Nevil Shute wrote a great novel about this kind of scenario, called, “No Highway” (1948). If you are not interested in reading the book, a reasonable movie was made a few years later (“No Highway in the Sky”). Gives a good perspective about seemingly trivial little things that aircraft engineers fret about, as written by an aeronautical engineer turned novelist.
I stand by my conclusion regarding the wing fittings on this late VariEze. Moreso, I’m glad you got out alive, Mike, and that it was not a failure of the wing attach structure that caused the accident.
For what it is worth, my “opinion” about the wing fitting configuration on this airplane was, in detail:
1. My initial engineering assessment, back in 2005, for this airplane, based on direct airframe repair/modification engineering design experience (big aluminum beasties, and yes, believe it or not, the same engineering principles, analysis, material characteristics, etc., that apply to the big ones also apply to the little ones…)
2. On-site detailed examination & measurement of the wing fittings by one of the most-respected VariEze builder/drivers in the Realm (also happens to be an exceptional engineer).
3. Actual, formal (not just thumbnail) engineering analyses (has to be done under the requirements of evaluating what is referred to as Statically Indeterminate structure), evaluating to the absolute worst-case scenario (worst-case, based on epoxy-rich sparcaps, aft cg loading at 1200 pound weight because I know that’s where most VariEzes end up, when loaded full…), etc.
4. Peer review/independent analysis of the above by two veteran airframe structures/stress analysts. I always seek qualified Second Opinions when dealing with such issues, as this is the way we solve such problems in my profession.
5. Assessment of this condition by the designer’s Right Hand Man, when presented with the configuration and dimensions of the wing fittings (direct quotes copied and pasted out of the email I received back on this issue):
"Ooohh, that's not good".
and:
"I wouldn't fly it like that - would you?".
I also considered having this looked at by a DAR (Designated Airworthiness Representative) I work with, but knew his final assessment of whether or not this configuration constituted Condition for Safe Operation would only weaken the above positions that much more…
Regarding the substantiation of 4 g’s continuous loading, how much above 4 g’s would this structure take (assuming that it was truly 4 g’s of flight loading, at aft cg, at the highest weight the airplane would ever be operated at)? Unknown, and only truly “knowable” under formal, documented load testing (which would have to allow for measurements of yielding/deformation in the outer .125 plates, in the outer taper pin bores, etc., among other things). Long and short of it is, the fitting installation/geometry did not meet the structural design requirements, and could not be guaranteed to provide the necessary structural performance over the life of the airplane.
What if it took 10 more repetitions at x.x (pick a number here…) g’s before more bore yielding in the outer upper plate shifted the load transfer primarily from the outer plate to the induction of local bending moment in the upper composite spar cap due to primary load transfer being mostly/wholly reacted by the inner upper .125 plate??? The taper pin bore in one outer upper .125 plate had already been yielded at least once before, possibly twice, as evidenced by visible material upset/plastic deformation on the 2024-T3 alloy. This is the sort of circumstance that was quantitatively analyzed (among others).
All told, the players in 1 – 4, above collectively had 10 – 15 some man-hours invested in all of this effort. No. It was not just a case of my “opinion”. The overall situation honestly scared the hell out of me, and weighed heavily on my mind. Engineering ethics, dontchaknow...
Given the same set of circumstances again, in the future, I would maintain the same position.
