Rocket Stability
Forces Acting on a Rocket
 Gravity
 Thrust
 Air Drag
Inertia
 The tendency of all bodies to resist any
change in motion
Newton’s Laws
 Law of Inertia: A body at rest stays at
rest, a body in motion stays in motion
unless there is another force acting on
that body.
 Law of Acceleration:: Motion is
proportional to the forces exerted
 Law of Reaction: For every action there
is an opposite and equal reaction
Center of Gravity CG
The Center of Gravity or CG is the
balancing point of a free body that
can rotate around all axis. It is an
imaginary point at which all mass
seems to be concentrated.
Center of Pressure CP
Center of Pressure is a point where
all air pressure forces converge or
act.
CG -CP Relationship
Inherently Stable Rocket
 CG must be forward of CP or CP must be aft
of CG
Changing CG to make a Stable
Rocket
 Use Lighter Motor
 Add Weight to Nosecone
 Make rocket Longer
Changing CP to make the Rocket
Stable
 Use Larger Fins
 Increase the number of Fins
 Make Nose Cone Longer
Stability Characteristics
 A positive stability rocket will have a stable
flight
 A neutral stability rocket might have a
stable flight
 a negative stability rocket will not have a
stable flight
Flight paths