# Substituting wing fabric with plywood

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##### Well-Known Member
Multiple cross lamination layer will act like plywood. Plywood is fabricated same way, grains of wood is at angle on each other in a different layers and that make plywood hard to do 3D shape, same effect for multiple layer of glass, if laminated like that.

F

#### fly scared!

Sorry, I have no experience bending cured glass. I presumed you wanted to position it just before the last bond.
If the glass is fully cured than I guess it would support itself like plywood, as you say (isn't the epoxy too fragile to be bended that way ?)

##### Well-Known Member
If the glass is fully cured than I guess it would support itself like plywood, as you say (isn't the epoxy too fragile to be bended that way ?)
There is lot of glass fiber landing gear for example, so that bending glass is not problem, more like bonding it.

F

#### fly scared!

...more like bonding it.
Yes, especially if you need to bond the skin to some old wood surface...
So something like this would do, instead of plywood ? http://www.online-shop.carbon-composite.com/index.php?cat=KAT11-10161&lang=ENG&product=06310.1

The panels should be joined with a strong, elastic tape, possibly with some slack in the gap (or even with ordinary tape? this looks like a good one 3M Industrial Products Catalog: adhesives, tapes, abrasives and more:*3M)

( small OT: I've read good results have been achieved with epoxy bonding using some "surface re-activators" agents (n-HMR based), but I could not find any commercial product / source)

#### TFF

##### Well-Known Member
You need to build a Wittman Tailwind or at least study the plans. There is a Yahoo group with lots of construction pictures. There is also the Hiperbipe Yahoo group, which is like a biplane Tailwind; it has some pictures too. It was a kit only.

#### Dan Thomas

##### Well-Known Member
Do you think that would apply also to a plywood skin covered with some glass ? I've had bad experiences with boats built this way, but I guess a clean hangar is a very different environment...
Glass adds a LOT of weight. The glass fabric is heavy and the resins add even more weight. It's fine for plywood boats and amphibian hulls, but not for the rest of it.

Get some Poly-Fiber materials and their instruction manual. Make some simple wooden frames, and cover them with fabric and finishes using the instructions. It all becomes quite clear once you tackle it.

Dan

F

#### fly scared!

You need to build a Wittman Tailwind or at least study the plans. There is a Yahoo group with lots of construction pictures. There is also the Hiperbipe Yahoo group, which is like a biplane Tailwind; it has some pictures too. It was a kit only.
Yes, the Tailwind is a very interesting design, but its wing was designed in plywood from the start.
Even if braced, the skin will probably be loaded the way the designer intended (including compression).
I would like to mimic the fabric working, that is resist to pression (/depression) and traction only.

F

#### fly scared!

Glass adds a LOT of weight. The glass fabric is heavy and the resins add even more weight. It's fine for plywood boats and amphibian hulls, but not for the rest of it.

Dan
Yes, as 4trade said, it would probably be better to use a composite from the start, rather then adding glass to plywood just for weather protection

#### DangerZone

##### Well-Known Member
HBA Supporter
Glass adds a LOT of weight. The glass fabric is heavy and the resins add even more weight. It's fine for plywood boats and amphibian hulls, but not for the rest of it.

Dan
It's true that glass is heavy but it's interesting whether an airfoil made of styrofoam and covered with glass like the KR2S would be heavier than a wing made of plywood cover with dacron..? The glass wing COULD be lighter (if properly built of course) than the airfoil covered with plywood and dacron if plywood is 2.5mm or thicker, it's simple math. A 200g/m2 glass with epoxy and resin is quite lighter than a m2 (meters square) of 3mm plywood covered with dacron. The core of the glass wing could be styrofoam and the plywood has to have wooden ribs, another weight saving for the glass type of wing. There was also an old video by Burt Rutan where he demonstrated that the glass airfoil would be stronger, lighter and even more flexible than the wooden wing.

In my opinion it would be possible to substitute the styrofoam and glass wing of the KR2S with wooden spars, plywood to cover the airfoil and dacron on top to hold the structure. Yet it would take at least twice more time to produce such a wing because the small wooden parts have to be glued together and left to dry. Then, the wing would be heavier by quite a bit meaning that would also contribute to the structural strength. Then, the wing would be weaker and less flexible, meaning lighter G-loads possible with the airplane. The good side is the wing materials would be cheaper but that cost difference would be lost due to more work hours needed to produce the wooden wing.

So it is a good question why would anybody want to do such a thing, lack of composite materials nearby or something, maybe an allergy to epoxy/resin, could be various reasons..? If a wooden airframe composite airplane is in question I'd recommend the glass over plywood for structural element and styrofoam over a wooden wingspar, it would also last longer and be more resistant to humidity.

#### TFF

##### Well-Known Member
Tailwind wing skin sizes are 1/16 for 45deg and 3/32 for 90 deg ply. Builders choice.

#### djschwartz

##### Well-Known Member
PROPERLY DESIGNED wood, aluminum, and fiberglass aircraft structures all end up essentially the same weight for the same overall capabilities. The choice between them is based on other characteristics including things like builder fabrication preferences and expected component production volumes, among many others. Some designs will lend themselves more to one construction method than the other. The same can be said for fabric covering vs. solid sheeting. As an example, despite all the urban legends to the contrary, the fabric winged and metal winged Luscombe 8's weigh almost exactly the same if equipped the same. Graphite will result in a lighter structure but at a significant cost, and only if a knowledgable design job and proper part manufacturing are done to take full advantage of its characteristics.

"Converting" a design from one construction method to another will almost always result in a sub optimal outcome. Unless of course, the conversion means keeping only the general layout and a few design details amenable to the new method; and then, designing everything else from scratch with the new material.

#### Dan Thomas

##### Well-Known Member
In my opinion it would be possible to substitute the styrofoam and glass wing of the KR2S with wooden spars, plywood to cover the airfoil and dacron on top to hold the structure. Yet it would take at least twice more time to produce such a wing because the small wooden parts have to be glued together and left to dry. Then, the wing would be heavier by quite a bit meaning that would also contribute to the structural strength. Then, the wing would be weaker and less flexible, meaning lighter G-loads possible with the airplane. The good side is the wing materials would be cheaper but that cost difference would be lost due to more work hours needed to produce the wooden wing.

So it is a good question why would anybody want to do such a thing, lack of composite materials nearby or something, maybe an allergy to epoxy/resin, could be various reasons..?
The KR series started when Ken Rand took the plans for the Taylor Monoplane and started using some model airplane methods, like foam covered with fabric impregnated with epoxy. The Taylor's wing had built-up wooden spars and built-up wooden ribs, and the leading edge and inboard areas aft of the spar were sheeted in plywood. The whole thing was fabric covered. It could have been entirely sheeted with ply but would have been heavier, and the weather resistance wouldn't be very good.

Taking the KR-2 and making the wing of traditional built-up wooden construction would just be taking it back to its roots. Nothing new there at all except that the build time goes way up.

Wooden-sheeted wings that are the same weight as fabric-covered wings probably use lighter wing rib stock. The ply glued to the ribs adds strength beyond the rib's original strength, so it can be made lighter. There's no point making stuff stronger than it needs to be, especially where weight is concerned.

Dan

#### rabel

While I agree basically with everything that's been said, I am in the process of building an UL that uses fiberglass instead of fabric. The fiberglass is also providing structural support in certain key areas. In fact, to hair-lip the Pope, I am also using plywood/glass in a sandwich configuration instead of foam/glass. The thing is, the aircraft is being engineered in this fashion from the ground up. Also, I will have constructed the rough equivalent of four airplanes just to get one because of my insistance upon testing components to failure both as an individual piece and as a part of the larger structure! Unless you are prepared to do the same, then changing one building technique for another is a sure receipe for disaster - plus, it is rarely, if ever, cheaper, better, or ??? I wont say all, but most of the people on here are more concerned w/ your safety than anything else including an airplane that flies! Please dont take offense of their criticisms, but they have a LOT of combined experience,..and they are going to err on the side of caution each and every time! If you want to try something out,...try it,..but test it, re-test it,...and then test it again! ...just my $1.50 F #### fly scared! I wont say all, but most of the people on here are more concerned w/ your safety than anything else including an airplane that flies! Please dont take offense of their criticisms, but they have a LOT of combined experience,..and they are going to err on the side of caution each and every time! I know. But you can't stop any discussion just because "the right way is this". With an approach like this nobody would need this forum, just build by the book. But "the book" was written for some good reasons: I find interesting to understand the book, not just follow it. #### DangerZone ##### Well-Known Member HBA Supporter The KR series started when Ken Rand took the plans for the Taylor Monoplane and started using some model airplane methods, like foam covered with fabric impregnated with epoxy. The Taylor's wing had built-up wooden spars and built-up wooden ribs, and the leading edge and inboard areas aft of the spar were sheeted in plywood. The whole thing was fabric covered. It could have been entirely sheeted with ply but would have been heavier, and the weather resistance wouldn't be very good. Taking the KR-2 and making the wing of traditional built-up wooden construction would just be taking it back to its roots. Nothing new there at all except that the build time goes way up. Wooden-sheeted wings that are the same weight as fabric-covered wings probably use lighter wing rib stock. The ply glued to the ribs adds strength beyond the rib's original strength, so it can be made lighter. There's no point making stuff stronger than it needs to be, especially where weight is concerned. Dan Would there be any advantage to take a design 'back to it's roots'..? If someone successfully converted a ply glued and fabric covered airplane and made it of spruce and foam covered with glass and epoxy would it not be lighter, stronger, more resistant to age, humidity and heat? They are both basically wooden frame aircraft yet the advantages of the composite aircraft seem to point in the right direction. I analyzed a conversion of a well designed wooden airplane to a composite construction. Instead of glued spruce ribs covered with birch/Okumé plywood and Dacron, some parts of the plane (wings, tail and stabilizers) were made of foam and epoxied with glass. The plane was slightly lighter yet much stronger, it was a difference of around 10kg for a plane that weights 275kg. I've seen the Taylor Monoplane and had no idea that it inspired Ken Rand for the KR1 which seemed quite original for that time. How many other similar successful conversions of wooden airplanes to composite are there..? #### Kristoffon ##### Well-Known Member If someone successfully converted a ply glued and fabric covered airplane and made it of spruce and foam covered with glass and epoxy would it not be lighter, stronger, more resistant to age, humidity and heat? I suspect if that were actually all true people would be doing that wholesale. Glasair SII: 1325lbs empty / 2200 lbs gross, 180 hp, 238 mph cruise GP-4: 1260lbs empty / 2000 lbs gross, 200 hp, 240 mph cruise Both retractable gear, +6/-4G. The empty wooden aircraft is 65lbs lighter. Fun fact: the oldest airworthy aircraft is a 1909 Bleriot, wooden. IMHO we see so many glass aircraft today because manufacturers love selling kits (much more profitable than plan sets) and you can't really produce wooden kits on a large scale nearly as cheap as fiberglass. 4000 hour build logs for Cozy MK IVs would suggest it's not that quicker either when building without pre-molded parts. #### djschwartz ##### Well-Known Member ...Taylor Monoplane and had no idea that it inspired Ken Rand for the KR1. How many other similar successful conversions of wooden airplanes to composite are there..? "Inspired" is NOT the same as "converted". #### DangerZone ##### Well-Known Member HBA Supporter I suspect if that were actually all true people would be doing that wholesale. Glasair SII: 1325lbs empty / 2200 lbs gross, 180 hp, 238 mph cruise GP-4: 1260lbs empty / 2000 lbs gross, 200 hp, 240 mph cruise Both retractable gear, +6/-4G. The empty wooden aircraft is 65lbs lighter. Fun fact: the oldest airworthy aircraft is a 1909 Bleriot, wooden. IMHO we see so many glass aircraft today because manufacturers love selling kits (much more profitable than plan sets) and you can't really produce wooden kits on a large scale nearly as cheap as fiberglass. 4000 hour build logs for Cozy MK IVs would suggest it's not that quicker either when building without pre-molded parts. Airplanes don't have to be made exclusively of only wood or only glass. The KR2 that we talked about is a good combination of a wooden airframe and foam/glass wings&tail, a wooden composite. And it takes lass than half of the 4000 hours for the Cozy. "Inspired" is NOT the same as "converted". Indeed. So if you know of both successfully inspired or converted airplanes feel free to provide more details. #### djschwartz ##### Well-Known Member BTW, the KR1 and 2 did not have foam/glass wings. As originally designed they had a wood structure consisting of main and rear spars and widely spaced ribs. The volume between the ribs was filled with low density foam to give the wing shape. The foam was sanded to shape using the ribs and spars as templates. The wing was then skinned with Dynel fabric (a form of dacron) and polyester resin. Later builders did switch to fiberglass for the skins because the Dynel/polyester method, while cheap, produced a poor quality structure. I cannot speak to later changes that may have been made. I have not paid much attention to this design for many years. #### DangerZone ##### Well-Known Member HBA Supporter BTW, the KR1 and 2 did not have foam/glass wings. As originally designed they had a wood structure consisting of main and rear spars and widely spaced ribs. The volume between the ribs was filled with low density foam to give the wing shape. The foam was sanded to shape using the ribs and spars as templates. The wing was then skinned with Dynel fabric (a form of dacron) and polyester resin. Later builders did switch to fiberglass for the skins because the Dynel/polyester method, while cheap, produced a poor quality structure. I cannot speak to later changes that may have been made. I have not paid much attention to this design for many years. True, there were various methods until people switched to fiberglass but the wooden airframe still remains spruce and most of the fuselage is made of plywood. And thank you for pointing it out, it took some time for people to realize that converting to fiberglass and foam improved the KR2 structure and quality, even though the price of materials is slightly higher. There's another thing that FlyScared and Kristoffon mentioned. People have to understand what they are doing. And that could be the reason why there are not so many of such successful conversions... Quite frankly, if everyone says 'Don't do it!' because it is not 'by the book' and there is no understanding or learning possibility then of course, it would seem impossible. Yet it is done. By people who know understand what they are doing when converting such airplanes in the past and nowadays. While I agree basically with everything that's been said, I am in the process of building an UL that uses fiberglass instead of fabric. The fiberglass is also providing structural support in certain key areas. In fact, to hair-lip the Pope, I am also using plywood/glass in a sandwich configuration instead of foam/glass. The thing is, the aircraft is being engineered in this fashion from the ground up. Also, I will have constructed the rough equivalent of four airplanes just to get one because of my insistance upon testing components to failure both as an individual piece and as a part of the larger structure! Unless you are prepared to do the same, then changing one building technique for another is a sure receipe for disaster - plus, it is rarely, if ever, cheaper, better, or ??? I wont say all, but most of the people on here are more concerned w/ your safety than anything else including an airplane that flies! Please dont take offense of their criticisms, but they have a LOT of combined experience,..and they are going to err on the side of caution each and every time! If you want to try something out,...try it,..but test it, re-test it,...and then test it again! ...just my$1.50
One thing comes to my mind... Couldn't you have used at least some of the solutions other people had when converting from fabric to fiberglass..? Or is the design of your airplane specific, so none of the proven ideas could apply..?

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