Lift Strut attach to Spar

[Varmint]

The "original" plans show the brackets on the spar to which the lift struts attach to be something near vertical which puts it aligned with the loads that "intuitively" seem to be applied to this bracket to resist the wings upward deflection. But in analysis the lift strut can really only apply loads to this bracket that are along the lift struts long axis. This is reflected in a few photos I've seen of Piets under construction that do install this bracket at a much "shallower" angle along the spar, aligned with the lift struts. This of course puts a compression load on the spars inboard of the attach brackets and across the center section. These compression loads are there regardless of how the attach bracket on the spar is aligned, its just a matter of if the bracket is loaded along its length or somewhat "across" the straps.

Has there been discussion or "credentialed input" on the matter of how best to align these brackets?

Also, the plans I have show 1/8" plywood doublers on both sides of the spar under these lift strut brackets although I have not seen these in most photos I've found. What is the consensus on these plywood doublers? If used, both front and rear spars?

Thanks for listening

[danoliver]

There is a very in-depth article by Oscar Zuniga in the 2019 fourth quarter BPA Newsletter about that very subject.
Check it out.

[Varmint]

OH that is great. Is there a link to this article somewhere or a place it can be purchased?

[Pat Weeden]

OH that is great. Is there a link to this article somewhere or a place it can be purchased?

Back issues of the BPA newsletters are $5 each. If you're a member already, I can send it to you for free.

E-mail me at bpa@pietenpols.org

Pat Weeden
BPA newsletter editor guy

[at7000ft]

Hey Varmit

Using the newer plans my spar attach fitting angle ended up directly in line with the lift struts.
(My spars are 3/4" requiring the added 1/8" birch plywood under the fitting you can see in the pictures).

Rick

https://drive.google.com/file/d/0B1Y1jV ... sp=sharing

https://drive.google.com/file/d/0B1Y1jV ... sp=sharing

[Varmint]

Rick,

Thanks for the pics. That is pretty much just was I was picturing as "ideal".

What do you mean by "newer plans"? I just bought some from the Pietenpol Family. Are those the newer ones (as compared to the Flying and Glider manual) or is there yet another updated version?

Thank you