Fiberglass tape hinge

Will fiberglass tape resist stretching when used as a hinge?

I have a flop wing glider and the hinge would be under a lot of stress when the wings deploy. I've tried mylar, blenderm, and even duct tape (because the adhesive is so strong). They all tend to stretch due to the force of the wings opening, so that the wing joint gets wider and wider. (The glider is a diagonal flop wing, so strong elastic is required to pull the wings open at ejection).

You could try CA hinge material. I hate epoxied fiberglass hinges as they seem to be very brittle (maybe I don't know some secret about how to make them.)

A hinge that has to work over 180 degrees is a really stressing case, of course. Maybe Monokote would work?

Yeah, that's a lot of stress. Is there sufficient thickness for a Klett type hinge? If not, could you attach it to the surface?

mikec said:

You could try CA hinge material. I hate epoxied fiberglass hinges as they seem to be very brittle (maybe I don't know some secret about how to make them.)

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Is it the one that Great Planes carries? Are they like Dubro hinges or is it a flat piece of flexible plastic that can bend backward on itself 180°? I can't tell from the drawings on the website. (Dubro hinges can't bend 180°so I couldn't use them in my situation).

mbeels said:

Yeah, that's a lot of stress. Is there sufficient thickness for a Klett type hinge? If not, could you attach it to the surface?

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Unfortunately not, as the wing folds backward on itself 180°. That's why I was forced to try flat tape-type material (which didn't work out very well).

Rktman said:

Is it the one that Great Planes carries?

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I was thinking of https://www.greatplanes.com/accys/gpmq3950.php but that was before I realized you needed 180 degrees of travel. I'm not sure if a nylon hinge, mounted on the surface, would have 180 degrees of travel.

All the flop wing plans I found used tape hinges, but they were scissor flop designs that just flop the tips out, so they probably don't load the hinges as much as your design does.

I have no good answer...

Have you tried a double tape hinge with gorilla duct tape sewn in with dental floss soaked in thin CA?

This will NOT stretch or deform. Your balsa will break before this fails. Your tape pieces will only need to be 3 CM long and the width of the wing

Gorilla duct tape also comes in white, which makes it look a little bit classier in my opinion for whatever that's worth

i haven't tried this but at one of the last couple of NARAMs I heard about people using Tyvek material from those ultra strong/thin mailer envelopes. Dental floss stitching is a good idea because acrylic adhesives (i.e. pretty much all normal pressure sensitive tape adhesive) will flow under stress.

BABAR said:

Have you tried a double tape hinge with gorilla duct tape sewn in with dental floss soaked in thin CA?

This will NOT stretch or deform. Your balsa will break before this fails. Your tape pieces will only need to be 3 CM long and the width of the wing

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My latest iteration uses duct tape but after seeing how it tends to stretch and open up the joint, I may have to resort to sewing the hinges as well. I was just concerned that getting the thread tight enough to close the hinge gap might hinder the opening of the wings at deployment?

caveduck said:

i haven't tried this but at one of the last couple of NARAMs I heard about people using Tyvek material from those ultra strong/thin mailer envelopes. Dental floss stitching is a good idea because acrylic adhesives (i.e. pretty much all normal pressure sensitive tape adhesive) will flow under stress.

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If tyvek doesn't stretch, then I'm strongly considering using it or maybe carbon fiber weave and adhering them with epoxy. That would solve the other problem of tape adhesives failing under stress.

https://www.rocketryforum.com/threads/build-thread-for-whopper-flopper-chopper.28887/

See posts 3-5

The floss, when placed directly through the hinge, does not restrict movement at all.

You do need to use good quality duct tape, a lot of stuff out there now, especially the bright colored stuff, is wimpy

Try it on some scrap balsa

BABAR said:

https://www.rocketryforum.com/threads/build-thread-for-whopper-flopper-chopper.28887/

See posts 3-5

The floss, when placed directly through the hinge, does not restrict movement at all.

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Thanks, those pics really help!

BABAR said:

Try it on some scrap balsa

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Really good idea.
I've tried stitching in Heliroc blades to their Dubro hinges to ensure they don't come off and it was easier than I thought it would be, but I haven't tried using it as part of the hinging mechanism itself. The glider may not be all that "aesthetically pleasing" to look at afterwards, but if it does the job I'm all for it.

Having the tape on BOTH sides prevents the floss from cutting through the balsa. Wicking the floss (regular thread would probably work, but floss comes with a cutter, makes it quick to grab a piece) with thin CA keeps the thread tight.

The whopper flopper chopper was my first heavy duty use of a tape hinge.

For weight savings, you probably can get by with two smaller hinges, one on each edge, rather than a contiguous edge to edge hinge.

BABAR said:

The whopper flopper chopper was my first heavy duty use of a tape hinge.

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I love that name, and the rocket. What a sight it would be to see fly.

I'm (a little) surprised no one has mentioned this possibility: cotton. For the material forming the hinge that has to fold 180° and not stretch, consider using canvas or some such, attached by any of the means above. It's liable to end up a bit unsightly, but it'll damn well work.

jqavins said:

I'm (a little) surprised no one has mentioned this possibility: cotton. For the material forming the hinge that has to fold 180° and not stretch, consider using canvas or some such, attached by any of the means above. It's liable to end up a bit unsightly, but it'll damn well work.

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My situation requires a hinge material that won't stretch. Unfortunately cotton does. (Remember old style denim jeans? They'd stretch out and get baggy after wearing them just a couple of times).

How about Kevlar?

Rktman said:

My situation requires a hinge material that won't stretch. Unfortunately cotton does. (Remember old style denim jeans? They'd stretch out and get baggy after wearing them just a couple of times).

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Felix-Hoenikker said:

How about Kevlar?

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Been doing some research and it appears the other materials under consideration do stretch, at least to some degree, but the kevlar doesn't. I ordered some 1" kevlar tape and will experiment with using epoxy as an adhesive, as CA will make the kevlar weave rigid and inflexible if it wicks across the area that needs to bend. I'm also considering the earlier suggestion of also sewing in the hinge material.

Cuben ( dyneema-reinforced mylar IIRC ) ?

did you try the sewn in double tape hinge with gorilla duct tape? I'd be surprised if that stretches much, if at all.

dhbarr said:

Cuben ( dyneema-reinforced mylar IIRC ) ?

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Really interesting stuff, very stretch resistant, which is a major plus. I'd think it wouldn't have a problem bonding with an epoxy adhesive either. Only problem is it only seems to be available in large tent-sized sheets, and all I really need are a couple of 1" x 3" strips of it.

BABAR said:

did you try the sewn in double tape hinge with gorilla duct tape? I'd be surprised if that stretches much, if at all.

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I meant to ask you about that. I tried it on some scrap today, and putting another strip of tape on the opposite side of the fold prevents the wing from folding all the way backward. The only way around that is to leave a space between the wing portion that folds and the portion that doesn't to allow enough "slack" in the tape to bend. But doing that allows the folding part to hyperextend beyond the 180° it's supposed to and the glider then won't fly (which is the problem I've been having). Putting in thin music wire stops didn't work too well either. The force of the wings opening eventually caused the wires to pop off even though I CAd them in. I had to stich the wire in and glop a lot of thick CA over it, but it tends to leave dents in the balsa that get deeper each time.

Rktman said:

Really interesting stuff, very stretch resistant, which is a major plus. I'd think it wouldn't have a problem bonding with an epoxy adhesive either. Only problem is it only seems to be available in large tent-sized sheets, and all I really need are a couple of 1" x 3" strips of it.

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ripstop by the roll will sell you a sample swatch, I almost guarantee.

Rktman said:

The force of the wings opening eventually caused the wires to pop off even though I CAd them in.

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It sounds like you were laying the wire on the balsa and gluing it there. If I've read it right, that means the glue joint is loaded in shear. In a shear joint like that, CA is just about the worst choice of glue. Also, any glue is likely to fail at holding a piece of music wire there, because there's so little contact area, so CA is doubly damned.

What you might try if you want to attach piano wire in that position is 1) bend a small loop in each end of the piece of wire. I realize that's easier said than done since the wire wants to spring back; it's not impossible. Then 2) use epoxy* to attach it. With any luck, the epoxy will key into the loops, giving you a compression loading. I can't guarantee it'll work; I'm brainstorming.

* While this is not a sheer load, where CA is at its worst, it's still not that great. In tension it shines, but otherwise it's just not "all that". I only use CA myself for temporary holding, like fin roots, before I can apply something better, like wood glue or epoxy fillets. I might use it for low stress joints if they're mainly in tension. And I use it for temporary hold that I want to be able to break apart.

Shouldn't roughing the loops of the flats also help?