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SIFT (Army Aviation Information Practice
Test) Questions and Answers
A helicopter is: A. A type of gyrocraft. B. A type of rotorcraft. C. A category of rotary-wing airplanes. D. A sub-group - ANSWER-B. A type of rotorcraft. Helicopter turbine engines produce ___________ thrust per pound than piston engines: A. less. B. the same. C. more. D. the same, but only after factoring n the effect of density altitude. - ANSWER-C. more. The main forces acting on a helicopter are: A. Induced lift, mass, thrust, and form drag. B. Lift, weight, thrust, and drag. C. Lift, gravity, air resistance, and rotor vortex drag. D. None of the above. - ANSWER-B. Lift, weight, thrust, and drag. Helicopters typically have between ___ and ___ main rotor blade(s): A. 2, B. 2, C. 3, D. 3,7 - ANSWER-A. 2, Depending on the type of helicopter, main rotor system components can include: A. A stabilizer bar, upper and lower swash plates, and counterweights. B. Pitch horns, teeter or coning hinges, and blade grips. C. Pitch and scissor links, and control rods. D. All the above. - ANSWER-D. All the above. The function of the flybar is:
A. To decrease thrust on the blades and enhance flight stability by keeping the bar stable as the rotor spins. B. To increase thrust and modify flight stability by allowing the bar to spin at a slower speed than the main rotor. C. To decrease crosswind thrust and augment flight stability by maintaining the bar at an acute angle to the main rotor. D. To spin in a direction opposite to the main rotor's, thereby reducing induced drag. - ANSWER-A. To decrease thrust on the blades and enhance flight stability by keeping the bar stable as the rotor spins. Many helicopters have a horizontal stabilizer located: A. On the mast. B. On the tail boom. C. On the fin. D. None of the above. - ANSWER-B. On the tail boom. The purpose of the tail rotor is: A. To create kinetic energy that is transformed into potential energy as the helicopter climbs. B. To produce rotational momentum that is used by the transmission to drive a generator. C. To produce an anti-torque force acting perpendicular to the helicopter's longitudinal axis. D. All the above. - ANSWER-C. To produce an anti-torque force acting perpendicular to the helicopter's longitudinal axis. Wheels on _____ types of helicopters are _____: A. all, retractable (to reduce drag). B. some, supplementary to skids. C. some, retractable. D. all, supplementary to skids. - ANSWER-C. some, retractable. A pilot controls a helicopter using: A. Flight instruments, hydraulic actuators, and a cyclic with a twist throttle. B. Flight instruments, pedals, two or more throttle levers, and avionics. C. Pedals, a throttle, with a twist grip, collective link rods, and a cyclic. D. Pedals, and a collective, throttle, and cyclic. - ANSWER-D. Pedals, and a collective, throttle, and cyclic. From a physics perspective, the ______ force is deemed to act through a helicopter's __________:
When a helicopter engine ________, a clutch mechanism called a __________________: A. fails; governing transmission is disconnected from the engine by the pilot, which allows the main rotor to spin freely. B. is shutdown after landing; gearbox controller is disconnected from the engine by the pilot, which allows the main and tail rotors to spin freely. C. accelerates too rapidly; terminal speed unit automatically disconnects the engine from the tail rotor, allowing it to spin freely. D. fails; freewheeling unit automatically disconnects the engine from the main rotor, allowing it to spin freely. - ANSWER-D. fails; freewheeling unit automatically disconnects the engine from the main rotor, allowing it to spin freely. During an autorotation in forward flight, the rotor disk takes in ________ air and the driven, driving, and stall regions of each blade move ________ along its length (span), but only on the ________ side of the disk: A. upward flowing, outboard, retreating. B. downward flowing, inward, advancing. C. upward flowing, inward, retreating. D. ambient, outward, advancing. - ANSWER-A. upward flowing, outboard, retreating. In the case of helicopters, lift is produced by ________ moving through the air at a speed sufficient to create _______________: A. rotor blades, gyroscopic precession. B. the flybar, an anti-drag force. C. airfoils, a pressure differential. D. None of the above. - ANSWER-C. airfoils, a pressure differential. Thrust acts ________ to the aircraft's ________________________: A. at an acute angle, driven portion of the tail rotor disk. B. perpendicular, rotational relative wind. C. laterally, outer two-thirds of the main rotor disk. D. parallel, longitudinal axis. - ANSWER-D. parallel, longitudinal axis. Profile drag consists of __________ created by __________ and __________: A. induced drag, angular momentum, aircraft components that do not contribute to lift. B. skin friction, surface imperfections, form drag. C. an inclined main rotor disk, increasing angle of attack, high blade rpm. D. None of the above. - ANSWER-D. None of the above. Vortices produced by spinning rotor blades create:
A. Form drag. B. Rotational drag. C. Parasite drag. D. Induced drag. - ANSWER-D. Induced drag. When plotted on a graph, L/DMAX is the point where the helicopter's _____________. A. Total lift-to-drag ratio is the greatest. B. Induced lift-to-drag ratio is maximized. C. Perpendicular lift component exceeds the rotational drag vector by at least 50 percent. D. Ability to carry pilots, cargo, etc. at the maneuvering speed is most fuel-efficient. - ANSWER-A. Total lift-to-drag ratio is the greatest. A helicopter's potential energy is affected by: A. The tail rotor's anti-torque force. B. The relative wind. C. The aircraft's height above the ground. D. All of the above. - ANSWER-C. The aircraft's height above the ground. Which of the following factors affect the lift produced by spinning rotor blades: A. Airfoil coefficient of lift. B. Air density. C. Blade area. D. All of the above. - ANSWER-D. All of the above. What happens when a helicopter's main rotor blades spin rapidly? A. The angle of incidence decreases causing more lift on the retreating blades. B. The upper and lower sides of each blade experience a difference in pressure. C. Gyroscopic precession acts laterally on the aircraft. D. The center of pressure on each blade moves forward, creating a vortex. - ANSWER- B. The upper and lower sides of each blade experience a difference in pressure. Newton's Third Law of Motion applies to helicopters because: A. The spinning main rotor makes the aircraft try to spin in the opposite direction. B. Torque is balanced by the longitudinal drag vector. C. A ducted-fan helicopter produces less torque than an un-ducted one. D. Rotational relative wind opposes the angular momentum force. - ANSWER-A. The spinning main rotor makes the aircraft try to spin in the opposite direction. When the pilot pushes the cyclic forward:
B. furthest from, 30 C. mid-span from, 50 D. nearest, 50 - ANSWER-nearest, 30 The _______ region is normally between a blade's _______ and _______ regions: A. stall, driven, high AOA B. stall, driving, low AOA C. driven, high AOA, stall D. driving, stall, driven - ANSWER-D. driving, stall, driven 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: A. 9 B. 6 C. 12 D. 3 - ANSWER-C. 12 Helicopters experience effective translational lift while transitioning to forward flight at approximately __ to __ knots: A. 20, 28 B. 10, 20 C. 16, 24 D. 12, 24 - ANSWER-C. 16, 24 Maximum ground effect occurs during a hover up to a height equal to ___ percent of the main rotor's diameter: A. 50 B. 100 C. 150 D. None of the above - ANSWER-B. 100 A pilot can worsen a helicopter's pendular action by: A. Applying too much angle of incidence. B. Over-controlling the aircraft. C. Moving the cyclic left while pushing on the right pedal. D. Moving the cyclic left while pulling up on the collective. - ANSWER-B. Over- controlling the aircraft. The phenomenon of a helicopter sinking into its own downwash is called:
A. L/Wmin (minimum lift-to-weight ratio). B. An airfoil stall. C. Vortex torque state. D. Settling with power. - ANSWER-D. Settling with power.
