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Which of these statements about the gust load factor on an aeroplane are correct or incorrect?

I. When the slope of the lift versus angle of attack curve increases, the gust load factor decreases.
II. When the wing loading increases, the gust load factor increases.

  • A
    I is correct, II is incorrect.
  • B
    I is correct, II is correct.
  • C
    I is incorrect, II is correct.
  • D
    I is incorrect, II is incorrect.

Refer to figures.
A gust is a localized sudden and rapid change to the speed of the air in the atmosphere that can be either horizontal or vertical. The horizontal gust is of little importance because it causes a change to an airplane’s dynamic pressure that results in an insignificant change to the load factor. The vertical gusts are far more important because they change the effective angle of attack, total lift, and the load factor.
The gust load is the extra load imparted to the airplane by vertical gusts or turbulence. Its magnitude is unaffected by increased altitude but is increased with increased aspect ratio and/or decreased mass.
The load factor for any given angle of attack can be derived from the basic load factor for the normal cruise angle of attack because it is increased by the same percentage as the increase of angle of attack.
The load factor deriving from a gust is determined by the magnitude of the vertical velocity of the gust and the forward speed of the airplane.
Vertical gusts will affect the load factor (n) by changing the angle of attack of the wing.
For a given gust speed and aircraft TAS, the increment in the load factor depends on the increase in CL per change in angle of attack due to the gust (the slope of the lift curve). If the lift curve has a steep slope, the ‘g’ increment will be greater. Factors which affect the lift curve are aspect ratio and wing sweep.
Wings having a low aspect ratio, or sweep, will have a lower lift curve slope, and so will give a smaller increase in ‘g’ when meeting a given gust at a given TAS. Therefore, statement 1 is incorrect.
High wing loading reduces the ‘g’ increment in a gust. This is because the lift increment produced is a smaller proportion of the original lift force for the more heavily loaded aircraft.
For a given TAS and gust speed, the increase of lift will be proportional to the wing area. Therefore, the increase in load factor is inversely proportional to the wing loading.

Wing Loading = Weight/(Wing Area)

Therefore, statement 2 is incorrect.

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