Any Commercial Pilots Here? I Have A Question.

[scloyd]

Yesterday I had to go to the airport and pick up my son who was flying from Seattle to Chicago on Alaska Airlines...no, he is not a "knucklehead spring breaker". On the drive home he stated that the plane was half full and the passengers were told not to move to other seats because they need to keep the plane balanced.

What? ?

Is this true? I've never heard of this...keeping the plane balanced? Really?

 

[Casual]

This plane could only turn right.

 

[shanez]

I've flown on a number of smaller commercial flights that had this requirement.

 

[scloyd]

I've flown on a number of smaller commercial flights that had this requirement.

The plane was a Boeing 737-900. Almost 200 seats, 100 of them empty. I don't know if that matters.

I'd like to hear from a pilot and find out what effect it has on the plane or the ability to fly the plane.

 

[3rdguy]

Had this happen to me. They asked me to move from one seat to another as to balance the plane out. Happens on flights that are mostly empty.

BTW I am not fat lol. I think since I am 6'3, 215 I was the biggest thing to move around.

 

[elessar]

This sounds reasonable. Fuel is even pumped around or used from certain tanks in a specific sequence to maintain balance or trim. Chances are the plane could easily fly with everyone moving around but if the cg shifts the pilot must trim for it which causes extra drag and fuel usage. The flight plan probably accounts for some extra fuel but I imagine pilots don't want to eat into that for balance issues.

 

[elessar]

I should add that I am not a commercial pilot, just making observation. My thoughts are worth what you paid for them lol.

 

[alaskanpiper]

I am a private pilot. Weight and balance is absolutely essential to any aircraft. So much so that it should be calculated for each flight and you are required to have a copy of the aircrafts empty weight and balance information on the aircraft, and it must be recalculated and signed off by a licensed mechanic for a change even as small as relocating the battery.

Without proper weight and balance calculations the aircraft can have it’s center of gravity too far forward, or too far aft which can cause all kinds of very dangerous problems aerodynamically.

Most notably, it can increase the stall speed on the aircraft, making it stall at a higher rate of speed than expected (not good) and create very dangerous aerodynamic challenges on takeoff and landing.

 

[alaskanpiper]

For more details:

Center of gravity of an aircraft - Wikipedia

en.m.wikipedia.org

 

[alaskanpiper]

Forward CG:

Aft CG (due to load shifting):

And over gross weight:

That last one happened on the same lake we keep our plane on in Anchorage.

 

[anotherbob]

never heard that before and would assume that is something that was already taken care of. I'd assume before this discussion that there would be systems in place to counter such things. My first gut feeling was it's a way to keep people from spreading germs.

 

[alaskanpiper]

never heard that before and would assume that is something that was already taken care of. I'd assume before this discussion that there would be systems in place to counter such things. My first gut feeling was it's a way to keep people from spreading germs.

I promise you it has little to do with germs. If any commercial pilots show up they will tell you that having passengers move for weight and balance when an aircraft is not full is very common practice and was implemented long before covid-19 showed up.

 

[Akousticplyr]

It’s a weight and balance issue. The center of gravity is always calculated before every flight - factors include # passengers and their baggage, any additional cargo (you’d be surprised how much shipping commerce is also in commercial flights), fuel load and distribution (wing tanks vs main tanks) etc.

It’s pretty automated regarding seating with computerized algorithms to avoid shifting the CG to an undesirable or unlikely but extreme worst case uncontrollable position.

 

[mso489]

Talk about taking things for granted, flying along at 20,000 feet sipping ginger ale. I guess weight and balance might play a role. They do when you and a few friends get in a fishing skiff. But I admit, I never gave it much thought, probably thinking that fewer people would be factored out in the engineering of passenger planes. Well, now I can think again.

 

[alaskanpiper]

It’s a weight and balance issue. The center of gravity is always calculated before every flight - factors include # passengers and their baggage, any additional cargo (you’d be surprised how much shipping commerce is also in commercial flights), fuel load and distribution (wing tanks vs main tanks) etc.

It’s pretty automated regarding seating with computerized algorithms to avoid shifting the CG to an undesirable or unlikely but extreme worst case uncontrollable position.

View attachment 23490

I would add that in addition to this, you must calculate the fuel burn rate and its impact as well. At 6lbs per gallon (thats avgas, im sure jet fuel is different but close) and with a 747 burning something like a gallon per minute, the weight and balance shifts rapidly and significantly. Pre-flight includes making sure your aircraft remains in the appropriate CG window throughout the flight as fuel burns off and thus changes both weight and balance.

 

[alaskanpiper]

Talk about taking things for granted, flying along at 20,000 feet sipping ginger ale. I guess weight and balance might play a role. They do when you and a few friends get in a fishing skiff. But I admit, I never gave it much thought, probably thinking that fewer people would be factored out in the engineering of passenger planes. Well, now I can think again.

Hahaha this is why flying commercial is such a distinct pleasure for me. I can sip my beer and for once not be the guy doing all these calculations, hahaha.

 

[Akousticplyr]

Talk about taking things for granted, flying along at 20,000 feet sipping ginger ale. I guess weight and balance might play a role. They do when you and a few friends get in a fishing skiff. But I admit, I never gave it much thought, probably thinking that fewer people would be factored out in the engineering of passenger planes. Well, now I can think again.

When all the factors are calculated from aircraft structural design to aerodynamics —It’s really a beautiful dance. The ultimate expression of how science, math and form are applied to advancing our lives. (Yes, I nerd out about this stuff).

It is an absolute marvel to me how all the engineering & equations culminate into something so sublime and simple for the end user to execute safely.

I also feel the same way about orbital mechanics. ?


*Speaking as an aerospace engineer with a concentration in aerodynamics, reserve Naval Aviator, commercial multi engine instrument rated pilot.

 

[Richmond B. Funkenhouser]

I was once an aircraft mechanic, I can assure you weight and balance is a thing. Smaller planes use ballast, to correct this.

 

[Akousticplyr]

I would add that in addition to this, you must calculate the fuel burn rate and its impact as well. At 6lbs per gallon (thats avgas, im sure jet fuel is different but close) and with a 747 burning something like a gallon per minute, the weight and balance shifts rapidly and significantly. Pre-flight includes making sure your aircraft remains in the appropriate CG window throughout the flight as fuel burns off and thus changes both weight and balance.

Absolutely. Flying fighters, we also had to pay particular attention to load outs of bombs, missiles, pods, drop tank fuel transfer, and the real killer- asymmetric loads which could cause big problems during dynamic maneuvering (high G tactics, dogfights, etc ) and single engine operations - especially during carrier takeoffs and landings. That’s what the Jettison stores button and the ejection handle are for! It’s also why the a Blue Angels fly”slick”- no bomb/missile racks or rails and no centerline drop tank.

*We use 6.8 lbs per gallon as our rule of thumb for JP gas calculations.

 

[alaskanpiper]

Absolutely. Flying fighters, we also had to pay particular attention to load outs of bombs, missiles, pods, drop tank fuel transfer, and the real killer- asymmetric loads which could cause big problems during dynamic maneuvering (high G tactics, dogfights, etc ) and single engine operations - especially during carrier takeoffs and landings. That’s what the Jettison stores button and the ejection handle are for!

*We use 6.8 lbs per gallon as our rule of thumb for JP gas calculations.

Haha I was just looking up the weight used out of curiosity. I only speak 100LL and/or 50/50 with auto gas, hahaha. If it’s not Continental or Lycoming It’s as good as greek to me, hahaha.

Can’t imagine flying a fighter. Going from a 172 to a 185 was like going from a go cart to a ferarri to me.

When I went back to the 172 to get some night hours after a year in the 185 (185 is on floats) on the takeoff roll I was like “Jesus, is this thing even gonna get off the ground!?!?” Hahaha.