Reply to post: Wing loading?

This isn't Boeing to end well: Plane maker to scrap some physical cert tests, use computer simulations instead


Wing loading?

I was surprised to see wing loading tests given as an example of something that might be modeled rather than destructively verified. Is that an El Reg speculation, or did Boeing actually mention that as a specific example?

I think there have been at least three, possibly four occasions in the last 20—30 years when major transport-category aircraft (civilian or military) have failed load tests at less than the required margin (usually 150% I think)—in all cases a surprise to the designers and engineers, and in all cases necessitating strengthening of some structural components. This would suggest that despite extremely thorough materials assessment and engineering calculations, the models just were not accurate enough. (There have been numerous incidents where less strongly built and tested wings would have killed a planeload of people: for just one example, think of the Chinese 747 whose pilots buggered up a cruise-altitude flameout over the Pacific in the 90s).

Given that 150% isn't an exceptionally large margin by engineering safety standards, you must ask: what margin will be designed for, if testing is no longer destructive? 200%? 300%? Because if your "testing" becomes less rigorous (which is by definition the case, for anything less than destructive) you have to increase margins. That means that planes will become unnecessarily heavier, and less efficient, as you add material to bring wings up to, say, a 200% margin.

I can imagine there is actually a good case for model-based certification in some cases—think about simulation of performance of electronic circuits, power buses, insulation—but equally it becomes very bad idea in others. Once a while an engine manufacturer straps a chunk of plastique to a fan blade and blows it off, destroying several million dollars of engine, just to prove—prove!—that a failure will be contained and not chop a plane to pieces. At the kind of phenomenal energies, power and performance levels concerned, no conceivable simulation would be good enough.

Not least because GIGO. Even a supremely well designed computer system is susceptible to bad input. (Indeed, a few plane incidents themselves have been caused by this: mistaking a FPS descent rate for a degrees descent, for example; getting a pounds-to-kilos fuel weight conversion wrong; dialling in the wrong air temps before takeoff; I could go on.)

I think I'd like to know that when my family travels, the wings on their model of plane were actually physically broken in a way and at a loading that cannot lie; rather than depend on a tired engineer getting the rarefied subtleties of tensor calculus right every single time.

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