**3.5 AIRCRAFT BALANCE**

The wing/fuselage configuration and the state of loading are in special relation with the appearing aircraft balance. The wing/tail configuration is in special relation with the permissible aircraft balance limits. The respective aircraft balances are given in percentage of the Mean Aerodynamic Chord (M.A.C.).

**The permissible aircraft balance limits **have to be between the following limits:

- the front limit is given at the highest possible lift coefficient (c
_{lmax}) of the tail unit, at which the aircraft is still controllable. The minimum Mach number is taken with Ma=0.2. Also the maximum nose wheel load should not be exceeded. - the tail limit is given by the combination of:
- the aerodynamic centre of the wing/tail combination and the movement of the stability limit of the wing/fuselage combination (the Mach number is taken as Ma=0.88),
- the engine influence and
- the minimum stability of the aircraft.

The permissible aircraft balance limits are between 9.9% – 40% of the mean aerodynamic chord.

The minimum stability is given as 5% of the mean aerodynamic chord.

The permissible aircraft balance limits for the C601 are in between 9.9% – 40% of the mean aerodynamic chord.

The **appearing aircraft balance **is given by the empty aircraft on the one hand and by the loading state on the other hand. There are five characteristic cases of loading to be considered.

- in two cases the passengers sit relatively at the back (1,2),
- in two others they sit relatively in front (3,4),
- and in the last one all seats are taken (5).

These cases, combined with maximum cargo and fuel load, lead to extreme aircraft balances, which have to be within the permissible limits.

The next figure shows the characteristic load and trim sheet for the C601 (see appendix III.5).