Aerodynamics

Question 1

Define airfoil

Answer 1

A surface body or structure producing lift

Question 2

“If you increase the velocity of air over the top of an airfoil surface what will happen to dynamic pressure

what will happen to static pressure

Answer 2

Dynamic pressure increases

static pressure decreases

Question 3

Define chord line

Answer 3

The chord line is an imaginary line protruding through the leading edge on which all angles and winds are measured

Question 4

Blade span

Answer 4

The length of a single blade from its tip to its root

Question 5

Why is center of pressure important?

Answer 5

because it is a point along the chord line through which all aerodynamic forces are considered to act

Question 6

Rotational wind

Answer 6

Parallel and in the same direction as the blades

Question 7

Induced flow/angle of attack standard rule

Answer 7

Increase induced flow, decreased AOA, decreased lift

Can only diminish effects of induced flow with forward airspeed

Question 8

Define angle of attack

Answer 8

Angle between the chord of an airfoil and the resultant relative wind

An aerodynamic angle

Question 9

What are the two components of total aerodynamic force

Answer 9

Lift

Drag

Question 10

What is the relationship of lift to resultant relative wind

Answer 10

perpendicular

Question 11

What is the relationship of drag to resultant relative wind

Answer 11

Parallel to and in the same direction of the resultant relative wind

Question 12

Induced drag

Answer 12

By-product of lift, most important in helo operations. Caused by vortices and induced flow

Question 13

Profile drag - caused by

Answer 13

Main rotor ONLY

Question 14

Parasite drag -

Answer 14

Tail rotor, fuselage, skids etc

Question 15

Dissymmetry of lift

Answer 15

Unequal lift between advancing and retreating halves of the rotor disk

Question 16

No lift area

Answer 16

Where reverse flow is the greatest, you get no lift assist (0 velocity)

The 9 O clock position near the root of the rotor blades

Question 17

Differences in lift due to airspeed (advancing/retreating) are

Answer 17

significant

Question 18

Differences in lift due to flap up/flap down are

Answer 18

insignificant

Question 19

“How does the helicopter compensate for dissymmetry of lift

Answer 19

Blade flapping

Question 20

Four causes of excessive coning

Answer 20

Low rotor RPM

High gross weight

High G manuvers

Turbulent air

Question 21

why is blade twisting necessary

Answer 21

to distribute the lifting force more evenly along the blade

Question 22

Three ways to compensate for translating tendency

Answer 22

At the factory, they rig the cyclic left

Tilt the mast slightly left

Left cyclic input by pilot

Question 23

What are the three conditions for settling with power

Answer 23

-A vertical or near vertical descent rate of at least 300 FPM

-The engine must be using 20 to 100% of available power

-airspeed less than ETL (dont need numbers here)

Question 24

Settling with power recovery procedures

Answer 24

Increase airspeed with cyclic

Reduce collective pitch as altitude permits

Question 25

Autorotation - two key descriptions

Answer 25

no engine power supplied

rotors driven by relative wind only

Question 26

Dynamic rollover onset conditions

Answer 26

Pivot point

Rolling motion

Exceed critical angle

Question 27

What is the primary cause of retreating blade stall

Answer 27

Excessive airspeed

Question 28

Two symptoms of retreating blade stall

Answer 28

Pitch up of the nose

Followed by a roll to the left

Question 29

What are the two initial recovery procedures for blade stall

Answer 29

Reduce collective pitch

Regain control of aircraft

Question 30

How does induced drag change with increased airspeed

Answer 30

drops off sharply, stays low as airspeed increases

Question 31

How does profile drag change with increased airspeed

Answer 31

Steady climb up

Question 32

How does parasitic drag change with increase with airspeed

Answer 32

Rapid climb up

Question 33

Get paper and draw an airfoil

Answer 33

bitch