Moderators: richierich, ua900, PanAm_DC10, hOMSaR

seat1a
Topic Author
Posts: 876
Joined: Mon Jan 11, 2010 7:52 pm

### Is an Aircraft Perfectly Balanced 50/50?

Not sure how to phrase the question - but is a Boeing 787 or Airbus A321 without the airline customers configuration of seats, etc., perfectly balanced 50/50? If you were to draw a line down the middle of the plane, would both sides be equal in weight?

GalaxyFlyer
Posts: 9422
Joined: Fri Jan 01, 2016 4:44 am

### Re: Is an Aircraft Perfectly Balanced 50/50?

Probably within manufacturing tolerances, but we’d never know it. We could load one side of a C-5 with 18 pallets of about 100.000#, leave the other side empty and notice it. Lots of weight, little arm

StereoTechque
Posts: 230
Joined: Sat Nov 28, 2015 7:24 am

### Re: Is an Aircraft Perfectly Balanced 50/50?

seat1a wrote:
Not sure how to phrase the question - but is a Boeing 787 or Airbus A321 without the airline customers configuration of seats, etc., perfectly balanced 50/50? If you were to draw a line down the middle of the plane, would both sides be equal in weight?

Whether an Aircraft is loaded or no it always has a desired CG range in which it has to be operated. An airliner also relies but not neccessarrily on systems such as Trimmable Horizontal stabilisers/trim tanks to assist in CG balancing.

phugoid1982
Posts: 331
Joined: Sat Sep 10, 2016 4:02 am

### Re: Is an Aircraft Perfectly Balanced 50/50?

The CG will vary upon a loading as will the center of pressure but there is range of motion that must be maintained for stability. For longitudinal static stability the CG should be forward of the center of Lift. That way, if there is a pitch disturbance upwards, the resulting change in AOA and increase in lift will produce a torque downwards back to trim. Conversely, if downward pitch is induced a reduction in lift will produce a restorative torque to trim. Once the, CG is aft of the center of pressure, the reverse happens and a positive disturbance in AOA will produce an even more positive destabilizing torque and a negative AOA will produce a further downwards pitching moment.

ReverseFlow
Posts: 396
Joined: Mon Mar 14, 2022 4:40 pm

### Re: Is an Aircraft Perfectly Balanced 50/50?

StereoTechque wrote:
seat1a wrote:
Not sure how to phrase the question - but is a Boeing 787 or Airbus A321 without the airline customers configuration of seats, etc., perfectly balanced 50/50? If you were to draw a line down the middle of the plane, would both sides be equal in weight?

Whether an Aircraft is loaded or no it always has a desired CG range in which it has to be operated. An airliner also relies but not neccessarrily on systems such as Trimmable Horizontal stabilisers/trim tanks to assist in CG balancing.
The aircraft has to stay in its limits of a fan diagram.

Woodreau
Posts: 2300
Joined: Mon Sep 24, 2001 6:44 am

### Re: Is an Aircraft Perfectly Balanced 50/50?

For an aircraft athwartship CG is not as critical as it is for helicopters

We care where CG is longitudinally but don’t consider where it is left/right of the buttline.

Posts: 3729
Joined: Wed Mar 01, 2006 4:29 am

### Re: Is an Aircraft Perfectly Balanced 50/50?

Given latest discussion about manufacturing tolerance affecting empty weight, as well as design asymmetry - such as different doors for R1 and L1, I doubt there is a perfect symmetry.
Arm is small, as it was pointed out, so effect is limited

ReverseFlow
Posts: 396
Joined: Mon Mar 14, 2022 4:40 pm

### Re: Is an Aircraft Perfectly Balanced 50/50?

Given latest discussion about manufacturing tolerance affecting empty weight, as well as design asymmetry - such as different doors for R1 and L1, I doubt there is a perfect symmetry.
Arm is small, as it was pointed out, so effect is limited
There are tolerances on the lateral roll/trim which are checked out during production flights.
But that's probably more to do with aerodynamic effects than weight.

ReverseFlow
Posts: 396
Joined: Mon Mar 14, 2022 4:40 pm

### Re: Is an Aircraft Perfectly Balanced 50/50?

Woodreau wrote:
For an aircraft athwartship CG is not as critical as it is for helicopters

We care where CG is longitudinally but don’t consider where it is left/right of the buttline.
You will get a fuel imbalance alert if your tank balance left/right exceeds a threshold.

Posts: 3729
Joined: Wed Mar 01, 2006 4:29 am

### Re: Is an Aircraft Perfectly Balanced 50/50?

ReverseFlow wrote:
Woodreau wrote:
For an aircraft athwartship CG is not as critical as it is for helicopters

We care where CG is longitudinally but don’t consider where it is left/right of the buttline.
You will get a fuel imbalance alert if your tank balance left/right exceeds a threshold.

Can you give an idea of what that threshold is? I suspect around 1% of max fuel or so?

ReverseFlow
Posts: 396
Joined: Mon Mar 14, 2022 4:40 pm

### Re: Is an Aircraft Perfectly Balanced 50/50?

ReverseFlow wrote:
Woodreau wrote:
For an aircraft athwartship CG is not as critical as it is for helicopters

We care where CG is longitudinally but don’t consider where it is left/right of the buttline.
You will get a fuel imbalance alert if your tank balance left/right exceeds a threshold.

Can you give an idea of what that threshold is? I suspect around 1% of max fuel or so?
From here

https://www.boeing.com/commercial/aerom ... tonly.html

This table for example

https://www.boeing.com/commercial/aerom ... ble01.html

GalaxyFlyer
Posts: 9422
Joined: Fri Jan 01, 2016 4:44 am

### Re: Is an Aircraft Perfectly Balanced 50/50?

ReverseFlow wrote:
Woodreau wrote:
For an aircraft athwartship CG is not as critical as it is for helicopters

We care where CG is longitudinally but don’t consider where it is left/right of the buttline.
You will get a fuel imbalance alert if your tank balance left/right exceeds a threshold.

Can you give an idea of what that threshold is? I suspect around 1% of max fuel or so?

Varies by design, how spread across the wings the fuel tanks.

jetmech
Posts: 2414
Joined: Wed Mar 29, 2006 2:14 am

### Re: Is an Aircraft Perfectly Balanced 50/50?

seat1a wrote:
If you were to draw a line down the middle of the plane, would both sides be equal in weight?

Probably not, but it'd be close to within a very small percentage of the overall OEW.

As others have said, any lateral weight imbalance from airline specific cabin fitouts acts upon a very small moment arm relative to the wingspan, as such; lateral balance would be achievable with very small amounts of lateral trim.

Regards, JetMech

Florianopolis
Posts: 378
Joined: Sun Mar 29, 2015 2:54 pm

### Re: Is an Aircraft Perfectly Balanced 50/50?

seat1a wrote:
Not sure how to phrase the question - but is a Boeing 787 or Airbus A321 without the airline customers configuration of seats, etc., perfectly balanced 50/50? If you were to draw a line down the middle of the plane, would both sides be equal in weight?

The airplane isn't symmetrical left/right, so no. The cargo doors add weight to the right side, the hydraulics and pneumatics bowels are not perfectly symmetrical, there probably isn't a nose wheel steering tiller on the right side, the cockpit jumpseats aren't symmetrical...but like everyone has said, all of it adds up to imperceptible when it comes to flying.

ReverseFlow
Posts: 396
Joined: Mon Mar 14, 2022 4:40 pm

### Re: Is an Aircraft Perfectly Balanced 50/50?

Florianopolis wrote:
seat1a wrote:
Not sure how to phrase the question - but is a Boeing 787 or Airbus A321 without the airline customers configuration of seats, etc., perfectly balanced 50/50? If you were to draw a line down the middle of the plane, would both sides be equal in weight?

The airplane isn't symmetrical left/right, so no. The cargo doors add weight to the right side, the hydraulics and pneumatics bowels are not perfectly symmetrical, there probably isn't a nose wheel steering tiller on the right side, the cockpit jumpseats aren't symmetrical...but like everyone has said, all of it adds up to imperceptible when it comes to flying.
There are nose wheel steering tillers on both cockpit sides (just outboard of the sidestick on this picture)

https://www.airliners.net/photo/VivaAer ... o2lQ%3D%3D

A tiller is the least of your worries in a lateral (im)balance

26point2
Posts: 1155
Joined: Wed Mar 03, 2010 6:01 am

### Re: Is an Aircraft Perfectly Balanced 50/50?

The Global is certified to fly with wing fuel out of balance by max 1100#. Conceivably you could do this all day long without trouble.

Posts: 3729
Joined: Wed Mar 01, 2006 4:29 am

### Re: Is an Aircraft Perfectly Balanced 50/50?

ReverseFlow wrote:
ReverseFlow wrote:
You will get a fuel imbalance alert if your tank balance left/right exceeds a threshold.

Can you give an idea of what that threshold is? I suspect around 1% of max fuel or so?
From here

https://www.boeing.com/commercial/aerom ... tonly.html

This table for example

https://www.boeing.com/commercial/aerom ... ble01.html

Well, for 737 an imbalance of 1000lb is about 3% of total fuel capacity.
And just to compare - if an arm of fuel tank is 1/3 of wing length, or 1/6 of wingspan = 6 m; and an arm for the window seat passenger is about 1.5 meter - total momentum of that imbalance is the same as 18 pax in window seats on one side without counterparts on the other. 739 has 32 rows in DL configuration
These are the back of envelope numbers, of course.

Starlionblue
Posts: 21137
Joined: Fri Feb 27, 2004 9:54 pm

### Re: Is an Aircraft Perfectly Balanced 50/50?

ReverseFlow wrote:
Florianopolis wrote:
seat1a wrote:
Not sure how to phrase the question - but is a Boeing 787 or Airbus A321 without the airline customers configuration of seats, etc., perfectly balanced 50/50? If you were to draw a line down the middle of the plane, would both sides be equal in weight?

The airplane isn't symmetrical left/right, so no. The cargo doors add weight to the right side, the hydraulics and pneumatics bowels are not perfectly symmetrical, there probably isn't a nose wheel steering tiller on the right side, the cockpit jumpseats aren't symmetrical...but like everyone has said, all of it adds up to imperceptible when it comes to flying.
There are nose wheel steering tillers on both cockpit sides (just outboard of the sidestick on this picture)

https://www.airliners.net/photo/VivaAer ... o2lQ%3D%3D

A tiller is the least of your worries in a lateral (im)balance

That depends on the aircraft. Lots of smaller airliners and business jets only have a tiller on the left hand side, e.g. the DC-9.

### Who is online

Users browsing this forum: stackelberg and 19 guests

### Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos