Alternative leading edge material?

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karmarepair

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Some possible LE materials, comparing the elastic modulus (stiffness) and density:


Modulus, MPaDensity, gm/cm^3
Polypropylene1325.92
Polystyrene32501.05
Acrylic (plexiglass)28551.185
Aluminum690002.70
Wood12000 - 16000 depending on species.5 - 1.1

Me, I think I'd try the Polystyrene first. Cessna wingtips since Jesus was a Airman Recruit. You MIGHT have to heat form it, which would be a PITA, since the temperature difference between Formable and A Sagging Mess is about Not Much. Better if you can find it thin enough so it bends as easily, and probably in the elastic range, as .016 aluminum.

I also thought of laying up fiberglass or carbon on a sheet of glass, then wrapping it while it's still "green", then post curing, but that sounds like a lot of bother.

And the leading edge cover needs to be stiff enough to hold the shape, but not so stiff that it tries to take the primary bending loads, unless it's DESIGNED to take the primary bending loads as a D-Cell spar....
 

cluttonfred

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This thread seems to have opened up the proverbial can of worms!

I agree with the idea that nailed-on aluminum as per the VP-2 plans (which also give a 1/16” plywood option) is the easiest to do, the toughest part is carefully locating and perhaps predrilling the holes with a tiny bit so the nails don’t split the ribs. I am intrigued by the batting solution to reduce or hide dents.

After that the plywood seems like a good option. I could see skipping the scarf joints in this non-load-bearing application and just butting the sections together over a rib, perhaps with a little epoxy and a single thin strip of fiberglass to reinforce the joint.
 

Bill-Higdon

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This thread seems to have opened up the proverbial can of worms!

I agree with the idea that nailed-on aluminum as per the VP-2 plans (which also give a 1/16” plywood option) is the easiest to do, the toughest part is carefully locating and perhaps predrilling the holes with a tiny bit so the nails don’t split the ribs. I am intrigued by the batting solution to reduce or hide dents.

After that the plywood seems like a good option. I could see skipping the scarf joints in this non-load-bearing application and just butting the sections together over a rib, perhaps with a little epoxy and a single thin strip of fiberglass to reinforce the joint.
Or make the rib under the joint under size enough to take a strip of plywood to meet the proper regulatory guidance.
 

cluttonfred

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Thanks for that, very helpful, here's the one where he starts putting the plywood leading edges on the wing.

One question I have is that on something like the VP-2 the leading edge wrap does not end on the spar, it's unsupported between the ribs. The plans say to put a crimp in edge of the aluminum wrap between the ribs for rigidity. Would 1/16" plywood need any additional support and, if so, how would you do that?


Makes it look doable.
 
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Bille Floyd

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In many fabric-covered, strut-braced wing designs, the leading edge wrap is there primarily for aerodynamics.
...
Anyone have any experience with something other than aluminum or plywood in this sort of application?
Lifted a set of D-tubes, made from 3mm Nomex honeycomb, and Kevlar
that did not need to carry any twisting load ; could pick up both, with
one hand, and the arm extended out straight. They were for a 40' span
hang glider.

I beat the weight of those kevlar D-tubes, with samples that were made with
1/4-oz carbon mat, which gave much better peel-shear from off the 3mm Nomex
and (1) 3K tow, +/- 45, of Carbon each lnch, and a 1/4-oz Kevlar mat on the outside
to help carry the puncture resistance between the 1/8" nomex cell, (it was Really light).

Need to build for a twisting moment ? Add more 3K carbon towes , to the same matrix.

Bille
 
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n45bm

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Another off the wall idea:
Cardboard - of the single sided variety.
Dip in thin West System, drain, drape over form (smooth side out), let cure.
Something similar was tried by Molt Taylor. He talked about fiberglass reinforced cardboard, I think.
 

Aesquire

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A mylar or foam or??? sheet is often inserted in a "pocket" ( actually double layer of fabric sewn on 3 edges ) to stiffen the upper leading edge of hang glider wings, just to smooth out the sag between ribs. The mylar is a bit prone to fold creases, so my old Duck used a foam sheet. Current high performance gliders use a combination of heavier material and multiple layers often with multiple materials all sewn together.

Keep in mind the leading edge upper reinforcement is not all that rigid, it has to roll up when you fold up the glider, but the conical curvature ( on a tapered wing a long trapezoid ) adds remarkable stiffness in the other direction.

One of the problems with composites in thin wall applications is the material strength of the fibers, Kevlar, or cardboard, isn't a lot of help in dents/breaks at right angles to the surface, that becomes more a matter of resin properties.
 

Hot Wings

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Something similar was tried by Molt Taylor. He talked about fiberglass reinforced cardboard, I think.
That would be TPG.
_______________________
UUUUUUUUUUUUUU This kind of single sided cardboard has much greater "I" (stiffer) than 90# liner board but can still be bent easily in one plane. It - might - be less dent prone than the typical aluminum LE material?
 

Richard Roller

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Thanks for that, very helpful, here's the one where he starts putting the plywood leading edges on the wing.

One question I have is that on something like the VP-2 the leading edge wrap does not end on the spar, it's unsupported between the ribs. The plans say to put a crimp in edge of the aluminum wrap between the ribs for rigidity. Would 1/16" plywood need any additional support and, if so, how would you do that?

What is the rib spacing on your a/c project? The Piet I fly is about 11". There is little sag between ribs caused by the fabric shrinkage, very minor. I'm not familiar with the mini-max, I was surprised at the large rib spacing.
 

cluttonfred

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VP-2 wing ribs are spaced 8-12"" on center with most at 10".

What is the rib spacing on your a/c project? The Piet I fly is about 11". There is little sag between ribs caused by the fabric shrinkage, very minor. I'm not familiar with the mini-max, I was surprised at the large rib spacing.
 

TFF

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With something like a MiniMax, every ounce might put it over. You are building bare minimum. A Piet is a much sturdier airplane.
 

starrtit

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Hot Wings has a VERY valid point regarding cardboard. I am reminded of the great advances that have been made to this simple medium every time I open a new case of beer. It also brings to mind the designer [name slips my mind] with a pusher who advocated very thin
F/glass to cardboard as an excellent material.
 

Hot Wings

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brings to mind the designer [name slips my mind] with a pusher who advocated very thin
F/glass to cardboard as an excellent material.
Thinking of the Taylor Micro Imp?

Cardboard for aircraft construction is, IMHO, kind of in the same situation as electric power. It can work in some limitited applications but still needs a lot of innovation/discovery before it can be really viable.
 

TFF

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The issue with cardboard is lifespan and it’s heavy if protected from elements. I have built cardboard RC planes and they can be fun. If you varnish the cardboard for protection, you have two glues; one glue holding the fibers together and then a second to protect. Double of something you want one of. Waterproof cardboard that is not waxy or glossy that you can cover with airplane covering. It can’t be able to absorb water. Wash, rain, or humidity. Cant rot or mold easily. Starting to ask for a miracle material. It would be well known if it was out there.
 

mcrae0104

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If we're considering "disposable" materials, why not get all Sripol on it with foam & aluminum tape? Not very tough, but cheap and easily repaired.
 
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