# Does the MD-80 seat layout affect the balance of the aircraft?

The MD-80 family has a 2-3 seat layout as seen in this image:

Does the layout have any influence on the balance of the aircraft and if so what is used to balance out the weight?

Image from seatguru.com

Based on this diagram—found in this Boeing MD-80 series document—we can estimate the average lateral center of gravity along the buttock line for each passenger seat:

Using the seating diagram that you provided in your question, I estimated the average center of weight along the buttock line for A, C, D, E, and F to be -50, -30, +10, +31, and +51 respectively.

We can use the following formula to calculate the lateral CG for the full load of passengers.

Where:

• $A_w$ is the sum of all weights for passengers in A seats (and so also for C, etc)
• $A_a$ is the lateral moment arm location along the buttock line for passengers in A seats (and so also for C, etc)
• $C_G$ is the solution to the lateral center of gravity for all seat loads.

$$C_G=\frac{(A_w\cdot A_a)+(C_w\cdot C_a)+(D_w\cdot D_a)+(E_w\cdot E_a)+(F_w\cdot F_a)}{A_w+C_w+D_w+E_w+F_w}$$

If we assume that every seat depicted in the question diagram is occupied by a 170 lb person, the solution $C_G$ is $3.4$—that is, 3.4 inches right of the center of the cabin, under the left side of seat D.

3.4 inches is very little variation in lateral CG, especially for so large an aircraft.

Other load considerations notwithstanding, I don't think the assymetrical seating arrangement is cause for concern.

• Your first link not worketh. – Sean Mar 3 at 3:56

The "D" seat is very near the aircraft centerline, and thus the roll axis. Since roll moment is the distance from the roll axis times weight, if the distance is small, the roll moment is very small. What roll moment is created can easily be canceled by a little bit of aileron trim if needed.

The water tank on MD-80s is also placed on the LH side of the cargo. Full this is about 350 lbs, further from the centerline than the "D" seats. Also the LH side has an extra service door in the aft and the front LH door is larger than the R1 door, although the RH side also has the cargo doors.