AER2: Lift Flashcards
Define Camber
A measure of the wing’s curvature
along the chord.
Define Chordline
The straight line joining the centres
of curvature of the leading and
trailing edges.
Define Mean Camber line
The line equidistant between upper
and lower surfaces of the wing.
This line is a measure of the wing’s
camber.
Define relative airflow
The relative direction and speed of the air before it is influenced by the presence of an aircraft. Always equal and opposite to the flight path.
Define Angle of Attack
The angle between the chord line
and the relative airflow. Usually
refered to as a (alpha)
Define Air density
Is the mass of the air per unit of volume (Mass/Volume). Is given the greek letter (p) or rho.
Define the aerofoil section
A body with a cross-sectional area
shaped to produce an aerodynamic
force.
Define Static pressure
Pressure due to molecular motion at rest and atmospheric pressure.
Define Dynamic pressure
Pressure caused due to motion
Define total air pressure
Static plus dynamic is total air pressure.
Define Bernoulli’s theorem and explain how this relates to a wing.
- In a steady streamline flow (outside the boundary layer) the sum of the energies is constant.
- the relative airflow over the top of the wing is accelerated, producing Low pressure over the top of the wing. The airflow underneath the wing is not accelerated, producing a High pressure system underneath. This produces lift.
Define the co-efficient of lift
The aircraft’s ability to produce lift. (via the aerofoil).
Co-efficient of lift depends on?
a. Angle of attack.
b. Shape of the wing section and planform.
c. Condition of the wing surface.
d. Speed of sound.
e. Reynolds’ number.
What is the name of the maximum angle of attack?
The critical angle. Exceed this and you will stall the aircraft.
What is the formula for lift?
𝐿= 1/2 𝜌𝑉^2 𝑆𝐶_𝐿
Define centre of pressure
The point at which the total reaction
is assumed to act.
Define total reaction
The resultant of all aerodynamic forces acting on the wing of the aircraft.
Identify some lift/drag devices of an aircraft
Flaps, slats, slots, spoilers, speed brakes.
Define Flaps
Besides increasing the
camber of the wing, many types of flap also increase the wing
area. Trailing edge flaps reduce the stalling angle;
Define Slats/Slots
Slats - Aerofoils attached to the leading edge of the wing, provides an energised air channel that activates the upper layer of the wing, increases lift at high angles of attack.
Slots - Slots provide a corridor for air to pass through under the slat.
Define Spoilers and speed brakes
Spoilers are located on wings and ‘spoil’ the airflow over the upper surface, increasing drag and reducing lift. Speed brakes are located in many places (think F-15). Increase drag.
Define stalling
An aircraft stalls when the lift can no longer support
the weight. Air separates from the upper surface of the wing
due to the adverse pressure gradient.
Recovery from Stalling
Increase power, lower attitude
Symptoms of a stall
a. High nose.
b. Low and deceasing airspeed.
c. Less effective controls.
d. Light buffet.
Leading to:
e. Heavy buffet.
f. Nose drop/Sink.
g. Possible wing drop.
