Advancing Blade
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The portion of the rotor disc in which the rotation of the blade is
moving in the direction of the aircraft's travel.
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Aerodynamics
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Hydrodynamics and aerodynamics are both branches of fluid dynamics,
which is the study of fluids in motion. The fundamental laws governing the
movements of gases, such as air, and liquids, such as water, are identical.
Although many liquids are almost incompressible.
The equations representing these natural laws are, however, so complex that
although formulated over a hundred years ago, they cannot be easily solved
to account for all situations and conditions. The equations which describe
in a general fashion the motion of fluids were developed in 1820 and
subsequently perfected by G.G. Stokes.
At the beginning of the present century, aerodynamics was introduced with
the possibility of flight in air. It started with the same assumption as
hydrodynamics with the added assumption of incompressibility replacing what
was a fact for water.
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Airfoil
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A surface designed to produce lift from the movement of air over it.
Ideally, it should present the greatest amount of lift with the least
amount of drag.
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Anodizing
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Anodizing is the deposition of a thin film of synthetic oxide on a light
metal, such as aluminium, to prevent the further access of air to the
surface, preserving the lustre and preventing corrosion. The article is
made to anode in 3% solution of chromic acid at about 104 degrees F. The
voltage is gradually increased to a maximum of 50 volts and the process may
take an hour. Sulphuric and oxalic acid processed are also used, and the
anodic film may be dyed various colours.
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Autogyro
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A heavier-than-air flying machine which derives its lift from a rotor
system mounted above the machine, with blades rotating more or less
horizontally.
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Autorotation
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A flight condition made possible by the vertical or horizontal movement
of air through the rotor system.
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Blade Loading
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The load placed on the rotor blades of a gyroplane, determined by
dividing the gross weight of the craft by the total combined areas of all
blades (not the disc area, but the blade area).
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Balance
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Rotor blades that are equal in weight will balance each other.
Unbalanced rotor blades may cause control stick shake and instability when
in flight.
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Bank
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Sideward tilt of the aircraft in flight. When correctly executed, the
bank compensates for centrifugal force, and the passengers will be pressed
straight down in their seats.
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Ceiling
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The maximum altitude to which a gyroplane can climb. Because of thin
air, the engine decreases in power, or the rotor blades no longer provide
lift to climb.
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Centre of Gravity
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Called CG. A point where the resultant of all weight forces will hang
evenly from this point Usually at or very near to the main mast.
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Centre of Pressure
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An imaginary point on the cord lines of all the rotor blades where all
the aerodynamic forces of the airfoil surfaces are concentrated.
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Centrifugal Force
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The force caused by the rotation of an object with mass.
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Chord
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A straight line between the exact center of the leading and trailing
edge of the rotor blade.
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Chordwise Balance
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A term that refers to the mass balance of an airfoil. It is designed to
be in the center of lift.
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Compressibility
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Forces acting on a rotor blade when its tip speed approaches the speed
of sound.
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Coning
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The blades tend to bend upward in flight, when they are lifting the
weight of the aircraft. Referred to as the coning angle.
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Cruise Speed
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An airspeed that usually results in the best fuel economy and is usually
between 112 and 2/3 of full power.
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Density Altitude
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Pressure altitude calculated from air temperature, altitude and
humidity.
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Disc
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The area swept by the blades of the rotor.
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Disc Loading
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The gross weight of the gyroplane divided by the rotor disc area. The
greater the disc loading, the gyroplane's sinking speed will increase, and
its glide-angle will become steeper.
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Dissymmetry of Lift
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The unequal lift across the rotor disc, caused from the advancing blade
creating more lift than the retreating blade.
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Dynamic Roll Over
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A roll over on the ground caused by violent rotor flapping. Caused by
insufficient rotor rpm combined with excessive ground speed.
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Downwind
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Flying with the wind direction. Flying downwind near the ground is
dangerous, true airspeed is lower than groundspeed and the aircraft's lift
is less.
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Endurance
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The maximum length of time a gyroplane can stay aloft on its fuel
supply.
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Flapping
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The up and down motion of the rotor blade on its hinge. Without
flapping, a gyroplane would roll over on its side during flight because of
the unequal lift of the rotor disc.
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Flare
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A landing maneuver performed near the ground to slow the gyroplane's
rate of descent and air speed. The gyroplane is in a nose-high attitude
during the execution of this maneuver.
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Flutter
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A self-induced oscillating motion of improperly designed rotor blades.
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Ground Effect
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Also known as ground cushion, A beneficial increase in lift near the
ground. Readily apparent when the rotor height is one-half of the rotor's
diameter over the ground. Less engine power is required due to the air
being thrust downward to meet the ground. This denser air is partially
trapped beneath the rotor disc.
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Ground Vortex
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The horizontal whirlwind thatforms at the forward edge of the rotor wake
when the gyroplane flies at low speeds close to the ground.
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Gyroplane
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An aircraft whose lift is developed by the rotor blade system using the
principles of autorotation.
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Horsepower Loading
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The ratio of gross weight to horsepower, obtained by dividing the total
weight by the engine's horsepower rating.
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Induced Power
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The power associated with developing rotor thrust from the movement of
air passing the rotor blade.
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Induced Velocity
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The downward air velocity generated in the process of developing rotor
thrust.
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Laminar Flow &
Turbulent Flow
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The air flow immediately against the rotor blade (boundary layer) is of
most importance in the efficiency of the blade. Two kinds of fluid flow are
possible - laminar and turbulent. In laminar flow, the fluid moves as a
series of sheets or lamina, sliding one over the next where there is a
difference of speed between them (velocity gradient).
In turbulent flow, particles of fluid (air) can move in any direction -
only the mean velocity and direction being defined. This flow can be caused
by the overall shape of the object (rotor blade) or disturbances in the
surface polish have a noticeable effect on efficiency.
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Laminar Flow Blades
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Laminar Flow Blades are fibreglass blades which cause unusually low drag
in the rotorcraft operation. During World War II when experimental planes
began to approach the speed of sound, laminar flow wing sections
contributed to their success. In the beginning development stages, thin
gauges of sheet metal were used in forming the "skin". It was determined
that the slightest buckle forming in the "skin", caused by a counter sunk
rivet, could nullify the advantages of the blade section. With the advent
of fibreglass, it was determined that the blade could carry as much load as
aluminium-alloy sheets, but had a much greater resistance to damage and
guaranteed a smoother surface. Continuing development of these materials
has resulted in stronger bonding methods and resins which in turn have led
to the laminar-flow rotor system currently being offered for rotorcraft.
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Lead-Lag
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The tip movement needed to adjust the rotor blades in a two-bladed
system to get the weight of the whole rotor exactly equal on each side of
the main shaft laterally.
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Life
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The recommended safe duration (in hours or measurable wear on the
component) of any part on an aircraft. This length of time is determined by
either fatigue or the operational wear on the part.
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Load Factor
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The ratio of rotor thrust to gross weight of the gyroplane. Mast - The
main structural member of the gyroplane. The mast is the vertical assembly
that connects the rotor blades to the airframe.
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Parasite Power
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The power used to overcome the drag of all non-lifting components of the
rotorcraft.
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Pattern
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The in-plane alignment of all rotor blades so they perfectly balance
each other.
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Period
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The time it takes for an oscillating system to complete one full cycle.
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P.I.O.
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Pilot induced Oscillation - Caused by delays in the human reaction time.
Also known as porpoising, which is caused by over control and inexperience.
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Pitch
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The angle between a blade's chord line and a plane perpendicular to the
rotor bearing.
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Power Loading
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The ratio of the gross weight to the horsepower rating of the
rotorcraft's engine.
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Pull Out
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A flight manoeuvre at the bottom of a dive or descent.
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Push Over
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A flight manoeuvre at the top of a climb or a nose-down dive from level
flight.
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Radius of Action
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The maximum distance a gyro-plane can fly down and return to without
refuelling.
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Range
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The maximum distance a gyroplane can fly without landing or refuelling.
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Redundancy
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A fail-safe design which provides a secondary standby structural member.
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Retreating Blade
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This blade is on the opposite side of the advancing blade. It travels
with the wind created by the forward motion of the rotorcraft.
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Roll
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Tilt of the gyroplane along its longitudinal axis. Controlled by lateral
movements of the joystick.
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Rotor
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The lift-producing airfoil system of a rotorcraft. Rotor blade refers to
a single blade only.
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Service Ceiling
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The altitude at which the rotorcraft still maintains the potential to
climb at 100 feet per minute.
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Side Force
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The force on the side of a rotorcraft due to a side slip.
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Slip
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The controlled flight of a rotorcraft in a direction not in line with
its fore and aft axis.
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Solidity Ratio
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The portion of the rotor disc which is filled by the rotor blades. A
ratio of the total blade area to the total disc area.
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Spar
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The main load-carrying member of the rotor blade's structure. It carries
the centrifugal force as well as loads from the root attachments to the tip
of the blade.
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Speed Stability
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The tendency of the rotorcraft to pitch up or down when the forward
speed is changed.
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Stall
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The separation of the airflow from the surface of the airfoil or any
other component. The resulting loss of lift is a stall.
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Static Stability
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The tendency of a rotorcraft to return to its original flight condition
after a disturbance.
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Teetering Rotor
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A two-bladed rotor with a single horizontal hinge for flapping.
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Thickness Ratio
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The ratio of maximum thickness of the airfoil to the chord length of the
airfoil.
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Thrust
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The rotor force perpendicular to the tip path plane.
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Tip Path Plane
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The plane in which the tip paths travel when the blades are rotating.
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Tip Speed
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The airspeed at the top of the rotor blade in flight.
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Tip Stall
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The stall condition of the retreating blade which occurs at high forward
speeds (approx. 150mph).
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Torque
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A rotary force. A reaction to the turning effort supplied by the engine
is an example.
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Tracking
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Rigging the rotor so that each blade passes through the same slot of
air.
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Yaw
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Turning of the gyroplane to the right or left by changing the direction
of the airflow over the tail surface through the use of the foot petals.
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