Helicopter Rotor Dynamics Simulation

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Flapping to Equality

During the movement of a helicopter rotating blade , the speed of airflow over the advancing blade is more than the retreating blade , resulting in the production of an unequal amount of lift . This is called a dissymmetry of lift . To correct this aerodynamic imbalance , the blades are allowed to perform a series of controlled movements to produce equal amounts of lift . This process of equalization is called flapping to equality . Nil wind hover, no flapping, AOA is constant, the lift is equal on all sides Advancing Blade, Flapping up, AOA is reduced, the lift is reduced Retreating Blade, Flapping down, AOA is increased, the lift is increased The following project demonstrates the flapping to equality of helicopters. The project is interactive and the user can increase or decrease the velocity of the helicopter. The following link will redirect

In the aerodynamics of rotorcraft like helicopters , phase lag refers to the angular difference between the point at which a control input to a rotor blade occurs and the point of maximum displacement of the blade in response to that control input , said displacement occurring in the direction of rotor rotation. ' Phase lag' differs from ' advance angle' in the latter referring to the mechanically fixed angle between the pitch link attachments at the blade and the swashplate. Phase lag may vary depending on rotor tilt rate, the ratio of aerodynamic damping to blade inertial forces (Lock number), offset of flapping hinge from the axis of rotation (e/R ratio), and coupling of blade flap, drag, and feather motions, and often results in cross-coupling between the aircraft control axes; advance angle is fixed and cannot vary. Consequent to phase-lag, rolling a rotorcraft to the left or right would theoretically require a forward or backward cyclic i

Coning angle is the angle formed between the plane of rotation of a helicopter rotor blade when it is producing lift and a line perpendicular to the rotor shaft. Also, Coning Angle is formed by the rotor blades with the tip path of the plane. ( Tip Path Plane is the imaginary circular plane outlined by the rotor blade tips in making a cycle of rotation) Coning happens primarily because of the variation of rotor thrust from root to tip. The degree of the coning angle is determined by the relationship between the centrifugal force acting on the blades and the aerodynamic lift produced by the blades. From the figure, as the blade is rotating, there is a centrifugal force, which is throwing the blades outside. The force between upward and the centrifugal force when balanced results in one particular cone angle, which is called coning angle. An increase in helicopter weight results in an increase in coning angle. There are upper limits and lower limits of coning angle. The upper limi

Hover Condition with Wind During hovering flight, a helicopter maintains a constant position over a selected point, usually a few feet above the ground. For a helicopter to hover, the lift and thrust produced by the rotor system act straight up and must equal the weight and drag, which act straight down. If there is a wind in a specific direction, the rotor blades must be tilted to the opposite direction to counter the wind movement. Cyclic to be adjusted accordingly. The phenomenon is as simple as this. The following project demonstrates the hover condition of helicopters with variable wind speeds. The project is interactive and the user can change the direction and speed of the wind. The following link will redirect you to the project page. (For the mobile version, please go to the bottom of the page) Hover Condition on Scratch Press the Left or Right arrow keys to change the wind speed. Minus means the opposite direction. This project demonstrates how the lift and weight react to c

During hovering flight, a helicopter maintains a constant position over a selected point, usually a few feet above the ground. For a helicopter to hover, the lift and thrust produced by the rotor system act straight up and must equal the weight and drag, which act straight down. If there is a wind in a specific direction, the rotor blades must be tilted to the opposite direction to counter the wind movement. Cyclic to be adjusted accordingly. The phenomenon is as simple as this. But if the CG is shifted to say forward, the cyclic must be adjusted to tilt the aircraft back and vice versa. The following project demonstrates the hover condition of helicopters with variable CG. The project is interactive and the user can change the position of CG as well as change the direction and speed of the wind. The following link will redirect you to the project page. (For the mobile version, please go to the bottom of the page) Hover Condition Variable CG on Scratch Press the Left or Right arrow key

The rotor blades in a fully articulate blade system are attached to the rotor hub through a series of hinges so that it can move in three ways and each blade can move independently of the other. The blades can move up and down, back and forth in the horizontal plane, and can change in the pitch angle (the tilt of the blade). The hinges present in the articulate blade system are: Flapping Hinge/Horizontal hinge Lead-lag hinge/Drag hinge/Vertical hinge Feathering Hinge/Pitch change hinge Flapping hinges The flapping hinges are horizontal hinges of a helicopter rotor that allow the blades to move up and down. This up and down motion of blades is called flapping. The flapping motion created by flapping hinges can compensate for the dissymmetry of lift. For this purpose, the flapping hinges may be located at varying distances from the rotor hub. When a blade is on the advancing side, its increased lift causes the blade to flap upwards, which effectively reduces its incidence. The

Ground effect is the positive influence on the lifting characteristics of the horizontal surfaces of an aircraft wing when it is close to the ground. This effect is a consequence of the distortion of the airflow below such surfaces attributable to the proximity of the ground. IGE (In-Ground Effect) IGE conditions are usually found within heights about 0'5 to 1 times the diameter of the main rotor. So if a helicopter has a rotor diameter of 48 ft, the IGE region will be about 24-48ft above the ground. The height will vary depending on the type of helicopter, the slope and nature of the ground, and any prevailing winds. The air impacting the ground creates a small build-up of air pressure in the region below the rotor disc. It seems as if the helicopter is floating upon a cushion of air. The stagnated air will form a high-pressure zone just underneath the fuselage body of helicopters. There is basically no more motion inside this. Which will cause the air to not enter into it. Hence,

Imagine the airflow which was directed to the ground to create the air cushion in a ground effect is now rebounding off the ground going back up into the top of the rotor system. When it passes back through the rotor again it gets accelerated. This process may continue with the air velocity increasing each time as it passes through the rotor. Eventually, the velocity is so great that the air going into the rotor from above causes a loss of lift and the helicopter will sink toward the ground unless the pilot increases power. This means that i f recirculation is occurring, the helicopter will need mone power to hold a constant height. Recirculation will not always happen but will be aggravated by the type of ground or nearby obstacles causing the air which is trying to escape out to the sides of the helicopter to be directed back up toward the rotor system. The result is 'recirculation' of downwash air. The following Scratch Project explains the whole process of recirculation i

Autorotation is a condition of helicopter flight during which the lifting rotor of a helicopter is being turned by the force of the relative wind with no power from the engine. It is a maneuver where the engine is disengaged from the main rotor system and the rotor blades are driven solely by the upward flow of air through the rotor. The most common reason to perform an autorotation is engine failure. But autorotation is also performed during complete tail rotor failure as it produces virtually no torque, and a safe landing is possible. At the instant of engine failure or tail rotor failure, the main rotor blades are producing lift and thrust from their AOA and velocity. By immediately lowering the collective pitch, the lift and drag of the helicopter are lowered and the helicopter begins to descend producing an upward flow of air through the rotor system immediately. This upward flow provides sufficient thrust to maintain rotor rpm throughout the descent. Airspeed and rotor rpm

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Helicopter Rotor Dynamics Simulation

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Featured

Introduction

Flapping to Equality

Helicopter Phase Lag

Coning Angle

Hover Condition

Hover Condition Variable CG

Helicopter Hinges

Ground Effect

Recirculation

Autorotation