0
$\begingroup$

What I mean by this question is cases of airliners or private jets.

You have possibilities of luggage shifting mid-flight, people changing seats (occasional but it does happen), and on private jets, you have people walking around the cabin maybe to visit or in the case of larger private jets people walking all over the plane.

People will be of varying weight by age, size, and height. Would this not cause balance issues with shifts in weight around the cabin and cargo compartments? What typically happens to help account for these situations?

Is it as simple as adjusting trim? Or are there other considerations/operations to take into account?

$\endgroup$

1 Answer 1

5
$\begingroup$

Luggage shifting generally isn't a problem, since large luggage volumes are containerized and therefore compartmentalized, and in smaller jets like corporate aircraft, the luggage is confined to a small space.

With swept wing airplanes, fuel burn causes a natural and significant C of G shift as fuel C of G moves forward as fuel level declines in the outer extremities of the tanks, which is more aft.

If the plane has a center wing tank that is depleted first, the C of G shifts aft, then forward during the flight. When you do weight and balance on a jet with a center tank, the fuel C of G curve on the weight and balance graph looks like a bit like a cursive letter Z in depicting this shift, and the curve has to respect the C of G limits at all points.

People moving around will have subtle effects on trim, but nothing like the fuel effects in a swept wing airplane, unless you have entire groups all moving at once. It's all about proportion. If you are a small two seat homebuilt, just leaning forward in your seat will give you a 5 or 10 knot increase in trim speed.

In any case, any C of G shift changes the airplane's trim nose up (slower) or nose down (faster). If you are hand flying, you will have to adjust trim as you notice the plane pitching in response to the change in trim. Most of the time however, the autopilot is on, and it takes care of the trim on its own.

If you are hand flying and some passengers move forward or aft enough to make a noticeable change, you will just be instinctively blipping the trim to make the airplane do what you want.

$\endgroup$
2
  • $\begingroup$ Thanks for the great answer! I’ve always been curious about how much of an effect that has and in those cases how detrimental it is towards the operation of the aircraft. A friend of mine took me up in a small Piper once and mentioned how even the smallest shift in weight or C of G could cause adjustments to have to be made so it made me curious about bigger private jets and even airliners. $\endgroup$
    – Jon
    Sep 14, 2022 at 3:33
  • 1
    $\begingroup$ You rarely hand fly a jet in cruise. Just too much work. So the AP masks the changes 98% of the time. My father flew C-47s during WW2 in Burma, doing combat support airdrops into jungle clearings near Japanese lines and such, and they would take a crew of 3 or 4 extra "kickers" to help move and push the bundles of ammo and food out the door during the drop. On the way back with an empty airplane, they would have fun by running back and forth in the cabin to make him have to constantly retrim. Bunch of 19-21 year olds, what do you expect? $\endgroup$
    – John K
    Sep 14, 2022 at 4:47

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .