Laminating stringers

Designs for inboard or outboard power

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Billy
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Laminating stringers

Post by Billy »

For my motor stringers I was thinking of laminating 1x2,s together as a stack so that I would end up with a vertical grain 2x6 when finished, I have a lot of short,(8 foot) lengths of mahogany left over from building my frames that I want to use. Just thought this would have been done before, and would like the pro,s and con,s thrown out there. Thanks.
working on a Tahoe 24

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Bill Edmundson
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Re: Laminating stringers

Post by Bill Edmundson »

Billy

My stringers are laminated 1x6 Douglas Fir as are my stem and keel. Many people feel that laminated stringers are less likely to warp.

Bill
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Oyster
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Re: Laminating stringers

Post by Oyster »

You do not want to end up with a vertical grained stringer. Thats the weakest form of grain even laminated, from my personal point of view.

Billy
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Re: Laminating stringers

Post by Billy »

Thanks for the replies, so no vertical grain stringers, ok, best way to go will be to buy some long 1x6's, clear fir if I can find some and glue them together. thanxs.

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Caber-Feidh
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Re: Laminating stringers

Post by Caber-Feidh »

Oyster wrote:You do not want to end up with a vertical grained stringer. Thats the weakest form of grain even laminated, from my personal point of view.

I would agree completely.
Rift sawn material is less likely to fracture.
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lakeracer69
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Re: Laminating stringers

Post by lakeracer69 »

Ok I'll disagree here and so will the FAA. On wooden aircraft wing spars and all structural wood components are quartersawn. An inspector would never approve rift sawn components.

A wing spar and a motor stringer are very similiar. On my crackerbox I used 2 X 6 vertical grain Douglas Fir and laminated 1/2" plywood to one side.

YMMV
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Re: Laminating stringers

Post by Oyster »

Vertical grain lumber stacked and glued creating a 2x6 gives no real holding power for any fasteners run into the grains Its like running a screw into an end grain to some extent. He is creating stringers to hold his motor.
laminating 1x2,s together as a stack so that I would end up with a vertical grain 2x6 when finished,
Vertical lumber is more stable for sure and does not check out. But since I have never built an airplane with any wood, I do think that you fasten the parts together with different methods when using hardware. If I recall correctly, I think a lot of glue makes up the wings too, but not really sure.

In numerous cases we do sandwich glued beams with plywood as on deck beams or even cabin tops for serious crowns which saves weight for the strongest free standing parts. Do you have some link in which the full context is described for my own interest?

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Re: Laminating stringers

Post by lakeracer69 »

Oyster,

Do a google search for wooden wing spars and laminated wing spars. Holes are drilled in them for metal attachment plates and fittings much like a stringer for a boats motor mounts. You could also look for an FAA publication. I think it's something like ANC-18. There is also an aircraft building series of books by Tony Bignelis where things are described in detail.
As Conan the Barbarian says, " It's not how hard you can hit, it's how hard you can get hit and remain standing".

Oyster
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Re: Laminating stringers

Post by Oyster »

lakeracer69 wrote:Oyster,

Do a google search for wooden wing spars and laminated wing spars. Holes are drilled in them for metal attachment plates and fittings much like a stringer for a boats motor mounts. You could also look for an FAA publication. I think it's something like ANC-18. There is also an aircraft building series of books by Tony Bignelis where things are described in detail.
Well the spar is only a rigid brace and only one part that requires other bits and pieces to create a sound component with the additional parts . Without the additional bits and pieces, it would not hold an engine or keep the plane in the air either. :wink: I also agree that the spar must be stable materials. An distortion would ruin your day.

http://en.wikipedia.org/wiki/Spar_(aviation)
Image
Other structural and forming members such as ribs may be attached to the spar or spars, with stressed skin construction also sharing the loads where it is used. There may be more than one spar in a wing or none at all, however where a single spar carries the majority of the forces on it, it is known as the main spar.[1]
In this particular application, the stringer needs to do an additional job with having an engine mounted to it and stay in place with mechanical fasteners. Fasteners do not hold long term in vertical grains when repeated stresses are applied to the weak grain pattern.

There are ways to secure mounts with fabricated saddles that can be additionally addressed.. But this was just a generic request and I replied only to the point in the original posting.

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jamundsen
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Re: Laminating stringers

Post by jamundsen »

Oyster
The FAA material is located in AC43.13-1B and deals with wood for aircraft construction and repair. As an A&P I dont really worry about the way the wood is cut but rather the way it is installed. we order the spars from an approved facility. There arent a lot of factory built wood planes still around. I think all these discussions are very interesting and always learn a lot.
Here is a link to the wood section in AC43.13
http://www.airweb.faa.gov/Regulatory_an ... r%2001.pdf
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Re: Laminating stringers

Post by Oyster »

I dont really worry about the way the wood is cut but rather the way it is installed.
Thanks for the informative information. The "c" section addresses some areas that applies.. Indeed there are differences. Honeycomb composite materials are very structual as a unit, but not as much or at all with its parts and pieces independant of other components making a sound part.

In the section about choices of wood, note they also mention Northern White pine and not being a substitute for Spruce. Even though that wood is used in numerous boats in the northern regions, its not considered to be structual lumber at all. But all the woods are also considered soft woods in boat building lumbers too. The use of these woods incorporates multiple other parts installed in such a way combining multiple parts to make a structual part in the plane.

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billy c
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Re: Laminating stringers

Post by billy c »

in the aviation link posted above, i liked this diagram on the scarf joint grain direction deviation. goes a long way to visualize the difference in strength of a spar.
it would also make sense to those who are making chines or sheers that are breaking them to consider this when selecting pieces for such parts.
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jamundsen
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Re: Laminating stringers

Post by jamundsen »

In my post above I think I made it sound like we didnt care about the wood. i dont mean that at all. We just dont have the skills to make a built up spar so we buy them from someone else. We are able to repair but it takes a real craftsman to build a spar. There are so many pieces that make up a wing and all contribute in the load carrying abilites. A lot like I have learned about boats and transoms and the way all the different parts have their place. Since I am building a boat I have been tasked with the wood work on some of our planes. Somehow that made me the expert which terrifys me as all I know I have learned from this forum.
If I can figure out how to add a picture I will post one of the Stearman wing we are recovering. It shows many of the different componets that make up the strength of the wing. Changing one part design could casue a major problem. I think thats something the builders should keep in mind when making boat design changes.
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Oyster
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Re: Laminating stringers

Post by Oyster »

John I do not think that anyone and certainly not I took your previous posts that you did not care about the woods. I attempted to point out the differences from which I responded to from the original post. For me I personally have learned a bit in this thread, something that I had never given a thought to at all.

Your link provided good imput and context into the notion that what we consider to be non structual woods in boating joined and configured in such a manner that the same wood was and is considered to be very structual. Context is everything when discussing certain woods and even grains and where to use each cut.

Billy
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Re: Laminating stringers

Post by Billy »

wow, that stired the pot a little; just to give it another swirl; the 1x2's are not truly vertical grain because they are cut out of flat grain boards and I would arrange the end grains so that no two 1x2 have the same grain pattern.
Anyway, I get the idea, I think I will run my 1x6 boards through the bandsaw (on edge)to make a bunch of 1/2" wide boards,clean them up with the planer and then scarf and epoxy pieces together to get the lenght I need,about 17 feet, then layup those (being carefull to stager all the scarf joints ) probably four layers, and epoxy that together to get the 1 1/2" thickness that I need. That way I end up with a laminated Flat grained board, stringer. By the way I'am building a 23 foot Tahoe, if that makes any difference. Thanks again for all the input.
working on a Tahoe 24

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