Watertight Hinge Cavities

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Watertight Hinge Cavities

Postby SheepdogRD » Sun Apr 06, 2014 8:36 pm

There was a thread in 2012 called "Watertight Hinge Cavities" (http://www.wingsforum.com/viewtopic.php?f=218&t=21984). I decided to take a run at sealing those flap and aileron openings, too. After a couple of failed methods, I found a system that works well and adds very little weight.

I put some parchment paper on the worktable and laid up two layers of fiberglass fabric and resin. A couple of hours later I had a 16” x 20” sheet of flat material. I cut strips of it (with scissors) to fit the bottoms of the openings, with slits cut so they fit around the hinges.

There were some openings where the nose rib was positioned too far from the slot, or there wasn’t a nose rib at all. For these, I cut fiberglass nose rib shapes from the sheet and trimmed them so they just fit inside the leading edge. Using the kit’s packing foam, I cut nearly-weightless spacers that held the pieces in place. There were still a few gaps, and I filled the larger ones with bits of glass fiber, and the smaller ones with bits of packing foam. Once I had several openings fitted, I mixed up a small batch of resin and bonded the pieces into the openings. After the next batch was done, I went back and checked for gaps and re-coated.

I tried to keep things smooth enough that they wouldn't be too hard to rough up for paint. Here are examples, shown after the second coat of resin, but before any sanding. The fabric plates look odd because I’d already zinc chromated them before deciding to seal the openings.
Hinge Seals 1s.jpg
Hinge Seals 3s.jpg

I’m a newbie at working with fiberglass, but this wasn't too hard to figure out. All the seals are strong and the openings are watertight.

One thing to note: positioning the seals is pretty easy on the flaps. But, on the ailerons, if the seals aren't low enough, they interfere with the full motion of the control surfaces. It’s particularly critical on the ends. When I went back for a fit check on the wings, I found that three of the six aileron seals (including the one in the first picture) were too high, and the ailerons were limited to 20 degrees up travel. Oops. I had to cut the offending seals out and place new strips, making sure they were as low as possible. Space is pretty tight in there, and a fit check is a good idea before adding resin.

The one good thing that came of that mistake was knowing the seals are in there solidly. I had to use a vibratory multi-tool to saw the mistakes out.

The fiberglass sheet is surprisingly light, and it doesn't take much resin to seal everything up. Seems like having dry flaps and ailerons is well worth the few ounces added.

By the way, these control surfaces still need drain holes so they don't turn into balloons in the sun.

If I were starting the control surfaces anew, I’d make some changes:
(1) I'd be a lot more careful about cutting the slots in the leading edge. A couple of them were crooked, and they were tough to straighten out.
(2) I’d put a fiberglass cap on the sides of each hinge slot to go with the fiberglass strip on the bottom, and then I’d resin-coat the entire slot. That would make each leading edge a single waterproof piece.
(3) I’d make a smaller sheet of two-layer fiberglass; I used less than half of what I made.
(4) I’d make some three-layer fiberglass and use it for at least some of the fabric plates, too. It’s lighter than the aluminum, easier to shape, and could just be bonded in place.
Richard Holtz
Highlander N570L -- Ms. Tonka -- in gestation

If just enough is really good, then too much ought to be perfect.
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SheepdogRD
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Re: Watertight Hinge Cavities

Postby CanadianSheepHunter » Tue Nov 05, 2019 1:54 am

When you say you would "make some three layer fibreglass and use it for at least some of the fabric plates"...which plates are you referring to?
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Re: Watertight Hinge Cavities

Postby SheepdogRD » Tue Nov 05, 2019 7:55 pm

CanadianSheepHunter wrote:When you say you would "make some three layer fibreglass and use it for at least some of the fabric plates"...which plates are you referring to?

Fabric plates are aluminum plates in the Highlander kit that provide a place to adhere fabric around some feature in the wing -- like where the pulleys come through. I don't know if fabric plates are required on the SS wing.
Richard Holtz
Highlander N570L -- Ms. Tonka -- in gestation

If just enough is really good, then too much ought to be perfect.
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Re: Watertight Hinge Cavities

Postby CanadianSheepHunter » Tue Nov 05, 2019 10:38 pm

Ok, thanks
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