Aerodynamics

Question 1

Improved rotor efficiency resulting from directional flight is called ____.

Answer 1

Translational lift

Question 2

____ is a flight condition where a helicopter starts to fly out of its own rotor downwash and moves into clean, undisturbed air that reduces wing tip vortices and causes the rotor to become more efficient (usually between 16 – 24 knots)

Answer 2

Effective Translational Lift (ELT)

Question 3

____ is a condition of increased drag and decreased lift in the aft portion of the rotor disk compared to the front portion. (Caused by the air having a greater induced velocity and reduced angle of attack in the aft portion of the disk)

Answer 3

Transverse Flow

Question 4

____ is the tendency of single rotor helicopters to translate in the direction of tail rotor thrust.

Answer 4

Translating Tendency

Question 5

The difference in lift between the advancing half of the rotor disk and the retreating half is called ____.

Answer 5

Dissymmetry of Lift

Question 6

____ is the phenomenon resulting from the advancing blade approaching Mach 1 (because of excessive forward speed).

Answer 6

Compressibility

Question 7

____ is an aerodynamic phenomenon that is characterized by an uncommanded yaw which does not subside of its own accord. (if not corrected can result in the loss of aircraft control)

Answer 7

Loss of Tail Rotor Effectiveness (LTE)

Question 8

A powered flight condition in which the helicopter settles in its own downwash (resulting in a descent that is aggravated by the increase in power) is known as ____.

Answer 8

Vortex Ring State

Question 9

____ is when a helicopter exceeds its critical rollover angle with one skid or wheel on the ground. (Requirements: pivot point, roll rate, exceed critical angle – TH-1 is 150)

Answer 9

Dynamic Rollover

Question 10

____ is when the retreating blade exceeds the critical angle of attack and stalls (causing the aircraft’s nose to pitch up and roll in the direction of the stall).

Answer 10

Retreating Blade Stall

Question 11

Wind that flows opposite the physical flight path of the airfoil, striking the blade at 90 degrees to the leading edge and parallel to the plane of rotation, and is constantly changing in direction during rotation is known as ____.

Answer 11

Rotational Relative Wind

Question 12

____ is the downward flow of air through the rotor blades caused by the increased blade pitch angle. (this downward component of air is added to the rotational relative wind.)

Answer 12

Induced Flow

Question 13

____ is rotational relative wind modified by induced flow.

Answer 13

Resultant Relative Wind

Question 14

____ is the force that opposes the motion of an aircraft through the air and is the force produced by the resistance of the air on an object passing through it. It’s always parallel to relative wind.

Answer 14

Drag

Question 15

____ Drag is incurred from frictional resistance of the blades passing through the air.

Answer 15

Profile Drag

Question 16

____ Drag is incurred as a result of production of lift.

Answer 16

Induced Drag

Question 17

____ Drag is incurred from the non-lifting portions of the aircraft.

Answer 17

Parasitic/Parasite Drag

Question 18

The S in the lift equation is ____.

Answer 18

Surface Area

Question 19

In Ground Effect hover power can be up to ___% less than Out of Ground Effect.

Answer 19

30%

Question 20

____ and ____ compensate for tail rotor dissymmetry of lift

Answer 20

Flapping and Feathering

Question 21

Any descent of ____ KIAS and ____ FPM or more with power applied may result in Vortex Ring State

Answer 21

40 KIAS / 800 FPM

Question 22

In the even of a complete loss of tail rotor thrust, aft cyclic application should be very slow and small to avoid ____.

Answer 22

Mast Bumping

Question 23

Newton’s 1st Law of motion (inertia) states what?

Answer 23

A body at rest will remain at rest, and a body in motion will remain in motion until acted upon by an external force

Question 24

What is Newton’s 2nd law of motion? (Acceleration)

Answer 24

The force required to produce change in the motion of a body is directly proportional to it’s mass and the rate of change of it’s velocity.

Question 25

What is Newton’s 3rd law of motion? (Action/Reaction)

Answer 25

For every action there is an equal and opposite reaction

Question 26

Tail rotors on average consume __% of available power

Answer 26

30%

Question 27

Blade twist helps ____ more evenly and control ____.

Answer 27

distribute lift more evenly and control coning

Question 28

When force is applied to a gyro at a given point in a plane of rotation, the gyro responds by tilting in the direction of the applied force __ degrees later in the direction of rotation.

Answer 28

90 degrees

Question 29

Why does in ground effect hover take less power than out of ground effect?

Answer 29

Reduction in downward velocity of induced flow caused by proximity of the ground / disruption in size and number of wing tip vortices.

Question 30

____ is a condition of INCREASED DRAG and DECREASED LIFT in the AFT portion of the rotor disk.

Answer 30

Transverse Flow

(Most noticeable at approx 20 knots

Question 31

What percent is the Driven Region of the blade during autorotation?

Answer 31

30%

Question 32

What percent is the Driving Region of the blade during autorotation?

Answer 32

45%

Question 33

What percent is the Stall Region of the blade during autorotation?

Answer 33

25%

Question 34

What are the aircraft characteristics of a retreating blade stall?

Answer 34

The aircraft’s nose will pitch up and roll in the direction of the stall

Question 35

What conditions can cause a retreating blade stall?

Answer 35

High gross weight
Low rotor RPM
High DA
Steep or abrupt turns
Turbulent air

Question 36

What corrective actions can you do to counteract loss of tail rotor effectiveness (LTE)?

Answer 36

Lower the collective if possible and establish forward flight

Question 37

What is the critical rolling angle during dynamic roll over?

Answer 37

15 degrees