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Discussion in 'Hangar Flying' started by Alan Waters, Sep 20, 2019.
Not quite sure that Ag planes are the right thing to use as an example - they don't fly high nor particularly fast
Steel tube structures are probably the best overall for crash protection, given what we see in motor sports and as mentioned in the link above. Unfortunately its getting harder to find the skill sets necessary to fabricate a tubular structure nowadays......I seriously need to get back to redeveloping my mediocre skills. AG planes are perfectly good examples in my opinion.
Considering most crashes occur at ground level, the cruising altitude of the aircraft is almost irrelevant.
You can attain fatal deceleration from less than 10 feet altitude if you get it wrong
I think they are a good proxy, especially as many times when they hit the ground/an object it is not under ideal conditions (e.g they hit an unseen wire or don't quite clear a treeline, they aren't necessarily slowed down for landing/impact when bad things happen).
OTOH, I'm not ready to say that a designed-for-crashworthiness composite cockpit can't be as good as a steel tube fuselage. Those Formula 1 cars hit some unforgiving things at tremendous speeds and unusual orientations and the drivers often come away uninjured. There are lightweight (and expensive) composite sailplanes that have good crashworthiness. And there are AL frame airplanes that also do well in crashes. I do think it's easier to design and build a very safe steel tube airplane than just about any other kind, and as a bonus it provides a very handy way to distribute the point loads we have in airplanes (landing gear mounting locations, engine mounts, wing spar carrythroughs, occupant restraints, etc).
Ag planes are designed for loads far in excess of other aircraft, and have specific structure to protect the pilot in a crash. Comparing them to a typical HBA is akin to comparing a Sherman tank to a go-cart.
There are valid comparisons to be made wrt crashworthiness of a structure, but direct comparisons are difficult due to performance differences of aircraft, design margins in structures (a Pitts S-1S, for example, is certificated at +6 / -3 g, not too different that several semi-monocoque aluminum fuselages, but the Pitts is routinely flown at load factors up to +9 and -7, values that would fail the aluminum fuselages. I.e., Their designs are very different, even though they are considered to be designed for the same load factors.) and treatment of factors such as injury from splintering carbon, etc.
Steve probably has some relevant information.
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