Fir vs Birch plywood??

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Aerowerx

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I see that Aircraft Spruce has "Royal Marine A-A Fir Plywood".

It is less than 1/3 the price of their domestic Birch plywood.

How do the properties compare?

And before you ask, no the plans do not specify what type of plywood to use.
 

wwkiefer

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Aerowerx, your question was timely, i am currently in the planning stage of my first build. I believe columns spec the wood thus. t" thickness. ,== tension load with the plane of the wood, next is tension load perpendicular to the surface, next compression with the plane of the wood and compression perpendicular to the surface, then sheer load on the ply at 0 and 90 deg. and finally at 45 deg. Hope that helps.
 

FritzW

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I'd add it's based on the orientation of the grain on the surface plys. So, the chart shows the ultimate load in PSI for compression and tension, parallel to and perpendicular to the grain of the surface plys.

I'd have to check ANC-18 (downloadable on HBA) again but the "0 & 90" and "45" might mean the angle between the surface and core plys. ie...the "Degree" column you see on the Dom Birch ply page at AS&S.
 

Aerowerx

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FritzW: I was asking what "HTH" meant. And, yes, the angles are the orientation between the face and core.

wwkeifer: I understand the chart. I was just wondering how Birch and Fir ply compared. From what I see the Birch is stronger. I guess I will have to save some more pennies.

[Edit] I just took a more careful look at the chart. For tension, the Birch ply is stronger. But for compression the Douglas Fir is stronger. For shear, it depends on the angle. That makes the decision more difficult. I do like the looks of the Birch ply more than the Fir.
 

Joe Fisher

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I use 1/4" marine grade for floor boards in Cubs, Tcrafts. The Aeronca Champs use it for the fuselage formers. It is just common 3ply grade "A" construction plywood except the inside ply has on voids. The birch aircraft plywood is 5 ply. The aircraft plywood doesn't split and tare when drilling and cutting.
 

davidb

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Vacaville, CA
I see that Aircraft Spruce has "Royal Marine A-A Fir Plywood".

It is less than 1/3 the price of their domestic Birch plywood.

How do the properties compare?

And before you ask, no the plans do not specify what type of plywood to use.

From your other thread I see you are also concerned about cost of shipping. Have you considered local sources? AA fir might be hard to find but if you can safely use AB fir or okoume marine grade you could save some money on the product and shipping. You might even find a place willing to order some AA as part of their normal restocking--could save on shipping. Some phone calls and a drive might be worth your while. Here's one site: https://marine-plywood.us/douglas%20fir.htm
 
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