Physics
behind
the
flying
disc
When looking at the flight characteristics of frisbee's there
are a few
basic principles that must be taken into consideration. These
principles are aerodynamic lift, Bernoulli's principle, Newtons third
law, angular momentum, and gyroscopic stabilization.
Aerodynamic Lift
There are some controls on the aerodynamics of a Frisbee. One
control is the deep lip. This lip controls the pitch moment so that it
retains managable values. The second control is the thickness of the
plastic that comprises the Frisbee. The thickness of the plactic varies
across the disc. Most of the Frisbee's mass is concentrated at the
edges making a thick lip. This distribution of mass maximizes the
moment of inertia resulting in a flight patern similar to that of a
spinning flywheel.
Affects of the angle of attack on the trailing air during disc flight
Bernoulli's Principle
Bernoulli's principle states that moving air has less less
pressure than still air. This can be related to a Frisbee's flight
because when air travels over the curved top surface of a disc it is
traveling faster than the air below. This creates low pressure on top
of the disc and high pressure below. This is the main principle that
drives lift. The image below is representative of the flight
characteristics of a Frisbee thrown both rightside-up and upside-down.
Graphical representation of
Bernoulli's Principle
Newton's Third Law
Newton's third law when relating to a Frisbee's flight is very
similar to Bernoulli's principle. Newton's third law states that with
every action force there is an equal and oppsite reaction force. The
Frisbee is able to fly due to the fact that when a Frisbee flys it
forces air downward and the air forces the disc upward.
Angular Momentum and Gyroscopic
Precession
People are capable of controlling the flight that a Frisbee
takes. This is due to the implementation of angular momentum and
gyroscopic precession. When someone throws a Frisbee they impart spin
on the disc, this gives the Frisbee more angular momentum which in
combination with gyroscopic precession stabilizes the disc during
flight. The more spin you impart when throwing a Frisbee the longer and
more stable the disc will fly. The angle and pitch at which you throw
the Frisbee at also affect the flight pattern. If you throw a Frisbee
slightly tilted it will follow that pattern until it hits the ground.
This is characteristic is also controlled by gyroscopic precession.
Comparison between spinning and
non-spinning discs
The phenomenon of gyroscopic
precession
The precessional frequency is represented by the equation
courtesy of blaze labs research:
wp = (Frsinθ) / Iw
where
w is the angular velocity of rotation
wp is the precessional frequency
F is the external influence force acting on the gyro
r is the distance at which force F is acting from the spinning axis
I is the moment of inertia of the gyro
θ is the angle which force F makes with the spinning axis