Is helicopter material really on the FAA Airframe written test?

Yes. Rotorcraft is one of the airframe subject areas, so helicopter questions can appear on your Airframe written test even if you never plan to work on helicopters. How many show up varies by test form. Treat it as required vocabulary: rotor system types, control functions, hinge names, and a handful of aerodynamic terms cover most of what is asked.

What is the difference between the collective and the cyclic?

The collective raises or lowers the pitch of all main rotor blades at once and by an equal amount, which changes total rotor thrust. The cyclic varies each blade's pitch as it travels around the disc, so lift is greater on one side than the other and the tip-path plane tilts. One control changes how much lift; the other changes where it acts.

What is the difference between fully articulated, semirigid, and rigid rotor systems?

A fully articulated system gives each blade its own flapping hinge, lead-lag hinge, and feathering bearing, and normally carries three or more blades. A semirigid or teetering system has two blades that flap as a single unit about one central hinge and has no lead-lag hinges. A rigid system has neither flapping nor lead-lag hinges, so the blades flex to absorb that motion.

What causes dissymmetry of lift on a helicopter rotor?

In forward flight the advancing blade adds the helicopter's airspeed to its own rotational speed while the retreating blade subtracts it, so the advancing side would generate more lift if nothing corrected it. Blade flapping, along with the cyclic feathering built into the control system, equalizes lift across the disc so the aircraft does not roll toward the retreating side.

What do the anti-torque pedals actually do?

On a single main rotor helicopter the pedals change the pitch of the tail rotor blades, which changes tail rotor thrust. That controls yaw, or movement about the vertical axis, and it also balances the torque reaction the main rotor transmits to the fuselage. The pedals do not change main rotor pitch and they do not tilt the rotor disc.

In a typical single main rotor helicopter, what is the primary purpose of the tail rotor?

To counteract the torque produced by the main rotor and provide directional control

To produce most of the lift that keeps the helicopter airborne in flight

To increase forward airspeed by adding thrust along the longitudinal axis

Dissymmetry of lift on a helicopter main rotor is caused by what?

The difference in airspeed between the advancing and retreating blades in forward flight

The torque reaction of the main rotor acting on the fuselage

The reduction in air density as the helicopter climbs to higher altitudes

On a helicopter rotor blade, the angle of attack is the angle between the blade chord line and the

relative wind meeting the blade.

plane of rotation of the rotor.

A helicopter rotor blade is an airfoil. It produces lift primarily by

creating a region of low pressure above the blade

acting like a screw that bites into the air

simply pushing a column of air downward

The angle of attack of a rotor blade is the angle between the

rotor spin axis and the relative wind.

On a helicopter rotor, blade dragging (lead-lag) refers to the

horizontal movement of each blade about its vertical hinge.

contact of the blade tips with the ground surface.

vertical movement of each blade about its horizontal hinge.

The lift generated by a rotor blade is proportional to the

relative wind and the angle of attack.

aircraft airspeed and the angle of attack.

relative wind and the blade pitch angle.

What effect does ground effect have on a hovering helicopter?

It increases the lift produced by the rotor.

It increases the tail rotor thrust required.

It has no measurable effect on the rotor.

In forward flight, the relative wind acting on a helicopter main rotor

is greatest on the advancing blade.

is equal for all of the blades.

is greatest on the retreating blade.

When a rotor blade moves about its flapping hinge,

the blade angle of attack changes and the drag forces change.

the drag forces change but the angle of attack stays fixed.

the blade pitch angle is always automatically reduced.

The coning angle of a helicopter rotor is determined by the balance between

rotor lift and centrifugal force.

rotor thrust and centrifugal force.

As a single-rotor helicopter accelerates in level forward flight past about 15 knots, the pilot will need to

reduce power because of the additional lift from effective translational lift.

increase power because the rotor RPM is increasing.

reduce power because the rotor profile drag is reduced.

A helicopter has a main rotor that turns counterclockwise as viewed from above and an anti-torque tail rotor. The helicopter will tend to drift sideways toward the

right, regardless of how the tail rotor is mounted.

left, if the tail rotor is mounted on the right side.

left, if the tail rotor is mounted on the left side.

The tail rotor of a single-main-rotor helicopter

produces a force that opposes the main-rotor torque reaction.

is not subject to dissymmetry of lift in forward flight.

produces a force in the same direction as the torque reaction.

Certain helicopters tend to tilt laterally during landing. This tendency can be overcome by locating the tail rotor thrust line

in line with the main rotor hub.

below the line of the main rotor hub.

above the line of the main rotor hub.

Ground effect for a helicopter in a hover is produced by

increased pressure under the main rotor disc.

recirculating air providing additional lift.

an increase in air density above the fuselage.

During a power-on descent of a helicopter, which forces are acting on the aircraft?

Lift, drag, thrust, and weight.

Main rotor blades commonly use a symmetrical airfoil section because it

keeps the center of pressure from shifting.

is reverse cambered for added lift.

is highly cambered for added lift.

Autorotative force is the

component of the total reaction acting forward in the plane of rotation, opposing drag.

force the pilot applies to the collective to obtain a controlled descent.

force required to turn the helicopter while in a hover.

Autorotation in a helicopter is

the production of lift by freely rotating rotor blades without engine power.

a condition that results in a loss of engine power.

a condition that leaves the aircraft with no directional control.

A helicopter rotor blade derives its lift from the fact that

the blade creates a region of low pressure above it.

the rotor acts purely as an airscrew.

the blade simply pushes air downward.

A two-bladed helicopter rotor head mounted on a central gimbal that allows the blades to flap as a unit is called a

fully articulated rotor system.

Because of phase lag (gyroscopic precession), the maximum displacement of a rotor blade occurs

approximately 90 degrees of rotation after the pitch input is applied.

at the same point where the pitch input is applied.

approximately 180 degrees of rotation after the pitch input is applied.

Vortex ring state (settling with power) in a helicopter occurs when

the rotor settles into its own recirculating tip-vortex wake at low forward speed.

tip vortices interfere with the rotor at high forward speed.

the rotor encounters ground vortex interference while hovering near the ground.

Horizontal (translational) flight in a helicopter is achieved by

tilting the rotor disc in the direction of flight with cyclic.

raising or lowering the collective lever.

changing from one steady flight condition to another.

The most desirable rotor blade design is one in which the center of pressure

does not move along the chord of the blade.

has an insignificant effect on the blade.

moves freely along the length of the blade.

When the cyclic stick is eased forward from a hover, what happens to the rotor's vertical lift?

Total rotor thrust is increased.

Static stability of a helicopter is best defined as which of the following?

The initial tendency to move back toward neutral after a disturbance.

The tendency to oscillate repeatedly until neutral is reached.

The tendency to continue diverging away from neutral.

In forward flight, the increased relative airflow over the advancing blade causes it to do what?

Flap up, which reduces its angle of attack and lift.

Flap down, which increases its angle of attack and lift.

Lag rearward and gain additional lift.

When transitioning from a hover to forward flight, what change in engine power is generally required?

Maintain constant engine power.

Rotorcraft Fundamentals — FAA A&P Test Questions (ACS AM.II.N)

Rotorcraft Fundamentals is the airframe subject area that asks you to think like a helicopter mechanic rather than a fixed-wing one. The written test does not ask you to fly a helicopter, but it does expect you to know what each rotor control does, what each hinge in a rotor head allows, and why a blade behaves differently on the advancing side than on the retreating side. Most questions are definitional and mechanical: name the motion, name the hinge, name the control. Get the vocabulary exactly right and this area becomes some of the most reliable points on the Airframe test.

Written by the AMTprep editorial team · Published July 27, 2026 · Last reviewed October 21, 2026

Written against the FAA primary sources cited at the foot of this page.

What ACS AM.II.N covers

Questions in this area come from the rotorcraft material in FAA-H-8083-31, and they cluster around four things. First, the controls: the collective changes the pitch of every main rotor blade simultaneously and by an equal amount, the cyclic varies blade pitch through each revolution so the tip-path plane tilts, and the anti-torque pedals change tail rotor pitch to control yaw, which is movement about the vertical axis. Second, the tail rotor itself, which on a single main rotor helicopter counteracts the torque reaction applied to the fuselage by the driven main rotor and also gives the pilot directional control. Third, rotor head types and their hinges. A fully articulated head gives each blade a flapping hinge for up-and-down motion, a lead-lag or drag hinge for fore-and-aft motion in the plane of rotation, and a feathering bearing for pitch change. A semirigid, or teetering, head carries two blades that flap together as a single unit about one central hinge. A rigid head has no flapping or lead-lag hinges and depends on blade flexing instead. Fourth, rotor aerodynamics: angle of attack is the angle between the blade chord line and the relative wind, not between the chord line and the plane of rotation, and dissymmetry of lift appears in forward flight because the advancing blade meets a higher relative airspeed than the retreating blade. Expect questions on how blade flapping and cyclic feathering equalize that difference, on the Coriolis effect and why lead-lag motion has to be allowed and damped, and on autorotation, ground resonance, and rotor track and balance terminology.

Where this sits on the test

ACS AM.II.N is tested on the FAA Airframe written test, one of 1,739 ACS-tagged questions in the Airframe bank. Every question tagged to this area carries a worked rationale and its FAA handbook reference, so you can drill the code itself rather than the whole test.

FAA handbook references

FAA-H-8083-31

Three traps candidates fall into

Candidates reverse the hinges. A flapping hinge is oriented horizontally but permits vertical, up-and-down blade motion, while a lead-lag hinge is oriented vertically but permits horizontal, fore-and-aft motion in the plane of rotation. Name the hinge by the motion it allows, not by the axis it looks like.
Collective and cyclic get swapped. The collective changes every blade's pitch by the same amount at the same time and mainly changes total rotor thrust. The cyclic changes each blade's pitch as it travels around the disc, so pitch varies with position and the rotor disc tilts.
Dissymmetry of lift gets blamed on engine torque or on the tail rotor. It comes from the airspeed difference between the advancing and retreating blade in forward flight, and blade flapping is what compensates for that difference rather than what creates it.

50 free sample questions from ACS AM.II.N

AM.II.NTap an answer
In a typical single main rotor helicopter, what is the primary purpose of the tail rotor?
Show the answer and explanation
Answer: To counteract the torque produced by the main rotor and provide directional control
Why: The spinning main rotor applies a torque to the fuselage that tends to rotate it in the opposite direction. The tail (anti-torque) rotor produces sideward thrust to counteract this torque and, through pedal inputs, allows the pilot to control the helicopter's heading about the vertical axis. Lift is produced by the main rotor, not the tail rotor.· FAA-H-8083-31 — Helicopter structures / anti-torque systems
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Which control changes the pitch of all main rotor blades simultaneously and by an equal amount?
Show the answer and explanation
Answer: The collective pitch control
Why: The collective changes the pitch angle of all main rotor blades at the same time and by the same amount, which changes total rotor thrust and governs the helicopter's climb and descent. The cyclic changes blade pitch individually as the blades rotate, tilting the rotor disc; the pedals control tail rotor thrust.· FAA-H-8083-31 — Helicopter flight controls
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On a fully articulated rotor head, which hinge allows each blade to move forward and aft in the plane of rotation?
Show the answer and explanation
Answer: The lead-lag (drag) hinge
Why: A fully articulated rotor provides three independent blade motions. The lead-lag (drag) hinge permits each blade to move fore and aft in the plane of rotation to accommodate the acceleration and deceleration caused by Coriolis effect. The flapping hinge allows up-and-down motion, and the feathering hinge allows the blade to change pitch.· FAA-H-8083-31 — Rotor systems / fully articulated rotor
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The up-and-down movement of a rotor blade about a horizontal hinge is known as what?
Show the answer and explanation
Answer: Flapping
Why: Flapping is the vertical movement of a blade about a flapping hinge, which compensates for the dissymmetry of lift that occurs in forward flight between the advancing and retreating blades. Feathering is the pitch-change motion about the feathering hinge, and lead-lag is the fore-and-aft motion in the plane of rotation.· FAA-H-8083-31 — Rotor systems / blade motions
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A two-bladed rotor system in which the blades flap as a single unit on a central hinge is referred to as which type of rotor?
Show the answer and explanation
Answer: Semirigid
Why: A semirigid rotor is usually a two-bladed system in which the blades are rigidly attached to the hub but the hub is free to teeter; as one blade flaps up the other flaps down about a common teetering hinge. A fully articulated rotor has separate flapping, lead-lag, and feathering hinges for each blade; a rigid rotor has no flapping or lead-lag hinges.· FAA-H-8083-31 — Rotor systems / semirigid rotor
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Dissymmetry of lift on a helicopter main rotor is caused by what?
Show the answer and explanation
Answer: The difference in airspeed between the advancing and retreating blades in forward flight
Why: In forward flight the advancing blade has the helicopter's forward speed added to its rotational speed while the retreating blade has that speed subtracted, so the two sides of the disc develop unequal lift. This is dissymmetry of lift, which is compensated for by blade flapping and cyclic feathering. It is not caused by altitude density changes or torque reaction.· FAA-H-8083-31 — Helicopter aerodynamics / dissymmetry of lift
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In a single main rotor helicopter, the anti-torque pedals primarily control movement about which axis?
Show the answer and explanation
Answer: The vertical (yaw) axis
Why: The anti-torque pedals change the pitch and thrust of the tail rotor, which controls the helicopter's heading by rotating the nose left or right about the vertical axis (yaw). Pitch and roll about the lateral and longitudinal axes are controlled by the cyclic, which tilts the main rotor disc.· FAA-H-8083-31 — Helicopter flight controls / anti-torque
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On a helicopter rotor blade, the angle of attack is the angle between the blade chord line and the
Show the answer and explanation
Answer: relative wind meeting the blade.
Why: Angle of attack is the aerodynamic angle between the blade chord line and the relative wind actually meeting the blade, and it changes with induced flow and blade flapping. The angle between the chord line and the plane of rotation is the pitch (blade) angle, which is set mechanically and is a different quantity. (FAA-H-8083-31, Rotorcraft Fundamentals — rotor blade aerodynamics.)· FAA-H-8083-31 — Rotorcraft Fundamentals
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A helicopter rotor blade is an airfoil. It produces lift primarily by
Show the answer and explanation
Answer: creating a region of low pressure above the blade
Why: A rotor blade is an airfoil, and as it moves through the air the cambered upper surface accelerates the airflow and lowers the static pressure above the blade while the lower surface stays at higher pressure. This pressure differential is the source of rotor lift. Although the blade does deflect air downward, the lift mechanism is the low-pressure region created above the blade, not a screw-like action.· FAA-H-8083-31 — Rotorcraft Fundamentals
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The angle of attack of a rotor blade is the angle between the
Show the answer and explanation
Answer: chord line and the relative wind.
Why: Angle of attack is the angle between the blade chord line and the relative wind (relative airflow) meeting the blade. The angle between the chord line and the plane of rotation is the blade pitch (feathering) angle, and the angle to the rotor spin axis is not a recognized aerodynamic definition.· FAA-H-8083-31 — Rotorcraft Fundamentals
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On a helicopter rotor, blade dragging (lead-lag) refers to the
Show the answer and explanation
Answer: horizontal movement of each blade about its vertical hinge.
Why: Blade dragging, or lead-lag, is the in-plane fore-and-aft movement of a blade about its vertical (drag) hinge, accommodating Coriolis effect and cyclic drag variations. Vertical movement of the blade about a horizontal hinge is flapping, which is a separate motion.· FAA-H-8083-31 — Rotorcraft Fundamentals
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The lift generated by a rotor blade is proportional to the
Show the answer and explanation
Answer: relative wind and the angle of attack.
Why: Blade lift increases with the square of the relative wind (the velocity the blade actually sees) and with the angle of attack up to the stall. Aircraft airspeed alone is not the relevant velocity for a rotor, and blade pitch only affects lift indirectly through the resulting angle of attack.· FAA-H-8083-31 — Rotorcraft Fundamentals
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What effect does ground effect have on a hovering helicopter?
Show the answer and explanation
Answer: It increases the lift produced by the rotor.
Why: When hovering close to the surface the downwash is restricted and a high-pressure air cushion forms beneath the rotor disc, so for a given collective setting the rotor produces more lift (or the same lift for less power). Ground effect therefore increases rotor lift rather than having no effect.· FAA-H-8083-31 — Rotorcraft Fundamentals
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Which device is commonly used to dampen in-plane vibration at a helicopter rotor head?
Show the answer and explanation
Answer: A bifilar vibration absorber.
Why: A bifilar (pendulum) vibration absorber fitted to the rotor head tunes itself with rotor speed to cancel in-plane rotor vibration. The swashplate transmits pitch inputs and the scissors (drive) links turn the swashplate with the mast, so neither performs a vibration-damping function.· FAA-H-8083-31 — Rotorcraft Fundamentals
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In forward flight, the relative wind acting on a helicopter main rotor
Show the answer and explanation
Answer: is greatest on the advancing blade.
Why: In forward flight the aircraft's airspeed adds to the rotational speed on the advancing blade and subtracts on the retreating blade, so the relative wind is greatest on the advancing blade. This dissymmetry of lift is the reason blade flapping is needed to equalize lift across the disc.· FAA-H-8083-31 — Rotorcraft Fundamentals
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As outside air temperature (OAT) increases, the operating ceiling of a helicopter will
Show the answer and explanation
Answer: decrease.
Why: A rise in outside air temperature reduces air density, so the rotor produces less thrust for a given power and the engine also delivers less power. Both effects lower the maximum altitude at which the helicopter can sustain flight, so the operating ceiling decreases.· FAA-H-8083-31 — Rotorcraft Fundamentals
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When a rotor blade moves about its flapping hinge,
Show the answer and explanation
Answer: the blade angle of attack changes and the drag forces change.
Why: Flapping alters the blade's vertical velocity, which changes the direction of the relative wind and therefore the angle of attack; the accompanying change in lift and the Coriolis effect also alter the in-plane drag. Blade pitch (feathering) angle is set by the controls and is not automatically reduced by flapping.· FAA-H-8083-31 — Rotorcraft Fundamentals
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To maintain a hover when air density decreases, the pilot must increase
Show the answer and explanation
Answer: collective pitch.
Why: Lower air density gives less thrust for a given blade pitch, so to hold position the pilot raises the collective, increasing the pitch of all blades equally to restore total rotor thrust. Rotor RPM is held constant by the governor, and cyclic only tilts the disc to change direction rather than total lift.· FAA-H-8083-31 — Rotorcraft Fundamentals
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The coning angle of a helicopter rotor is determined by the balance between
Show the answer and explanation
Answer: rotor lift and centrifugal force.
Why: The coning angle is the balance between rotor lift bending the blades upward and centrifugal force holding them out in the plane of rotation. A higher lift or lower rotor RPM increases coning; the controlling pair is lift and centrifugal force, not thrust.· FAA-H-8083-31 — Rotorcraft Fundamentals
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As a single-rotor helicopter accelerates in level forward flight past about 15 knots, the pilot will need to
Show the answer and explanation
Answer: reduce power because of the additional lift from effective translational lift.
Why: At roughly 15 knots the rotor outruns its own recirculating downwash and meets cleaner air, gaining translational lift and working more efficiently, so power can be reduced for the same lift. Rotor RPM is held constant by the governor, so the reason is the efficiency gain from translational lift, not an RPM change.· FAA-H-8083-31 — Rotorcraft Fundamentals
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A helicopter has a main rotor that turns counterclockwise as viewed from above and an anti-torque tail rotor. The helicopter will tend to drift sideways toward the
Show the answer and explanation
Answer: right, regardless of how the tail rotor is mounted.
Why: The tail rotor produces sideways thrust to counter main-rotor torque, and that thrust pushes the whole helicopter sideways (translating tendency, or tail-rotor drift). For a counterclockwise main rotor this drift is toward the right, and it occurs regardless of which side the tail rotor is mounted on.· FAA-H-8083-31 — Rotorcraft Fundamentals
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The tail rotor of a single-main-rotor helicopter
Show the answer and explanation
Answer: produces a force that opposes the main-rotor torque reaction.
Why: Driving the main rotor produces a torque reaction on the fuselage that would spin it opposite to the rotor; the tail rotor produces a sideways thrust whose moment opposes this torque reaction and holds heading. A force in the same direction would aggravate the yaw, and the tail rotor, being a rotor in forward flow, does experience dissymmetry of lift.· FAA-H-8083-31 — Rotorcraft Fundamentals
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With the anti-torque (tail rotor) pedals in the neutral position, the tail rotor blade pitch is normally
Show the answer and explanation
Answer: positive.
Why: With the pedals at neutral the tail rotor is rigged with positive pitch so it still produces thrust to counter the main-rotor torque present in normal powered flight. A neutral or negative setting would leave the torque reaction uncountered and the helicopter would yaw.· FAA-H-8083-31 — Rotorcraft Fundamentals
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On some helicopters, the main rotor mast is tilted laterally to correct for tail rotor
Show the answer and explanation
Answer: drift.
Why: Translating tendency (tail rotor drift) pushes the helicopter sideways during a hover because the tail rotor produces a side thrust. Tilting the main rotor mast laterally a few degrees inclines the rotor thrust to oppose that sideways force, so the helicopter can hover level. It addresses drift, not torque (which the tail rotor counters) or roll.· FAA-H-8083-31 — Rotorcraft Fundamentals
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Certain helicopters tend to tilt laterally during landing. This tendency can be overcome by locating the tail rotor thrust line
Show the answer and explanation
Answer: in line with the main rotor hub.
Why: If the tail rotor thrust acts at a different height from the main rotor hub, the two opposing side forces form a couple that rolls the aircraft, felt as a lateral tilt at touchdown. Locating the tail rotor thrust line in line with the main rotor hub removes the rolling couple.· FAA-H-8083-31 — Rotorcraft Fundamentals
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Ground effect for a helicopter in a hover is produced by
Show the answer and explanation
Answer: increased pressure under the main rotor disc.
Why: Close to the ground the rotor downwash cannot escape freely, so a region of increased pressure builds up beneath the rotor disc that helps support the helicopter. This increased pressure under the disc, not recirculation or a density rise above the fuselage, provides the extra support known as ground effect.· FAA-H-8083-31 — Rotorcraft Fundamentals
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A helicopter hovering close to a tall building will tend to
Show the answer and explanation
Answer: drift toward it.
Why: The rotor downwash striking the building is deflected, lowering the pressure in the gap between the helicopter and the structure, so the machine is drawn toward the building. The pilot must apply cyclic away from the wall to hold position, confirming the natural tendency is to drift toward it.· FAA-H-8083-31 — Rotorcraft Fundamentals
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The drooping of helicopter rotor blades at rest is overcome in flight by
Show the answer and explanation
Answer: centrifugal force.
Why: On the ground or at low rotor speed the blades droop under their own weight, but once the rotor turns the centrifugal force acting outward along each blade greatly exceeds the weight and pulls the blades up toward the horizontal. This centrifugal effect counters static droop and sets the coning angle in flight.· FAA-H-8083-31 — Rotorcraft Fundamentals
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During a power-on descent of a helicopter, which forces are acting on the aircraft?
Show the answer and explanation
Answer: Lift, drag, thrust, and weight.
Why: In a powered (power-on) descent the engine still drives the rotor, so thrust is present alongside the ever-present weight, the rotor lift, and the drag opposing motion. All four forces therefore act, unlike an autorotative descent where engine thrust would be absent.· FAA-H-8083-31 — Rotorcraft Fundamentals
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Main rotor blades commonly use a symmetrical airfoil section because it
Show the answer and explanation
Answer: keeps the center of pressure from shifting.
Why: A symmetrical airfoil keeps the center of pressure essentially fixed as angle of attack changes, avoiding large pitching (feathering) moments and twisting loads as each blade cycles. A highly cambered or reverse-cambered section would move the center of pressure and impose unwanted torsional loads on the blade.· FAA-H-8083-31 — Rotorcraft Fundamentals
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Autorotative force is the
Show the answer and explanation
Answer: component of the total reaction acting forward in the plane of rotation, opposing drag.
Why: In autorotation the upflow tilts the total reaction of part of the blade ahead of the rotor axis; the in-plane component of that reaction acts forward, opposing profile drag and keeping the rotor turning. It is an aerodynamic driving force, not a control input the pilot applies.· FAA-H-8083-31 — Rotorcraft Fundamentals
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Autorotation in a helicopter is
Show the answer and explanation
Answer: the production of lift by freely rotating rotor blades without engine power.
Why: Autorotation is the condition in which airflow up through a descending rotor keeps the blades turning and still generating lift without engine power, allowing a controlled power-off descent. Directional control is retained, and it is the normal response to a power loss rather than a cause of one.· FAA-H-8083-31 — Rotorcraft Fundamentals
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A helicopter rotor blade derives its lift from the fact that
Show the answer and explanation
Answer: the blade creates a region of low pressure above it.
Why: Like any airfoil, the rotor blade accelerates air over its upper surface and creates a region of low pressure there; the pressure difference across the blade is what produces lift. Treating the rotor as a simple airscrew or as merely pushing air downward misstates the actual lift mechanism.· FAA-H-8083-31 — Rotorcraft Fundamentals
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A two-bladed helicopter rotor head mounted on a central gimbal that allows the blades to flap as a unit is called a
Show the answer and explanation
Answer: semirigid rotor system.
Why: A two-bladed head mounted on a central gimbal (teetering or see-saw) lets the two blades flap as one unit without individual flapping or drag hinges; this is the semirigid rotor system. A fully articulated head has separate flap, drag, and feather hinges, while a rigid head allows no flapping at all.· FAA-H-8083-31 — Rotorcraft Fundamentals
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Because of phase lag (gyroscopic precession), the maximum displacement of a rotor blade occurs
Show the answer and explanation
Answer: approximately 90 degrees of rotation after the pitch input is applied.
Why: A spinning rotor behaves like a gyroscope, so the maximum blade displacement occurs approximately 90 degrees of rotation after the point at which the pitch input is applied. This phase lag is why cyclic pitch changes are mechanically fed into the disc ahead of the direction in which the disc is intended to tilt.· FAA-H-8083-31 — Rotorcraft Fundamentals
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Vortex ring state (settling with power) in a helicopter occurs when
Show the answer and explanation
Answer: the rotor settles into its own recirculating tip-vortex wake at low forward speed.
Why: Vortex ring state arises when the rotor settles into its own recirculating tip-vortex wake at low or zero forward speed, so the blades meet their own downwash and lift collapses. It is a low-speed recirculation phenomenon, not something that occurs at high forward speed or simply from proximity to the ground.· FAA-H-8083-31 — Rotorcraft Fundamentals
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A helicopter climb with forward airspeed requires less power than a vertical climb because of
Show the answer and explanation
Answer: translational lift.
Why: As a helicopter gains forward speed it leaves its own downwash and the rotor meets cleaner, less disturbed air, providing extra lift for the same power. This efficiency gain, known as translational lift, is why a climb with forward airspeed needs less power than a pure vertical climb.· FAA-H-8083-31 — Rotorcraft Fundamentals
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Horizontal (translational) flight in a helicopter is achieved by
Show the answer and explanation
Answer: tilting the rotor disc in the direction of flight with cyclic.
Why: Translational, or horizontal, flight is produced by tilting the rotor disc with cyclic so a component of rotor thrust acts in the direction of travel. Raising the collective changes total lift, not direction, so the disc tilt is what produces horizontal movement.· FAA-H-8083-31 — Rotorcraft Fundamentals
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The most desirable rotor blade design is one in which the center of pressure
Show the answer and explanation
Answer: does not move along the chord of the blade.
Why: The best rotor blade design keeps the center of pressure essentially fixed (as with a symmetrical section), so changing angle of attack does not generate a varying pitching moment that would twist the blade. A wandering center of pressure imposes cyclic torsional loads and control difficulties.· FAA-H-8083-31 — Rotorcraft Fundamentals
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When the cyclic stick is eased forward from a hover, what happens to the rotor's vertical lift?
Show the answer and explanation
Answer: Vertical lift is reduced.
Why: Easing the cyclic forward tilts the rotor disc forward so that total rotor thrust gains a forward (propulsive) component and a smaller vertical component. With the vertical lift reduced, the helicopter begins to descend and accelerate forward unless collective is increased.· FAA-H-8083-31 — Rotorcraft Fundamentals
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The coning angle of a spinning main rotor is established by the balance between which two forces?
Show the answer and explanation
Answer: Centrifugal force and lift.
Why: Rotor coning results from the balance between lift, which bends the blades upward, and centrifugal force, which holds them outward in the plane of rotation. Centrifugal force alone would keep the blades flat, so both forces are required to form the cone.· FAA-H-8083-31 — Rotorcraft Fundamentals
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The purpose of main rotor blade tracking is to bring the blade tips into a common plane of rotation, which is described as bringing them into what condition?
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Answer: Aligned to a common tip path.
Why: Tracking adjusts the rotor so that every blade follows the same tip path, aligning all tips into one common plane of rotation. Proper alignment eliminates the once-per-revolution vibration caused by a blade flying high or low relative to the others.· FAA-H-8083-31 — Rotorcraft Fundamentals
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Most of the lift produced by a rotor blade is the result of which pressure condition?
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Answer: Low pressure above the blade.
Why: Lift comes mainly from the reduced (low) pressure created over the cambered upper surface of the blade as airflow accelerates there. The underside carries higher pressure, and downwash is a result of lift rather than its cause, so the low pressure above the blade is the key factor.· FAA-H-8083-31 — Rotorcraft Fundamentals
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Static stability of a helicopter is best defined as which of the following?
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Answer: The initial tendency to move back toward neutral after a disturbance.
Why: Static stability is the initial tendency of a disturbed helicopter to return toward its original (neutral) condition. A tendency to oscillate about neutral describes dynamic behavior, and stability while hovering is only one specific flight case rather than the general definition.· FAA-H-8083-31 — Rotorcraft Fundamentals
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In forward flight, the increased relative airflow over the advancing blade causes it to do what?
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Answer: Flap up, which reduces its angle of attack and lift.
Why: In forward flight the advancing blade meets a higher relative velocity and tends to generate more lift, so it flaps upward. Flapping up reduces its angle of attack and therefore its lift, which helps equalize lift across the rotor disc.· FAA-H-8083-31 — Rotorcraft Fundamentals
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When transitioning from a hover to forward flight, what change in engine power is generally required?
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Answer: Increase the engine power.
Why: Leaving the hover for forward flight requires tilting the disc with cyclic, which diverts some rotor thrust into propulsion. To keep vertical lift supporting the weight, collective and therefore engine power must be increased; holding or reducing power would let the helicopter sink as it accelerates.· FAA-H-8083-31 — Rotorcraft Fundamentals
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The momentary rise and fall of rotor RPM that occurs immediately after a change in collective pitch is called what?
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Answer: Transient droop.
Why: Immediately after a collective change the governor lags slightly, so rotor RPM momentarily overshoots or dips before settling; this temporary excursion is transient droop. Static droop is the small steady RPM difference that remains, which is a different effect.· FAA-H-8083-31 — Rotorcraft Fundamentals
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Because a rotor system behaves gyroscopically, the maximum flapping response to a blade pitch change occurs approximately how far around the disc?
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Answer: 90 degrees later in the direction of rotation.
Why: Owing to gyroscopic precession, the maximum response to a force applied to a rotor appears about 90 degrees of rotation later (phase lag). A blade given a pitch and lift change therefore reaches its maximum flap displacement roughly 90 degrees further around the disc.· FAA-H-8083-31 — Rotorcraft Fundamentals
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The rotor disc of a helicopter is best described as which of the following?
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Answer: The circular area swept by the rotating blade tips.
Why: The rotor disc is the circular area swept by the turning blades, whose diameter equals the blade tip-to-tip distance. The rotor head hub is the central mounting and ground cushion is a near-surface effect, so neither describes the disc.· FAA-H-8083-31 — Rotorcraft Fundamentals
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A delta-three hinge in a rotor head is designed to achieve which result?
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Answer: Pitch-flap coupling through an offset hinge axis.
Why: The delta-three hinge skews or offsets the flapping hinge axis so that blade flapping is mechanically coupled to a change in blade pitch. This pitch-flap coupling, produced by the offset hinge geometry, reduces flapping and helps stabilize the rotor.· FAA-H-8083-31 — Rotorcraft Fundamentals

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Frequently asked questions

Is helicopter material really on the FAA Airframe written test?: Yes. Rotorcraft is one of the airframe subject areas, so helicopter questions can appear on your Airframe written test even if you never plan to work on helicopters. How many show up varies by test form. Treat it as required vocabulary: rotor system types, control functions, hinge names, and a handful of aerodynamic terms cover most of what is asked.
What is the difference between the collective and the cyclic?: The collective raises or lowers the pitch of all main rotor blades at once and by an equal amount, which changes total rotor thrust. The cyclic varies each blade's pitch as it travels around the disc, so lift is greater on one side than the other and the tip-path plane tilts. One control changes how much lift; the other changes where it acts.
What is the difference between fully articulated, semirigid, and rigid rotor systems?: A fully articulated system gives each blade its own flapping hinge, lead-lag hinge, and feathering bearing, and normally carries three or more blades. A semirigid or teetering system has two blades that flap as a single unit about one central hinge and has no lead-lag hinges. A rigid system has neither flapping nor lead-lag hinges, so the blades flex to absorb that motion.
What causes dissymmetry of lift on a helicopter rotor?: In forward flight the advancing blade adds the helicopter's airspeed to its own rotational speed while the retreating blade subtracts it, so the advancing side would generate more lift if nothing corrected it. Blade flapping, along with the cyclic feathering built into the control system, equalizes lift across the disc so the aircraft does not roll toward the retreating side.
What do the anti-torque pedals actually do?: On a single main rotor helicopter the pedals change the pitch of the tail rotor blades, which changes tail rotor thrust. That controls yaw, or movement about the vertical axis, and it also balances the torque reaction the main rotor transmits to the fuselage. The pedals do not change main rotor pitch and they do not tilt the rotor disc.

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