rotating portion of the head to the non-rotating torque
tube. The torque tube is mounted to the airframe
through attachments allowing both lateral and longitu-
dinal movement. This allows the movement through
which control is achieved.
FULLY ARTICULATED ROTOR SYSTEM
The fully articulated rotor system is found on some
gyroplanes. As with helicopter-type rotor systems, the
articulated rotor system allows the manipulation of
Coning Angle—An angular
deflection of the rotor blades
upward from the rotor hub.
Undersling—A design character-
istic that prevents the distance
between the rotor mast axis and
the center of mass of each rotor
blade from changing as the
blades teeter. This precludes
Coriolis Effect from acting on the
speed of the rotor system.
Undersling is further explained
in Chapter 3—Aerodynamics of
Flight, Coriolis Effect (Law of
Conservation of Angular
Momentum).
Gyroplanes are available in a wide variety of designs
that range from amateur built to FAA-certificated air-
craft. Similarly, the complexity of the systems inte-
grated in gyroplane design cover a broad range. To
ensure the airworthiness of your aircraft, it is important
that you thoroughly understand the design and opera-
tion of each system employed by your machine.
PROPULSION SYSTEMS
Most of the gyroplanes flying today use a reciprocating
engine mounted in a pusher configuration that drives
either a fixed or constant speed propeller. The engines
used in amateur-built gyroplanes are normally proven
powerplants adapted from automotive or other uses.
Some amateur-built gyroplanes use FAA-certificated air-
craft engines and propellers. Auto engines, along with
some of the other powerplants adapted to gyroplanes,
operate at a high r.p.m., which requires the use of a reduc-
tion unit to lower the output to efficient propeller speeds.
Early autogyros used existing aircraft engines, which
drove a propeller in the tractor configuration. Several
amateur-built gyroplanes still use this propulsion con-
figuration, and may utilize a certificated or an uncer-
tificated engine. Although not in use today, turboprop
and pure jet engines could also be used for the propul-
sion of a gyroplane.
ROTOR SYSTEMS
SEMIRIGID ROTOR SYSTEM
Any rotor system capable of autorotation may be utilized
in a gyroplane. Because of its simplicity, the most widely
used system is the semirigid, teeter-head system. This
system is found in most amateur-built gyroplanes.
[Figure 18-1] In this system, the rotor head is mounted
on a spindle, which may be tilted for control. The rotor
blades are attached to a hub bar that may or may not
have adjustments for varying the blade pitch. Aconing
angle , determined by projections of blade weight,
rotor speed, and load to be carried, is built into the hub
bar. This minimizes hub bar bending moments and
eliminates the need for a coning hinge, which is used
in more complex rotor systems. A tower block pro-
vides the undersling and attachment to the rotor head
by the teeter bolt. The rotor head is comprised of a
bearing block in which the bearing is mounted and
onto which the tower plates are attached. The spindle
(commonly, a vertically oriented bolt) attaches the
Figure 18-1. The semirigid, teeter-head system is found on
most amateur-built gyroplanes. The rotor hub bar and blades
are permitted to tilt by the teeter bolt.
Tower Plates
Hub Bar
Tower Block
Bearing Block
Teeter Bolt
Spindle Bolt
Torque Tube
Fore / Aft Pivot Bolt
Lateral Pivot Bolt
rotor blade pitch while in flight. This system is signifi-
cantly more complicated than the teeter-head, as it
requires hinges that allow each rotor blade to flap,
feather, and lead or lag independently. [Figure 18-2]
When used, the fully articulated rotor system of a gyro-
plane is very similar to those used on helicopters, which
is explained in depth in Chapter 5—Helicopter Systems,
Main Rotor Systems. One major advantage of using a
fully articulated rotor in gyroplane design is that it usu-
ally allows jump takeoff capability. Rotor characteristics
required for a successful jump takeoff must include a
method of collective pitch change, a blade with sufficient
inertia, and a prerotation mechanism capable of approxi-
mately 150 percent of rotor flight r.p.m.
Incorporating rotor blades with high inertia potential is
desirable in helicopter design and is essential for jump
takeoff gyroplanes. A rotor hub design allowing the
rotor speed to exceed normal flight r.p.m. by over
50 percent is not found in helicopters, and predicates a
rotor head design particular to the jump takeoff
gyroplane, yet very similar to that of the helicopter.
PREROTATOR
Prior to takeoff, the gyroplane rotor must first achieve
a rotor speed sufficient to create the necessary lift.
This is accomplished on very basic gyroplanes by ini-
tially spinning the blades by hand. The aircraft is then
taxied with the rotor disc tilted aft, allowing airflow
through the system to accelerate it to flight r.p.m.
More advanced gyroplanes use a prerotator, which
provides a mechanical means to spin the rotor. Many
prerotators are capable of only achieving a portion of
the speed necessary for flight; the remainder is
gained by taxiing or during the takeoff roll. Because
of the wide variety of prerotation systems available,
you need to become thoroughly familiar with the
characteristics and techniques associated with your
particular system.
MECHANICAL PREROTATOR
Mechanical prerotators typically have clutches or belts
for engagement, a drive train, and may use a transmis-
sion to transfer engine power to the rotor. Friction
drives and flex cables are used in conjunction with an
automotive type bendix and ring gear on many gyro-
planes. [Figure 18-3]
The mechanical prerotator used on jump takeoff gyro-
planes may be regarded as being similar to the helicopter
main rotor drive train, but only operates while the air-
craft is firmly on the ground. Gyroplanes do not have an
antitorque device like a helicopter, and ground contact is
necessary to counteract the torque forces generated by
the prerotation system. If jump takeoff capability is
designed into a gyroplane, rotor r.p.m. prior to liftoff
must be such that rotor energy will support the air-
craft through the acceleration phase of takeoff. This
combination of rotor system and prerotator utilizes
the transmission only while the aircraft is on the
ground, allowing the transmission to be disconnected
from both the rotor and the engine while in normal
flight.
HYDRAULIC PREROTATOR
The hydraulic prerotator found on gyroplanes uses
engine power to drive a hydraulic pump, which in turn
drives a hydraulic motor attached to an automotive type
bendix and ring gear. [Figure 18-4] This system also
requires that some type of clutch and pressure regula-
tion be incorporated into the design.
Figure 18-2. The fully articulated rotor system enables the
pilot to effect changes in pitch to the rotor blades, which is
necessary for jump takeoff capability.
Figure 18-3. The mechanical prerotator used by many gyro-
planes uses a friction drive at the propeller hub, and a flexi-
ble cable that runs from the propeller hub to the rotor mast.
When engaged, the bendix spins the ring gear located on the
rotor hub.
ELECTRIC PREROTATOR
The electric prerotator found on gyroplanes uses an
automotive type starter with a bendix and ring gear
mounted at the rotor head to impart torque to the rotor
system. [Figure 18-5] This system has the advantage of
simplicity and ease of operation, but is dependent on
having electrical power available. Using a “soft start”
device can alleviate the problems associated with the
high starting torque initially required to get the rotor
system turning. This device delivers electrical pulses to
the starter for approximately 10 seconds before con-
necting uninterrupted voltage.
TIP JETS
Jets located at the rotor blade tips have been used in sev-
eral applications for prerotation, as well as for hover
flight. This system has no requirement for a transmission
or clutches. It also has the advantage of not imparting
torque to the airframe, allowing the rotor to be powered
in flight to give increased climb rates and even the ability
to hover. The major disadvantage is the noise generated
by the jets. Fortunately, tip jets may be shut down while
operating in the autorotative gyroplane mode.
INSTRUMENTATION
The instrumentation required for flight is generally
related to the complexity of the gyroplane. Some gyro-
planes using air-cooled and fuel/oil-lubricated engines
may have limited instrumentation.
ENGINE INSTRUMENTS
All but the most basic engines require monitoring
instrumentation for safe operation. Coolant tempera-
ture, cylinder head temperatures, oil temperature, oil
pressure, carburetor air temperature, and exhaust gas
temperature are all direct indications of engine opera-
tion and may be displayed. Engine power is normally
indicated by engine r.p.m., or by manifold pressure on
gyroplanes with a constant speed propeller.
ROTOR TACHOMETER
Most gyroplanes are equipped with a rotor r.p.m. indica-
tor. Because the pilot does not normally have direct
control of rotor r.p.m. in flight, this instrument is most
useful on the takeoff roll to determine when there is suf-
ficient rotor speed for liftoff. On gyroplanes not
equipped with a rotor tachometer, additional piloting
skills are required to sense rotor r.p.m. prior to takeoff.
Figure 18-4. This prerotator uses belts at the propeller hub to drive a hydraulic pump, which drives a hydraulic motor on the
rotor mast.
Figure 18-5. The electric prerotator is simple and easy to use,
but requires the availability of electrical power.
Certain gyroplane maneuvers require you to know pre-
cisely the speed of the rotor system. Performing a jump
takeoff in a gyroplane with collective control is one
example, as sufficient rotor energy must be available
for the successful outcome of the maneuver. When
variable collective and a rotor tachometer are used,
more efficient rotor operation may be accomplished by
using the lowest practical rotor r.p.m. [Figure 18-6]
SLIP/SKID INDICATOR
A yaw string attached to the nose of the aircraft and a
conventional inclinometer are often used in gyroplanes
to assist in maintaining coordinated flight. [Figure 18-7]
AIRSPEED INDICATOR
Airspeed knowledge is essential and is most easily
obtained by an airspeed indicator that is designed for
accuracy at low airspeeds. Wind speed indicators
have been adapted to many gyroplanes. When no air-
speed indicator is used, as in some very basic
amateur-built machines, you must have a very acute
sense of “q” (impact air pressure against your body).
ALTIMETER
For the average pilot, it becomes increasingly difficult
to judge altitude accurately when more than several
hundred feet above the ground. A conventional altime-
ter may be used to provide an altitude reference when
flying at higher altitudes where human perception
degrades.
IFR FLIGHT INSTRUMENTATION
Gyroplane flight into instrument meteorological condi-
tions requires adequate flight instrumentation and navi-
gational systems, just as in any aircraft. Very few
gyroplanes have been equipped for this type of operation.
The majority of gyroplanes do not meet the stability
requirements for single-pilot IFR flight. As larger and
more advanced gyroplanes are developed, issues of IFR
flight in these aircraft will have to be addressed.
GROUND HANDLING
The gyroplane is capable of ground taxiing in a manner
similar to that of an airplane. A steerable nose wheel,
which may be combined with independent main wheel
brakes, provides the most common method of control.
[Figure 18-8] The use of independent main wheel
brakes allows differential braking, or applying more
braking to one wheel than the other to achieve tight
radius turns. On some gyroplanes, the steerable nose
wheel is equipped with a foot-operated brake rather
than using main wheel brakes. One limitation of this
system is that the nose wheel normally supports only a
fraction of the weight of the gyroplane, which greatly
reduces braking effectiveness. Another drawback is the
Figure 18-6. A rotor tachometer can be very useful to deter-
mine when rotor r.p.m. is sufficient for takeoff.
Figure 18-7. A string simply tied near the nose of the gyro-
plane that can be viewed from the cockpit is often used to
indicate rotation about the yaw axis. An inclinometer may
also be used.
Figure 18-8. Depending on design, main wheel brakes can be
operated either independently or collectively. They are con-
siderably more effective than nose wheel brakes.
inability to use differential braking, which increases
the radius of turns.
The rotor blades demand special consideration during
ground handling, as turning rotor blades can be a haz-
ard to those nearby. Many gyroplanes have a rotor
brake that may be used to slow the rotor after landing,
or to secure the blades while parked. A parked gyro-
plane should never be left with unsecured blades,
because even a slight change in wind could cause the
blades to turn or flap.