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A friend who flew the L1011s loved them because of their stability. His joke was that you could put the plane into a banked turn , go to the bathroom, come back, and you would still be in the same banked turn. He felt that other planes like the 767 require far more concentration.

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Can a pilot explain to me how an aircraft not returning to straight and level flight on it's own decreases workload? Would you not have to correct every small bank error just to not go off course?

Edit Jan Hudec is correct when he says that it may involve s comparison of spiral dive tendency. But

still be in the same *banked" turn. H

Makes me wonder why it doesn't right itself

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    $\begingroup$ Why do you think it's being compared with returning to wings-level? It's being compared to continuing to bank into the graveyard spiral. $\endgroup$
    – Jan Hudec
    Apr 24, 2021 at 9:54
  • $\begingroup$ @JanHudec well, I see no evidence that it doesn't work both ways. But yes, comparing the he spiral behaviour makes sense $\endgroup$ Apr 24, 2021 at 10:00

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It's because, while neutral roll stability (tendency to stay at a bank angle until disturbed) is an undesirable characteristic for an aircraft that is flying straight and level because more attention is required to keep it there, it's a desirable characteristic while maneuvering.

Normally, you have to choose one or the other, so you choose positive roll stability because that's the priority for an airplane designed to cruise.

Airplanes that spend a lot of time, or are optimized for maneuvering, like aerobatic aircraft and gliders, tend to make neutral roll stability a priority. This is a really desirable feature on a glider that spends perhaps a majority of its time in thermals in 30 degree banked turns. When you spend extended periods turning, the tendency to hold a bank angle is a great feature.

As well, when flying on instruments, a tendency to hold a bank angle naturally is a useful feature. You are generally either in level flight where you want positive roll stability, or are in a standard rate turn, where a tendency to retain the turn rate without input is nice to have.

So, an airplane that had positive roll stability while level and neutral roll stability while maneuvering (on purpose) can be the best of both worlds.

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