Another spar question

[gmackay]

After already having trimmed my new spars to the standard height of 5&11/16", and then later deciding to buy the 85HP STC, I see that they list the spar height as 5 & 15/16". Mr. Harer said later models used the taller spar, but either one was ok.

So my question is, "is it legal to glue capstrips on top and bottom of the spar to make it 5 & 15/16" and wouldn't that make it stronger? Or is that a bad idea? It looks like it would fit.

Also, could this "different" spar height be related to the mystery 1/32" doublers listed in another thread about the STC?

Just thought I'd stir things up a bit.

[crispy critter]

Re: Another spar question

Greg,
I wouldn't glue the cap strips on top or bottom of the spar.When the spar is flexed up and down or twisted it could cause pressure points that may cause the spar to crack.A spar cap on the butt ends is fine to seal the grain but you don't want them running the length of the spar.

[Guest]

Re: Another spar question

Greg,
I wouldn't glue the cap strips on top or bottom of the spar.When the spar is flexed up and down or twisted it could cause pressure points that may cause the spar to crack.A spar cap on the butt ends is fine to seal the grain but you don't want them running the length of the spar.

Hi Kevin,
I am not precisely sure what glueing on cap strips means but my intuition tells me that if one added 5/16" to to spar height in the same manner as making a laminated spar it would be just fine. Just another laminated spar.

Haven't thought it completely thru but that was my first consideration.

The same intuition tells me that most of us are not able to make a laminated spar.

So I also wouldn't recommend it but for different reasons.

Dave.

[crispy critter]

Re: Another spar question

Dave,
When the spars are laminated they are almost always done on an angle and and not the full length of the spar.

[VictorBravo]

Re: Another spar question

Spar REPAIRS are done on an angle. I believe laminated spars are fairly common in older airplanes, and discussed in AC 43-13.

I would guess that laminating a spar full length will require a whole lot of very good wood clamps to apply even gluing pressure.

[Robert Lees]

Re: Another spar question

gmackay I would suggest that you have trimmed your spar to the original dimensions? Is your craft a BC model?

If the above are correct, then I would choose to use the front page of the STC as guidance, in that "This STC applies to BC models" or words to that effect.

So you are legal as you are. No need to glue anything.

could this "different" spar height be related to the mystery 1/32" doublers

It could be...perhaps the "newer" spars were taller & thinner, or something.

I did actually add a capstrip to one of my new aileron spars, after I balls'd up the height in a similar way, but this was only because the leading edge needed to be right; it's not an issue in this regard for the mainplane leading edges. But note the huge number of G-cramps needed...imagine what you would need for 16 feet of wing!

Kevin I have laminated spars for both my front spars...they are laminated along the full length, about half way up. Further, the top lamination is made up of two pieces, scarfed at about 15 degrees. So each of my main spars id made of three pieces. And they are the original spars, I am sure.
I guess they used what wood was available. On the right hand side of this photo, you can see the horizontal lamination, and here is the splice.

Rob

[gmackay]

Re: Another spar question

Thanks everyone for the responses. Adding height to the spar was just a thought and wondered what people smarter than myself thought of the idea. I agree that I could not splice a spar, and yes it would take many more clamps than I currently have. I'm just always looking for ways to make things stonger.

Rob, mine is a BC12D and the original spar (or at least the one I just took out) is 5 & 11/16. It also has several splices like you mention.

I'll just stick with the 5 &11/16.

Thanks

[Robert Lees]

Re: Another spar question

I'll just stick with the 5 &11/16.

That's the spirit!

[crispy critter]

Re: Another spar question

Rob,
I looked at Gregs spars before he disassembled his wings and they had several splices in the main spars as if they had used this method for lamination.Correct me if I'm wrong but when laminating length ways down the spar isn't the sections of wood staggard,like you would do with hard wood floors,exterior house siding or log homes.The sections do not run full length of the spar....do they?
PS.Greg,your original size spar wil be fine...no need to add extra strenght to something that has been greatly proven for well over 60 years.Also,in most cases,the more you try to strenghten it the more wieght you will add,and in the long run the extra weight may weaken the entire design.More weight means more stress on the structure.