Basic Aerodynamic Theory, Lift and Drag

Question 1

Describe what an aerofoil is and distinguish between aerofoil designs

Answer 1

An aerofoil is a wing or blade that is shaped and positioned in such a way that it can redirect airflow and generate forces that create a reaction.
For helicopters we work with symmetrical and asymmetrical aerofoil or blade shapes.

Question 2

Review 3
1. Blade angle is the angular difference between the ——- of the blade and the ( plane of rotation/ axis of rotation)

Answer 2

Chord
Plane of rotation

Question 3

Review 3
2. Feathering a blade means changing its ——— angle around the ——- axis.

Answer 3

Pitch
Feathering

Question 4

Review 3
3. When an airflow is deflected by an airfoil, the force acting more or less at right angles to the airfoil is called ( total reaction/ lift/ drag)

Answer 4

Total Reaction

Question 5

Review 3
4. The two components of total reaction are lift,acting ( at right angles/parallel) to the relative airflow and drag, ( at right angles/ parallel) to the relative airflow.

Answer 5

Right angles
Parallel

Question 6

Review 3
5. When an airflow is made to speed up, the pressure within the flow ( increases/ decreases) provided the flow remains———-

Answer 6

Decreases
Streamlined

Question 7

Review 3
6. When a symmetrical airfoil is placed at 0 degrees angle of attack to an airflow, pressures are ( different/ the same) above and below the airfoil.

Answer 7

The same

Question 8

Review 3
7. The lift co-efficient of an airfoil is determined by its——- and ——-

Answer 8

Shape
Size

Question 9

Review 3
8. The peak of the CL (remember lift co-efficient) curve represents( C L max/CL min), the associated angle of attack is called the ——— angle.

Answer 9

C L max
Stall

Question 10

Review 3
9. The centre of pressure is the point on the ——- line through which all ——— are said to act.

Answer 10

Chord
Pressures

Question 11

Review 3
10. The centre of pressure of a symmetrical airfoil (moves forward/ moves aft/ remains steady) with changes in angle of attack.

Answer 11

Remains steady

Question 12

Review 3
11. The point on the chord line about which no change in pitching moments is felt with changes in angle of attack is called the ( centre of pressure/ aerodynamic centre)

Answer 12

Aerodynamic centre

Question 13

Explain Bernoulli’s theorem in simple terms

Answer 13

In a streamlined flow of fluid, the sum of all energies is a constant.

Question 14

The drag coefficient of an airfoil is determined by its——-, and ——-, its minimum value is found at ( zero/four) degrees angle of attack

Answer 14

Shape
Angle of attack
Zero

Question 15

The three types of drag experienced by a helicopter in forward flight are ——-,——- and ——-

Answer 15

Induced
Parasite
Profile

Question 16

When the speed of a helicopter increases from 20 kts to 60 kts, parasite drag increases by a factor of ( 3,6,9)

Answer 16

9

Question 17

Form drag can be reduced by——-

Answer 17

Shape

Question 18

Skin friction drag is caused by friction between molecules in the ——- layer which is a ( retarded/ accelerated) layer of air between the airfoil and the ———-

Answer 18

Boundary
Retarded
Relative airflow

Question 19

A laminar boundary layer is normally (thick/thin), it producers ( much/little) skin friction drag and it ( is/is not) readily subject to separation from the airfoil surface.

Answer 19

Thin
Little
Is

Question 20

A turbulent boundary layer is normally ( thick/thin), it produces ( much/little) skin friction drag and it ( is/is not) readily subject to separation from the airfoil surface

Answer 20

Thick
Much
Is not

Question 21

The point where the laminar boundary layer changes into the turbulent boundary layer is called the ( separation/transition) point

Answer 21

Transition

Question 22

With an increase in airspeed, skin friction drag ( increases/decreases) because the transition point moves ( forward/aft) and the boundary layer ( thickens/thins)

Answer 22

Increases
Forward
Thickens