Principles of Flight

Question 1

What is the Center of Pressure?

Answer 1

The point on the chord line through which lift is considered to act. its a function of camber and angle of attack. Its where the combined aerodynamic force around an aerofoil is called the total reaction and acts through a single point on the chord line.

Question 2

What is a Cord Line?

Answer 2

A straight line joining the centres of curvature of the leading and trailing edges of an aerofoil.

Question 3

Angle of Attack?

Answer 3

(α or alpha) (can also be referred to as Aerodynamic Incidence). The angle between the chord line and the Relative Airflow.

Question 4

How does the CP move as the angle of attack increases?

Answer 4

Th CP will move forward with increasing angle of attack.

Question 5

What is lift Coefficient CL?

Answer 5

Lift related to AOA. it is the ratio between lift divided by the wing planform area and dynamic pressure. (L/0.5pV2s)

Question 6

Aerodynamic Centre?

Answer 6

The point where all changes in the magnitude of the lift force effectively take place

Question 7

Density Definition?

Answer 7

denoted by Rho (p) ratio of mass to volume

Question 8

Wing loading?

Answer 8

Weight supported per unit area of the wing (N/m2)

Question 9

Pitch angle?

Answer 9

Angle between the Chord line and the horizon

Question 10

Bernoullis Theorem?

Answer 10

It uses the principle of conservation of energy. I states that when a fluid flows at a stead rate through a pipe its total energy remains constant. Total Pressure = Dynamic + Static.

Question 11

Aspect Ratio?

Answer 11

Ratio of wingspan to average chord.

Question 12

How is wing sweepback measured?

Answer 12

Angle between the 25% tip chord and 25% root chord. Measured from the lateral axis

Question 13

Aerodynamic Center?

Answer 13

It centers the turning moment center between the trailing and leading edge points on the chord line. The size of this moment depends on the product of lift force and the ditance between AC and CP.

Question 14

What is the effect of High Lift Devices?

Answer 14

1- It alters the position of CP
2- The aerofoil with turn around its AC while A/C around its CG
3- CP to CG relation is what determines the pitch change for a given AOA or configuration

Question 15

What is the effect of CP with leading edge devices?

Answer 15

A nose up moment is produced by the CP moving forward (distance between CP and CG reduced)

Question 16

What is the effect of CP with trailing edge devices?

Answer 16

They have the opposite effect to LE devices, as they produce a nose down pitching moment by the movement to the CP to the aft increasing its arm with the CG.
But conventional aircraft with horizontal tail planes will be affected by the increased downwash from the wings when TE devices extend causing a pitch up moment that cancels out some of the pitch down moment.

Question 17

What is the Influence of CL between a symmetrical and Assym. aerofoil?

Answer 17

Assy. will have a higher CL max but stalls more sharp and at a lower AOA

Question 18

How does the leading edge thickness influence CL?

Answer 18

Thick leading edge stalls less abruptly at the same AOA but has a lower CL max.

Question 19

How does the camber thickness influence CL?

Answer 19

The thicker the camber the higher the CL max and less abrupt the stall. does not affect max AOA

Question 20

How do trailing edge devices affect CL?

Answer 20

The increase CLmax but reduce the stall AOA

Question 21

How do leading edge devices affect CL?

Answer 21

They increase both the CLmax and the Stall AOA

Question 22

What are the two main types of drag?

Answer 22

Parasite and Induced

Question 23

What does Parasite drag divide to

Answer 23

Form, Skin Friction and Interference Drag. Its denoted by Dº and is proportional to double the speed.

Question 24

Form drag?

Answer 24

caused by airflow separation

Question 25

Skin friction drag?

Answer 25

caused by surface roughness and or Icing

Question 26

Interference Drag?

Answer 26

exists where two bodies on an A/C meet. caused by the difference in local airflow speed thus pressure which causes vortices

Question 27

Induced drag?

Answer 27

Drag caused from lift production

Question 28

How does Induced drag happen?

Answer 28

The span wise flow from the upper wing towards the root and the lower wings flow towards the tip meet and create vortices. These vortices increase the downwash behind the wing causing the lift vector to tilt rearward creating an backwards horizontal lift component that opposes forward flight.

Question 29

How does Induced drag change with AOA?

Answer 29

CL increases with increased AOA which causes a greater pressure differential between the lower and upper wing airflow which increases the downwash thus induced drag.

Question 30

What is the principal design factor that affects induced drag?

Answer 30

Wing planform (shape)