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Wing spar load testing question

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rtfm

Well-Known Member
Joined
Jan 3, 2008
Messages
3,900
Location
Brisbane, Australia
Hi,
I've decided to test my spar only, not my entire wing. If the spar fails, no big real. If the wing itself fails, I'll be thoroughly pissed off.
I recently watched a video by Mike Patey () where he tests the "Scrappy" spar. I found this a novel way to test the wing's ability to allow you to land alive.

However, I have a number of issues with his testing method:

(1) He applies force to the tip of the wing
(2) His method applies a point load at the centre of the wing.

Neither of these are applicable to real-world situations.
I would have applied the pulling force inward of the tip, but I'm having some difficulty determining exactly where. Looking at the lift distribution of a typical rectangular wing plan *seems* to suggest somewhere near the centre of the wing half. Would this be reasonable?

And if this is a reasonable assumption, then how much pulling force is required? The Fleabike fully loaded will weigh in the region of 256kg. The rear wing (for example) carries 40% of the load. Under 4G this equates to 409,6kg, and therefore each wing half needs to support 204.8kg

My problem is: do I apply 205kg at the half-span? Is my thinking correct? My wing is strutted, with the strut half-way between the wing centre and the half-span position. It seems to me that the strut is going to carry the lion's share of the load, with the 560mm outboard section (ie from the strut to the half-span position) bearing a significantly reduced load. This is important, because the wing folds at the strut, and all outboard loads will be referred back to the hinge.

I really like Mike's flat-on-the-floor testing method, by the way.

Regards,
Duncan
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