...isn't this part of the ol' cg vs cp issue.
That is exactly what my first thought was.
Primarily, gravity exerts a constant pull on the body and acts through the center of gravity (CG) which is determined by the distribution of weight throughout the body. Gravity always produces a uniform vertical acceleration of about 9.8 m/s2.
Next we have aerodynamic forces which provide lift and drag the body as its driven through the air. Aerodynamic forces are generally proportional to the velocity squared. The aerodynamic forces act through the center of pressure (CP) which is a function of the body's shape.
There are three types of drag force which apply:
1. Skin drag- friction on the outer surface as it moves through the air
2. Shape drag- caused by low pressure behind the body due to the flow of air around its shape.
3. Wave drag - a loss of energy that is put into acoustic LF waves as the body passes through the air. (Particularly strong near the speed of sound in air.)
All drag forces act at the center of pressure and are in the opposite direction as the motion of the projectile. The drag force can be written as:
Fdrag = CD(a) A ½ rv2
where:
CD(a)= the coefficient of drag, which is a function of the angle of attack, a;
A = the effective area of the body ;
r = the density of air (~1.2 Kg/m3); and
v = the velocity of the body relative to the air stream.
The lift force acts perpendicular to the direction of motion relative to the air stream. It has the same form as drag
Flift = CL(a) A ½ rv2
where: CL(a) = the coefficient of lift, which is a function of the angle of attack, a.
If the center of pressure is located behind the center of gravity, the aerodynamic forces create a restoring torque which tend to drive the body back to its neutral angle, where all the torques are balanced. This situation is therefore inherently stable, since the body will always be driven back to neutral angle.
... just a thought.
