Spruce plywood source?

Coachwood was used in Australian made Mosquitos, along with Hoop Pine. In fact, the Daintree in Queensland was declared a National Park in Australia, originally to preserve the supplies of Coachwood for aircraft production. 🙂

Afaik, ALL aircraft plywood is birch. I cannot see that spruce would have the right grain for stripping down into ultra thin sheets.

To add a little to the confusion, some birch ply sheets came with the stamp “Mahogany” on them. I think this must have been the name of the maker, rather than the type of wood.

There are several types of ply approved for aircraft use. Mahogany (often with a poplar inner), Okoume (French Gaboon ,lighter than Birch) Ash (again with poplar inner) Australian Coachwood, Finnish and English Birch , Basswood, and yes, Spruce which we use a lot of on the Mosquito. Ref your stamp “Mahogany” , that is Mahogany Oy, a Finnish ply manufacturer as is Vilkon Oy Koskisen.

Here’s a copy of MIL-S-6073

http://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-S/MIL-S-6073_50468/

Thanks Sopwith that’s great.

Hi, I have a query regarding spruce which I hope somebody can help with. I have got a number of lengths of spruce some of the longest are 17ft long x 4inches square with various lengths in between all 4 inches square. I read somewhere that in order to find out if it is suitable for a flying aeroplanes I need to measure water content and the grain per inch. Is that correct?

Probably your best bet would be to pop it over to SkySport Aviation at Hatch and get their wood dept to check it out for you. They are very helpful

Hi, I have a query regarding spruce which I hope somebody can help with. I have got a number of lengths of spruce some of the longest are 17ft long x 4inches square with various lengths in between all 4 inches square. I read somewhere that in order to find out if it is suitable for a flying aeroplanes I need to measure water content and the grain per inch. Is that correct?

I know Kevin Kimball and have talked to him about it. The spruce plywood for the Vega wings was not only authentic, it apparently saved a lot of weight over the birch ply. I don’t remember the exact weight saving, but I think it was 100 pounds or more, it was more than I expected to hear anyway. He did say that they had a hard time finding suitable trees that could be cut for spruce veneer, apparently it’s much easier to find spruce trees for boards. I only need enough for the gussets in the aft fuselage, so have asked him if I could buy the scraps left over from the Vega wing. Birch ply would work fine, but I’m trying to keep in the spirit of 1934.

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Good point Old Stager, of course, it was Birch ply that I was thinking of, sorry about that.
Incidentally Okoume is also used in French aircraft

Afaik, ALL aircraft plywood is birch. I cannot see that spruce would have the right grain for stripping down into ultra thin sheets.

To add a little to the confusion, some birch ply sheets came with the stamp “Mahogany” on them. I think this must have been the name of the maker, rather than the type of wood.

My buddy in the Forestry Commission spends his days ripping through Sitka Spruce plantations. I could put in a good word?

More realistically, the move towards commercial forestry lead to trees being planted very close together. These trees then compete for light, and as such grow very quickly. This is the reason Scotland is carpeted in stands of uniform-height Sitka Spruce. As a building material the stuff is junk, unless you are making pallets. The trees grow fast, so aren’t really structurally sound. Those around the perimeter of the stands fare a little better, but those in the middle have poor root systems and are effectively dead just below the canopy. Felled Sitka Spruce was sent to the papermills for a while, but I understand it is now pelleted and sold as a biofuel. I wouldn’t be making any aircraft out of this stuff!

Kermit Weeks had some spruce plywood especially made for the wings on his Lockheed Vega. I guess it is one of those materials that was available in the twenties and thirties, but not now. Check out his Facebook page, because he had a report a month or so ago about the Vega rebuild at Jim Kimball’s place.

Afaik, ALL aircraft plywood is birch. I cannot see that spruce would have the right grain for stripping down into ultra thin sheets.

To add a little to the confusion, some birch ply sheets came with the stamp “Mahogany” on them. I think this must have been the name of the maker, rather than the type of wood.

How odd that the well known aircraft building supplies “Aircraft Spruce” no longer supplies aircraft spruce!

Good luck with your search, and your project.

Moggy

Moggy

They still supply Spruce “boards & scantlings”, but they do not “nor to my knowledge have they ever supplied” Spruce plywood, the only ply they stock tends to be Birch ply.
I had a similar problem when I tried to find Ash plywood for the Brisfit rear fuselage bulkhead, there was plenty of Ash faced ply, but non that was made entirely of Ash.

Bob T.

Hi there , are you a member of the EAA? I would have thought that you’d be able to get a contact amongst the membership who would know where to obtain it. A lot of our ply over here is Finnish. Good luck with the Piet, I hope you are not very tall as the one that I look after over here is a very tight squeeze, too small for me at 6′ 1″ to be comfortable really.

How odd that the well known aircraft building supplies “Aircraft Spruce” no longer supplies aircraft spruce!

Good luck with your search, and your project.

Moggy