# Homework Help: Seat position in plane

1. Sep 24, 2016

### ChloeYip

1. The problem statement, all variables and given/known data
Finding yourself in a nearly empty airplane, you take a seat other than your allotted seat. Soon, an air hostess comes up to you and requests you to occupy a different seat.

What may be the reason?
A) The plane momentum can change if the passengers change their position that affects the safety of the flight.
B) Certain seating positions, when occupied in a nearly empty plane, would raise the center of gravity of the plane.
C) Depending on the places occupied, inertia of the plane may decrease that allows the engine to provide less thrust and expend less fuel.
D) Changing seats may keep the position of the center of mass of the plane unchanged.

2. Relevant equations
Momentum
Center of gravity

3. The attempt at a solution
B or D?
But I m not sure whether "raise center of gravity" would affect anything of the flight...
As the weight is still remain the same...(vertical?)

Thanks.

2. Sep 24, 2016

### phinds

I cannot imagine that a single passenger can meaningfully change ANY of A->D unless it's an awfully small plane. Where is this question from?

3. Sep 24, 2016

### CWatters

I used to be a glider pilot. In my opinion none of the answers are particularly good.

I suppose answer D is the most reasonable but even so it's badly worded.

4. Sep 24, 2016

### ChloeYip

Thank you.
I agree with you, but I think it just theoretically about a very unstable plane.
This question is from Pearson university physics.
But can anyone of you tell me how can the change of seat can affect the center of gravity thus the plane?
Moreover, "keep something (i.e. center of gravity) unchange" is quite a strange reason or explanation for "changing something (i.e. the seat)"... Can you explain more why you choose this option?
Thanks.

Last edited: Sep 24, 2016
5. Sep 25, 2016

### CWatters

D is badly worded. If a significant number of passengers decide to sit at the back then the centre of mass of the whole aircraft can move towards the rear of the plane. That can affect the stability. The steward asks you to move forward so that does not happen.

6. Sep 25, 2016

### ChloeYip

So, for B, it would not "raise" the centre of gravity because the passenger is still on the same horizontal level compared with the plane, am I right?
Thanks.

7. Sep 25, 2016

### CWatters

Well there are planes like the Boeing 747 that have a small upper deck so yes it is possible for a moving passenger to raise the centre of gravity. However this effect is unlikely to have a significant impact on the aircraft so the steward is unlikely to ask you to move for thst reason. Im afraid this whole question is badly worded.

8. Sep 25, 2016

### Staff: Mentor

E) None of the above.

The stewardess just wants you closer to the galley, so less walking for the stewardesses.

9. Sep 25, 2016

### Filip Larsen

It would make sense that D is appropriate answer if the airline company has opted to not calculate the CG contribution from the actual passengers seating but instead use a seating schedule that dictates a certain load spread across passenger zones, meaning that the CG contribution may possibly be calculated from the number of passengers alone. See [1] for an FAA Advisory that seems relevant to this issue.

10. Sep 25, 2016

### hmmm27

Trim tabs on control surfaces are positioned to compensate for, among other things, cg effects. More tab equals more parasitic drag. Less tab equals less drag. However "inertia of the plane may decrease" ?

Last edited: Sep 25, 2016
11. Sep 29, 2016

Thanks