User Guide

LONGBOW 2
C.1
GLOSSARY
Advancing blade. Blade during the half of its revolution in which it travels in the same direction as the aircraft.
Airfoil. Curved wing or blade surface that produces lift when air passes over it.
Airframe. Basic structure of an aircraft (doors, landing gear, seats, cabin, etc.).
Angle of attack. Angle between the chord of a rotor blade and the direction of air passing over it.
Angle of incidence. Angle between the chord of a rotor blade and the plane of rotation of the rotor disc.
Asymmetry of lift. Unequal lift that results when the helicopter is in horizontal motion. The retreating rotor
blades move more slowly than the advancing blades, and create less lift. This causes single-rotor helicopters
to veer upward and sideways. Pilots compensate by using the directional control pedals.
Autorotation. Non-powered flight; air passing through the rotor disc causes the rotor blades to turn,
maintaining lift.
Battalion. U.S. military unit with two or more companies and anywhere from 500 to 1,500 men. (Cavalry
and helicopter battalions are often called “squadrons.”)
Bernoulli’s principle. As the speed of a fluid increases, its pressure decreases. Air behaves like a fluid as it
flows around an airfoil. The foil is designed so that the top surface is longer than the bottom; air must travel
faster over the top surface, creating a low pressure area above the airfoil and adding to the airfoil’s lift.
Blade. Airfoil surface of a helicopter used to create lift.
Blade stall. Condition that occurs when the angle of attack of the blades is so great that no lift is generated.
Chaff. Small filaments or metallic strips released to reflect/confuse signals from radar-guided weapons.
Chord. Imaginary line that passes through the leading and trailing edges of an airfoil.
Collective. Helicopter control used to collectively alter the pitch (angle) of all the rotor blades simultaneously.
Company. U.S. military organization consisting of two or more platoons and anywhere from 100 to 300
soldiers. (Cavalry or helicopter companies are often called “troops.”)
Coning. Upward “flexing” of a helicopter’s rotor blades. The coning angle is determined by the weight of
the helicopter and the rotor RPM.
Coordinated turn. What happens when tail rotor and cyclic (linked via computer) work together to produce
a smooth, constant banking turn. When the coordinated turn feature of the Longbow Apache is activated,
the directional control pedals automatically coordinate with the cyclic control to produce a smooth turn.
Countermeasures. Defensive measures used by aircraft against air-to-air or surface-to-air weapons (chaff,
flares and jammers).
Cyclic. Helicopter control used to selectively change pitch (angle) of individual rotor blades as they move
through the path of revolution. The cyclic controls the “tilt” of the rotor disc, and affects direction and speed.
Disc area. Area through which the rotor blades pass during each revolution.
Drag. Force that counteracts an object in motion through the air, also called air resistance.
Force Trim. Resetting the centered position of the cyclic stick to maintain a contant horizontal velocity,
instead of a stationary hover.