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[SIFT] ARMY AVIATION INFORMATION

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A helicopter is:
A. A type of gyrocraft.
B. A type of rotorcraft.
C. A category of rotary-wing airplanes.
D. A sub-group of gyrocopters.
b
Helicopter turbine engines produce ___ thrust per pound than piston engines:
A. less
B. the same
C. more
D. the same, but only after factoring in the effect of density altitude
c
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.
b
Helicopters typically have betweeen __ and __ main rotor blade(s):
A. 2, 6.
B. 2, 10.
C. 3, 8.
D. 3, 7.
a
Depending on the type of helicopter, main rotor system components can include:
A. A stabilizer bar, upper and lower swashplates, and counterweights.
B. Pitch horns, teeter or coning hinges, and blade grips.
C. Pitch and scissor links, and control rods.
D. All of the above.
d
The function of the flybar is:
A. To decrease crosswind thrust on the blades and enhance flight stability by keeping the bar stable as the rotor spins.
B. To increase crosswind 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.
a
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.
b
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 of the above.
c
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.
c
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.
d
From a physics perspective, the ___ force is deemed to act through a helicopter's ___:
A. lift, center of motion.
B. total weight, center of gravity.
C. induced drag, longitudinal axis.
D. total mass, center of motion.
b
When a pilot banks a helicopter, causing it to turn, ___:
A. The machine's weight increases.
B. The machine's weight decreases.
C. The machine's gravitational drag increases.
D. The vertical component of the lift vector remains the same.
a
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 these.
c
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.
d
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.
d
Vortices produced by spinning rotor blades create:
A. Form drag.
B. Rotational drag.
C. Parasite drag.
D. Induced drag.
d
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.
a
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.
c
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.
d
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.
b
Newton's Third Law of Motion applies to helicopter's because:
A. The spinning main rotor blades 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.
a
When the pilot pushes the cyclic stick forward:
A. The main rotor disk tilts forward.
B. The blades' angle of attack on the rearward section of the tail rotor disk decreases.
C. The angle of attack of the driven portion of the main rotor disk increases.
D. All of the above.
a
Multi-engine helicopters have:
A. A supplementary freewheeling clutch.
B. A coaxial drive shaft and two transmissions.
C. A throttle lever for each engine.
D. All of the above.
c
When the pilot want the helicopter's nose to move left or right, he or she:
A. Pushes down on the collective for left motion and pulls up on it to turn right.
B. Tilts the main rotor disk left or right while keeping the pedals neutral.
C. Pushes on the left or right pedal while adjusting the cyclic to compensate for greater rotational drag.
D. Pushes on the corresponding pedal.
d
For helicopter's with a main rotor disk that spins counter-clockwise, the ___ airflow speed happens when each blade reaches the ___ position:
A. median, nine o'clock (left)
B. minimum, three o'clock (right)
C. maximum, three o'clock (right)
D. L/DMAX, six o'clock (aft)
c
On the advancing rotor blade, lift ___ an the blade ___:
A. increases, angles up near the tip due to greater centripetal force.
B. increases, moves upward.
C. transitions outward, experiences stronger lateral torque.
D. None of the above.
b
The angle between the ___ of a rotor blade and its direction of motion relative to the ___ is the angle of attack (AOA), which is ___ angle.:
A. mean camber line, air, a constant.
B. chord line, air, an aerodynamic.
C. chord line, longitudinal airflow, a variable.
D. mean camber line, longitudinal airflow, an acute.
b
The angle of incidence is between the ___ line of each blade and the rotor system's ___:
A. mean camber, forward-flight relative wind.
B. mean camber, rotational relative wind.
C. chord, angular momentum.
D. chord, plane of rotation.
d
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.
d
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.
a
Where there is too much lift, the main rotor blades will:
A. Torque on the retreating blades.
B. Twist.
C. Flap.
D. Create vortices in the driven region.
c
Centrifugal force ___ spinning helicopter main rotor blades ___.
A. pushes, inward.
B. pulls, outward.
C. angles down, during autorotation.
D. angles up, during liftoff.
b
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 ___:
A. fly in a sideslip.
B. vibrate excessively and come apart.
C. torque clockwise.
D. uncontrollable.
d
The driven region is ___ the blade tips and normally __ percent of the radius:
A. nearest, 30.
B. furthest from, 30.
C. mid-span from, 50.
D. nearest, 50.
a
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
d
Because of gyroscopic precession, if a wind gust applies a downward force on the left side of 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.
c
Helicopter's 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.
c
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.
b
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.
b
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. Setting with power.
d
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