not "aircraft use" plywood?

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cls

Well-Known Member
hmmm... this evening in Michael's craft store I saw some birch plywood, over at the balsa section. the ply is all marked "not for aircraft use". the finish looks OK. it's made of 3 plies, the real stuff looks like 5 plies. I can't see any voids or checks in the edge, no hollow sounds when I tapped it ... the sheets are just as warped as the stuff in the hobby shop

it's very inexpensive compared to the "aircraft" plywood in the hobby shop: 3mm 12" x 24" is less than $4, compared with$12 for the real stuff.

tempting tempting! anyone ever try this stuff? did it work or did it shred on the first launch?

rstaff3

Oddroc-eteer
I've bought plywood from Michaels once. Just had to use a coupon. Never noticed or heeded any warning on it. What I bought were a couple smallish slabs of fairly thin stock and it was fine. Check that what you get look flat.

Now the wood experts will chime in.....

vjp

Well-Known Member
Originally posted by cls
hmmm... this evening in Michael's craft store I saw some birch plywood, over at the balsa section. the ply is all marked "not for aircraft use". the finish looks OK. it's made of 3 plies, the real stuff looks like 5 plies. I can't see any voids or checks in the edge, no hollow sounds when I tapped it ... the sheets are just as warped as the stuff in the hobby shop

it's very inexpensive compared to the "aircraft" plywood in the hobby shop: 3mm 12" x 24" is less than $4, compared with$12 for the real stuff.

tempting tempting! anyone ever try this stuff? did it work or did it shred on the first launch?
It just means that the ply does not meet FAA requirements for use in *manned* aircraft. For hobby use, it may be just fine. Test it for suitability the same way you'd test any other rocket component, e.g. cardstock, balsa, lite ply, cardboard, etc.

Micromeister

Micro Craftman/ClusterNut
Vince:
Your just pulling our leg.. Right! I wouldn't want to be riding in an aircraft constructed of 1/64" 3 ply Aircraft plywood... no matter what! I'm sure the "not for aircraft use" label has some other meaning.
Any R/C guys out there have a clue on this stuff.

I have used some the the 3/32" 5 ply birch ply from Micheals with that designation for fins without any noticable problems.

Larry

Well-Known Member
I think the hobby plywood is probably fine to use for some projects. I was going to pick some up from Hobby Lobby the other day, but decided I wanted the aircraft grade plywood. The aircraft grade is 5 ply and won't have any voids. It is also stronger. All the larger rockets use aircraft grade for centering rings, or at least most do. NCR kits use to use basswood. I made the centering rings for the Interceptor G I built out of aircraft ply.

Micromister....I fly an airplane that is all wood including some thin plywoods. Depends on where and how you use them Larry

SwingWing

Well-Known Member
Small ply is often used for gussetts in wing rib construction in wood wing aircraft. I doubt that 1/64" stuff is used much, but likely all of the sizes form that mill are stamped. There is a trend for manufacturers to purposely distance themselves from having to warranty their products in aircraft use, particulary experimental aircraft use. A certain belt and hose manufacturer is real big on this.

vjp

Well-Known Member
Originally posted by Micromister
Vince:
Your just pulling our leg.. Right! I wouldn't want to be riding in an aircraft constructed of 1/64" 3 ply Aircraft plywood... no matter what! I'm sure the "not for aircraft use" label has some other meaning.
Any R/C guys out there have a clue on this stuff.

I have used some the the 3/32" 5 ply birch ply from Micheals with that designation for fins without any noticable problems.
Nope, not pulling your leg at all! There are lots of aircraft out there built all-wood construction. Do a Google search on "all wood aircraft" or check out https://www.aircraftspruce.com or the homebuilt sites. The really thin stuff is probably only used for sheeting.

Here's a REALLY BIG and famous example :
https://www.sprucegoose.com/Specification.htm

powderburner

Well-Known Member
You would be amazed at what some of the homebuilt aircraft guys use for structural materials.
I helped one guy haul home a whole bunch of blue foam blocks (he didn't have anything to carry a 12 foot piece) that he was gonna hot-wire to shape and cover with glass. I think I'll stay on the other side of town on first-flight-day.

SwingWing

Well-Known Member
Done properly, the "moldless composite" construction method popularized by Burt Rutan can make a very strong airframe.

astronboy

Well-Known Member
There should be no problem using the 'non aircraft' ply. I have used it a few times for fins that are strangely shaped and would break along the grain.

For low and mid power rocket use, plywood is overkill anyway, so 'aircraft approved' should not matter.

But, as you said, it is all warped anyway!!

One trick I have seen is to buy two sheets that are 1/2 the thickness of what you will use, then glue the two together, and put a pile of books on top of them while drying in order to correct the warp.

cls

Well-Known Member
wow, what a bunch of great replies, and quick too... TRF rocks!!!!

of course covering basic ply with fiberglass makes it a lot stronger. and you can make good structures out of basic foam & glass like the blue styrofoam from home repo.

I am looking for 1/8" ply for fins for a MPR/low HPR rocket. they will be mounted TTW and just painted, fiberglass not really desireable here.

I guess I will get a small sheet of 3-ply and 5-ply and cut some pieces and put 'em in the vice and pull on 'em and see what breaks!!

Justy

Well-Known Member
I work at a Michael's in Canada, and we carry both types of plywood (in some sizes it's "aircraft plywood", and in other sizes it's labelled "birch plywood - not for aircraft use"). And to the best of my knowledge, Vince is right. Aircraft plywood is approved for use in manned aircraft. I think it has to do with how it deals with moisture... aircraft plywood being more tolerant, so it won't mould, rot, and fall apart while your ultralight plane is flying 5,000' above suburbia.

Or that could be a myth formed by the fact that I live in a place where the seasons are "rain on green stuff", "summer", "rain on red and brown stuff", and "cold rain".

Unless you're building an O1500-powered bowling ball lofter (in which case, may I suggest stepping up to 3/16" ply? ), non-aircraft grade plywood should be fine for rocket fins.

cls

Well-Known Member

the Custom Tristar is a 2 fin with end-plates design and the fins and plates take a lot of abuse on landing so it's going to have to be sturdy. my 4x upscale is going to fly on some big motors. I am going to use the cheap ply and WEST epoxy and E glass.

... I found Drake's "Rocket Materials" web site:

https://www.rocketmaterials.org/

lotsa good info there and while it might settle some arguments it is sure to start others but you can't argue with actual test data!!

hope this helps!

from the sprinkle-rain-on-the-brown-stuff season in California

bsexton

Well-Known Member
I found this statement about "aircraft" plywood that I thought was interesting:

"I want to add to the recent discussion about aircraft plywood. This is coming both from my own experience and a page in the Aircraft Spruce and Specialty catalog. Aircraft Spruce caters to aircraft home builders and restorers and have a website at www.aircraftspruce.com. They send free copies of their catalog. I'm not connected with them but have dealt with them from time to time.

Aircraft plywood may or may not be lighter than other plywood, depending on the type of wood it made from. It's made in a hot press and subject to extremely high standards: quality of plies, absence of voids, quality of adhesives (example - the adhesives are subjected to shear strength tests immediately after being immersed in boiling water for three hours). It's expensive, which may not be that big a deal for a small project. Because it is expensive it is often available in small quantities, usually 1/4, 1/2 and full sheets. A full sheet is four by eight feet.

The most common certified material is made with birch or African mahogany exterior plies over basswood or poplar cores. The birch is heavier and stronger than the mahogany. The material is available with ninety degree or forty-five degree plies, and thicknesses of 1/16 to 1/4 inch (roughly 1.5 to 6.5 mm).

Basswood plywood is avalable which is lighter but not as strong. It is usually not used for structural applications in aircraft but might work well for a lightweight camera. The Basswood plywood comes only with 90 degree plys.

Finnish birch plywood is often called aircraft plywood. You find this stuff in small quantities with very high markups in hobby shops. It is also relatively widely available from craft supliers and other kinds of outlets. It is all birch and made to high standards, and is about 20% heavier than the poplar core material. People building homebuilt aircraft often use it instead of the certified material, but it can't be used to repair a certificated production aircraft. This stuff is available as thin as 1/64 inch (0.4mm) up to 6mm (about 1/4 inch) and usually comes in about one meter by one meter square sheets (4 by 4 ft). The stuff in the Aircraft Spruce catalog is 3 ply up to 3mm (1/8) thick and five ply for larger thicknesses although I've seen 1.5 mm (1/16 in) five ply material before.

These materials work well without splintering if you work carefully with sharp tools. Whether it looks good is up to the eye of the beholder.

This is oriented towards the US but the same or similar materials are available elsewhere.

Jerry Henneman"