# How are the dimensions of the empennage determined for jetliners?

How is the height of the vertical and span of the horizontal stabilizers determined for different turbofan aircraft like the Airbus A380 and the Boeing 747-8?

What are the maximum forces (in kilograms or Newtons) acting on both the horizontal and vertical stabilizers for aircraft like the Airbus A380 or the Boeing 747-8?

• That's practically four separate questions--pitching and yawing moments have different sets of causes. Consider aviation.stackexchange.com/questions/45996/… (which has an answer addressing one of your four questions: "it's complicated"). – David K Dec 26 '17 at 0:03

The tail volume coefficients for the horizontal stabilizer ($C_H$) and vertical tail ($C_V$) for jet transports are 1.00 and 0.08 respectively.

For the horizontal stabilizer, for example, with the $C_H$ given, and the lever arm, [main] wing reference area ($S_W$), and MAC known, the area can be calculated.

The shape, sweep angles, aspect ratio, etc., of each surface have their own rules.* Knowing the shape and area, the span or height is calculated.

Example 1: When the lever arm was reduced when the A319 was shortened to become the A318, they had to compensate by increasing the vertical stabilizer area, which meant a higher tail.

Example 2: Boeing designed the 757 and 767 simultaneously, so in order to reduce the fabrication and tooling costs, both shared the same tail, with the 757 tail shortened at the root (Flight, 1979).

(Own work)

* Reference and further reading on the aforementioned rules: Empennage General Design (.pdf), Hamburg University of Applied Sciences.

• Another example and a very noticeable one is the Boeing 747SP which was approximately 41 feet shorter than the 747-200. Five feet was added to both the vertical stabilizer and each of the horizontal stabilizers. – Gerry Dec 29 '17 at 19:53