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An aeroplane maintains straight and level flight at a speed of 1.4 VS. If, at this speed, a vertical gust causes a load factor of 2.4, the load factor n caused by the same gust at a speed of 2 VS would be:
  • A
    n = 1.96.
  • B
    n = 2.10.
  • C
    irrelevant, since the aeroplane would already be in a stalled condition at 1.4 VS with that gust.
  • D
    n = 3.00.
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.

To solve this exercise, consider figure 2:
An aircraft travelling at a certain speed (Vold, in black) encounters a vertical gust which increases its load factor (nold) to a certain amount.
The objective is to compare the effect of the same gust on an aircraft travelling at a different speed (Vnew, in blue) and assessing the resultant load factor (nnew).
Vold = 1.4VS
nold = 2.4g
Vnew = 2VS
nnew =?

The first thing we should do is check if in the first situation the aircraft is stalled by comparing the two VS0:
VS1 = VS0 ∗ √(nold)
VS1 = √2.4 ∗ VS0  = 1.55VS0
1.55VS0  > 1.4VS0

In these conditions, the aircraft is stalled!

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