SIFT Army Aviation Practice Test

Questions and Answers

What is a helicopter?

A type of rotorcraft

Helicopter turbine engines produce ___________ thrust per pound than piston engines.

What are the four main forces working on a helicopter?

Lift, weight, thrust, drag

Helicopters typically have between _ and _ main rotor blades.

2 and 6 Signup and view all the answers

What components can be included in a helicopter's main rotor system?

A stabilizer bar, upper/lower swashplates, counterweights, pitch horns, teeter/coning hinges, blade grips, pitch/scissor links, control rods Signup and view all the answers

What is the function of the flybar?

To decrease crosswind thrust on the blades and enhance flight stability by keeping the bar stable as the rotor spins Signup and view all the answers

Where is the horizontal stabilizer located on many helicopters?

On the tail boom Signup and view all the answers

What is the purpose of the tail rotor?

To produce an anti-torque force acting perpendicular to the helicopter's longitudinal axis. Signup and view all the answers

Wheels on _ types of helicopters are _

Some, retractable Signup and view all the answers

What controls does a pilot use to operate a helicopter?

Pedals, a collective, throttle, cyclic Signup and view all the answers

From a physics perspective, the _ force acts through a helicopter's _

Total weight, center of gravity Signup and view all the answers

What happens when a pilot banks a helicopter to turn?

The machine's weight increases Signup and view all the answers

Lift is produced by _____ moving through the air at a speed sufficient to create?

Airfoils, a pressure differential Signup and view all the answers

Thrust acts _ to the aircraft's _

Parallel, longitudinal axis Signup and view all the answers

Profile drag consists of?

The sum of form drag and skin friction Signup and view all the answers

What do vortices produced by spinning rotor blades create?

Induced drag Signup and view all the answers

When plotted on a graph, L/DMAX is the point where the helicopter's _____ is the greatest.

Total lift-to-drag ratio Signup and view all the answers

A helicopter's potential energy is affected by?

The aircraft's height above the ground Signup and view all the answers

Which factors affect the lift produced by spinning rotor blades? (Select all that apply)

Air density Signup and view all the answers

What happens when a helicopter's main rotor blades spin rapidly?

The upper and lower sides of each blade experience a difference in pressure Signup and view all the answers

Why does Newton's third law of motion apply to helicopters?

The spinning main rotor makes the aircraft try to spin in the opposite direction Signup and view all the answers

What happens when the pilot pushes the cyclic forward?

The main rotor disk tilts forward Signup and view all the answers

What do multi-engine helicopters have?

A throttle lever for each engine Signup and view all the answers

When the pilot wants the helicopter's nose to move left or right, what does he do?

Pushes on the corresponding pedal Signup and view all the answers

For helicopters with a main rotor disk that spins counter-clockwise, the _ airflow speed happens when each blade reaches the _ position.

Maximum, three o'clock (right) Signup and view all the answers

On the advancing rotor blade, lift _ and the blade _

increases, moves upward Signup and view all the answers

The angle between the ___ of a rotor blade and its direction of motion relative to the _ is the angle of attack, which is ___ angle.

Chord line, air, an aerodynamic Signup and view all the answers

The angle of incidence is between the _ line of each blade and the rotor system's _

Chord, plane of rotation Signup and view all the answers

When a helicopter engine fails, what mechanism automatically disconnects the engine from the main rotor?

Freewheeling unit Signup and view all the answers

During an autorotation in forward flight, what type of air does the rotor disk take in?

Upward flowing Signup and view all the answers

Where there is too much lift, what will the main rotor blades do?

Flap Signup and view all the answers

What does centrifugal force do to spinning helicopter main rotor blades?

Pulls, outward Signup and view all the answers

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 _____

Uncontrollable Signup and view all the answers

The driven region is _ the blade tips and normally _ percent of the radius.

Nearest, 30 Signup and view all the answers

The ___ region is normally between a blade's _ and ___ regions.

Driving, stall, driven Signup and view all the answers

Because of gyroscopic precession, if a wind gust applies a downward force on the left side of a helicopter's main rotor disk, the movement response occurs at the _____ position.

12 Signup and view all the answers

Helicopters experience effective translational lift while transitioning to forward flight at approximately _ to _ knots.

16, 24 Signup and view all the answers

Maximum ground effect occurs during a hover up to a height equal to _____ percent of the main rotor's diameter.

100 Signup and view all the answers

What can worsen a helicopter's pendular action?

Over-controlling the aircraft Signup and view all the answers

What is the phenomenon of a helicopter sinking into its own downwash called?

Settling with power Signup and view all the answers

Study Notes

Helicopter Basics

A helicopter is classified as a type of rotorcraft.
Turbine engines in helicopters produce more thrust per pound compared to piston engines.

Forces Involved

The four main forces acting on a helicopter are lift, weight, thrust, and drag.

Rotor Blade Characteristics

Helicopters commonly have between 2 and 6 main rotor blades.
Main rotor system components may include stabilizer bars, swashplates, and control rods.
Flybars help reduce crosswind thrust and improve flight stability.

Flight Control and Mechanisms

Many helicopters feature a horizontal stabilizer located on the tail boom, enhancing stability.
The tail rotor's primary purpose is to generate an anti-torque force perpendicular to the helicopter’s longitudinal axis.
Pilots use pedals, a collective, a throttle, and cyclic to control the helicopter.

Aerodynamic Principles

The total weight of a helicopter acts through its center of gravity, influencing balance.
Banking causes an increase in the helicopter's perceived weight.
Lift is produced by airfoils moving at a speed that creates a pressure differential.

Thrust and Drag

Thrust acts parallel to the aircraft's longitudinal axis, essential for forward movement.
Profile drag comprises form drag and skin friction, impacting the aircraft's performance.
Vortices from spinning rotor blades result in induced drag.

Energy and Performance

A helicopter's potential energy is contingent on its altitude above the ground.
Factors affecting lift from rotor blades include airfoil coefficient of lift, air density, and blade area.

Rotor Blade Mechanics

Rapid spinning of blades causes pressure differences across the upper and lower sides, generating lift.
Newton's third law indicates the opposite spin of the aircraft caused by the main rotor’s rotation.

Operational Maneuvers

Pushing the cyclic forward tilts the main rotor disk, influencing movement direction.
Multi-engine helicopters utilize a throttle lever for each engine.
Left or right movements of the helicopter’s nose are controlled by corresponding pedals.

Rotor Blade Dynamics

In helicopters with counter-clockwise spinning rotors, maximum airflow occurs as blades reach the three o'clock position.
During forward flight, the rotor disk takes in upward flowing air, affecting its driving and stall regions.

Mechanical Failures

In the event of an engine failure, a freewheeling unit disconnects the engine from the rotor, allowing it to spin freely.

Flight Conditions

Excessive lift leads to blade flapping, which can alter flight dynamics.
Centrifugal force pulls rotor blades outward during operation.
Unchecked lift discrepancies between advancing and retreating sides can cause uncontrollable flight.

Blade Regions and Effects

The driven region is closest to blade tips, typically within 30% of the rotor radius.
The driving region lies between the stall and driven regions, essential for rotor efficiency.

Gyroscopic Precession

A gust of wind affecting the left side results in movement response at the 12 o'clock position due to gyroscopic precession.

Translational Lift and Effects

Effective translational lift is experienced during forward flight between 16 to 24 knots.
Maximum ground effect occurs during hover when at a height equal to 100% of the rotor diameter.

Pilot Control Challenges

Over-controlling a helicopter can exacerbate pendular movements, making stability harder to achieve.
Settling with power occurs when a helicopter sinks into its own downwash, affecting performance during landing and hovering.

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Description

Test your knowledge of helicopter aviation with this informative practice quiz. Covering key concepts such as rotorcraft definitions, engine thrust comparisons, and forces acting on helicopters, this test is perfect for aviation enthusiasts and professionals alike. Improve your understanding of helicopter mechanics and terminology.