The plane is off balance???

"deekster_caddy" (deekster_caddy) 11/30/2016 at 05:38 • Filed to: None

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So I have flown a fair amount... but never on a flight have I heard them asking for passengers in the front rows to volunteer to make ve to the back of the plane to balance it out? Jetblue, what I consider a ‘normal mid-large passenger jet’... Is this for real or are they just trying to accomodate someone’s late stubborn seating request?

I mean, if the plane is that empty it wouldn’t be that big a deal would it? It’s the flight at the next gate which doesn’t appear to be sold out but isn’t deserted either...

victor > deekster_caddy 11/30/2016 at 06:09

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It’s quite common

random001 > deekster_caddy 11/30/2016 at 06:23

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Balance is very real to aircraft. Basically, you want the lift from the wings to be as close to a vertical force as possible. If the lift force is responsible also for tilting the plane, you lose a lot of efficiency, which makes the plane slower, uses more fuel, etc.

Ever stick your hand out the window in a moving car? If you hold it perfectly perpendicular to the direction of travel, it’s easy to just hold it right there, but tilt it slightly forward or back and either your hand goes flying down or up, or you have to put a lot more force to hold it steady. Even when you do that, you get wind eddy effects, buffeting, that makes your hand not steady. Same principle.

If they were required to take a particularly heavy cargo shipment, and could only fit it in one door of the plane and secure it in one spot, that could also require people to move. They have sensors in the landing gear that measure the distributed load in the plane for that sort of thing.

facw > deekster_caddy 11/30/2016 at 06:46

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You don’t see it much on mainline airliners, but it’s common enough on regional flights. Too much weight at the back and you may not be able to keep the wing down to avert it stalling, too much weight in the front and you may not be able to generate enough lift.

Or more weirdly, on a recent flight (on a 737-900) we had to wait at the gate because apparently the loading of the plane was such that if the passengers at the front got off before the luggage was partially unloaded, the plane was in danger of tipping backwards. Then they decided that unloading baggage from the rear hold would take too long, and apparently set some sort of jack stand at the rear of the of the aircraft (apparently this is not unusual with the 737-900, here’s a Delta one with the pole):

deekster_caddy > random001 11/30/2016 at 06:47

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Cool, thanks. I get it, but I didn’t think moving a couple hundred pounds around would make that much difference on a plane weighing many many thousands... On a snall plane I can understand it making a big difference...

deekster_caddy > facw 11/30/2016 at 06:48

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Wow, I never realized they could handle enough cargo weight that that was even possible!

Cé hé sin > deekster_caddy 11/30/2016 at 06:51

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I’ve been there a couple of times. You’ll also note that if they’re not full the front few rows will be left empty.

bhtooefr > deekster_caddy 11/30/2016 at 06:51

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It also depends on how far you move the weight.

If you’ve got a couple hundred pounds right at the front, and move them all the way to the back, that’s a considerable balance shift.

random001 > deekster_caddy 11/30/2016 at 07:48

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I agree, but they are surprisingly sensitive to that. Now you might be saving, say 3% in fuel, but to the money people that’s a lot.

Rico > deekster_caddy 11/30/2016 at 07:55

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Too bad it wasn’t the other way around

“Would anyone like to volunteer for first class, we need to balance the plane”

GTiceman > deekster_caddy 11/30/2016 at 08:03

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I actually read this and was thinking I haven’t heard this recently, likely because most of my flights have been full. This is certainly a common thing being reviewed before every flight liek others have said. It happens when you have open seating or if a number of people don’t show up for a flight or seats don’t get filled.

AuthiCooper1300 > deekster_caddy 11/30/2016 at 08:05

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I remember a documentary about the early days of BA in the late 30s - when it was still Imperial Airways – and a charming old lady telling the story of a one trip to the far East in a Short Empire flying boat. She had just had a baby, who was put at the very back of the cabin. Said baby must have been very cute because the passengers went all to see him... until a cabin steward asked them to return to the front because they were affecting quite badly the trim of the aircraft.

TheRealBicycleBuck > deekster_caddy 11/30/2016 at 08:22

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This videos focuses on r/c planes, but the same principals apply to full-size aircraft.

Weight distribution affects handling, even in cars. Front-heavy cars push in turns, rear-heavy cars tend to spin. Moving the center of gravity of a plane, even a small amount, has similarly affects handling. The most dangerous flight condition is a tail-heavy plane.

Jayhawk Jake > deekster_caddy 11/30/2016 at 09:01

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I’ve seen it. If the plane is empty and a lot of people went to the back then it’s a very big deal.

Jayhawk Jake > deekster_caddy 11/30/2016 at 09:03

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The aircraft itself is relatively light. Takes surprisingly little to tilt it back, and the gear location doesn’t help static stability. The Center of Gravity is about 15 degrees forward of the main gear to allow the plane to rotate, so it doesn’t have to move far for the plane to start tipping

EDIT: For fun I looked up some weights. 737-700 empty weight is 83,000 pounds, but max takeoff weight is 154,500 pounds. 46,000 of that capacity is fuel.

shop-teacher > Rico 11/30/2016 at 11:21

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I actually got to do that once. I offered to move up, and they were going to move me into a more forward coach seat. When I saw they were going to sit me next to a big dude (I am also a big dude), I asked if I could just go back to my old seat so we wouldn’t both be super uncomfortable. Then the flight attendant said, “Would you like to move up to first class instead?” Yes ... yes I would! It was a less than 2-hour flight, so I didn’t get to enjoy it long ... but man was that nice!

haveacarortwoorthree2 > GTiceman 11/30/2016 at 11:45

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Was thinking the same thing about full flights. Had the middle seat next to me on my flight last night and it was like Nirvana. OTOH, I was stuck in the middle seat on my flight Monday due to a last minute booking, although it was at least an exit row thanks to my airline “status.”

MM54 > deekster_caddy 11/30/2016 at 20:03

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I’ve had it happen on regional jets before, they had people move back since there wasn’t much checked baggage.

Santiago of Escuderia Boricua > deekster_caddy 11/30/2016 at 22:54

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Pilots suck at math