PHAK 6: Flight Controls Flashcards
Introduction
What are the basic components of mechanical flight control systems?
Rods, cables, pulleys, and sometimes chains transmit the forces from the flight deck controls to the control surfaces.
Introduction
Why were hydromechanical systems introduced in aircraft?
To manage the increasing aerodynamic forces acting on control surfaces in larger and faster aircraft, reducing complexity, weight, and limitations of mechanical systems.
Introduction
What is “fly-by-wire”?
A system that replaces physical connections between pilot controls and flight control surfaces with an electrical interface, often boosted by hydraulics or electricity.
Introduction
What is the purpose of NASA’s Intelligent Flight Control Systems (IFCS)?
To adaptively improve aircraft performance, enhance safety, manage system failures, and ease pilot workload using neural network-based control adjustments.
Introduction
How do flight controls differ across aircraft types?
- Sport pilot aircraft: Use weight-shift control.
- Balloons: Use standard burn techniques.
- Helicopters: Use cyclic for direction, collective for rotor pitch, and anti-torque pedals for yaw.
Flight Control Systems
What are the primary flight control systems?
The ailerons, elevator (or stabilator), and rudder.
Flight Control Systems
What are the secondary flight control systems?
Wing flaps, leading-edge devices, spoilers, and trim systems.
Flight Control Systems
What is the purpose of the primary flight control system?
To control an aircraft safely during flight.
Flight Control Systems
What is the purpose of the secondary flight control system?
To improve performance characteristics and relieve the pilot of excessive control forces.
Flight Control Systems: Primary Flight Controls
How do primary flight controls affect an aircraft?
Movement changes the airflow and pressure distribution over and around the airfoil, affecting lift and drag to control the aircraft’s motion.
Flight Control Systems: Primary Flight Controls
How does airspeed affect the feel of flight controls?
At low airspeeds, controls feel soft and sluggish, while at higher airspeeds, they become firm and responsive.
Flight Control Systems: Primary Flight Controls
What design feature limits the deflection of flight control surfaces?
Control-stop mechanisms or limitations in the movement of control columns and rudder pedals prevent overstressing the aircraft.
Flight Control Systems: Primary Flight Controls
Why are limits on control surface deflection important?
To prevent the pilot from overcontrolling and overstressing the aircraft during normal maneuvers.
Flight Control Systems: Primary Flight Controls: Ailerons
What axis do ailerons control?
The longitudinal axis, controlling roll.
Flight Control Systems: Primary Flight Controls: Ailerons
Where are ailerons located?
On the outboard trailing edge of each wing.
Flight Control Systems: Primary Flight Controls: Ailerons
How do ailerons move in relation to each other?
Ailerons move in opposite directions—one deflects upward while the other deflects downward.
Flight Control Systems: Primary Flight Controls: Ailerons
What happens when the control wheel or stick is moved to the right?
The right aileron deflects upward, decreasing lift on the right wing, and the left aileron deflects downward, increasing lift on the left wing, causing the aircraft to roll right.
Flight Control Systems: Primary Flight Controls: Ailerons
How are ailerons connected to the control wheel or stick?
By cables, bellcranks, pulleys, and/or push-pull tubes.
Flight Control Systems: Primary Flight Controls: Adverse Yaw
What causes adverse yaw?
Differential drag from the downward-deflected aileron, causing the aircraft to yaw opposite the direction of the turn.
Flight Control Systems: Primary Flight Controls: Adverse Yaw
When is adverse yaw most pronounced?
At low airspeeds, high angles of attack, and with large aileron deflections.
Flight Control Systems: Primary Flight Controls: Adverse Yaw
How is adverse yaw counteracted?
By applying rudder pressure in the direction of the turn.
Flight Control Systems: Primary Flight Controls: Adverse Yaw
Why is rudder use critical at lower airspeeds?
The vertical stabilizer and rudder are less effective, requiring more rudder input to counteract adverse yaw.
Flight Control Systems: Primary Flight Controls: Adverse Yaw
What controls are used to coordinate a turn?
Ailerons for bank, rudder to counter adverse yaw, and elevator to maintain altitude by increasing the angle of attack.
Flight Control Systems: Primary Flight Controls: Adverse Yaw
What is the roll-out procedure from a turn?
Apply aileron and rudder toward the high wing and reduce elevator back pressure to maintain altitude.
Flight Control Systems: Primary Flight Controls: Adverse Yaw
What systems reduce adverse yaw?
Differential ailerons, frise-type ailerons, coupled ailerons and rudder, and flaperons.
Flight Control Systems: Primary Flight Controls: Differential Ailerons
What are differential ailerons?
Ailerons where the upward deflection is greater than the downward deflection for a given control input.
Flight Control Systems: Primary Flight Controls: Differential Ailerons
What effect do differential ailerons have?
They increase drag on the descending wing to help reduce adverse yaw.
Flight Control Systems: Primary Flight Controls: Differential Ailerons
Do differential ailerons eliminate adverse yaw?
No, they reduce but do not completely eliminate adverse yaw.
Flight Control Systems: Primary Flight Controls: Differential Ailerons
How do differential ailerons affect drag?
The up aileron on the descending wing creates more drag than the down aileron on the rising wing.
Flight Control Systems: Primary Flight Controls: Frise-Type Ailerons
What is a frise-type aileron?
An aileron with an offset hinge that projects the leading edge into the airflow when raised.
Flight Control Systems: Primary Flight Controls: Frise-Type Ailerons
How do frise-type ailerons reduce adverse yaw?
The raised aileron creates drag by projecting its leading edge into the airflow, balancing the drag of the lowered aileron.
Flight Control Systems: Primary Flight Controls: Frise-Type Ailerons
What additional feature does a frise-type aileron provide?
It forms a slot, allowing smooth airflow over the lowered aileron, improving its effectiveness at high angles of attack.
Flight Control Systems: Primary Flight Controls: Frise-Type Ailerons
Can frise-type ailerons eliminate adverse yaw completely?
No, they reduce adverse yaw but do not eliminate it entirely. Coordinated rudder use is still necessary.
Flight Control Systems: Primary Flight Controls: Frise-Type Ailerons
What are coupled ailerons and rudder?
Controls linked by interconnect springs to coordinate rudder and aileron deflections.
Flight Control Systems: Primary Flight Controls: Frise-Type Ailerons
Can frise-type ailerons be designed to function differentially?
Yes, they can be combined with differential movement for additional control.
Flight Control Sys.: Primary Flight Controls: Coupled Ailerons & Rudder
What are coupled ailerons and rudder?
Controls linked by interconnect springs to coordinate rudder and aileron deflections.
Flight Control Sys.: Primary Flight Controls: Coupled Ailerons & Rudder
How do coupled ailerons and rudder reduce adverse yaw?
The rudder automatically deflects slightly when ailerons are moved, counteracting yaw caused by aileron drag.
Flight Control Sys.: Primary Flight Controls: Coupled Ailerons & Rudder
What happens when rolling left with coupled controls?
The interconnect system pulls the left rudder pedal forward, preventing right yaw.
Flight Control Sys.: Primary Flight Controls: Coupled Ailerons & Rudder
Can the rudder be used independently with coupled controls?
Yes, the spring force can be overridden to intentionally slip the aircraft.
Flight Control Sys.: Primary Flight Controls: Coupled Ailerons & Rudder
What is the primary benefit of coupled ailerons and rudder?
They simplify coordinated flight by reducing the need for manual rudder input.
Flight Control Systems: Primary Flight Controls: Flaperons
What are flaperons?
A control surface combining the functions of both ailerons (bank control) and flaps (lift enhancement).
Flight Control Systems: Primary Flight Controls: Flaperons
How do flaperons work?
They can move differentially to control roll or lower together to act like flaps
Flight Control Systems: Primary Flight Controls: Flaperons
What device integrates the controls for flaperons?
A mixer combines the pilot’s separate aileron and flap inputs.
Flight Control Systems: Primary Flight Controls: Flaperons
Why are flaperons often mounted away from the wing?
To ensure undisturbed airflow at high angles of attack or low airspeeds.
Flight Control Systems: Primary Flight Controls: Flaperons
What is the primary advantage of flaperons?
They simplify design by combining roll control and lift augmentation in a single control surface.
Flight Control Systems: Primary Flight Controls: Elevator
What does the elevator control?
Pitch about the lateral axis.
Flight Control Systems: Primary Flight Controls: Elevator
How is the elevator connected to the flight deck?
By a series of mechanical linkages connected to the control column.
Flight Control Systems: Primary Flight Controls: Elevator
What happens when the control column is pulled aft?
The elevator deflects up (up-elevator position), decreasing camber and creating a downward aerodynamic force, pitching the nose up.
Flight Control Systems: Primary Flight Controls: Elevator
What happens when the control column is pushed forward?
The elevator deflects down, increasing camber and reducing tail-down force, pitching the nose down.
Flight Control Systems: Primary Flight Controls: Elevator
What factors affect elevator effectiveness?
Stability, power, thrustline, and the position of horizontal tail surfaces (e.g., conventional, mid, or T-tail designs).
Flight Control Systems: Primary Flight Controls: Elevator
Where does the pitching moment occur?
About the center of gravity (CG).
Flight Control Systems: Primary Flight Controls: T-Tail
What is a T-tail configuration?
The horizontal stabilizer is mounted on top of the vertical stabilizer, away from downwash and fuselage airflow.
Flight Control Systems: Primary Flight Controls: T-Tail
Why are T-tails common on certain aircraft?
They avoid propeller downwash, exhaust blasts, and water spray (e.g., seaplanes) while reducing cabin noise and vibration.
Flight Control Systems: Primary Flight Controls: T-Tail
What is a disadvantage of T-tail aircraft at slow speeds?
Greater control force is required to raise the nose due to the lack of propeller downwash assistance.
Flight Control Systems: Primary Flight Controls: T-Tail
How does the T-tail design affect flutter?
The high placement of horizontal surfaces requires increased stiffness in the vertical stabilizer to prevent flutter, adding weight.
Flight Control Systems: Primary Flight Controls: T-Tail
What is a deep stall?
A condition where airflow separation from the wings blankets the tail, reducing or eliminating elevator effectiveness, common in T-tails at high AOAs and low speeds.
Flight Control Systems: Primary Flight Controls: T-Tail
What factors increase the risk of a deep stall?
High AOAs, low airspeeds, aft CG, and configurations with tail-mounted engines.
Flight Control Systems: Primary Flight Controls: T-Tail
How is a deep stall mitigated?
Systems like stick pushers, elevator down springs, and proper CG management.
Flight Control Systems: Primary Flight Controls: T-Tail
What is the function of an elevator down spring?
It mechanically drives the elevator to a nose-down position to prevent a stall when trim tabs become ineffective.
Flight Control Systems: Primary Flight Controls: T-Tail
What challenge does a forward CG create during landing?
Reduced airflow over the empennage and landing speeds can make it harder for the elevator to maintain nose-up authority in the landing flare.
Flight Control Systems: Primary Flight Controls: T-Tail
Why must pilots follow proper CG loading procedures?
To ensure safe handling and prevent instability during critical phases of flight, such as stalls or landings.
Flight Control Systems: Primary Flight Controls: Stabilator
What is a stabilator?
A one-piece horizontal stabilizer that pivots around a central hinge point to control pitch.
Flight Control Systems: Primary Flight Controls: Stabilator
How does the stabilator respond to control inputs?
- Pulling the control column back raises the stabilator’s trailing edge, pitching the nose up.
- Pushing the control column forward lowers the trailing edge, pitching the nose down.
Flight Control Systems: Primary Flight Controls: Stabilator
Why is the stabilator sensitive to control inputs?
It pivots around a central hinge point, making it highly responsive to aerodynamic loads and pilot input.
Flight Control Systems: Primary Flight Controls: Stabilator
What is the purpose of antiservo tabs?
To decrease stabilator sensitivity by deflecting in the same direction as the stabilator, increasing the force required for movement.
Flight Control Systems: Primary Flight Controls: Stabilator
How does a balance weight help a stabilator?
It offsets aerodynamic loads by projecting into the empennage or being incorporated into the forward portion of the stabilator tips.
Flight Control Systems: Primary Flight Controls: Canard
What is a canard?
A horizontal stabilizer located in front of the main wings, functioning as a lifting surface.
Flight Control Systems: Primary Flight Controls: Rudder
What happens when the rudder is deflected?
A horizontal force is exerted in the opposite direction, yawing the aircraft.
Flight Control Systems: Primary Flight Controls: V-Tail
What is the V-tail design?
A tail configuration with two slanted surfaces that combine the functions of a conventional elevator and rudder.
Flight Control Systems: Primary Flight Controls: V-Tail
What do the fixed surfaces of a V-tail act as?
Both horizontal and vertical stabilizers.
Flight Control Systems: Primary Flight Controls: V-Tail
What are the movable surfaces of a V-tail called?
Ruddervators.
Flight Control Systems: Secondary Flight Controls: Flaps
What are the four common types of flaps?
- Plain Flaps
- Split Flaps
- Slotted Flaps
- Fowler Flaps
Flight Control Systems: Secondary Flight Controls: Flaps
How does a plain flap work?
Increases airfoil camber, significantly raising lift but also increasing drag and creating a nose-down pitching moment.
Flight Control Systems: Secondary Flight Controls: Flaps
What is the function of a split flap?
Deflects from the lower airfoil surface, producing more lift than a plain flap but creating higher drag due to turbulence.
Flight Control Systems: Secondary Flight Controls: Flaps
What is a slotted flap, and how does it function?
- Uses a slot to duct high-energy air to the upper surface, delaying separation and significantly increasing lift.
- Common on small and large aircraft, with variations like double- or triple-slotted designs.
Flight Control Systems: Secondary Flight Controls: Flaps
What makes Fowler flaps unique?
- Slides backward on tracks, increasing wing area and camber.
- Initial extension increases lift significantly with minimal drag; later extension increases drag.
Flight Control Systems: Secondary Flight Controls: Leading Edge Devices
What are four common types of leading edge devices?
- Fixed Slots
- Movable Slats
- Leading Edge Flaps
- Leading Edge Cuffs
Flight Control Systems: Secondary Flight Controls: Leading Edge Devices
What is the function of fixed slots?
Direct airflow to the upper wing surface, delaying airflow separation at higher angles of attack without increasing wing camber.
Flight Control Systems: Secondary Flight Controls: Leading Edge Devices
How do movable slats work?
- Move on tracks and open at higher angles of attack to delay stall by allowing airflow to pass to the wing’s upper surface.
- Can be automatic or pilot-operated.
Flight Control Systems: Secondary Flight Controls: Leading Edge Devices
What is the purpose of leading edge flaps?
- Increase maximum lift coefficient (CL-MAX) and wing camber.
- Often used with trailing edge flaps to reduce nose-down pitching moments.
Flight Control Systems: Secondary Flight Controls: Leading Edge Devices
What are leading edge cuffs?
- Fixed aerodynamic devices extending the leading edge down and forward.
- Improve airflow attachment at high angles of attack, reducing stall speed but slightly reducing maximum cruise speed.
Flight Control Systems: Secondary Flight Controls: Spoilers
What are spoilers?
High-drag devices deployed from the wings to reduce lift and increase drag.
Flight Control Systems: Secondary Flight Controls: Trim Tabs
What happens when the trim tab is set to the full nose-down position?
- Trim tab moves up.
- Airflow forces the elevator’s trailing edge down.
- Tail moves up, and nose moves down.
Flight Control Systems: Secondary Flight Controls: Trim Tabs
What happens when the trim tab is set to the full nose-up position?
- Trim tab moves down.
- Airflow forces the elevator’s trailing edge up.
- Tail moves down, and nose moves up.
Flight Control Systems: Secondary Flight Controls: Antiservo Tabs
What is the function of an antiservo tab?
It decreases the sensitivity of the stabilator and serves as a trim device to relieve control pressure.
Flight Control Sys’: Secondary Flight Controls: Ground Adjustable Tabs
What are ground adjustable tabs?
Nonmovable metal trim tabs on the rudder that are adjusted on the ground.
Flight Control Systems: Secondary Flight Controls: Adjustable Stabilizer
What is an adjustable stabilizer?
A system where the horizontal stabilizer pivots about its rear spar instead of using a trim tab.
Flight Control Systems: Secondary Flight Controls: Adjustable Stabilizer
How is an adjustable stabilizer operated?
By a jackscrew mounted on the leading edge of the stabilizer.
Flight Control Systems: Secondary Flight Controls: Adjustable Stabilizer
What controls the jackscrew on larger aircraft?
A motor-driven mechanism.
