Alternative leading edge material?

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cluttonfred

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In many fabric-covered, strut-braced wing designs, the leading edge wrap is there primarily for aerodynamics. That can even be the case in some cantilever designs like the Ercoupe that don’t use a D-cell spar.

The Volksplanes specify easily-dented sheet aluminum or more resilient but still fragile thin plywood, but this seems like a great application for thin fiberglass sheet or some planstic like acrylic or polycarbonate. I do wonder about varying rates of thermal expansion creating wrinkles, though.

Anyone have any experience with something other than aluminum or plywood in this sort of application?
 

challenger_II

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There is a Russian lightplane that uses fiberglass to sheet the entire wing. I do not see why, if properly engineered, why FG would not work as a leading edge material. The one key would be finding a source of thin, flexible, FG sheet, here in the States.
 

cluttonfred

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Thanks, challenger_II. To be clear, I am not talking about a full covering or using the leading edge as a stressed skin, just to keep the fabric from sagging between the ribs. Here’s an example from the VP-2 plans:

38EBF7F6-AD74-4148-A655-C7EDAE96F728.jpeg
 

Vigilant1

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"Filon" is a sheet material widely used in the RV industry as an external cladding. It is fiberglass reinforced polyester. I believe it is available in a gloss finish, though mostly we see a matt finish. I'm sure it's not as strong as a sheet with an epoxy matrix would be, but it is widely available in sheet form and apparently tough enough for RV use. In .045" thickness it weighs about 8oz psf, so that wouldn't be very light (compared to thin AL or esp thin plywood) but maybe thinner gauge Filon is available. And, if only used for the LE, maybe the weight is acceptable.
 

dog

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Very thin stainless steel,slightly thicker aluminum,aluminum or stainless with fabric atached with adhesive under tension.
Titanium,have seen prices that are no more eye
watering than say fuel or beer.
Do some test articles.
Interested as this subject comes up and the wing on my project would benifit from something other than the beer can stock that is
used normaly.
 

Tiger Tim

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Aluminum leading edges are more resilient when they get a layer of thin cotton batting applied before covering. The little bit of give in the cotton helps prevent dents and the puffiness of it fills in any small dents that do find their way in. Obviously this is for a Cub or something, not a racer or anything that lives out on the edges of the envelope.
 

TFF

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If you use a composite, the decision is needed on if it is just aerodynamic or structural. It’s probably the only substitute over aluminum or ply.

The Ercoupe open D is structural, just not as ridged as a full D. Ply subbed for aluminum on a wood wing gets a free boost in rigidity. If you sub with a composite or anything else, you have to match the character you want or when the wing flexes or it will pop free or break something that has never broken built normal.
 

cluttonfred

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That's something I have never seen. So the cotton is glued to the aluminum and then the fabric glued to the cotton? And what exactly counts as "batting" in this context? I am very curious.

Aluminum leading edges are more resilient when they get a layer of thin cotton batting applied before covering. The little bit of give in the cotton helps prevent dents and the puffiness of it fills in any small dents that do find their way in. Obviously this is for a Cub or something, not a racer or anything that lives out on the edges of the envelope.
You're right, of course, I think we have discussed before that the Ercoupe leading edge does provide more an aerodynamic fairing. That last point is what I was getting at when I mentioned thermal expansion but I should have included any unintended consequences of changing the material.

If you use a composite, the decision is needed on if it is just aerodynamic or structural. It’s probably the only substitute over aluminum or ply.

The Ercoupe open D is structural, just not as ridged as a full D. Ply subbed for aluminum on a wood wing gets a free boost in rigidity. If you sub with a composite or anything else, you have to match the character you want or when the wing flexes or it will pop free or break something that has never broken built normal.
 

BBerson

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the leading edge wrap is there primarily for aerodynamics.
I think it is strictly for looks. The aerodynamics are not much different from fabric alone unless you seek laminar flow and that requires rigid skin. I would like a light plastic skin for looks that doesn't dent. Plastic weighs about half of aluminum so could replace .016" aluminum with .032" plastic for the same weight. May only need .020" or even .010" plastic and reduce weight. I don't know yet. Might need to heat mold the plastic to prevent springback bulge.
 

mcrae0104

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Hey, don't bash Saturn, I really liked ours, bought a used one at the dealer in late 1999 or early 2000 and it served us well, only sold it because we moved overseas. ;-)
I liked mine too. Pretty good transportation appliance (esp. w/ a 5-speed). No bashing intended. But, as we've established, they can take a bashing if they have to. :)
 

Steve Gawler

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In many fabric-covered, strut-braced wing designs, the leading edge wrap is there primarily for aerodynamics. That can even be the case in some cantilever designs like the Ercoupe that don’t use a D-cell spar.

The Volksplanes specify easily-dented sheet aluminum or more resilient but still fragile thin plywood, but this seems like a great application for thin fiberglass sheet or some planstic like acrylic or polycarbonate. I do wonder about varying rates of thermal expansion creating wrinkles, though.

Anyone have any experience with something other than aluminum or plywood in this sort of application?
 

Steve Gawler

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I have wondered about this. Legal Eagle builders report challenges with scarfing or otherwise joining the thin leading edge pieces and having the piece holding its shape. Why not use the thinnest ply that will form the shape, glue it to the wing per plans, cover the entire leading edge with lightweight cloth and epoxy, SuperFill any low spots then add at least one more layer of cloth. You’d have to experiment to determine the number of plys required but it would be at least as strong as nailed on aluminum sheet, such as on the Boredom Fighter, which is only there for aerodynamic reasons. The Legal Eagle might not be the best example because of weight concerns, but many other designs would be I think.
 

Richard Roller

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That's something I have never seen. So the cotton is glued to the aluminum and then the fabric glued to the cotton? And what exactly counts as "batting" in this context? I am very curious.



You're right, of course, I think we have discussed before that the Ercoupe leading edge does provide more an aerodynamic fairing. That last point is what I was getting at when I mentioned thermal expansion but I should have included any unintended consequences of changing the material.
N34KP, a Pietenpol, has had polyester batting between the leading edge fabric and the 1/16" plywood for 21 years now. It works well, no obvious dents. The batting gives a little. I was tech councilor on a Hatz project 25 years ago where the builder used fiberglass for the leading edge wrap. He glued sheet foam between the ribs, not full depth, hot wire cut to shape and layed the glass over the top, spar to spar. I remember thinking he went a little overboard with the amount of glass/resin, but as far as I know it's worked well all these years.
 

Richard Roller

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Very thin stainless steel,slightly thicker aluminum,aluminum or stainless with fabric atached with adhesive under tension.
Titanium,have seen prices that are no more eye
watering than say fuel or beer.
Do some test articles.
Interested as this subject comes up and the wing on my project would benifit from something other than the beer can stock that is
used normaly.
Very thin stainless, titanium and aluminum all have the same problem, dents.
 

Hot Wings

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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.
 

TFF

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It’s all case by case. Effort to implement is really a bigger importance if an option, because that seems to be why you would not do it as prescribed. First assume a wood wing.

Easiest, aluminum. The aluminum is easy to work. You get your little cobbler hammer and smash little AN nails in. Follow around the ribs a row at a time until finished. Monotonous, but hardly skillful. The thin aluminum requires no effort to bend.

Ply probably the most wrestling, probably with the best the benefits. Dry bend, wet bend or prebend? Wrestling on the wing or in a mold? Do you have enough straps and weights to do the job? The wing will be very happy though. Not really that big a deal.

Composite. Everything except the aluminum is composite. Ply is composite. Papier-mâché, composite. Plastic, ok might be argued either way. Off the bat, you have to make a mold; a relatively nice mold. That’s the money shot. Once it’s done, it would be relatively easy to put on. A short stiff wing, like a biplane, probably no issues. Any wing that flexes a lot, requires thought.

Easy in this instance is not having to be creative. Just do. Plug in a temp worker kind of work.
Hard would be having to be creative in the moment. Nothing here is full artistic, but if something is not laying down like you want, you have to solve it fast with something at hand. Cant go to the store with epoxy curing.
 
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