Wing and Control Theory Flashcards
What is the state of equilibrium?
All four forces (lift, thrust, drag, weight) are balanced
What 3 ways an aircraft can travel in equilibrium?
Straight and level flight, constant climb, or constant descend
When does acceleration occur?
All four forces (lift, thrust, drag, weight) are not completely balanced
What happens when thrust is greater than drag?
Aircraft accelerates
What happens when drag is greater than thrust?
Aircraft decelerates
What happens when lift is greater than weight?
Aircraft climbs
What happens when weight is greater than lift?
Aircraft descends
What is the purpose of elevators?
To divide the power of the engine into lift and thrust
Where does the power that produces lift and thrust originate from? How does the pilot control it?
The power originates from the engine, which the pilot controls with the throttle
Describe the two types of boundary layers
The laminar layer occurs when the boundary layer is smooth. When the boundary layer is turbulent, it is called the turbulent layer
Describe what happens when the critical angle of attack is reached
The boundary layer can no longer flow smoothly over the wing and the centre of pressure rapidly moves backward. This causes the wing to stall
What happens to the centre of pressure of the airfoil when the angle of attack is increased?
The centre of pressure moves forward as the stall is approached, and then at the point of stall it rapidly moves backward
What is the relationship between the angle of attack and the turbulent layer?
Increasing the angle of attack increases turbulent airflow over the airfoil
At what point does every aircraft stall regardless of airspeed?
At the critical angle of attack
What happens to the boundary layer in a stall?
Air can no longer flow smoothly over the wing resulting in a turbulent layer
Can you stall at a high speed?
Yes, speed does not matter
Define the following: wing platform, span, area, and chord?
Wing platform - the shape of the wing as seen from above Span - the distance from one wing tip to another Chord - the distance between the leading edge and trailing edge of a wing
Define aspect ratio. What is the benefit of a high aspect ratio?
The relationship between the span and the chord of the wing. Higher aspect ratios have lower induced drag
What is the angle of incidence?
The angle of the chord line relative to the longitudinal axis of the aircraft
Define stability
The ability of an aircraft to correct for conditions that act on it, such as turbulence and flight control inputs
What type of stability is this?
Negative dynamic stability
What type of stability is this?
Neutral dynamic stability
What type of stability is this?
Positive dynamic stability
What type of stability is this?
Negative static stability
What type of stability is this?
Neutral static stability
What type of stability is this?
Positive static stability
Describe the different stabilities along the axes
Longitudinal stability (pitch) works about the lateral axis
Lateral stability (roll) works about the longitudinal axis
Directional stability (yaw) works about the vertical axis
What is inherent stability?
The tendency of an aircraft to return to straight and level flight due to its design
What kind of stability are most wings designed for?
Positive static and dynamic stability
Define dihedral
The upward angle of an aircraft’s wings
Define sweepback
The angle at which wings are slanted from root to rip
Describe the pendulum effect
A rolling effect resulting from sideforce-generating surfaces being above or below the centre of mass in an aircraft
How does an aircraft move during a slip?
The aircraft is moving somewhat sideways as well as forward relative to the oncoming airflow
How can the four forces be manipulated to maximize performance?
Increase lift, increase thrust, reduce weight, reduce drag
Describe streamlining
Contouring an airfoil to reduce it’s drag (increasing laminar flow and decreasing turbulent flow)
Describe what happens to the four forces when frost, snow, or ice is present on an aircraft. What is the related concept called?
Clean wing concept
Describe how drag affects performance
What is fairing?
A structure that produces a smooth outline along the surface of an aircraft to reduce drag
What are three ways of maximizing performance by reducing parasitic drag?
Streamlining, fairing, and the clean wing concept
When would you expect the most induced drag?
When lots of lift is being created at low speeds (heavy aircraft, high angle of attack, clean configuration)
Describe the ground effect
Reduction in induced drag occurs at the wing tips when an aircraft is in close promiximity to the ground. This increases lift
Describe the range and endurance curves
What increases every time you increase lift?
Induced drag
What is the relationship between the speed of the root and tip of a propeller?
The tip travels faster than the root
Why are propellers twisted?
The root has a greater angle of attack than the tip to balance the difference in speed, so propellers are twisted to maintain the same angle of attack at each radius location
Define pitch and describe the two different types
Pitch - angle of the propeller blade
Coarse pitch - high angle of attack, good for fast cruise yet sluggish in climb
Fine pitch - low angle of attack, great for climbing yet has slow cruising speed
Define fixed pitch
Angle of attack is set at installation and cannot be changed during aircraft operation
Define adjustable pitch
Pitch can be changed on the ground
Define variable pitch
Pitch can be changed from the cockpit in flight
Define constant speed pitch
Propeller rpm is selected and pitch is automatically adjusted by various mechanisms in order to maintain it
Compare what happens when oil pressure is lost in hydromatic and counterweighted constant speed propellers
Hydromatic: blades fail to the maximum rpm (fine) pitch position
Counterweighted: blades fail to the coarse pitch or feathered position
Define adverse yaw. What causes it?
The natural tendency for an aircraft to yaw in the opposite direction of a roll. It is caused by the difference in the lift and drag of each wing
Name the four causes of adverse yaw
Slipstream, asymmetric thrust, torque, gyroscopic effect
Name 3 design solutions to counter adverse yaw
Rudder offset, different washout, engine offset
When should you expect to use more right rudder?
At a high RPM and low speeds (accelerating or takeoff, in a climb, or in slow flight)
What wing properties do ailerons manipulate?
The effective camber, the effective chord, and the angle of attack
How do ailerons affect lift?
Raised aileron reduces lift, lowered aileron increases lift
What happens to the motion of an aircraft when the left aileron drops and the right aileron rises?
The left wing rises, the right wing lowers, and the aircraft rolls right
What happens when elevators produce lift on top?
The tail rises and the aircraft pitches nose down
What happens if the rudder produces lift the the right?
The tail is drawn to the right and the aircraft yaws left
How are flaps different than ailerons?
Both flaps are extended or retracted at the same time
How do fowler flaps affect the surface area, camber, and angle of attack?
Fowler flaps increase surface area, camber, and angle of attack
What are the advantages of flaps?
- Increase lift
- Lower stall speed
- Lower takeoff and landing speed
- Shorter landing and takeoff distance
- Easier on landing gear
- Better visibility
- Permits approach with power (less cooling)
What are the disadvantages of flaps?
- Increase induced drag
- Reduce climb performance
- Create momentary sink when retracted
Describe aileron drag
Yawing effect caused by asymmetric drag of aileron drag, causing yaw in direction of the rising wing
Describe the two solutions to aileron drag
Differential aileron: downgoing aileron moves through small angle, reducing drag. Upgoing aileron moves through large angle, increasing drag
Frise aileron: downgoing aileron streamlined into wing, reducing drag. Upgoing aileron nose projects into airflow, increasing drag
What is a trim tab?
Secondary flight control surfaces that are on the edge of larger, primary control surfaces
Describe the two different types of trim tabs
Anti-servo tabs: trim tab for stabilators
Servo tabs: device for moving flight controls on large airplanes
What factors should be considered when climbing?
Visibility, engine temperature, terrain
How should an aircraft be flow to obtain the greatest glide distance?
Aircraft should be flown at maximum load/drag ratio
What factors should be considered when gliding?
Windmilling propeller, effect of wind
Describe the forces acting when an aircraft climbs
Describe the forces acting when an aircraft glides
What is the load factor?
Ratio of load supported to weight of aircraft
What is the load factor in straight and level flight?
1G
What is the load factor when turning?
What is maneuvering speed and how is it relevant to gust loads?
Maneuvering speed is the airspeed limit for an aircraft chosen by the designer. At speeds greater than the maneuvering speed, vertical gusts can cause a sudden increase in the angle of attack which may cause failure of the aircraft
What is a stall?
Decrease in lift caused by angle of attack exceeding the critical angle
Describe washout and how it affects stalling
The wing is designed so that the angle of incidence is greater at the wing roots than the wing tips. This ensures that the root stalls before the tip, providing the aircraft with continued aileron control and resistance to spinning
What are stall strips used for?
Used to improve controllability of an aircraft when it enters stall at a high angle of attack
Describe the relationship between the boundary layer, lift, and drag
The longer the boundary layer adheres to the wing, the greater the lift and the less drag produced
Name ways to increase efficiency by decreasing the interference between the airflow on the underside of the wing and the the airflow on top of the wing
Slots/slats, vortex generators, winglets, drooped wings, wing tip tanks, wing fences
Desribe how vortex generators work
Name a design feature that prevents spanwise flow
Wing fences
How do winglets and drooped wings work?
Winglets reduce drag associated with vortices that develop at wingtips
Drooped wing tips minimize loss of lift from wing tip vortices
How do spoilers affect drag?
Increase drag, slowing an aircraft or making it descend
What flight regime lies between maximum endurance and the stall?
Slow flight
