Spar integrity

[CRG]

Looking for opinions on this spar build. It's 3" x 6" on a Cassutt wing. Half-inch pieces rather than the usual one inch. Three pieces have splices within the fuselage width, which are the area of concern. Quality of build appears high, T-88 was the adhesive used.

Thanks for any help.

Craig

 

[Dan Thomas]

Scarf joints are normally 15:1 slope. I don't see that those comply. AC 43.13-1B, https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_43.13-1B_w-chg1.pdf Pages 1-15 thru 1-19.

 

[TFF]

I’m going to be conservative and say no, not until more research. Not the number of laminations, that’s fine. It’s that they are putting the scarfs in the stack without bolstering scarfs themselves I would probably want an extra lamination on each side running past the farthest scarf. It’s already a lamination with full pieces. Can I be wrong, yes. I have not seen Cassutt plans in person. It might be standard practice. I would be talking to racers and looking at plans like the Falco that has splices. I would be talking to people who build wood wings for a living. I’m probably wrong which would be nice.

 

[proppastie]

Scarf joints are normally 15:1 slope. I don't see that those comply. AC 43.13-1B, https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_43.13-1B_w-chg1.pdf Pages 1-15 thru 1-19.

I do not think what he is showing is a scarf or splice.

Edit: Oops, I do see the splices.....

 

[proppastie]

A racing aircraft should be designed to high Gs....Were you to perhaps only fly it as a sport plane, no racing, or heavy aerobatics, it might be more than adequate.

 

[blane.c]

The wood grain does not look like it conforms to aircraft standards either.

 

[CRG]

Thanks for the input guys. I've been going back and forth on this one as it's a timesaver at a good price, but am not completely comfortable with the spar.

 

[Speedboat100]

Does anyone have an example of 1:15 joint ?

 

[BoKu]

Does anyone have an example of 1:15 joint ?

Here's what it shows in AC43.13. There are two or three of these in my Aeronca wings.

Looking closely at the photo in the OP, the slope appears to be around 10:1. If that is described as acceptable in the Cassutt plans, I'd accept it. But it seems to me bad form to use a slope substantially less than that allowed by AC43.13, and even worse form to locate it near the wing root where the tensile and compression forces on the spar caps are at their greatest. If this had been my build, I'd have chosen my sticks a bit more carefully so that the splices fell outside the inboard 1/3 of the span.

--Bob K.