When an aircraft is parked on the ground, the total weight will act vertically…
Refer to figure.
Although it is more common to consider the forces acting on an aircraft when in flight, as shown in the figure, the total weight will act vertically through the centre of gravity on the ground too.
CAP 758 defines the Centre of Gravity (CG) as:
That point through which the force of gravity is said to act on a mass.
Looking at the answers:
'through the main wheels of its undercarriage assembly.' --> INCORRECT. It is possible for the CG to act through the main wheels, but normally it is located between the nose wheel and main wheels. A CG behind the main wheels would cause the aircraft to tip over.
'through a point defined as the datum point.' --> INCORRECT. The datum point is the point on the longitudinal axis (or extension thereof) from which the centres of gravities of all masses are referenced, but not act through.
'through its centre of gravity.' --> CORRECT. See above from CAP 758
'through its centre of pressure.' --> INCORRECT. Lift acts through the centre of pressure.
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