HOWHELICOPTERSFLY CESAR VANDEVELDE ··· 3IO ··· TECHNOLOGICAL DESIGN ENGINEERING
Da Vinci 1480: Leonardo Da Vinci sketches his flying machine. This is the first time an aerial screw is used for flying. His machine is considered to be the first helicopter. Cornu 1907: Paul Cornu builds the first working helicopter. It could hover 30cm above the ground for 20s, and was the first truly free flight with a pilot. Gyroplanelaboratoire 1933: The gyroplane laboratoire was the first practical helicopter. This helicopter set new records for height (158m), distance (circle with 500m diameter), and duration (1h 2m 10s). Civilianuse 1940s: The first widespread usage of helicopters for civilian purposes. in 1947, a helicopter is used to deliver air mail for the first time. Turboshaft 1951: The turboshaft engine is invented. The turbine engine is lighter and can provide more power than piston engines. Turboshaft helicopters are bigger, faster, and can lift more.
PRINCIPLE OF AN AIRFOIL Bernoulli’s principle: ½ ρ·v² + ρ·g·z + p = constant v = speed p = pressure The shape of the airfoil makes air travel faster above it than below RESULT: High speed = Low pressure The airfoil is lifted up above the airfoil: v↗ p↘ below the airfoil: v↘ p↗
ROTORS & ANTI-TORQUE
Helicopters use rotors (spinning airfoils) to overcome gravity.
Newton’s laws dictate that every action has an equal and opposite reaction.
Because the rotor rotates in one direction, the rest of the helicopter has a tendency to spin in the opposite direction. This is the called the anti-torque effect.
Tail rotor: A second, vertically mounted tail rotor is added. It pushes the tail of the helicopter in the opposite direction, countering the anti-torque effect.
Dual rotors: The helicopter uses 2 main rotors, spinning in opposite directions. Because of this, the anti-torque effect of both rotors negate each other.
Coaxial rotors: 2 rotors on the same shaft spin in opposite direction.
NOTAR: Air is blown through slots on the side of the tail boom. Because of the Coanda effect, the air from the main rotor sticks to it, and amplifies the air flow.
STEERING A HELICOPTER
To steer a helicopter, the way the main rotor generates lift needs to be changed.
Certain areas of the rotor disk need to generate more lift than others.
The lift generated by an airfoil is changed by changing the angle of attack.
The angle of attack needs to be changed relative to the position of the blade.
This is done using a swashplatemechanism
The following slides will explain the swashplate mechanism of a Robinson R44 helicopter
Rotor systems are categorized by how many ways a blade can move independently from the rest of the rotor.
This helicopter has a semi-rigid rotor system.
Other rotor systems include fully articulated rotors and rigid rotors.
Connects the rotor to the transmission, which is connected to the engine.
Spins at 550 RPM
Needs to spin at a constant, predefined speed to maintain optimal performance.
Can slide up and down the shaft.
Allows the swashplates to tilt.
Supports the rotating swashplate
Position and tilt rotation of this component determines how much lift is generated, and in which direction.
Connects the lower swashplate to the helicopter fuselage.
Prevents it from rotating with the main rotor.
Allows the lower swashplate to move up and down, and tilt.
Is connected using a ball joint.
Controls the position and tilt of the lower swashplate.
Is controlled by the pilot using hydraulics.
A backup mechanical connection to the pilot controls exist, in case of hydraulics failure.
Rests on top of the lower swashplate
Is connected using 2 angular contact ball bearings
Is responsible for changing the blade angle of attack
Connects the upper swashplate to the shaft.
Makes sure the upper swashplate rotates with the main rotor.
Is connected with a ball joint.
Allows both blades to make a seesaw movement.
When one blade goes up, the other goes down.
The teetering hinge reduces stress on the blades caused by the Coriolis-effect.
Allows the blades to move up and down independently.
Rotorblade is connected using a plain bearing made from PTFE (Teflon)
The combination of centrifugal force and lift cause the blades to cone, the blades move upward depending on their lift, which in turn depends on their position.
Allows the blades to rotate along their length (= feathering)
Rods connect the pitchhorn to the upper swashplate, the position and rotation of the swashplate assembly controls amount and direction of the lift.
Rotor blade is connected to the rest of the rotor using 6 angular contact ball bearings.
Anti-torque pedals: Control the tail rotor. By changing the angle of attack of the tail rotor, the helicopter can turn left or right.
Throttle:Rotorblades are designed for a specific RPM. The throttle allows the pilot to increase or decrease the engine’s power output, so he can keep the rotor speed constant.
Cyclic control: Controlled by a joystick in the middle. Tilts the swashplate assembly, which changes the rotor blades’ pitch cyclically, and thus moves the helicopter in that direction
Collectivecontrol: Moves the swashplateassembly up and down, thusincreasingordecreasing the total lift.