Podcast
Questions and Answers
Which of the following is true about hovering flight?
Which of the following is true about hovering flight?
- The helicopter maintains a constant position above the ground (correct)
- The angle of attack of the main rotor blades remains constant
- The lift and thrust forces act straight down
- The drag incurred is mainly profile drag
What happens if the amount of thrust is greater than the actual weight during hovering flight?
What happens if the amount of thrust is greater than the actual weight during hovering flight?
- The helicopter gains altitude (correct)
- The helicopter loses altitude
- The helicopter maintains a constant altitude
- The helicopter experiences no change in altitude
What are the main aerodynamic forces acting on a helicopter in powered flight?
What are the main aerodynamic forces acting on a helicopter in powered flight?
- Lift and thrust (correct)
- Lift and drag
- Thrust and weight
- Drag and weight
Which direction does the helicopter fuselage turn when the engine turns the main rotor system counterclockwise?
Which direction does the helicopter fuselage turn when the engine turns the main rotor system counterclockwise?
What is the purpose of an antitorque rotor or tail rotor in most helicopter designs?
What is the purpose of an antitorque rotor or tail rotor in most helicopter designs?
What is translating tendency in hovering flight?
What is translating tendency in hovering flight?
What causes rotor blade coning in a helicopter?
What causes rotor blade coning in a helicopter?
Which part of the blade is known as the driven region?
Which part of the blade is known as the driven region?
What is the size of the driven region dependent on?
What is the size of the driven region dependent on?
Where does the driving region of the blade normally lie?
Where does the driving region of the blade normally lie?
During aerodynamic flapping of the rotor blades, the advancing blade achieves maximum upflapping displacement over the nose and maximum downflapping displacement over the tail. This causes the tip-path plane to tilt to the rear and is referred to as
During aerodynamic flapping of the rotor blades, the advancing blade achieves maximum upflapping displacement over the nose and maximum downflapping displacement over the tail. This causes the tip-path plane to tilt to the rear and is referred to as
In sideward flight, the tip-path plane is tilted in the direction that flight is desired. This tilts the total lift-thrust vector
In sideward flight, the tip-path plane is tilted in the direction that flight is desired. This tilts the total lift-thrust vector
In rearward flight, the tip-path plane is tilted
In rearward flight, the tip-path plane is tilted
During autorotation, the main rotor system is being turned by
During autorotation, the main rotor system is being turned by
Which of the following is true about the movement of the cyclic pitch control in a rotor system using three or more blades?
Which of the following is true about the movement of the cyclic pitch control in a rotor system using three or more blades?
What happens when the angle of attack of the rotor blades is increased while their velocity remains constant?
What happens when the angle of attack of the rotor blades is increased while their velocity remains constant?
What happens if lift and thrust are greater than weight and drag in a no wind condition?
What happens if lift and thrust are greater than weight and drag in a no wind condition?
What happens to the rotor system efficiency as the helicopter accelerates in forward flight?
What happens to the rotor system efficiency as the helicopter accelerates in forward flight?
What is the phenomenon known as ground effect?
What is the phenomenon known as ground effect?
What is gyroscopic precession?
What is gyroscopic precession?
How does gyroscopic precession affect the movement of the tip-path plane in a two-bladed rotor system?
How does gyroscopic precession affect the movement of the tip-path plane in a two-bladed rotor system?
Why are two-bladed rotor systems normally subject to Coriolis Effect to a much lesser degree than articulated rotor systems?
Why are two-bladed rotor systems normally subject to Coriolis Effect to a much lesser degree than articulated rotor systems?
Which one of these best describes the transverse flow effect?
Which one of these best describes the transverse flow effect?
Which one of these best describes dissymmetry of lift?
Which one of these best describes dissymmetry of lift?
Which one of these best describes the purpose of blade flapping in a rotor system?
Which one of these best describes the purpose of blade flapping in a rotor system?
Which one of these best describes retreating blade stall?
Which one of these best describes retreating blade stall?
The driven region of the rotor blade produces lift and drag simultaneously.
The driven region of the rotor blade produces lift and drag simultaneously.
The size of the driven region is solely dependent on the rate of descent.
The size of the driven region is solely dependent on the rate of descent.
There are two points of equilibrium on the rotor blade where total aerodynamic force is aligned with the axis of rotation.
There are two points of equilibrium on the rotor blade where total aerodynamic force is aligned with the axis of rotation.
The driven region, also called the ______ region, is nearest the blade tips.
The driven region, also called the ______ region, is nearest the blade tips.
The overall result is a ______ in the rotation of the blade.
The overall result is a ______ in the rotation of the blade.
There are two points of equilibrium on the blade—one between the driven region and the driving region, and one between the driving region and the ______ region.
There are two points of equilibrium on the blade—one between the driven region and the driving region, and one between the driving region and the ______ region.
The driving region, or ______ region, normally lies between 25 to 70 percent of the blade radius.
The driving region, or ______ region, normally lies between 25 to 70 percent of the blade radius.
The size of the driven region varies with the blade pitch, rate of descent, and rotor ______.
The size of the driven region varies with the blade pitch, rate of descent, and rotor ______.
Study Notes
Hovering Flight
- If the amount of thrust is greater than the actual weight during hovering flight, the helicopter will climb.
- Translating tendency in hovering flight refers to the sideways movement of the helicopter's center of gravity.
Aerodynamic Forces
- The main aerodynamic forces acting on a helicopter in powered flight are lift, weight, thrust, and drag.
Rotor System
- The direction of rotation of the main rotor system determines the direction of the helicopter's fuselage turn; counterclockwise rotation means the fuselage turns to the right.
- The antitorque rotor or tail rotor counteracts the torque created by the main rotor, preventing the helicopter from spinning.
- The driven region of the rotor blade produces lift and drag simultaneously, and its size is dependent on the blade pitch, rate of descent, and rotor RPM.
Rotor Blade Movement
- Rotor blade coning occurs due to the change in angle of attack and velocity of air particles along the blade span.
- The driven region of the blade is near the tip, while the driving region normally lies between 25 to 70 percent of the blade radius.
- During aerodynamic flapping, the advancing blade achieves maximum upflapping displacement over the nose and maximum downflapping displacement over the tail, tilting the tip-path plane.
Tip-Path Plane Tilt
- In sideward flight, the tip-path plane is tilted in the direction of desired flight, tilting the total lift-thrust vector.
- In rearward flight, the tip-path plane is tilted forward.
- During autorotation, the main rotor system is turned by the upward flow of air through the rotor disk.
Rotor Control
- The cyclic pitch control moves in the same direction as the rotor disk rotation in a three or more bladed rotor system.
- Increasing the angle of attack while maintaining velocity increases lift and drag.
Helicopter Performance
- If lift and thrust are greater than weight and drag in a no-wind condition, the helicopter will climb.
- Rotor system efficiency decreases as the helicopter accelerates in forward flight.
- Ground effect is the phenomenon where the rotor system efficiency increases due to the proximity of the ground.
- Gyroscopic precession causes the tip-path plane to tilt, affecting the movement of the rotor system.
Rotor System Design
- Two-bladed rotor systems are less affected by the Coriolis Effect than articulated rotor systems.
- The transverse flow effect refers to the uneven airflow around the rotor blades due to the angle of attack.
- Dissymmetry of lift occurs when the advancing blade produces more lift than the retreating blade.
- Blade flapping helps to equalize lift across the rotor disk.
- Retreating blade stall occurs when the retreating blade reaches a critical angle of attack.
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Description
Test your knowledge on aerodynamic flapping of rotor blades and the concept of blowback. Learn about the displacement of the advancing and retreating blades and how it affects the tilt of the tip-path plane.
