Aerodynamics Basic

Question 1

Relative Wind is…

Answer 1

airflow relative to an airfoil. Movement of an airfoil through the air creates relative wind.

Question 2

Rotational Relative Wind is…

Answer 2

produced from the rotation of rotor blades as they turn about the mast. Is highest at blade tips and decreases uniformly to zero at axis of rotation

Question 3

Induced Flow (Downwash) is…

Answer 3

a downward flow of air caused by rotor blades turning. Most pronounced at hover under no-wind conditions

Question 4

resultant relative wind is…

Answer 4

rotational relative wind modified by induced flow

Question 5

Up Flow is…

Answer 5

airflow approaching the rotor disk from below as the result of some rate of descent

Question 6

Angle of Incidence is…

Answer 6

angle between the chord line of a main or tail rotor blade and the rotational relative wind of the rotor system. It is a mechanical angle. AKA blade pitch angle.

Question 7

Angle of Attack

Answer 7

is an aerodynamic angle. between airfoil chord line and resultant relative wind. It can change with no change to angle of incidence.

Question 8

Feathering is…

Answer 8

rotation of the blade about its span wise axis by collective/cyclic inputs causing changes in blade pitch angle

Question 9

Collective feathering …

Answer 9

changes angle of incidence equally and in the same direction on all rotor blades simultaneously

Question 10

Cyclic feathering…

Answer 10

changes angle of incidence differentially around the rotor system

Question 11

Flapping is…

Answer 11

the up and down movement of rotor blades about a hinge. primary means of compensating for dissymmetry of lift.

Question 12

Lead and Lag (Hunting) …

Answer 12

fore and aft movement of the blade in the plane of rotation in response to changes in angler velocity.

Question 13

Drag is…

Types of Drag

Answer 13

force opposing the motion of an airfoil through the air

Parasite - non lifting components
Induced - a result of production of lift
Profile - frictional resistance of blades passing through the air.

Question 14

Airflow in Hovering Flight

Answer 14

for helicopter to hover, lift produced but the rotor system must equal the total weight of the helicopter.

At hover, rotor tip vortex reduces effectiveness of the outer blade portions.

High power requirements for hovering caused by vortices of preceding blade.

Question 15

In Ground effect

Answer 15

permits relative wind to be more horizontal, lift vector to be more vertical, and induced drag to be reduced. Left induced flow, increased AOA

Question 16

OGE

Answer 16

induced flow increase, decreased AOA. Higher blade pitch required. Increased pitch creates more drag. More power required due to the increased pitch angle and drag

Question 17

Translating Tendency

Answer 17

Tendency of helicopter to drift in direction of tail rotor thrust

Question 18

Features that help compensate for translating tendency

Answer 18

flight control rigging
transmission mounted
collective pitch control system
programmed mechanical inputs/AFCS/stabilization augmentation systems

Question 19

Dissymmetry of Lift

Answer 19

differential lift between the advancing and retreating halves of the rotor disk

Question 20

What compensates for dissymmetry of lift

Answer 20

cyclic feathering, blade flapping

Question 21

Translational Lift

Answer 21

improved rotor efficiency resulting from directional flight
As incoming wind enters rotor system, turbulence and vortexes are left behind and the flow of air becomes more horizontal

Question 22

Transverse Flow

Answer 22

Forward air more horizontal Aft air more vertical causes a pitch up. GP causes right roll. Occurs 10 to 20 knots
Most noticeable during takeoff and deceleration for landing

Question 23

Effective Translational Lift

Answer 23

occurs at 16 to 24 knots. Completely outruns the recirculation of old vortexes and begins to work in relatively undisturbed air.

Question 24

Autotrotation

Answer 24

To sustain rotor RPM when engine fails so continued flight can be conducted to the ground.

Airflow during helicopter descent provides energy ti overcome blade drag and turn the rotor

Question 25

Settling with power

Answer 25

helicopter settles in its own downwash. AKA vortex ring state

Question 26

conditions for settling with power

Answer 26

a vertical or near vertical descent of at least 300 FPM

slow forward airspeed (less than ETL)

Rotor system must be using 20 to 100 percent of available engine power with insufficient power remaining to arrest the descent

Question 27

Conditions conducive to settling with power

Answer 27

Steep approach at high rate of descent

downwind approach

formation flight approach

hovering above the maximum hover ceiling

not maintaining constant altitude control during an OGE hover

during masking/unmasking

Question 28

Dynamic Rollover

Answer 28

is the lateral-rolling tendency

Occurs: level ground, slope, crosswind landing, and takeoff

Conditions: pivot point, rolling motion, and exceeding critical angle

Question 29

Dynamic Rollover Human Factors

Answer 29

Inattention
Inexperience
Failure to take timely corrective action
Inappropriate control input
Loss of visual reference

Question 30

Retreating Blade Stall

Answer 30

decreasing velocity of airflow on the retreating blade demands a higher AOA to generate the same lift as the advancing blade. Left roll

Question 31

Retreating Blade Stall Conditions

Answer 31

high blade loading (high gross weight)
low rotor RPM
High-density altitude
High G-maneuvers
Turbulent air

Question 32

Recover from blade stall

Answer 32

reduce collective
reduce airspeed
descend to a lower altitude
increase rotor RPM to normal limits
reduce the severity of the maneuver