Theory of flight Flashcards
Bernoulli’s Principle
“The total energy in any system remains constant.”
Newton’s 1st Law:
A body (or gas) in motion, tends to stay in motion
Newton’s 2nd Law:
A force must be applied to alter the state of uniform motion of a body
Newton’s 3rd Law:
For every action there is an equal and opposite reaction.
Newton’s Laws in Action (example of each)
- -1st Law – Air flows over an airfoil (wing) and inertia causes it to remain in motion.
- -2nd Law – Introducing the airfoil into the airflow alters the flow of air.
- -3rd Law – The pressure exerted on the airflow creates an equal and opposite reaction. This reaction is Lift.
Camber
The camber of the above airfoil can be seen in its profile or thickness. The average thickness of the wing is known as the Mean Camber.
Chord
The line connecting the leading and trailing edge of the airfoil is known as the Chord Line.
Angle of Incidence
The wing of an airplane is permanently affixed to the fuselage at a slight positive angle. This angle between the chord line and the longitudinal axis of the airplane is called the Angle of Incidence.
Angle of Attack
The angle between the chord line and the relative airflow is the Angle of Attack.
Center of Pressure
The sum of all lift generated by the airfoil is said to act through a theoretical point called the Center of Pressure.
As the angle of attack increases what happens to the center of pressure?
moves forward.
& as the angle of attack decreases the center of pressure moves back (aka: aft)
2 types of drag:
- Parasite Drag
* Induced Drag
Parasitic Drag includes:
- Form Drag – the resistance of the shape of the aircraft colliding head on with the relative airflow.
- Skin Friction – the tendency of air to cling to the surface of the aircraft.
- Interference Drag – caused by the collision of differing streams of airflow as it flows over the structure of the airplane, (for example, airflow over the wings mixing with airflow around the fuselage.
Induced Drag includes:
created by the wing as a byproduct of lift
–can not be eliminated
Ex: Wing-Tip Vortices
• Drag Relationship
As airspeed is increased, more and more air molecules collide with the aircraft. = increase in parasite drag.
As airspeed is decreased, the wing is flown at an increasingly higher angle of attack. This displaces more air = increase in induced drag
Lift/Drag Max
the angle of attack that creates the most lift for the minimum amount of total drag.
Maximum Endurance
minimum amount of power is required to maintain altitude. From this point, an increase OR decrease in airspeed requires an increase in power. This is simply because an airplane needs to be moving to fly.
Weight
the force acting downward towards the centre of the earth as a result of gravity.
–act through the Center of Gravity
Equilibrium
LIFT = WEIGHT and THRUST = DRAG
An airplane in in Equilibrium will
maintain a constant, un-accelerated movement, (such as straight and level, constant speed climb or descent).
Lift always acts at a 90 degree angle to the ______
chord of the wing. In a turn, lift is inclined away from the vertical.
Consequently, in a turn, lift is divided into
vertical and horizontal components
- -vertical component will decrease with an increase in angle of attack.
- -Therefore, more lift is required in a turn to maintain speed and altitude.
- -Without corrective action to increase lift (increasing the angle of attack and power), an aircraft in a turn will lose altitude, airspeed, or usually both.
Forces in a Turn
horizontal component = Centripetal Force.
–Lift must be great enough to counter both weight and Centrifugal Force
Load Factor
- -the effective (or perceived) weight of the aircraft.
- -measured in “G’s” - One “G” equals 1 gravity
- -Negative “G’s” = floating & + = pushing into seat.
How many G’s on a 20 degree turn?
1.06g
How many G’s on a 40 degree turn?
1.31g
How many G’s on a 60 degree turn
2g
How many G’s on a 80 degree turn?
5.76g
Boundary Layer
thin layer of air lying over the wing surface.
- -flows smoothly = Laminar Flow.
- -point at which the laminar layer begins to break away = Transition Point
- -transition point moves forward with increasing speed or angle of attack.
- -rough flow = turbulent layer
Stalls
angle of attack increases, the transition point (where turbulent airflow breaks away from the wing) and the centre of pressure move forward.
Due to the lack of laminar flow, the wing loses its capability to produce lift. This condition is called a stall.
A wing will stall when the critical angle of attack is exceeded. This can happen:
At any Airspeed
At any Power Setting
At any Attitude
At any Weight
Factors Affecting a Stall
- -weight
- -centre of gravity
- -turbulance
- -flaps
- -contamination
- -turns
How does weight affect stalls?
- -heavier the plane = more lift is required
- -must be flown at a higher angle of attack = closer to the critical angle of attack
- -airplane will stall at a higher airspeed.
How does Center of Gravity affect stalls?
- -forward center of gravity = higher stall speed.
- -aft center of gravity = lower stall speed.
How does Turbulence affect stalls?
Gusts of wind can abruptly change the angle of attack, potentially exceeding the critical angle and inducing a stall at higher airspeeds.
How does Flaps affect stalls?
Flaps increase the lift potential of a wing resulting in a lower stall speed
How does Wing Contamination affect stalls?
Frost or ice alter the smooth air flow over the wing, causing the separation point to move much further forward than normal.
–stall at much higher airspeeds.
How does Turns affect stalls?
- -angle of bank increases = more lift is required to maintain level flight.
- -Angle of attack must be increased to bring the wing closer to the critical angle.
Laminar Flow Airfoil
•Laminar flow profiles were developed for higher speeds and better boundary layer control (less drag)
- transition point to turbulent flow is further back
- con = stall more abruptly
Planform
Planform is the shape of the wing as seen from above.
Aspect Ratio
relationship between a wings length and its width
aka: wing span and Mean Aerodynamic Chord
A wing with high aspect ratio =
generates more lift with less induced drag
Ex: glider/low power
wing with low aspect ratio =
greater maneuverability.
Ex: fighter aircraft that produce a large amount of thrust.
Dihedral
- -upward angle of the wing from the horizontal ~5degree
- -helps achieve greater roll stability.
Anhedral.
opposite of dihedral - downward angle
greater maneuverability
Wash-Out
twist in the wing, giving less incidence at the wing than at the root.
= better stall characteristics
Slats
Slats are moveable auxiliary airfoils that extend out ahead of the leading edge
–high angles of attack, slats are automatically pulled out by the low air pressure above the leading edge
Slots
Slots are fixed passageways allowing air to flow through them at low speeds and improving the laminar
flow over the wing.
What is the difference between Slats and Slots
Slats are moveable & Slots are fixed
Wing Fences
Wing fences are fin like vertical surfaces attached to the wing. They help control
airflow over specific areas of the wing.
Stall Strips
Are installed on the wing root of some airplanes to cause an earlier stall at the wing root, (similar to wash-out) while other areas of the wing remain effective.
Vortex Generators
are designed to re-energize the boundary layer and delay a stall in slow flight.
