SIFT Army Aviation Information Practice Test – Flashcards
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A helicopter is
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A type of rotorcraft
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Helicopter turbine engines produce ___________ thrust per pound than piston engines
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More
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The four main forces working on a helicopter are
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Lift, weight, thrust, drag
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Helicopters typically have between ___ and ___ main rotor blades
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2 and 6
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Depending on the type of helicopter, main rotor system components can include
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A stabilizer bar, upper/lower swashplates, counterweights, pitch horns, teeter/coning hinges, blade grips, pitch/scissor links, control rods
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The function of the flybar is
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To decrease crosswind thrust on the blades and enhance flight stability by keeping the bar stable as the rotor spins
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Many helicopters have a horizontal stabilizer located _____
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On the tail boom
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The purpose of the tail rotor is:
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To produce an anti-torque force acting perpendicular to the helicopter's longitudinal axis.
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Wheels on _____ types of helicopters are _____
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Some, retractable
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A pilot controls a helicopter using:
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Pedals, a collective, throttle, cyclic
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From a physics perspective, the _____ force is deemed to act through a helicopter's _____
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Total weight, center of gravity
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When a pilot banks a helicopter, causing it to turn, _____
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The machine's weight increases
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In the case of helicopters, lift is produced by _____ moving through the air at a speed sufficient to create
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Airfoils, a pressure differential
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Thrust acts _____ to the aircraft's _____
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Parallel, longitudinal axis
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Profile drag consists of
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Profile drag is usually defined as the sum of form drag(Shape of the object) and skin friction(imperfections)
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Vortices produced by spinning rotor blades create
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Induced drag
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When plotted on a graph, L/DMAX is the point where the helicopter's _____
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Total lift-to-drag ration is the greatest
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A helicopter's potential energy is affected by
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The aircraft's height above the ground
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Which of the following factors affect the lift produced by spinning rotor blades
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Airfoil coefficient of lift, air density, blade area
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What happens when a helicopter's main rotor blades spin rapidly?
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The upper and lower sides of each blade experience a difference in pressure
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Newton's third law of motion applies to helicopters because
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The spinning main rotor makes the aircraft try to spin in the opposite direction
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When the pilot pushes the cyclic forward
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The main rotor disk tilts forward
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Multi-engine helicopters have
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A throttle lever for each engine
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When the pilot wants the helicopter's nose to move left or right he
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Pushes on the corresponding pedal
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For helicopters with a main rotor disk that spins counter-clockwise, the _____ airflow speed happens when each blade reaches the _____ position.
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Maximum/ three o'clock (right)
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On the advancing rotor blade, lift _____ and the blade _____
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increases, moves upward
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The angle between the _____ of a rotor blade and its direction of motion relative to the _____ is the angle of attack, which is _____ angle
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Chord line, air, an aerodynamic
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The angle of incidence is between the _____ line of each blade and the rotor system's _____
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Chord, plane of rotation
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When a helicopter engine _____, a clutch mechanism called a _____
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fails, freewheeling unit automatically discinnects the engine from the main rotor, allowing it to spin freely
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During an autororation in forward flight, the rotor disk takes in _____ air and the driven, driving and stall regions of each blade move _____ along its length but only on the _____ side of the dick
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Upward flowing, outboard, retreating
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Where there is too much lift, the main rotor blades will
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Flap
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Centrifugal force _____ spinning helicopter main rotor blades _____
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Pulls, outward
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If left uncorrected, greater lift produced by the advancing side of the rotor disk compared to the lift created by the disk's retreating side could make the helicopter _____
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Uncontrollable
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The driven region is _____ the blade tips and normally _____ percent of the radius
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Nearest, 30
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The _____ region is normally between a blade's _____ and _____ regions
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Driving, stall, driven
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Because of gyroscopic precession, if a wind gust applies a downward force on the left side of a helicopter's main rotor disk as it spins clockwise(as viewed from above), the movement response occurs at the _____ o'clock position
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12
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Helicopter's experience effective translational lift while transitioning to forward flight at approximately _____ to _____ knots
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16, 24
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Maximum ground effect occurs during a hover up to a height equal to _____ percent of the main rotor's diameter
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100
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A pilot can worsen a helicopter's pendular action by
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Over-controlling the aircraft
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The phenomenon of a helicopter sinking into its own downwash is called
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Settling with power
