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Helicopter Engineering Glossary

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An overview of the most commonly used terms and their definitions.

Advancing bladeThe blade in the section of the rotordisc where rotation is in the same direction as the movement of the helicopter.Rotor system
AerofoilAny shape designed to obtain a useful reaction from the air through which it moves.Aerodynamics
AirfoilSee Aerofoil. 'Aerofoil' is English; 'Airfoil' is American English.Aerodynamics
FuselageThe frame and skin of an aircraft.General aviation
HullSee FuselageGeneral aviation
AirframeSee FuselageGeneral aviation
OleoSee oleo-pneumatic strutEngineering
Oleo-pneumatic strutA device that dampens a displacement by pushing oil through a small orifice every time the length of the strut changes.Engineering
Composite materialsA composite material (composite for short) is a material which is engineered from two distinct materials, the substrate and the resin. The substrate is usually a fibre structure, and the resin is a polymer that simply holds the fibres in place. Commonly used composites are fibreglass, carbon fibre, and kevlar.Engineering
LeadConsider a rotor that rotates with constant angular velocity. When, sometime during one revolution, the blade momentarily moves more quickly, it is said to lead, as it will move slightly more forwards than would normally be the case.Rotor system
LagConsider a rotor that rotates with constant angular velocity. When, sometime during one revolution, the blade momentarily moves at a lower speed, the blade is said to lag, as it will move slightly more backwards than would normally be the case.Rotor system
FlapA rotor blade can flap up or down at some point in one revolution. This displacement is orthogonal to the plane of rotation.Rotor system
Sampling rateThe frequency at which a measurement of an analogue signal is made and represented as a digital sequence.Miscellaneous
PayloadThe useful load that can be carried by an aircraft. It is defined as the difference of the gross weight of the helicopter minus empty weight, crew and fuel.General aviation
Blade angleAngle between a blade's chord line and the plane of rotation.Aerodynamics
Chord (line)Chord line. The straight line between the blades leading edge and it trailing edge.Aerodynamics
Rotor discImaginary disc spawn between the rotating rotortips.Rotor system
CyclicFlight control that controls the direction of flight by controlling the rotordisc orientation.Flight controls
CollectiveFlight control that controls the amount of lift generated by the rotordisc.Flight controls
PedalsFlight control that controls the helicopter's yaw by controlling tailrotor thrust.Flight controls
Pitch angleSee Blade angleAerodynamics
FeatheringRotation of a blade around its (feathering) axis. Feathering results in blade angle change.Rotor system
AlternatorDevice that generates electrical power.Miscellaneous
Induced flowThe airflow that exists solely as a result of the airmass that is forced down by rotoraction.Aerodynamics
DragThe resistance of an aerodynamic body moving through air. Drag is a resistance force and acts in the opposite direction of airmovement.Aerodynamics
Induced dragThe reaction force generated by an airfoil in the direction of the relative airflow.Aerodynamics
Profile dragThe amount of drag due to the airfoil shape and material.Aerodynamics
Inflow angleThe angle between the RAF (Relative Air Flow) vector and the plane of rotation.Aerodynamics
Angle of attackThe angle between the RAF (Relative Air Flow) vector and the blade's chord line.Aerodynamics
Relative airflowThe Relative Air Flow (RAF) is the airflow with speed and direction, relative to the airfoil.Aerodynamics
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