Following the liftoff of a model rocket,
it often turns into the wind. This maneuver is called
weather cocking
and it is caused by aerodynamic
forces on the rocket.
Wind striking the side of the rocket generates a side force which
acts through the
center of pressure. For
stability reasons,
the center of pressure is located below the
center of gravity of the rocket.
The effect of the side force is to rotate the rocket about the
center of gravity until the nose is inclined at the angle b
to the horizontal. Angle b is the effective flow direction.
If the wind velocity is w and the
flight velocity is V, then:
tan b = V / w
where "tan" is the trigonometric
tangent function.
The rotation of the rocket produces a new flight path into the wind, as shown at
the left of the figure. When the new flight path is aligned with the
effective flow direction, there is no longer any lift force and the
rocket will continue to fly in the new flight direction. The flight path is
inclined to the horizontal at angle b.
The chief effect of weather cocking is that the
maximum altitude
of the flight is reduced. We can estimate the amount of lost
altitude H by using some
trigonometry.
If the maximum, vertical altitude is denoted by A,
the lost altitude is given by:
H = A * (1  sin b)
where "sin" is the trigonometric
sine function.
As a check, if the wind velocity is zero, the angle b is
90 degrees, and the lost altitude is zero.
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