They're Soliciting Tail-strike Solutions
An airframe mechanic mate of mine and I were discussing the CI-611 accident and he sent me this:
The FAA a few years ago prohibited using dissimilar metals (such as stainless steel) in airframe doubler repairs because over each cycle of temperature and pressure they'd "work" and even the area being repaired (doublered) would be "worked" by the vastly different coefficients of expansion and ductility etc of a dissimilar metal (and disregarding any possible electrolytic interaction). However what they did NOT do was insist that previous repairs (the ones most at risk due to the nature of the glitch) be inspected or re-done. CI-611 was probably the legacy of that policy. Now that they've established that it's a definite problem, they are trying to head it off at the pass. Makes you wonder why their aeronautical engineers couldn't work out that any such dissimilar metal repair would work itself into a failure eventually. Think of it as the repaired section and the doubler both working on each other cyclically (and more importantly, on the riveting securing the repair).
Perhaps if they made manufacturers build longer undercarriage legs (especially for stretched models) there'd be less tail-scrapes (or the more injurious tail-hits on over-rotated landings). But that would mean more weight and less performance (and less carry-on future repair business). That engineering order we received at Eastern to get those stainless doublers off our DC-9s came from Douglas back in the late
70s when I was then assigned to structural repairs.
So some 30 years later, the FAA 'sees a problem'....
TO WHICH I REPLIED WITH THIS
Actually another way of avoiding tail-scrapes on landing would be to arrange the trailing-edge flaps such that they auto-deployed a little more during the landing flare (on a RADALT or body-angle cue perhaps) - and thus kept the body angle less pitched at oleo compression. That should be able to be contrived by the flight-control designers. In my experience, very few airframes on stretched models wouldn't have taken a hit or two on landing over the years (but admittedly, some worse than others). Having the standard fowler flap arrangement deploy a few extra degrees as the nosewheel comes off would also probably avoid the classic tailstrike because of overrotation on take-off. At take-off settings the fowler flap extends initially(without drooping much more) and at land-flap type settings it just droops, and although that creates instant lift there is much greater drag (which helps in particular for an early planting and stopping on contaminated runways). The pilot wouldn't notice the effect on take-off (except perhaps that the aircraft would seem to leap into the air). On landings he should (if it's done right by the flight-control designers) just find that he won't have to flare as much to achieve an acceptable descent rate.
I suppose you could achieve much the same thing (tail-clearance on stretched jets) on take-off by having a mechanism to fully extend the oleos at rotate. Not sure if that would/could be used to work for a late over-flared landing "save" though.
Each fuselage repair costs many millions and constitutes a future potential failure area, so the designer who comes up with a workable and patentable solution for it that doesn't lead to weight growth - well he would/should make millions (maybe).
Anybody agree (or have similar views but an alternate solution)? I hasten to add that I have had a landing tail-strike - but that was more related to idiocy/fatigue than anything else.
I'll post this in Rumours and News - and realize that it may be moved (but it's really a matter of soliciting wide-spread opinions and that may happen more readily through being initially there). Those who feel the need to suggest non-technical solutions should probably just save their verbiage. The requirement here is to eliminate as much as possible the human element (or rather, accommodate it).