Aerodynamic Terms Flashcards
Chord line
An imaginary straight line from the leading to the trailing edge of an airfoil. Lowering flaps changes the chord line
Relative wind
The wind felt by an airfoil. It is parallel to and travels the opposite direction of the flight path of the airfoil.
Angle of attack
Angle between the chord line and the relative wind
Angle of incidence
Angle that the wing is attached to the fuselage
Does the angle of attack that an airfoil stalls at change?
The indicated airspeed at which stalls occur is determined by weight and load factor, but the stall angle of attack is the same
Lateral axis
Imaginary line from wingtip to wingtip
Pitch
Rotation around the lateral axis. Controlled by the elevators.
Longitudinal Axis
Imaginary line from the nose to the tail
Roll
Rotation around the longitudinal axis. Controlled by the ailerons
Vertical axis
Imaginary line extending through the intersection of the lateral and longitudinal axes.
Yaw
Rotation about the vertical axis. Controlled by the rudder.
Center of gravity
Imaginary point where all the weight is concentrated and plane would balance if it were suspended. The 3 axes intersect here.
What are the 4 aerodynamic forces
Weight, lift, drag, and thrust
Bernoulli’s principle
As the velocity of a fluid increases, it’s pressure decreases
Lift
The result of a pressure difference between the top and bottom of the wing. Factors include: angle of attack, wing area and shape, air velocity, and air density.
Thrust
The forward force produced by the propeller
Drag
Rearward force which resists the forward movement of an airplane through the air. There is parasite drag and induced drag
Parasite drag
Resistance by any part of the plane that doesn’t produce lift, like the antennae and landing gear
Induced drag
As lift is developed, the high pressure air beneath the wing causes vortices all along the trailing edge of the wings. Increases as airspeed decreases
Unaccelerated (straight and level) flight
The four aerodynamic forces are in equilibrium. Lift=weight, Thrust=drag
What determines the longitudinal stability of an airplane
The location of the CG with respect tot he CL(center of lift).
3 effects of forward CG
1-increased longitudinal stability
2-lower cruise speed. Higher AoA to create more lift, more induced drag
3-higher stall speed.
4 effects of aft CG
1- decreased longitudinal stability
2- higher cruise speed
3- lower stall speed
4- poor stall/spin recovery
Why does a plane lose altitude on a turn?
A portion of the vertical lift is diverted to a horizontal lift component. So, this will happen unless you increase the AoA or airspeed.
What can increase the load factor on the airplane?
Overloading the plane, too steep an angle of bank, turbulence and abrupt movement of the controls.
What is a stall?
At an AoA of approximately 18-20, turbulence over the upper wing decreases lift so drastically that flight can’t be maintained.
Critical Angle of Attack
The angle at which a stall occurs. An airplane can stall at any airspeed or any attitude, but will always stall at the same critical AoA.
When will an aircraft spin?
Only after a stall, and for as long as the outside wing continues to provide more lift than the inside wing.
What wing is stalled in a spin
Both wings are stalled, but one is stalled more than the other.
What does extending flaps on landing do?
Increases lift and drag, allowing a steeper approach without an increase in airspeed.
What is ground effect
Occurs when flying one wingspan or less above the surface, and the airflow is modified and can cause an airplane to become airborne before takeoff speed or float on approach.
When are maximum vortexes created?
When an aircraft is heavy, clean, and slow. Land beyond the previous plane and takeoff before.
