write:the CL goes up by 0.1. So who cares? Well real wings have wing-tips and they are sometimes short and stubby (low aspect ratio) and/or are swept back. All of these things tilt the

the CL goes up by 0.1. So who cares? Well
real wings have wing-tips and they are sometimes short and stubby (low aspect ratio) and/or are swept back. All of these things tilt the lift curve back
decreasing its slope. Now
if a short
stubby
swept back wing gets hit by a gust which increases its AOA by one degree
the CL may only increase by 0.05
half of what we had before. And
checking the equation
you should be able to see that if m is decreased
∆G is also decreased. The bottom line is that straight
high aspect ratio wings are more sensitive to wind gusts. Low aspect ratio
swept wing aircraft are less sensitive to wind gusts. An aircraft with a low aspect ratio or swept wing might run through a gust and call it “moderate”
while a high aspect ratio or straight wing aircraft encountering the same gust could get “severe” results.σ = density ratio. If the air is more dense you can expect it to pack a greater wallop. If the gust is encountered at high altitude
all other things being equal
the ∆G caused by the gust will be less. At 40
000 feet this can reduce the impact of the gust by a factor of almost four.VE = equivalent airspeed. Equivalent airspeed is what your airspeed in-dicator would be showing if it didn’t have to contend with position and compressibility errors. In other words
it is pretty much a measure of dy-namic pressure. If the dynamic pressure of the air passing over the wing is higher
you can expect to get hit with a bigger bump. The faster of two otherwise equal aircraft running through the same gust will report the more severe jolt.U = Represents the vertical speed of the gust. The FAA requires aircraft to be structurally capable of withstanding a gust as high as ±66 fps at the aircraft’s Design Speed for Maximum Gust Intensity (VB)
as high as ±50 fps at the aircraft’s Design Cruise Speed (VC)
and as high as ±25 fps at the aircraft’s Design Dive Speed (VD).K = the “Gust Alleviation Factor”. Since it takes some time for an aircraft to fly though a gust
the gust doesn’t act on the whole aircraft at once. This delaying factor attenuates the effects of the gust and is a function of the aircraft design.W/S = the aircraft’s wing loading. Since this term is on the bottom of the DG equation
high wing loadings mean a smoother flight. Lower wing loadings mean a larger ∆G for a given gust intensity. Wing loading can be changed by changing the wing’s configuration (use of Fowler flaps or sweeping the wing) or by changing the weight. For most aircraft
changes in weight have the highest potential to change wing loading. Although effect of wing loading may superficially appear to mean that the heavier an aircraft is
the least likely it is to be over G’d by a wind gust
this is not necessarily true. More on this later.H. DESIGn REquIREmEntS. Since horizontal gusts do not cause signifi-cant changes in the G load experienced by an airplane
the design require-ments associated with gust-induced loads are concerned with the effects of vertical positive (up) and negative (down) gusts. FARs 23 and 25 address the gust magnitudes that an airplane’s structure must withstand without damage. Referring to the equation for the ∆G
you can see that the effects of a strong gust can be offset by sufficiently low airplane speed
while at high speeds the effects of a given gust magnitude will be more severe. Thus the maximum gust an airplane has to withstand at low speeds is higher than the maximum gust it has to withstand at high speeds. When flying at their “design speed for maxi-mum gust intensity” (VB) between sea level and 20
000 feet
airplanes certifi-cated under Parts 23 and 25 have to withstand a vertical gust of 66 feet per second (fps) without structural damage. When flying faster than this speed
an airplane’s ability to withstand severe vertical gusts is limited to lesser gusts. When flying at their “design cruising speed” (VC)
airplanes certified under Parts 23 and 25 have to withstand a vertical gust of 50 fps without damage. •••••