a new sound
but its the same old story
JCT crashin into the ground.

[Derek Barry]

My most recent bottom was below 8 feet.


Another ode....

We have the new technology
We fly with a new sound
but its the same old story
JCT crashin into the ground.

ouch!

[Eric Viglione]

PJ, that was cruel and unusual punishment! Of course that means I would normally be whole heartedly on board, but I do think there's an appropriate period of mourning that should be observed. Come on man, show some respect!   
...........................................................................there...that's about long enough.

When he flew glow
He used rhyme and meter
But now he's gone electric
Friends suggest an altimeter

[Mark Scarborough]

Hmm, 8 foot? Ah yea, right.

Hey some of them are 8 feet,, occasionally lower,, and of course there is Bruce's comment in Stunt news that will label me forever,, "Mark Scarboroughs beautifully finished Avenger seldom seen below 10 feet,, 

ARGHHHHHH
I am trying, really I am,, sigh

[Derek Barry]

PJ, that was cruel and unusual punishment! Of course that means I would normally be whole heartedly on board, but I do think there's an appropriate period of mourning that should be observed. Come on man, show some respect!  
...........................................................................there...that's about long enough.

When he flew glow
He used rhyme and meter
But now he's gone electric
Friends suggest an altimeter

Nice! But I'll do ya one better.

With props a spinnin
and shafts a pullin
a better power train
is where I'd be lookin

[Dick Pacini]

My new plane was launched
into the air

It fell back to earth
in that pile over there

[PJ Rowland]

Poor Howard...

 

If you cannot laugh with friends whats the point?

[Randy Powell]

Mark,

Don't worry, you will eventually move beyond wimp stage. Hey, you are flying a whole pattern now and you don't want to follow Howard's example.   

[Jim Morris]

I religiously gap seal elevator, ailerons and rudder on my R/C pattern aircraft. Haven't bothered with my ukie stunters because  I build with a tight hinge line.  I'm  also  mildly concerned that the seal would stiffen the movable surface.
After a summer's worth of flying in ridiculous N.E. turbulance, I'm inclined to ask others who   CURRENTLY FLY GAP SEALED  STUNTERS- Do you feel a difference?

The bottom line is, this is one of those things that always work. Sealing the hinge lines will never hurt more than it helps. I use clear scotch tape on a very clean surface then rub the tape with the round handle from a plastic screw driver to really get it down. It lasts quite a while.

[frank williams]

This has been published before, but once again might not hurt.  I did this in my small garage wind tunnel (12" dia section).  The stab was 3" long and the elevator was 3" long, the section was airfoiled, about 3/8" thick.  The hinge gap was probably less than 1/32 inch, I pushed them together as tight as possible.

I really didn't think I would see much difference between the sealed and unsealed, mainly because the hinge joint was so tight.  ..... but I did.  Past about 15 degrees of elevator deflection there is a real difference.  Sealing the linge line improves the efficiency of the surface when the elevator is deflected.

[PJ Rowland]

I was speaking to another top level flier who said

" Ive had my elevator gap so tight it was squeaking - Sealign the hinglines still improved performance "

[Dennis Adamisin]

I may as well pile on this thread.

I have had some really good airplanes that did not have hinge gap seals.  Yet the first time I used seals it was like night and day.  It has always been a head scratcher to me that some birds are far more sensitive to the gap seals than others.  I also wonder if some of my good old birds would have been noticeably better with seals - I believe they would have been.

When my Eclipse Mk1 (1980) was a dog, I literally gave up on it.  My brother Arch took it home and sealed the gaps - and the improvement was beyond major.  About a year later Ted & I were having a conversation and I mentioned gap seals.  He tried it on one of his birds that was giving him grief and promptly won the NATs.  Since then I have not built anything (CL or RC) that did not have seals - nor will I.  I no longer CARE whether they have an effect on a certain airplane.  As also mentioned in this thread (by Brett?), the overriding reason why seals should be used is that they eliminate any/all influences of the hinge gaps.

Frank's chart shows pretty compelling evidence WHY it works, please recognize that similar increments apply when sealing the flaps, trim tabs - or even your movable rudder!

By Eclipse Mk2 I had figured out how to install the seals (almost) invisibly by embedding a single layer of monocote backing into both sides of the hingeline - it is not that hard to do, and published my method with that construction article.

When I started flying RC Sailplanes I settled on a means of using thin CA style hinges then monocoting right over them.  Do this top & bottom and your seal is also a FUNCTIONAL full span hinge that is indestructible - and EASY to do.  Have done a similar thing successfully with CL by cutting the CA hinges in half to make them more flexible.  BTW, Sailplanes that do not have gap seals are typically nosier - the sound is DRAG.  While we do not have as much worry about drag, taking drag OUT is the same as putting power IN.

I only use tape seals on ARFs or other pre-finished applications.  Howard's suggestion about using Windex is golden. 

One thing that helps with the installation is to not lose any sleep over really tight gaps.  1/32" or even 1/16" is fine, a wider gap makes it easier to assure that the seal will be flexible.