Given the question What happens when all passengers jump at once?, I wonder what would happen if they all moved from side to side. If all the passengers moved from the front to the tail, or the other way around, there might be balance problems, but what if they moved from right to left (or vice versa)? I imagine the fuselage is not wide enough for this to seriously affect the aircraft's balance, but I would like confirmation for this assumption.

To have the greatest visible effect, the answer may focus on aircraft with relatively wide fuselages (for instance, A380, B747, B777). Maybe the effect is more visible for aircraft with smaller wingspans, thus, answers may also mention GA aircraft with a large enough body-width-to-wingspan ratio (the opposite of a glider).

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    $\begingroup$ Anecdotally: When you start learning to fly there's an even left/right distribution of weight (you + instructor). The first time you solo there''s a definite bias to the left which needs balancing. You soon become accustomed. $\endgroup$
    – Jamiec
    Sep 5 '19 at 7:47
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    $\begingroup$ I don't recall noticing anything different in the lateral balance when I "got rid of" the instructor. Peformance was notably better though, as I'd be taking off ~10% lighter :) $\endgroup$
    – Jpe61
    Sep 5 '19 at 15:14

You can get a significant rolling tendency if you shifted cargo or pax all to one side, but not enough to affect controllability; it would just be annoying. This would apply to most airplanes.

Transport airplanes will have a lateral Center of Gravity range that has to be respected, along with a maximum fuel imbalance limit, to ensure controllability in some critical case. In the CRJs, which are quite narrow, if everybody piled into the seats in one side, you (or the autopilot) would definitely notice it and have to correct with aileron, although it would be no problem trimming it out. A really large fuel imbalance would be a much bigger problem however and might use up quite a bit of the available roll authority, so there are fuel imbalance limits in addition to lateral CG limits.

FAR 25 requires that the roll trim system provide the ability to trim out the rolling moment from max lateral CG offset in the most critical case - on takeoff, one engine inoperative, climbing at V2 (engine failure safety speed), with maximum allowable fuel imbalance. On the CRJs this uses up only about a third of the airplane's total roll authority (the RJ's roll trim just offsets the neutral point of the control circuit).

  • $\begingroup$ On the other hand, the CRJ, having tail-mounted engines, has much less engine-failure-induced rolling tendency than (say) a 737. $\endgroup$
    – Vikki
    Sep 5 '19 at 21:08
  • $\begingroup$ Not that much less, because the engines aren't really that much closer to the center line. It still yaws fairly hard single engine and once the nose has moved 10 degrees or so it starts to roll hard and if you do nothing with the rudder you will be using most of your aileron to keep it from flipping over, while flying along all cockeyed. Pilots learn this quickly on their first V1 cut in training (the sim models this very well) and often hit the ground with a wingtip on the first try if they are late or not aggressive enough with rudder. $\endgroup$
    – John K
    Sep 5 '19 at 21:17

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