How do Helicopters Takeoff Vertically and Remain Stationary in Air
How do helicopters takeoff vertically? The helicopter needs to produce forces which are equal and opposite in order to fly. These are induced by air flowing over the wings, and must counteract the force of gravity or weight.
Helicopters generate these forces by tilting their rotor blades in flight. This is achieved by altering the angle of attack on each rotor blade using cyclic control.
How do helicopters takeoff vertically?
Helicopters take off vertically by using their rotor system to create thrust, like a propeller. This is augmented by a fixed wing which provides lift. This combination allows helicopters to fly horizontally as well as vertically. This is known as VTOL (vertical takeoff and landing).
As the helicopter moves forward during this transition it can only accelerate to a point determined by its rotor disc design and airspeed, if it has been trimmed properly. The pilot will first bring the aircraft to a hover, look ahead, then move the cyclic forward. As the helicopter moves forward it falls off a cushion of air which it has been creating during its hover, hence this effect is called ‘inflow roll’. As the helicopter speeds up it will also start to tilt forward and down due to dissymmetry in the lift, although the precise cause of this is a bit more complex than that.
How exactly do helicopters takeoff vertically? If the helicopter is departing from a helipad where there are no tall obstacles which are higher than it, then the pilot will normally follow a vertical takeoff profile and climb to a height of 70ft before accelerating away. This may seem quite straightforward, but there are many aerodynamic issues which can arise during this flight which require a high degree of concentration and coordination by the pilot.
How do helicopters float?
Helicopters fly and remain stationary in air by balancing all the forces acting on it. Since helicopters don’t have any horizontal thrust or drag, the only force they need to maintain altitude is vertical lift generated by the rotor blades. The faster the rotor rotates, the more lift it generates, but as the speed increases the rate of turn decreases because more and more of the lifting force acts horizontally rather than vertically.
During a stable hover the rotor accelerates the air downwards. This causes a different flow rate over the entire length of each rotor blade. The advancing blade reaches its highest point at the front while the retreating blade reaches its lowest point at the back. The asymmetrical flow rate results in dissymmetry of the total rotor thrust which can be corrected by means of cyclic input.
If the helicopter is close to ground a phenomenon called “ground effect” takes place. The airflow over the rotor disc is restricted by surface friction and this reduces the generation of blade tip vortices. This makes it possible to use a lower rotor blade angle for the same amount of lift, reducing induced drag and making the helicopter more efficient. Ground effect is influenced by the surface properties of the ground and varies from country to country.
Components of a helicopter engine
A helicopter engine consists of various parts that together produce thrust to lift the aircraft off the ground and in forward flight. The most important component is the main rotor which consists of two to eight blades connected in the center at a hub. This hub provides the means for feathering the rotor, which controls the helicopter.
The rotor is a giant rotating propellor that generates lift by air flowing over the blades, redirecting it in the same way wings do on planes. Air can flow over the rotor blades faster than on wings, which gives them a large amount of lift. The main rotor is connected to the fuselage through a hub, and can be made to tilt by moving the control stick in the cockpit. This is known as cyclic control. Moving the stick upwards makes the rotor spin faster, and downwards slows it.
The rotor is also controlled by changing the angle of attack of the blades. Each rotor blade has an airfoil shape similar to that of an airplane wing, and the angle at which the rotor spins through the air is determined by the pitch angle of the blade. The rotor blades can be raised and lowered by changing this angle, and the movement of the lever on the cüollective control corresponds to the directional movement of the helicopter; raising the lever raises the helicopter while lowering it causes it to sink.
Mechanism of flying a helicopter
Helicopters use their turning rotor blades to create lift (similar to a wing) and accelerate the airflow downwards. By increasing the angle of attack of all rotor blades simultaneously (also called collective pitch) more lift is created and the helicopter starts to ascend vertically. To descend again the rotor blades have to decrease their angle of attack. This is done using the collective control lever on the pilot’s left side.
With fixed rotors the helicopter is limited to a certain maximum forward speed, because at higher speeds large parts of the advancing and retreating rotor blade are in supersonic airflow and therefore stall. The solution is dual counter-rotating blades which prevent this by having two advancing and retreating blades with balanced forces.
To maintain a constant amount of lift over the entire rotor disc a flapping occurs: As the helicopter gets faster the advancing blade receives less induced flow (part of the airflow directed downwards through the rotor as it turns). The resulting dissymmetry of lift causes the advancing blade to flap up, while the retreating blade flaps down. The flapping continues until a state of equilibrium is reached with the advancing and retreating blades producing an equal amount of lift. This is called translational lift.
