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Author Topic: Hinge options  (Read 4790 times)

Offline FLOYD CARTER

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Hinge options
« on: February 03, 2009, 02:14:39 PM »
We typically install aileron and elevator hinges at the very leading edge, and then seal the gap with tape.   Full-scale aircraft design sometimes uses offset hinges, where the pivot point is behind the leading edge.  This is supposed to create a "duct" or tunnel at full deflection.

Is there any advantage in this?  It would be very easy to implement.

Floyd
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Offline Robert Schroeder

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Re: Hinge options
« Reply #1 on: February 03, 2009, 11:11:20 PM »
The airflow through the slot onto the other side of the moveable surface is known to cause the deflected surface to act in a more efficient manner, at least on full scale planes.  It is believed to work in like manner on models.  There was an article on it in Stunt News a couple years ago and I just saw a bit in Stunt News, Controlline World or Flying Models in the last couple months.  I'm thinking of trying it in one of the planes I'm currently building, but am not totally sure I will.
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Online Brett Buck

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Re: Hinge options
« Reply #2 on: February 04, 2009, 12:56:58 AM »
We typically install aileron and elevator hinges at the very leading edge, and then seal the gap with tape.   Full-scale aircraft design sometimes uses offset hinges, where the pivot point is behind the leading edge.  This is supposed to create a "duct" or tunnel at full deflection.

Is there any advantage in this?  It would be very easy to implement.

Floyd


 Frank Williams has been experimenting with that sort of thing for a few years now. It probably does something if it is shaped very carefully (what shape and dimensions you need probably require testing to figure out). Just leaving a gap definitely doesn't help, it reduces the lift noticeably. Even if you got it the right dimensions and increase the peak lift, I would be concerned that it would be very "non-linear", i.e.  at some point as you deflect it, the lift changes suddenly.

    BTW, Frank was running flow straighteners on the flap slots at last year's NATs. On one flight, the flow straightener fell off in flight. On the refly, he didn't have time to fix it, so he flew without it. On the top, on only one side. You would think, if it was doing anything, it would grotesquely screw up the trim. But it looked like it flew about the same as before!

   I am a big advocate of sealing the hinge lines, and although it hypothetically helps the lift, I do it to minimize the effects of the gap varying from side-to-side and as surface deflects. That greatly simplifies the trimming process. And if you want to see if it does anything, seal only *one side* (inside flap hinge line preferred) or remove the seal on the outboard. I guarantee you will be able to tell the difference with that!  No matter how tight you make the gap, it's still bigger than an air molecule.

    Brett

Offline FLOYD CARTER

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Re: Hinge options
« Reply #3 on: February 04, 2009, 12:53:34 PM »
Thanks for the info.  I typically seal hinge lines with Magic Mending tape, or similar.  I have a problem with the adhesive right in the gap sticking to one side or other, and making movement pretty stiff.

Monokote doesn't work.   Ironing it down distorts the material in the gap, and it gets worse.

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Offline Bootlegger

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Re: Hinge options
« Reply #4 on: February 05, 2009, 01:09:56 PM »
  Brett, would you say that using cloth hinges from fuse to tip on the wing and stab would be a good way to seal the hinge line(s) ??  Thanks, Gil
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Online Brett Buck

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Re: Hinge options
« Reply #5 on: February 06, 2009, 01:09:22 AM »
  Brett, would you say that using cloth hinges from fuse to tip on the wing and stab would be a good way to seal the hinge line(s) ?? 

   Sure, if you want to deal with that. I heard tell that when people first went to pinned hinges instead of cloth, they found the airplanes didn't fly like they expected. Later, somebody realized that it might be the big gaps, and sealed it up, and it then flew like they expected.

   Brett

Offline Larry Fulwider

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Re: Hinge options
« Reply #6 on: February 08, 2009, 08:57:34 AM »
. . .
. . .

   I am a big advocate of sealing the hinge lines, and although it hypothetically helps the lift, I do it to minimize the effects of the gap varying from side-to-side and as surface deflects. That greatly simplifies the trimming process. And if you want to see if it does anything, seal only *one side* (inside flap hinge line preferred) or remove the seal on the outboard. I guarantee you will be able to tell the difference with that!  No matter how tight you make the gap, it's still bigger than an air molecule.

    Brett

I am having trouble with hinge tape stiffening the controls. Can you describe the techniques / materials / that you and others use to get a fairly long lasting, decent looking hinge line seal that, from the handle, feels like a pair of loose shoes?
   Bob Whitely recommended Moore brand tape (in a Stuka Stunt thread) “available in most drafting and art supply stores”. Well, maybe in your part of the country, but I couldn’t find Moore tape anywhere around here. I bit the bullet and ordered some from a MisterArt internet site; the Moore tape should be here Monday. I assume the Moore tape is thinner than the 2.6 mil Crystal Clear (Duck Brand) I have been using? (At one time, I had another thread with a different tape recommendation, but darned if I can find it now.) What are other choices of tape?
   Is there any advantage in running a 1/16” bead of beeswax based lip balm (or some such) down in the valley between the flap and TE as a stick – re-stick preventer?
   I have tried segmenting the tape between the hinges and just putting on one big long strip. Which do you favor? Your "one molecule of air" comment implies one long strip?

I have to be doing something wrong, and I’m not sure it is just the brand / thickness of tape. This can’t be that hard if everyone else does it with no problem.

Larry Fulwider

Offline FLOYD CARTER

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Re: Hinge options
« Reply #7 on: February 08, 2009, 10:36:08 AM »
I got a roll of the "Moore" tape that was recommended here on the forum.  The only good thing about it is that it has a very agressive adhesive!  Sticks like crazy.  But this is exactly the problem.  The "sticky" part gets into the gap and grabs either the wing T.E. or the flap L.E. and the controls get real stiff. 

I haven't found the ideal gap tape.

Floyd in OR
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Offline Larry Fulwider

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Re: Hinge options
« Reply #8 on: February 08, 2009, 11:14:11 AM »
I got a roll of the "Moore" tape that was recommended here on the forum.  The only good thing about it is that it has a very agressive adhesive!  . . .
. . .  The "sticky" part gets into the gap and grabs either the wing T.E. or the flap L.E. and the controls get real stiff. . . .

Floyd in OR

Can you check to see if the Moore is 2.6 mil? Surprisingly, sticky tape can indeed be miked! I'm going to be real disappointed if I get the Moore tape and find it is identical to what I've been using!

Your description of the stickiness encourages me try the "beeswax down your crack" idea.

Larry Fulwider

Online Brett Buck

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Re: Hinge options
« Reply #9 on: February 08, 2009, 03:38:10 PM »
I am having trouble with hinge tape stiffening the controls. Can you describe the techniques / materials / that you and others use to get a fairly long lasting, decent looking hinge line seal that, from the handle, feels like a pair of loose shoes?
   Bob Whitely recommended Moore brand tape (in a Stuka Stunt thread) “available in most drafting and art supply stores”. Well, maybe in your part of the country, but I couldn’t find Moore tape anywhere around here. I bit the bullet and ordered some from a MisterArt internet site; the Moore tape should be here Monday. I assume the Moore tape is thinner than the 2.6 mil Crystal Clear (Duck Brand) I have been using? (At one time, I had another thread with a different tape recommendation, but darned if I can find it now.) What are other choices of tape?
   Is there any advantage in running a 1/16” bead of beeswax based lip balm (or some such) down in the valley between the flap and TE as a stick – re-stick preventer?
   I have tried segmenting the tape between the hinges and just putting on one big long strip. Which do you favor? Your "one molecule of air" comment implies one long strip?

I have to be doing something wrong, and I’m not sure it is just the brand / thickness of tape. This can’t be that hard if everyone else does it with no problem.

    Well, maybe we are all just super-geniuses!  Alternately, it could be a matter of technique.

     I have used the Scotch Clear plastic tape, and the Moore tape (originally discovered by Ted and slightly thinner than the scotch) with good results. The good thing about both is that the adhesive comes off with the tape if you have to remove it, which is a lot better than Fas-Cal or trim Monokote.

      The trick is to get it to cross the gap right at the hinge line. If you don't get it all the way to the hinge line, it will bunch up and stick together in one direction and get drawn tight and restrict movement in the other. Attach it to the moving part all the way to the point of the "wedge", then use a card to stick it to the TE of the fixed part right in line with the hinges, then up the TE. I have a drawing of it somewhere, there's a drawing somewhere on SSW that I can't find, but I will post it if I can find it.

     And just to be clear - regular old Scotch Tape, the frosted Cellophane type (magic mending tape) won't work. It needs to be the transparent mylar plastic type.

     Brett


p.s. Knew I had this somewhere. The trick is to hold the hinge at full deflection, and then *very carefully* apply the tape all the way to the point of the wedge. Fold the tape back against itself to prevent it from sticking to the trailing edge of the fixed surface, and use a card or bit of thin plywood to stick it firmly to the point. Once it's stuck all the way to the moving surface, use the card to push the tape across the gap so it sticks to the trailing edge right in line with the hinge. After that, you pretty much have it made, just stick the rest of the tape up along the TE and onto the surface until it's all stuck down. If you use a continuous hinge pin, it's easier because you can just stick it to the hinge pin wire. If you don't get the tape all the way to the hinge line, it either accordian folds when you move the surface down, or it gets pulled tight when you move it the other way. The way it's supposed to work is that the tape just bends at a single point, which takes almost no effort.

   Note that a lot of people make the hinge geometry wrong. The "point" on the elevator has to be in line with the point, or slightly in front of it. A lot of people inset the hinges into the moving surface about 1/16",  push the barrel of the hinge up against the TE, and then push the wedge until it touches the TE. IF you do that, the hinge is too far into the movable surface, and the point moves up and down. If you do that, you are causing two problems - if you don't seal the gap, it's closed when you are no deflection, and then opens up as it moves. This is a worst case, because I guarantee it won't open the same on both sides, creating a dramatic difference in the airflow from side to side.  You'd be better making the gaps huge because at least the difference between the sides is reduced. The other problem is that if you try to seal it, the tape *has to* translate up and down and will gum up the motion as the tape rolls up and down the TE.

   I make the gaps intentionally big enough to fit the hinge pin wire because I know I am going to seal it and that makes it easier to seal.


« Last Edit: February 13, 2009, 11:33:32 PM by Brett Buck »

Offline Larry Fulwider

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Re: Hinge options
« Reply #10 on: February 08, 2009, 08:55:36 PM »
    Well, maybe we are all just super-geniuses!  Alternately, it could be a matter of technique.
. . .
   
     Or maybe it’s an “In the land of the blind, the one-eyed man is king” story. “The land of the blind” part sure describes my struggles with the hinge tape issue.
      "Genius" is sure a better descriptor of you top PA guys than what Hollywood calls "genius"

. . .     
The trick is to get it to cross the gap right at the hinge line. If you don't get it all the way to the hinge line, it will bunch up and stick together in one direction and get drawn tight and restrict movement in the other. Attach it to the moving part all the way to the point of the "wedge", then use a card to stick it to the TE of the fixed part right in line with the hinges, then up the TE. I have a drawing of it somewhere, there's a drawing somewhere on SSW that I can't find, but I will post it if I can find it. . . .
. . .

Great! I’ll give it a real “wedgie” when I get the Moore tape.

It would be easier to get the tape in snugly by doing sections between hinges, as the hinges might hinder the tape from getting deep enough?
   Your “word picture” is clear enough that I don’t think I need the drawing.

. . .
     And just to be clear - regular old Scotch Tape, the frosted Cellophane type (magic mending tape) won't work. It needs to be the transparent mylar plastic type.

     Brett

That mistake I didn’t make. But I haven’t been able to find either clear (glossy) or crystal clear in ¾” or wider widths, Scotch brand or any brand (except for the heavy 2.6 mil), which is why I decided to go for the Moore.

Hey, thanks a bunch! Just the magic words I needed to explain what I was doing wrong, in addition to having the wrong tape.

Larry Fulwider

Online Brett Buck

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Re: Hinge options
« Reply #11 on: February 09, 2009, 12:48:14 AM »
     Or maybe it’s an “In the land of the blind, the one-eyed man is king” story. “The land of the blind” part sure describes my struggles with the hinge tape issue.
      "Genius" is sure a better descriptor of you top PA guys than what Hollywood calls "genius"

    I actually know quite a few geniuses. I'm going with the "technique" theory.

     Brett

Offline Larry Fulwider

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Re: Hinge options
« Reply #12 on: February 12, 2009, 10:46:45 AM »
    I actually know quite a few geniuses. I'm going with the "technique" theory.

     Brett

Hinge Sealing Follow-Up for non-geniuses with poor techniques

First, the good news – Using the Moore tape and Brett’s wedgie technique, I now have taped hinges as free (or 95% as free, subjectively) as the untaped hinges. Thanks a bunch!

The rest of the story: Critique this, please, as I’m still learning. To make sure I got the tape well down into the gap, I first stretched a loop of tape around to hold the controls full lock plus a little tension. The goal is the leave a hinge gap as large as possible – think “enthusiastic first-year gynecology student” when “prying” the gap open. The Moore tape is a little narrower than the advertised ¾” (more on that below) so I set up tape guides ¼” from the TE of the stab and wing to assure at least ¼” left to lap over to the movable surfaces (see pic). I prepped the surfaces with lacquer thinner followed by Prep-Sol. (The surfaces are all Monokote in this case)
   The tape tends to grab on the movable surface when trying to push it into the gap. To help prevent that, I put a piece of waxed paper on the movable surface, pressed the tape into the gap on the fixed surface side with a credit card (ever wonder how we were able built models in the cash era?), and only then removed the waxed paper and wedged the tape down onto the movable surface side of the gap. That seems to work pretty well for unskilled labor. I did not tape across the hinges on this first attempt. With this “success” under my belt, I’ll do it right on the next two planes I have to do, with the beeswax lip balm on the hinges themselves, but not in the gap. As an aside, it does take 24 hours for acrylic adhesives to “cure”, so taping should be done a day or more in advance of flying.
   I did do the beeswax down in the gap on the first flap segment, but decided it was too risky in terms of reliable adhesion (I had to re-clean around the gap as I smeared a little wax up on the surface). The rest of the segments on that wing and all the rest of the surfaces were done bare.

The “More Than You Wanted To Know” part: My first guess was that the Moore was a thin Taiwan OPP with acrylic adhesive, and was likely a 3M knock-off available under a variety of brand names. Actually, the Moore tape is Scapa 1250 (Swedish, but the 1250 is from the North American division), which is available under that name (and probably some others, although I couldn’t find any others). All of the “Crystal Clear” or “Water Clear” tapes of any caliper are in the acrylic adhesive OPP category (I think).
   On the theory that someone had an equivalent (3M surely has something in every market niche available), I had previously done some searching on the internet, telephone, and physical visits to craft / art / drafting supply / commercial big box sources to no avail.
   After all that, four feet from this computer, in the upper right hand drawer of my big, strong, handsome wife’s computer desk, I found a new roll of ¾” Scotch 3M “Transparent Tape” code 157s. It looked perfect to me. Back to the internet to get specs and compare to the published Moore specs. No luck. 3M seems to have a spec sheet on every tape they make – particularly the ones near our needs – the 600, 605, 610, 810, you name it. Nothing on 157s or a clue as to which “master film” is sliced down and packaged as 157s. A couple of calls to 3M customer service only proved how well-trained the reps are at keeping us riff-raff away from the folks there who actually know and do things. Their story, which I couldn’t get past, was that 157s was a unique product, the specs were proprietary, and that film / adhesive combo was in no other 3M products and was made in no other widths than ¾”. The reps said the 600 tape (2.4 mils) was the nearest equivalent. (I later found the same package advertised in ½” width.) Despite some flim-flam about being an ISO consultant needing written specs, I could not get past 3M customer service.
   Left to my own devices, I did some measuring and calculating. The spec for Scapa 1250 caliper is 1.9 mils. With a .001 mike, measuring that is like using bathroom scales to calculate grams of tip weight. I miked the roll (actual mike of total thickness of tape on the roll vs a check of core OD vs tape OD). Calculating the expected spiral thickness based on Scapa specs, it came out no thicker than advertised. For both the Scotch and the Moore, I used the advertised length as a hard number for the calculations. Reason is, in the consumer product world, the guy with his thumb on the volume knob has the quality / FTC flavored guy twisting his arm one way, and the bean counters twisting the other way, so consumer quantities are pretty reliable in the U. S. across the board – not much over, and no under (at least statistically 95% confidence level).
   I was a little concerned about how the 1.9 mil spec was calculated – compressed, as wound on the roll and as applied; or “fluffy”, as it came off the machine before winding. That could be a big difference – sort of like a 5’ 9” guy with a 4” Mohawk hair cut claiming to be 6’ 1”.
   With a sample size of one on both the Moore / Scapa and the Scotch 157s., the Scotch appears at least as thin, and possibly a little thinner. The actual numbers I got were 1.86 mils for Moore vs 1.77 mils for the Scotch. I wouldn’t bet the farm (with my methodology) the Scotch is thinner, but I can say with some confidence that the 3M is not any thicker (for our purposes) than the Moore. That is, I wouldn’t claim a solid (rounded) two digit accuracy.
   The Moore width was a minor bummer. In the tape world, ¾ is sometimes 19 mm. OK, but the Moore was .698 to .700 (soft edges, you know). That is less than 18 mm!
   I don’t know about adhesion differences, and I don’t know about stiffness differences. That is, thicker is stiffer all else being equal, but I don’t have a Gurley or equivalent tester available; I don’t have a breakdown (on these two specific tapes) as to how much of the spec mils is adhesive and how much is carrier; I don’t really know which one is thinner for sure. I don’t know if stiffness we feel is more dependent on film or adhesive characteristics / thickness anyway.

From the data I have and feeling the tapes I would say they are equally flexible for our purposes.  I am going to try the 3M 157s on the next plane, and will report any issues I find.

Larry Fulwider
« Last Edit: February 12, 2009, 11:06:38 AM by Larry Fulwider »

Offline tom hampshire

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Re: Hinge options
« Reply #13 on: February 13, 2009, 08:46:49 AM »
Hey Larry - I've had some luck with tape seals made by fastening the tape only to the fixed surface.  Start with half inch wide tape, overlength, held to the bench adhesive side up.  Add a second piece of tape about a quarter inch wide face down along one edge, so there is only adhesive showing on half the width of the half inch strip.  Trim to length and apply, leaving the non-adhesive half hanging over the hinge line and the movable surface.  Do both sides of each flap and elevator, and enjoy stiction free seals.  Real world, you can make the strips wholesale by taping two first strips down alongside each other, adding the second strip to both pieces at once, and slitting to finish width.
      One other thing that helps to keep the system free is to change out the hinge pins for straight pins that mike 5 thou or so smaller than the original pins.  Bend the pin alongside the hinge body and insert it in the surface in assembly. Tom H.

Online Larry Renger

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Re: Hinge options
« Reply #14 on: August 16, 2021, 12:31:43 AM »
I use polyspan over/under hinges full length on the surface. No extra seal needed and never a failure, even in an “early” landing. That stuff is tough!

Also, really flexible, the surfaces will deflect under their own weight. On a 1/2 A model!

Try pulling a strip of Polyspan apart against the grain to realize just how strong this stuff is. Your hinges just aren’t ever going to fail.

In addition it is so thin, it pretty much disappears in the finishing process. And I don’t try very hard.

And so far, after years of use, they have never degraded and failed.

What’s not to like? Try it on your next casual model. Then on your next serious competition wonder if you are happy with the result.
Think S.M.A.L.L. y'all and, it's all good, CL, FF and RC!

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 BTW, Dracula Sucks!  A closed mouth gathers no feet!


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