How are Airplanes Balanced in a 2–3 Configuration?
Nowadays, common single-body aircraft by Airbus and Boeing are arranged in a 3–3 configuration. That is, three seats on the left of the cabin, and three more seats on the right of the cabin, separated by an aisle. Smaller regional aircraft have a 2–2 configuration, such as the CRJs, the Q400s, and some larger ERJs. These planes have a typical symmetrical seating layout, nothing peculiar. However, a small percentage of planes are arranged in a 2–3 configuration — with more seats on the right side of the cabin. So, how are these planes able to counteract this imbalance and fly as usual?
Which modern aircraft types have a 2–3 configuration?
The 2–3 configuration has always been a rare sight. Larger single-aisle aircraft use a 3–3 configuration, while smaller turboprops and regional jets use a 2–2 configuration. In the modern era, only two noticeable aircraft use a 2–3 configuration: the Airbus A220 and the Sukhoi Superjet 100.
How do they balance?
So, let’s get to the point. How do these planes actually balance themselves if there seems to be a greater weight on one side of the cabin? Well… they don’t. It’s just that the difference is so trivial that it’s mostly unnoticeable by the pilots.
First of all, the weight of passengers is light relative to the aircraft’s total weight. Let’s take for example, the A220. The maximum takeoff weight of the A220–100 is 139,000lbs. In a 2–3 configuration, only one line of seats would be off-balance, and considering that the maximum capacity of the A220–100 is 145 passengers, this would translate to around 5,220lbs of mass off-center. This weight is much less significant than the MTOW of 139,000lbs, thus barely making any difference.
In addition, the extra line of seats is right around the centerline of the cabin. The weight of these passengers generates minimal torque that will rotate the aircraft, as the line of action is close to the axis of rotation. (To be precise, the center of gravity of the extra line of seats is only about 11in off from the axis of symmetry of the cabin).
τ = F · l (torque = force · lever arm)
If the artificial horizon is seen to be slightly off-balance during flight, pilots can easily transfer fuel from the right fuel tank to the left fuel tank to restore balance. As the fuel tanks are located in the wings, far from the longitudinal axis, just a tiny amount of fuel will cancel out the amount of torque generated by the extra line of passengers. So, you should never worry when stepping onboard a 717 or A220 and seeing an “unbalanced” cabin.
One more personal thought:
Some smaller propeller planes have a 1–2 configuration. Notice a pattern? The extra seats are almost always found on the right side of the cabin. Why is that?
One possible explanation is that the extra line of seats is installed on the right to counteract the left-turning tendencies propellers generate. Left-turning tendencies are a phenomenon that occurs naturally and rotates your plane towards the left. Having extra mass on the right side of the cabin will partially cancel out this force, making it less noticeable.
