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Mar 11, 2019, 09:25 AM
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Discussion

Which Plywood for dihedral brace


Needing to buy some plywood for making a dihedral brace so the question that came to mind is should it be regular 3 ply or 5 ply birch?
I attempted to use some 3 ply hobby stuff I bought at a home improvement store but it was very flimsy when cut to size so that's out. The digedral braces aren't large,...... for a kadet Senior. I reduced the dihedral by 66% so I need to make new ones.
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Mar 11, 2019, 10:09 AM
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piperjoe's Avatar
Hi John,

I use 5 ply Birch for dihedral braces.

Joe

Edit: Went into the shop, and, as the top of my Kadet Senior isn't covered yet (lucky you!) I was able to take a couple of photos to show what I used on my Kadet Senior wing. The original plans show 3-ply dihedral braces of 5/32" thickness; though I had changed the wing dihedral angle on my model I ended up throwing the original kit 3-ply dihedral braces away because they were of poor quality and I wasn't going to give them to another modeler to use on a model project. The kit dihedral braces were replaced with 7/32" thick 5-ply Birch aircraft plywood for my model and I have no regrets with regards to that decision. You may want to check out the posts and photos with regards to the dihedral braces in my build log:

https://www.rcgroups.com/forums/show...g-Kadet-Senior

Joe
Last edited by piperjoe; Mar 11, 2019 at 11:08 AM. Reason: Added additional information
Mar 11, 2019, 10:18 AM
Summit Model Aeronautics
Steve85's Avatar
Looking at the plan on the Outer Zone, it specifies 1/8" ply, and it appears to have been drawn as 3-ply. If you're building from a kit, what was the original made of? The Kadet isn't exactly a pattern plane, so unless you plan to do some really high-G aerobatics, either 3-ply or 5-ply birch aircraft plywood (not fir, poplar or luan like the hardware store sheets tend to be) should be fine.

Steve
Mar 11, 2019, 10:34 AM
AndyKunz's Avatar
Why ply? The vertical grain is doing nothing but adding weight.

I'd be inclined to use spar material in multiple layers.

Andy
Mar 11, 2019, 10:41 AM
A man with too many toys
I always use 5-ply aircraft quality plywood. Get it for a hobby shop. https://sigmfg.com/collections/plywo...x-6-x-12-5-ply

That home store stuff is usually very poor quality and does not have much strength.


.
Mar 11, 2019, 11:08 AM
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E-Challenged's Avatar
Hobby shops with builder's supplies sell "light ply" and regular ply in sheets. Use the regular ply for firewalls, dihedral braces and landing gear mount pieces.
Mar 11, 2019, 11:08 AM
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Thread OP
Quote:
Originally Posted by AndyKunz
Why ply? The vertical grain is doing nothing but adding weight.

I'd be inclined to use spar material in multiple layers.

Andy
Nit picking. Besides if plywood was that terrible, it wouldn't get used in homebuilt aircraft, boat building and just about everywhere else.
The structural strength of plywood depending on the use of good materials is better than just using layers of basswood.
Mar 11, 2019, 11:11 AM
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Thread OP
Quote:
Originally Posted by E-Challenged
Hobby shops with builder's supplies sell "light ply" and regular ply in sheets. Use the regular ply for firewalls, dihedral braces and landing gear mount pieces.
I found that out. Bought the 1/8 ply, when cut was very flimsy. Maybe good for making doll houses.
The Kadet Senior is not going to be a 3D plane, rather one with ailerons and reduced dihedral to make it a little more sporty. It's going to end up looking like a bush plane.
Mar 11, 2019, 11:13 AM
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piperjoe's Avatar
Quote:
Originally Posted by AndyKunz
I'd be inclined to use spar material in multiple layers. Andy

Well, I sure as heck would not...

Joe
Mar 11, 2019, 11:19 AM
I just want to go fly!
walter3rd's Avatar
i have found that the thicker ply plates that come in kits to be used as wing union reinforcement seem to be extremely strong.
Mar 11, 2019, 11:30 AM
AndyKunz's Avatar
Quote:
Originally Posted by jollyroger
Nit picking. Besides if plywood was that terrible, it wouldn't get used in homebuilt aircraft, boat building and just about everywhere else.
The structural strength of plywood depending on the use of good materials is better than just using layers of basswood.
In places where you need large areas of non-directional strength, ply is appropriate.

In places where you only have one bending moment, use of materials offering nothing in that bending moment is not appropriate. What strength is the vertical grain in ply providing?

Ply is also great for making things easy, but how difficult is joining two wings?

Yes, a lamination is good. But if you laminate spar materials, you have the strength needed without the useless weight of 2/5 of 5-ply material.

Andy
Mar 11, 2019, 11:31 AM
AndyKunz's Avatar
Quote:
Originally Posted by walter3rd
i have found that the thicker ply plates that come in kits to be used as wing union reinforcement seem to be extremely strong.
Yes, the vast majority of our models are over-built.

Andy
Mar 11, 2019, 11:39 AM
Registered User
piperjoe's Avatar
Quote:
Originally Posted by AndyKunz
In places where you need large areas of non-directional strength, ply is appropriate.

In places where you only have one bending moment, use of materials offering nothing in that bending moment is not appropriate. What strength is the vertical grain in ply providing?

Ply is also great for making things easy, but how difficult is joining two wings?

Yes, a lamination is good. But if you laminate spar materials, you have the strength needed without the useless weight of 2/5 of 5-ply material.

Andy

Well, John.....you just got it direct and straight from the GURU and what is there left to say? Oh, wait...you just might want to follow your OWN ideas on this one, my friend. Designers have called for the use of plywood dihedral braces for countless model aircraft designs, and with good sound reason; you might be happier in the long run using your common sense in the selection of the proper dihedral brace material for YOUR model aircraft.

Joe
Mar 11, 2019, 11:44 AM
AndyKunz's Avatar
Joe, how about elaborating on the reasons for ply rather than making a personal attack? You say there are reasons, and I even listed one for you (ease).

I listed the reasons for using laminated spar materials. Please educate me and everybody else who reads here.

Andy
Mar 11, 2019, 11:52 AM
Registered User
piperjoe's Avatar
Quote:
Originally Posted by AndyKunz
Joe, how about elaborating on the reasons for ply rather than making a personal attack? You say there are reasons, and I even listed one for you (ease).

I listed the reasons for using laminated spar materials. Please educate me and everybody else who reads here.

Andy

Andy, Andy, Andy....There is no personal attack on you...heaven forbid! I think the best thing to do with you is to just let you ramble on, my friend. Have a great day in your neck of the woods.

Joe


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