Forward Flight Aerodynamics Flashcards
What is the significance of understanding aerodynamics during the transition from hover to forward flight in helicopters?
It enhances performance and ensures safe operations.
What are the four basic forces in helicopter flight?
Lift, Thrust, Weight, and Drag.
Define ‘Lift’ in the context of helicopter flight.
Lift is the upward force generated by the rotor blades as they rotate, essential for keeping the helicopter aloft.
What are the two components of Lift?
Vertical Component (counters gravitational force) and Horizontal Component (provides thrust for forward movement).
How does Thrust function in helicopter flight?
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.
What is the definition of Weight in helicopter flight?
Weight is the gravitational force acting downward on the helicopter’s mass, countered by vertical lift for stable flight.
What does Drag represent in helicopter flight?
Drag is the resistance force opposing thrust, created by air friction and acting parallel to the relative wind.
What is required for a helicopter to maintain constant altitude and airspeed in forward flight?
Total thrust and lift must equal weight and drag.
What is Translational Lift?
Translational Lift is the increase in lift experienced when the helicopter moves forward, aided by horizontal airflow across the rotor disc.
How does Translational Lift improve helicopter performance?
It reduces induced drag and increases lift, allowing the helicopter to sustain flight with lower power demands.
What is Effective Translational Lift (ETL)?
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.
What effects does ETL have on flight characteristics?
It leads to the dissipation of tip vortices, resulting in smoother airflow and improved performance.
What might pilots feel during the transition to Effective Translational Lift?
A shuddering sensation due to interacting tip vortices with the airframe.
What is the Transverse Flow Effect (TFE)?
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.
Define ‘Dissymmetry of Lift’ in helicopter flight.
It refers to differences in airflow over the advancing and retreating sides of the rotor system, leading to unequal lift.
How does blade flapping compensate for Dissymmetry of Lift?
Blade flapping adjusts the angle of attack to balance the lift between advancing and retreating blades.
What is Retreating Blade Stall?
A condition occurring when the retreating blade’s angle of attack exceeds the critical angle, causing turbulence and airflow separation.
What are the symptoms of Retreating Blade Stall?
It can cause a nose-up pitch and handling difficulties, especially at high forward airspeeds and high-density altitudes.
What is Loss of Tail Rotor Effectiveness (LTE)?
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.
What symptoms might indicate Loss of Tail Rotor Effectiveness?
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.
What are the types of Loss of Tail Rotor Effectiveness?
Weathercock Stability, Tail Rotor Vortex Ring State, Main Rotor Disc Interference, and High-Density Altitude Issues.
What is Weathercock Stability in relation to LTE?
It affects helicopters in tailwind leading to uncommanded turns.
winds from 4-8 o’clock positions
What causes the Tail Rotor Vortex Ring State?
It results from left crosswinds causing turbulent air to interfere with the tail rotor.
winds from 8-10 o’clock positions
How does Main Rotor Disc Interference occur?
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
How do high-density altitudes impact tail rotor effectiveness?
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.
What recovery technique can help regain control during LTE?
Applying left pedal and forward cyclic can assist in recovery if altitude and space permit.
What is the purpose of initiating a hovering auto rotation in LTE recovery?
It manages violent yaw until landing when recovery is not possible.
How does airflow over the rotor system affect helicopter performance?
Managing airflow is critical to ensuring efficient rotor operation, reducing drag, and enhancing lift.
What does the horizontal airflow across the rotor disc do during forward flight?
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.
Why is it important for pilots to understand the aerodynamic principles of forward flight?
Understanding these principles is vital for enhancing flight safety, performance, and efficiency in various flight conditions.
