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A pilot is performing a flight in an aeroplane with mechanical flight controls. The aeroplane makes one flight at its MTOM of 1900 kg with a CG near the aft limit. On the following flight, the pilot is the only occupant on board; the aeroplane is approximately 400 kg lighter and the CG has moved forward. How will this change the feel of the aircraft as experienced by the pilot?
  • A
    There is NO change to the feel since the CG remains within its limitation and mass has NO effect on the stick force per g.
  • B
    There is NO change to the feel since the increased stick force per g, caused by the lighter mass, is offset by the forward CG.
  • C
    The stick force per g is reduced since the aeroplane is lighter, but the forward CG makes this reduction less noticeable to the pilot.
  • D
    The stick force per g is increased since the lighter aeroplane and forward CG both reduce the manoeuvrability of the aeroplane.

Important Note: This question ventures outside of the learning objectives and therefore should be appealed if seen in the exam. We have had various different pieces of feedback come through for this question and similar questions, and they don't really make sense. We do not know whether this question is currently being asked, and we very much hope that it has been removed. Please send us any further questions or exam feedback in the comments, or by email to [email protected], thank you!

The feel of an aeroplane is how much force is required to make a particular manoeuvre, often referred to in the units of "stick force per G" for longitudinal stability (pitch changes). Stability and manoeuvrability are intrinsically linked, in that the more manoeuvrable an aircraft is, the less stable it is, and vice-versa. Stick force per G simply measures how much force the pilot needs to exert on the controls to cause a 1G change in load factor, the higher this value, the more stable (less controllable) an aircraft is.

The movement (forward/aft) of the CG is incredibly important to longitudinal stability, as having a forward CG means that the CG is further in front of the neutral point. This means greater stability, and therefore lower manoeuvrability.

A change in mass (without a change in CG) is much more complicated. It appears that mass change has an effect on the manoeuvrability that cannot be simply stated for the average aircraft, as mass and wing loading (a function of mass) appear to have opposing effects, but with different values, and the effect of different speeds for higher masses is not accounted for anywhere in the question. As you can probably tell, this is already much too complex for the ATPL exams. This is likely why the effect of mass on manoeuvring stability/stick force per G is not on the learning objectives. It is intuitive to think that a lighter aircraft is more manoeuvrable, but that is not something that can be absolutely stated without further information, and not even something the learning objectives mention.

We think that the examiner has written a question to test knowledge of CG movements, assuming that their intuition on the change in weight is correct, but has ended up making a question much more complicated, which ventures outside the learning objectives.

Therefore, our new recommendation here would be to answer the question assuming that the weight reduction decreases the stick force per G, even though that is not an absolute statement.

This leaves us with the answer "The stick force per g is reduced since the aeroplane is lighter, but the forward CG makes this reduction less noticeable to the pilot."

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