Not really and that's the problem. Different load case combine for higher local loads.But for the aft fuselage as an example here, it all breaks down to a few worst cases of this much bending in this axis, that much bending in another, "x" amount of drag load, and so much torsion.
What experience?I don't believe you. My own experience says otherwise. HITC's own experience says otherwise. HotWing's own experience says otherwise.
HitC actually confirms my point. Make it heavier and physically smaller and it's less complex to design. But we can't do that for a FAR103-like design, since size (stall limit) is by definition big and weight (weight limit) by definition very low.
Yes, it does, unless you want to fly with an airplane that fails below limit load.I suspect you're doing a Boeing-level structural analysis on something that absolutely doesn't need it. No, the product won't be as optimized. It doesn't need to be. I'm talking about balance and you're talking about absolutes.
Simple fact. NO single design I'm aware of has passed actual load tests without failures and I can't think of one that didn't fail at least once before limit load. All designs now flying and tested either did the engineering properly, or after multiple failures concluded that they had to do it, since continuing breaking wings/tails was too expensive. Walking around all those broken constructions does give one a great understanding of actual design (vs analysis, which is what the books teach you)
Going through dozens of photos from different load tests is sobering and I've seen hundreds of thousands of euro's of trashed wings/fuselages etc because they didn't do their engineering. I'm not trying to argue Marc and this is not about belief.
This is about sharing some hard-learned lessons. That's what HBA is all about in the end.
Another then. You can replace LSA with FAR103. Exactly the same story:
Mainly because of experience, but a bit of analysis is behind it too. So far I've been asked to either design or consult to probably half a dozen different LSA developers, all of whom interestingly enough, had very similar attitudes regarding their airplanes and the development programs. I can sum them up into a few categories:
1) The first has several variations - basically this is where they show me an artistic sketch and a bit of what they call design work and then ask me to go from there and design the airplane. When I proceed to do so however, they respond with an attitude where they think that they already designed the airplane but what they really need from me is to essentially rubber-stamp their ideas. That's without any analysis or engineering though. When I refuse to do so they come back with an insulted attitude - one actually told me that I should feel privileged to be asked to work on their program and so should provide the verification they asked for.
2) The second is sort of a corollary to the first - it's where their "team" has come up with a design and they don't need me to actually design the plane but they do want me to look over a couple of the details. Usually I can't do this simply because I need to verify what I'm working on. Eventually they agree but when my BS detector is verified and I have to inform them that they have an unworkable design (and I do document my reasoning), they again come back very huffy, usually telling that I don't know what I'm talking about. One even threatened to sue me. When I provide them with my initial report (one that they actually never pay for), they often try arguing the points however usually with a lot of arm waving (and statements about having faith) but no actual verifiable proof.
3) The third is more basic and very common - an unrealistic budget. They think that because this is a light airplane that the design work should take no time (or money) at all. Interestingly enough, when I explain that the work to design an LSA and something high performance like a Glasair III is nearly identical they indicate that they understand, but they still think their project should be much cheaper. Virtually all of these had very unrealistic budgets to begin with and none have actually gone anywhere.
4) The last is more technical - I've had several discussions with other designers regarding this category and most of us feel that these are very marginal airplanes. If they were being used and marketed as originally proposed (fat ultralights) then I think there would be no problem. But instead these are now being marketed as trainers or cross country airplanes, equivalent to Part 23 production units. And here is where we have a problem - they simply are not. The structural design of many of these new airframes is short of what we'd have with Part 23 standards, and more so when you consider that most of them will be operated over weight. That's of course not to say that all are marginal (after all, some of the older production planes fall within the LSA limits and they did certify to Part 23) and some are honest enough to publish the lower load factors to which they were developed, but in our opinion there just is not sufficient structural mass margin in a two place LSA configuration to make us feel comfortable.
In short, the reason we stay away is due to many of the somewhat unpleasant personalities we've run into, and because we feel the category is too restricted and mostly a big step backwards for the light airplane industry.