LWX & LWY out of Maple?

[Cozy1200]

In this months issue of CSA, Terry suggests using Maple instead of spruce for LWX & LWY. What are the thoughts on doing this? I'll be to this point in a few weeks.

[rickh]

<opinion on>

Been my experience that maple (hard/soft/sugar) will warp/expand/move more than other woods if it gets wet. Humidity changes affect the wood a bunch, I think Marc Z's prop was maple laminates? Maple takes moderate shock, it's heavy, gluing is not the easiest.

 

For shock loading, ash might be a better choice. Takes high shock loads (baseball bats), glues better, it slightly lighter, not sure of the dimentional changes from humidity but will look

</opinion off>

 

Rick

[TMann]

What about poplar?

[rickh]

What about poplar?

Me? Well as long as you asked...

 

Poplar would be a choice also

 

Generally, softwoods grow/shrink in width/thickness the least with changes in humidity, generally (lengths basically stay constant in all woods). They hold fasteners the best (primarily nails), and glue up easily. Exceptions to gluing ease are the cedars and redwood. Softwoods will survive "OK" outside, if protected by a coat of paint (old barns for instance).

 

Hardwoods are, umm, hard... and heavy. They expand/contract more (generally), most have a higher bend/shock limit, though some will just plain old break if stressed. Hardwoods kinda look like bacon if used outside, though there are exceptions. Gluing varies, maple is difficult, poplar and basswood easier (relatively).

 

Sitka spruce can be had in incredibly long knot free straight grained uniform boards. It's light, and is an excellent choice for spars (IMHO) and such on wood frame planes (Spruce Goose), but it may lack in applications where shock loading may be involved... like the LWxx series of reinforcements for what I assume are the aft LG load transfer mechanism. I are knot an injineer so YMMV.

 

Pines will generally have a larger difference in properties across spring and summer growth, this is pronounced on woods grown far from the equator... typically all our hard and soft woods. Teak and mahogany (grown near the equator) have no real growth rings, and teak has a very low expansion/contraction ratio w/ humidity. It's a royal bear to glue though.

 

Thought for the day: Epoxy is used to glue the longeron strips together, epoxy does not expand/contract much. Elmo's glu-all does. So does recorcinol (isn't this used to glue-up spar strips on wood planes?).

 

I ran across the following, may be interesting reading:

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm

 

Lastly, the Cozy and derivatives have been around for a long time, no major problems, and no major changes from the plans materials

 

Rick

[Big Steve]

Why not just use what the plans call out? Sitka spruce it is light glues well and a few hundred flying eze's cant all be wrong?

[Cozy1200]

Why not just use what the plans call out? Sitka spruce it is light glues well and a few hundred flying eze's cant all be wrong?

I guess I'm not for or against it. It's just a suggestion out of CSA that I'm considering. (and as Chrissi would suggest reading CSA before building should be mandatory)

 

I don't recall anyone commenting that spruce in this area was too soft. The CSA article was the first I've heard of it, but Terry advice seems sound.

 

I not suggesting the plans are wrong or bad. But there always room for improvement with time/age. This may or may not be a possible change. For example, nearly everyone has progress past using the plans method of attaching screws to the firewall. Many better methods have been developed, I'm using click bonds.

 

When an avid builder/flyer suggests something, I think it's merits should be considered.

[Bruce]

Why not just use what the plans call out? Sitka spruce it is light glues well and a few hundred flying eze's cant all be wrong?

I talked with Terry (CSA) and his thoughts were not because they are wrong, it's worked fine for many years and many aircraft, however for the unfortunate ones that have had an issue in the area when the gear is stressed the spruce blocks that the LMGAs attach to are too soft. It's an area that can be improved on that's easy to do with negligible weight since the pieces of wood are so small. He also mentioned the nuts that attach the LMGAs should have AT LEAST wide area washers for bearing surface rather than the plans called for AN960-416 washers. "The small washers allow LMGA mount bolts torque to be lost when the wood crushes under heavy loads". It's a suggestion for improving the durability of our plane and I can only imagine how difficult it would be to repair this area if it did fail.

 

 

If you're not a member of the CSA I'd highly recommend it. Lot's of good wisdom from experienced builders and fliers.

 

Bruce

[Marc Zeitlin]

In this months issue of CSA, Terry suggests using Maple instead of spruce for LWX & LWY. What are the thoughts on doing this? I'll be to this point in a few weeks.

First of all, Terry S. is talking about Long-EZ's here, with his suggestion for the LWX/LWY material replacement. On the LE, the gear mounts bolt to these pieces of wood, and have loads transferred directly into them via the bolted joints.

 

On the COZY MKIV, there is no such loading or bolting - the gear tabs are bolted to the attachment points in the LG bulkheads. There's no reason to consider a different material for a COZY MKIV, which is what you're building :-).

[Cozy1200]

First of all, Terry S. is talking about Long-EZ's here, with his suggestion for the LWX/LWY material replacement. On the LE, the gear mounts bolt to these pieces of wood, and have loads transferred directly into them via the bolted joints.

 

On the COZY MKIV, there is no such loading or bolting - the gear tabs are bolted to the attachment points in the LG bulkheads. There's no reason to consider a different material for a COZY MKIV, which is what you're building :-).

Marc,

thanks for your input, I was hoping you'd answer. I had tried to visualize what all was bolted into this area, but couldn't. You're answer makes sense. Sticking with spruce (ok, approved local substitute: Australian Hoop Pine).