AER2: Lift

Question 1

Define Camber

Answer 1

A measure of the wing’s curvature

along the chord.

Question 2

Define Chordline

Answer 2

The straight line joining the centres
of curvature of the leading and
trailing edges.

Question 3

Define Mean Camber line

Answer 3

The line equidistant between upper
and lower surfaces of the wing.
This line is a measure of the wing’s
camber.

Question 4

Define relative airflow

Answer 4

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.

Question 5

Define Angle of Attack

Answer 5

The angle between the chord line
and the relative airflow. Usually
refered to as a (alpha)

Question 6

Define Air density

Answer 6

Is the mass of the air per unit of volume (Mass/Volume). Is given the greek letter (p) or rho.

Question 7

Define the aerofoil section

Answer 7

A body with a cross-sectional area
shaped to produce an aerodynamic
force.

Question 8

Define Static pressure

Answer 8

Pressure due to molecular motion at rest and atmospheric pressure.

Question 9

Define Dynamic pressure

Answer 9

Pressure caused due to motion

Question 10

Define total air pressure

Answer 10

Static plus dynamic is total air pressure.

Question 11

Define Bernoulli’s theorem and explain how this relates to a wing.

Answer 11

1. In a steady streamline flow (outside the boundary layer) the sum of the energies is constant.
2. 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.

Question 12

Define the co-efficient of lift

Answer 12

The aircraft’s ability to produce lift. (via the aerofoil).

Question 13

Co-efficient of lift depends on?

Answer 13

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.

Question 14

What is the name of the maximum angle of attack?

Answer 14

The critical angle. Exceed this and you will stall the aircraft.

Question 15

What is the formula for lift?

Answer 15

𝐿= 1/2 𝜌𝑉^2 𝑆𝐶_𝐿

Question 16

Define centre of pressure

Answer 16

The point at which the total reaction

is assumed to act.

Question 17

Define total reaction

Answer 17

The resultant of all aerodynamic forces acting on the wing of the aircraft.

Question 18

Identify some lift/drag devices of an aircraft

Answer 18

Flaps, slats, slots, spoilers, speed brakes.

Question 19

Define Flaps

Answer 19

Besides increasing the
camber of the wing, many types of flap also increase the wing
area. Trailing edge flaps reduce the stalling angle;

Question 20

Define Slats/Slots

Answer 20

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.

Question 21

Define Spoilers and speed brakes

Answer 21

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.

Question 22

Define stalling

Answer 22

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.

Question 23

Recovery from Stalling

Answer 23

Increase power, lower attitude

Question 24

Symptoms of a stall

Answer 24

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.