Forward Flight Aerodynamics

Question 1

What is the significance of understanding aerodynamics during the transition from hover to forward flight in helicopters?

Answer 1

It enhances performance and ensures safe operations.

Question 2

What are the four basic forces in helicopter flight?

Answer 2

Lift, Thrust, Weight, and Drag.

Question 3

Define ‘Lift’ in the context of helicopter flight.

Answer 3

Lift is the upward force generated by the rotor blades as they rotate, essential for keeping the helicopter aloft.

Question 4

What are the two components of Lift?

Answer 4

Vertical Component (counters gravitational force) and Horizontal Component (provides thrust for forward movement).

Question 5

How does Thrust function in helicopter flight?

Answer 5

Thrust, like lift, is generated by the rotation of the main rotor disk. In a helicopter, thrust can be forward, rearward, sideward, or vertical. The resultant lift and thrust determines the direction of movement of the helicopter.

Question 6

What is the definition of Weight in helicopter flight?

Answer 6

Weight is the gravitational force acting downward on the helicopter’s mass, countered by vertical lift for stable flight.

Question 7

What does Drag represent in helicopter flight?

Answer 7

Drag is the resistance force opposing thrust, created by air friction and acting parallel to the relative wind.

Question 8

What is required for a helicopter to maintain constant altitude and airspeed in forward flight?

Answer 8

Total thrust and lift must equal weight and drag.

Question 9

What is Translational Lift?

Answer 9

Translational Lift is the increase in lift experienced when the helicopter moves forward, aided by horizontal airflow across the rotor disc.

Question 10

How does Translational Lift improve helicopter performance?

Answer 10

It reduces induced drag and increases lift, allowing the helicopter to sustain flight with lower power demands.

Question 11

What is Effective Translational Lift (ETL)?

Answer 11

ETL is the point at which the benefits of translational lift become noticeable to the pilot, typically occurring at speeds of 16 to 24 knots.

Question 12

What effects does ETL have on flight characteristics?

Answer 12

It leads to the dissipation of tip vortices, resulting in smoother airflow and improved performance.

Question 13

What might pilots feel during the transition to Effective Translational Lift?

Answer 13

A shuddering sensation due to interacting tip vortices with the airframe.

Question 14

What is the Transverse Flow Effect (TFE)?

Answer 14

TFE is the difference in induced flow across the rotor disk, causing varying lift distribution and potentially leading to a right roll in counterclockwise-rotating helicopters.

Question 15

Define ‘Dissymmetry of Lift’ in helicopter flight.

Answer 15

It refers to differences in airflow over the advancing and retreating sides of the rotor system, leading to unequal lift.

Question 16

How does blade flapping compensate for Dissymmetry of Lift?

Answer 16

Blade flapping adjusts the angle of attack to balance the lift between advancing and retreating blades.

Question 17

What is Retreating Blade Stall?

Answer 17

A condition occurring when the retreating blade’s angle of attack exceeds the critical angle, causing turbulence and airflow separation.

Question 18

What are the symptoms of Retreating Blade Stall?

Answer 18

It can cause a nose-up pitch and handling difficulties, especially at high forward airspeeds and high-density altitudes.

Question 19

What is Loss of Tail Rotor Effectiveness (LTE)?

Answer 19

Loss of Tail Rotor Effectiveness (LTE) is a condition where the tail rotor loses efficiency, leading to uncommanded yaw. It can occur due to factors such as high-density altitude, tailwinds, crosswinds, or rotor disc interference.

Question 20

What symptoms might indicate Loss of Tail Rotor Effectiveness?

Answer 20

Symptoms of Loss of Tail Rotor Effectiveness (LTE) include uncommanded yaw and increased control inputs needed to counteract this yaw; may also experience a nose-up pitch as well as sluggishness when turning.

Question 21

What are the types of Loss of Tail Rotor Effectiveness?

Answer 21

Weathercock Stability, Tail Rotor Vortex Ring State, Main Rotor Disc Interference, and High-Density Altitude Issues.

Question 22

What is Weathercock Stability in relation to LTE?

Answer 22

It affects helicopters in tailwind leading to uncommanded turns.

winds from 4-8 o’clock positions

Question 23

What causes the Tail Rotor Vortex Ring State?

Answer 23

It results from left crosswinds causing turbulent air to interfere with the tail rotor.

winds from 8-10 o’clock positions

Question 24

How does Main Rotor Disc Interference occur?

Answer 24

It occurs when quartering headwinds blow main rotor vortices into the tail rotor vicinity and cause tail rotor inefficiency.

winds from 10-11 o’clock positions

Question 25

How do high-density altitudes impact tail rotor effectiveness?

Answer 25

High DA impacts tail rotor effectiveness by reducing air density, which diminishes the lift generated by the tail rotor. This decreased lift makes it harder for the tail rotor to counteract the torque from the main rotor, increasing the risk of uncommanded yaw.

Question 26

What recovery technique can help regain control during LTE?

Answer 26

Applying left pedal and forward cyclic can assist in recovery if altitude and space permit.

Question 27

What is the purpose of initiating a hovering auto rotation in LTE recovery?

Answer 27

It manages violent yaw until landing when recovery is not possible.

Question 28

How does airflow over the rotor system affect helicopter performance?

Answer 28

Managing airflow is critical to ensuring efficient rotor operation, reducing drag, and enhancing lift.

Question 29

What does the horizontal airflow across the rotor disc do during forward flight?

Answer 29

During forward flight, the horizontal airflow across the rotor disc pushes away tip vortices. This action allows the rotor to operate in cleaner, less disturbed air, which reduces induced drag and increases lift. As a result, the helicopter can achieve improved aerodynamic efficiency, requiring less power to maintain flight.

Question 30

Why is it important for pilots to understand the aerodynamic principles of forward flight?

Answer 30

Understanding these principles is vital for enhancing flight safety, performance, and efficiency in various flight conditions.