Aerodynamics

Question 1

Define center of pressure

Answer 1

The point along the chord line of an airfoil through which all aerodynamic forces are considered to act.

Question 2

Define airfoil

Answer 2

Any surface designed to produce lift when air is passed over it

Question 3

List two basic types of airfoils

Answer 3

Symmetrical

Unsymmetrical/Nonsymmetrical

Question 4

Define rotational relative wind as applied to an airfoil

Answer 4

That flow of air parallel and opposite to the flight path of an airfoil

Question 5

Define induced flow

Answer 5

Downward flow of air through the rotor blades

Question 6

Define resultant relative wind

Answer 6

Rotational relative wind modified by induced flow

Question 7

How is the angle of incidence measured in a rotary wing aircraft?

Answer 7

The angle between a chord of an airfoil and the plane of rotation (tip path plane)

Question 8

Define angle of attack

Answer 8

The angle between the chord and the resultant relative wind

Question 9

Describe the relationship of lift to resultant relative wind

Answer 9

Perpendicular to

Question 10

Describe the relationship between drag and the resultant relative wind

Answer 10

Drag is parallel to and in the same direction of the resultant relative wind

Question 11

The four types of drag:

Answer 11

Induced
Parasite
Profile
Total

Question 12

Which type of drag increases with airspeed?

Answer 12

Parasite drag

Question 13

Define dissymmetry of lift

Answer 13

Differential lift between advancing and retreating halves of the rotor disk

Question 14

How does the helicopter compensate for dissymmetry of lift?

Answer 14

With flapping

Question 15

How does the pilot correct for blowback?

Answer 15

With cyclic feathering

Question 16

Which forces in the lift equation can the pilot control

Answer 16

Coefficient of lift and airspeed

Question 17

Define blowback

Answer 17

Change in the attitude of the rotor system

Question 18

How does the pilot control dissymmetry of lift?

Answer 18

With cyclic feathering

Question 19

What types of rotor systems are there?

Answer 19

Rigid
Semi-rigid
Articulated

Question 20

Articulated tilts relative to the ________

Answer 20

Hub

Question 21

Semi rigid tilts relative to the ________

Answer 21

Mast

Question 22

Define centrifugal force

Answer 22

outward force produced whenever a body moves in a curved path

Question 23

Define rotor blade coning

Answer 23

Upward flexing of the rotor blades

Question 24

Rotor blade coning is a compromise between which two forces?

Answer 24

Centrifugal force and lift

Question 25

Define gyroscopic precession

Answer 25

When a force is applied to a rotating body it will manifest 90 degrees after application in the direction of rotation.

Question 26

Why is blade twisting necessary?

Answer 26

To distribute the lifting force more evenly along the blade.

Question 27

A pedal turn to the right requires _____(less/more) force than a pedal turn to the left

Answer 27

Less

Question 28

Define translating tendency

Answer 28

Tendency of a single rotor helicopter to drift right while hovering

Question 29

List four methods used to overcome translating tendency in single rotor helicopters

Answer 29

- Rigging the cyclic - Tilting the mast - Left cyclic - Automated flight-control/stabilization augmentation system

Question 30

List the four rotor blade actions

Answer 30

Rotation Flapping Feathering Hunting

Question 31

Describe the relationship of the total force to the tip path plane

Answer 31

Perpendicular

Question 32

When rotor disk is tilted what are the two components of total force?

Answer 32

Lift | Thrust

Question 33

What are the two flight conditions?

Answer 33

Balanced/Unbalanced

Question 34

Loss or apparent loss of ground effect is caused by?

Answer 34

- Altitude greater than rotor diameter - Trees and bushes - Tall grass and uneven terrain - Hovering over water - Beginning o translational movement - Hovering into a wind

Question 35

Define effective rotational lift

Answer 35

When the rotor completely outruns the recirculation of old vortices and begins to work in relatively undisturbed air

Question 36

Effective translational lift occurs at an airspeed of ______

Answer 36

16-24 kts

Question 37

Transverse flow effect is noticeable at an airspeed of_____

Answer 37

10-20 kts

Question 38

Define settling with power

Answer 38

A condition of powered flight in which the helicopter settles in its own downwash

Question 39

List the three simultaneous conditions required for settling with power

Answer 39

Vertical or near vertical descent of at least 300FPM 20%-100% engine power Slow airspeed less than ETL

Question 40

List the required procedures for settling with power

Answer 40

Increase airspeed with cyclic Reduce collective as altitude permits Adjust rotor RPM to normal operating range

Question 41

Define autorotation

Answer 41

The flight condition during which no engine power is supplied and the main rotor is driven only by the action of the relative wind

Question 42

Describe how a pilot prevents a rotor RPM overspeed during an autorotation with turn

Answer 42

Adjusting collective control

Question 43

List of the three contitions required for a dynamic rollover to occur

Answer 43

Pivot point Rolling motion Exceed a critical angle

Question 44

Dynamic rollover occurs due to a combination of which two factors

Answer 44

Physical and human

Question 45

Which control input is required to recover from dynamic rollover on level ground

Answer 45

Smooth moderate collective reduction

Question 46

Operating at what speed is most likely to produce retreating blade stall

Answer 46

High forward speed

Question 47

Describe the symptoms of retreating blade stall in a single rotor helicopter

Answer 47

Abnormal vibration, pitch up of the nose and left roll

Question 48

Describe the recovery procedure from retreating blade stall

Answer 48

Reduce collective pitch, regain control of the aircraft, reduce airspeed, increase rotor RPM to normal operating range, minimize maneuvering, and descend to a lower altitude