Page 8 - PDF_Flip_Book

Rod Machado’s Private/Commercial Pilot Handbook
2-60

G u s t E f f e c t o n t h e A i r p l a n e
o
Gust Effect n the Airplane
Down Moment *Angle Of
Attack
Nose A LIFT

Attack
Relative Wind *Angle Of WING Chord Line

Relative Wind
*Angle Of Chord Line
Attack TAIL

*Tail attached to rear of airplane LIFT
Center of at a negative angle of attack.
Gravity

MOVE New Relative Wind
Down Moment LIFT Gust

Nose B LIFT No-Gust Relative Wind .
*Exaggerated here
*Angle Of WING Chord Line
Attack Note: Vectors
Relative Wind not to scale.

Relative Wind *Angle Of TAIL Chord Line
Attack LIFT

Vertical
Center of WIND GUST = Gust Of Fig. 104
Gravity Wind
wings. As a result, after a gust-induced increase in angle to rise and add to the airplane’s nose-down pitching
of attack, the net pitching moment for the whole airplane moment. It's entirely possible that the airplane’s new
is in the nose-down direction. Ultimately, the airplane nose-down pitching moment can't counter the wing's
returns to a level flight attitude and a state of equilibri- nose-up pitching moment induced by the gust. Thus, the
um. This is what makes an airplane statically stable. nose continues to rise, making this airplane statically
Now let's load this airplane so that its CG is unstable.
located significantly aft of the CP. In fact,
the CG is located aft of its allowable CG
limit in this example (Figure 105). If we
encounter a vertical gust of air, the
wing's angle of attack increases, pro-
ducing a temporary increase in lift.
The lift acts through the CP and
a level arm to an aft located CG,
producing a nose-up moment
about the CG. But the tail will
certainly counter this motion,
correct? Maybe not. The verti-
cal gust caused a decrease in
(downward-acting) lift on the
tail, would normally allow the tail Fig. 105