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ABOUT
THE X-ZYLO™
X-zyLo™ was invented by a Baylor University student in 1991.
You will observe that it consists of a thin, heavy ring (the gyro)
that measures 3.75" in diameter and 1/2" wide and a
light, thin cylinder (the wing) that is approximately 2 1/2"
long. It is straight on the "leading" end and curved
or "scalloped" on the "trailing" end. X-zyLo
weighs 25 grams--less than one ounce (which equals 28 grams).
This deceptively simple device commonly flies in excess of 100
yards when thrown correctly. X-zyLo's™ world record throw
is 218 yards or 655 feet!! Nothing so light has ever been thrown
so far.
WHAT MAKES AIRPLANES FLY?
Planes fly because of their aerodynamics. Aerodynamics is the
study of air as it moves around objects. A wing flies because
of its cross sectional shape. In order to understand why a wing's
shape is important we have to understand Bernoulli's Principle,
which says that an increase in the velocity (speed) of air decreases
the air pressure. Likewise, a decrease in flow velocity causes
an increase in air pressure. Low pressure is like a vacuum that
pulls things toward it. A wing is curved on the top and flat on
the bottom, as shown in the diagram below.
So when a wing moves through the air, the air on top of the wing
has to travel faster than the air under the wing. To say it again,
because the wing is curved on the top, the air moving over the top
must travel farther and faster than the air under the wing to get
to the same place at the same time. This causes a decrease in pressure
on the top of the wing. The pressure difference between the top
and bottom of the wing causes a vacuum effect and the wing is pulled
upward and lifts the airplane. The curve of the wing is called a
dihedral. The body of the airplane is often streamlined
to provide the least amount of air resistance or drag possible.
To demonstrate Bernoulli's Principle try this simple
experiment:
- Take
a small piece of paper, about one inch wide and 10 inches
long, and wrap it around a pencil so most of the paper
hangs from the pencil away from you.
- Blow
over the top of the paper as shown.
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Which
way would you expect the paper to move? Why did the paper move upward
instead of downward or stay in the same position? Does this confirm
Bernoulli's principle?
Try another experiment. Observe the model airplane. Do its wings
have a dihedral shape? Throw it and note its flight
characteristics. Does it have lift? How far does it fly? Does it
fly straight? Do you think Bernoulli's principle applies
here?
Now throw the X-zyLo™. Does its surface have the same shape
as a plane's wing? Does it have lift? How far does it fly? Does
it fly straight? Why is its performance in terms of both distance
and accuracy far superior to that of an airplane wing with the
same weight and surface area? We will answer this later. First,
we need to consider not only why objects have lift but also what
keeps them stable in flight and prevents them from just tumbling
all over the place.
CENTER OF GRAVITY AND CENTER OF PRESSURE
Every flying object has what is called a center of gravity
and center of pressure. The center of gravity
and center of pressure must be in close proximity
to one another in order for a wing to have a stable flight. The
normal center of gravity is a fixed point on the object where
it is balanced by gravitational forces. To find the center of
gravity on X-zyLo, take a pen or pencil and move the tip up and
down the underside of the top surface of the cylinder until you
reach the point where the X-zyLo is balanced on the tip. This
is X-zyLo's approximate center of gravity. One of
the purposes of X-zyLo's heavy front ring is to place its center
of gravity near its center of pressure.
The center of pressure on a wing is the point through
which the most lifting pressure passes due to air flowing over
it. Just as the center of gravity on a wing is where
gravity focuses its pull, the center of pressure
is where the air pressure focuses its lift on a wing.
Why must the curve of an airplane wing bulge in front rather than
the middle or back of the wing? The reason is because the bulge
in the front causes the center of pressure to be
near or over the wing's center of gravity. In this
way, the two forces hold the plane straight as it glides through
the air. If the center of pressure is not over the
center of gravity, but at some other point of the
wing, it would push the plane over and cause it to tumble.
Can you guess where the center of pressure is on
the X-zyLo? It's where you located the center of gravity
- in the first 1/3 of the body. The weight of the ring causes
the center of pressure be near the center
of gravity.
Why does X-zyLo™ fly with a stable, straight flight whereas
the model plane does not? The answer lies in the fact that forces
other than aerodynamics are interacting with X-zyLo™. Contrary
to traditional planes, X-zyLo™ spins in flight, which creates
gyroscopic forces.
Before we talk about gyroscopic forces, let's look more closely
at X-zyLo's™ flight characteristics.
- Try
to throw the X-zyLo™ backwards. Where is X-zyLo's™
center of gravity when you throw it backwards?
Where is the center of pressure?
- Try
to throw X-zyLo™ with absolutely no spiral (or spin). Is
it stable? Does it fly straight? Does it fly predictably? Does
it fly far?
- Now
throw X-zyLo™ with rapid spin (remember fast and low).
Why is it stable? Why does it fly in a straight line? Why does
it turn left at the end of the flight? The answers all have
to do with spinning, which is discussed below.
WHAT
IS A GYROSCOPE?
A gyroscope is a spinning wheel or ring often mounted on a movable
frame. When rapidly spun it stands straight up. When it is not
spinning it is captured by gravity and falls down. Bicycle wheels
act as gyroscopes when they spin and thereby keep the bicycle
straight up. Also, tops act as gyroscopes when they stand straight
up while rapidly spinning. Gyroscopes seem to defy the laws of
gravity. By simply spinning, gyroscopes resist the forces of gravity.
Gyroscopic forces probably were first recorded by Isaac Newton
in the 17th century. Try this experiment with a gyroscope (top)
if you have one:
- Place
the gyroscope with its axle straight up and down. Let go. If
it's not spinning, it falls. Now get it spinning fast and place
it with its axle straight up and down. It does not fall. Why?
Now place the spinning gyroscope with its axle parallel to the
table. Why does it stay that way?
- Place
it on the end of your finger or on the edge of a drinking glass.
Push it gently down. Does it fall?
- Now
put your spinning gyroscope's axle parallel to the ground suspended
on a string. It stays up but slowly turns. Why? This turning
is called precession. We will learn more about
that later.
As you can see, by spinning, gyroscopes produce a force that resists
gravity, or any other force that tries to change its direction,
and that keeps it stable. X-zyLo™ is really a spinning gyroscope
with wings. Its spin allows it to fly stably and straight in flight
without nosing down. That's why it flies much straighter and farther
than the model plane. To demonstrate this point another way, try
the following:
- Hold
X-zyLo™ parallel to the ground without spinning it. Let
it fall to the ground. Which part of the X-zyLo™ hits the
ground first?
- Now
spin the X-zyLo™ parallel to the ground and let it drop
to the ground. What part hits the ground first? Gravity tries
to nose X-zyLo™ down (like it does with all "nose
heavy" objects) yet when X-zyLo™ is spinning, it resists
gravity from turning or torquing its nose toward
the ground.
To
understand the reasons behind gyrosopic forces we need to know
about angular momentum and precession.
ANGULAR MOMENTUM
The concept of "momentum" states that if any object
is in motion it will continue to stay in motion in the direction
it is moving unless another force acts upon it. Momentum equals
the object's mass times its velocity or speed.
Angular
momentum applies to objects that are moving in circles
or spinning. In other words, they are moving "angularly"
as opposed to a straight line. All spinning bodies exhibit angular
momentum which is the measure of how fast the body is
spinning, how much mass the body has, and how that mass is distributed.
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equation for angular momentum is: H=M*R*W where
M is the mass, R is the radius of the rim, and W is the spin
velocity. To make the point, angular momentum
is what keeps gyroscopes spinning in place and X-zyLo flying
straight and stably through the air. The force that it creates
is called centrifugal force. It resists any
other force that tries to change the gravity, wind, a collision
with another object, etc. Let's try another experiment.
Fill a bucket with water. Hold it to your side and then
start swinging it back and forth. Once you get the bucket
swinging fast enough, swing it all the way around so that
it makes an entire loop. Why didn't the water fall out when
the bucket was upside down? It is because angular
momentum created a centrifugal force
that held it in. Although there is not an actual "force"
that keeps the water in, the water wants to travel in a
straight line, but the bucket is spinning, so the water
stays in.
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GYROSCOPIC PRECESSION
You have observed that X-zyLo™ curves left at the end of its
flight. This is because its spinning slows down, which causes the
strength of its centrifugal force to weaken. When
this happens gravity pulls the nose of X-zyLo™ down and it
moves to the left in a direction opposite to its spin. Now throw
the X-zyLo™ with it spinning the opposite way (either have
a left-hander throw it or throw it under hand). Does it curve? Does
it curve the same way at the end of its flight, or does it curve
the other way? The curving of X-zyLo™ at the end of its flight
demonstrates gyroscopic precession.
Gyroscopic precession states that a spinning body
tends to react to a disturbing force by rotating in a direction
at right angles to the direction of the torque. The equation for
gyroscopic precession is P=T/H where P is the rate
of precession, T is the applied torque and H is the angular
momentum.
WHAT MAKES X-ZYLO™ FLY?
You have seen that:
- Airplanes
fly because of their aerodynamic characteristics.
- Gyroscopes
resist gravity and stand straight up because they efficiently
spin.
The
technology that enables the spectacular flight performance of
X-zyLo™ utilizes both aerodynamic and gyroscopic phenomena.
The top and bottom of the cylinder give X-zyLo™ lift similar
to that of a bi-winged plane, and the rapid spinning of the heavy
ring gives it stability and prevents it from nosing down to the
ground. However, it is unclear exactly how the two interact. The
interactions are very complex and there are different and conflicting
theories as to what really happens when X-zyLo™ flies.
How does X-zyLo™ fly straight when the principle of gyroscopic
precession states that rapidly spinning bodies should turn at
right angles when outside forces, such as gravity, are applied
against them? Some observers say that certain aerodynamic forces
affect the right angle turning tendency of gyroscopic characteristics.
Others are not so sure. What do you think?
If you have any insights or theories into this matter, please
contact the William
Mark Corporation.
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