17

Ground Manoeuvres

The behaviour of an aircraft in contact with the ground is not straightforward, mainly because of the complexity of the landing gears used to absorb energy on landing and to allow ground manoeuvrability. Dynamic loads are developed in the landing gear, and therefore in the airframe, when taxiing, turning, taking off, landing and braking (Lomax, 1996; Howe, 2004); all load cases may be important for dimensioning of some aircraft or gear component.

The certification requirements for ground loads are shown in CS-25 and FAR-25 for large commercial aircraft and some of the calculations are discussed in Lomax (1996) and Howe (2004), though some of the requirements have been revisited since their publication because larger aircraft with more than two main landing gears have been designed. The ground loads certification is considered under the headings of (a) landing and (b) ground handling (taxi, take-off and landing roll, braked roll, turning, towing, tie-down, jacking, etc.). The calculations outlined in CS-25 may be defined as being ‘rational’ or ‘bookcase’. Rational calculations employ a model that seeks to represent more accurately the real physics and dynamics of the system whereas bookcase calculations tend to be more artificial and usually require ground reactions to be balanced by inertia forces (and sometimes moments).

Because of the complexity of the landing gear and some of these ground operations, the treatment in this chapter will be kept fairly simple ...

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