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under the tail. The tricycle configuration also uses two
mains, with the third wheel under the nose. Early autogyros,
and several models of gyroplanes, use conventional
gear, while most of the later gyroplanes
incorporate tricycle landing gear. As with fixed wing
aircraft, the gyroplane landing gear provides the ground
mobility not found in most helicopters.
WINGS
Wings may or may not comprise a component of the
gyroplane. When used, they provide increased performance,
increased storage capacity, and increased
stability. Gyroplanes are under development with
wings that are capable of almost completely unloading
the rotor system and carrying the entire weight
of the aircraft. This will allow rotary wing takeoff
performance with fixed wing cruise speeds. [Figure
15-3]
Figure 15-3. The CarterCopter uses wings to enhance
performance.
15-4
16-1
Helicopters and gyroplanes both achieve lift through
the use of airfoils, and, therefore, many of the basic
aerodynamic principles governing the production of lift
apply to both aircraft. These concepts are explained in
depth in Chapter 2—General Aerodynamics, and constitute
the foundation for discussing the aerodynamics
of a gyroplane.
AUTOROTATION
A fundamental difference between helicopters and
gyroplanes is that in powered flight, a gyroplane rotor
system operates in autorotation. This means the rotor
spins freely as a result of air flowing up through the
blades, rather than using engine power to turn the
blades and draw air from above. [Figure 16-1] Forces
are created during autorotation that keep the rotor
blades turning, as well as creating lift to keep the aircraft
aloft. Aerodynamically, the rotor system of a
gyroplane in normal flight operates like a helicopter
rotor during an engine-out forward autorotative
descent.
VERTICAL AUTOROTATION
During a vertical autorotation, two basic components
contribute to the relative wind striking the rotor blades.
[Figure 16-2] One component, the upward flow of air
through the rotor system, remains relatively constant
for a given flight condition. The other component is the
rotational airflow, which is the wind velocity across the
blades as they spin. This component varies significantly
based upon how far from the rotor hub it is
measured. For example, consider a rotor disc that is 25
feet in diameter operating at 300 r.p.m. At a point one
foot outboard from the rotor hub, the blades are traveling
in a circle with a circumference of 6.3 feet. This
equates to 31.4 feet per second (f.p.s.), or a rotational
blade speed of 21 m.p.h. At the blade tips, the circumference
of the circle increases to 78.5 feet. At the same
operating speed of 300 r.p.m., this creates a blade tip
Direction of Flight
Relative Wind Relative Wind
Direction of Flight
Figure 16-1. Airflow through the rotor system on a gyroplane is reversed from that on a powered helicopter. This airflow is the
medium through which power is transferred from the gyroplane engine to the rotor system to keep it rotating.
Resultant Relative Wind
Wind due to Blade Rotation
Upward
Airflow
Figure 16-2. In a vertical autorotation, the wind from the
rotation of the blade combines with the upward airflow to
produce the resultant relative wind striking the airfoil.
16-2
speed of 393 feet per second, or 267 m.p.h. The result
is a higher total relative wind, striking the blades at a
lower angle of attack. [Figure 16-3]
ROTOR DISC REGIONS
As with any airfoil, the lift that is created by rotor
blades is perpendicular to the relative wind. Because
the relative wind on rotor blades in autorotation shifts
from a high angle of attack inboard to a lower angle of
attack outboard, the lift generated has a higher forward
component closer to the hub and a higher vertical component
toward the blade tips. This creates distinct
regions of the rotor disc that create the forces necessary
for flight in autorotation. [Figure 16-4] The
autorotative region, or driving region, creates a total
aerodynamic force with a forward component that
exceeds all rearward drag forces and keeps the blades
spinning. The propeller region, or driven region, generates
a total aerodynamic force with a higher vertical
component that allows the gyroplane to remain aloft.
Near the center of the rotor disc is a stall region where
the rotational component of the relative wind is so low
that the resulting angle of attack is beyond the stall
limit of the airfoil. The stall region creates drag against
the direction of rotation that must be overcome by the
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