Basic Helicopter & Propeller Design PDF

BASIC HELICOPTER & PROPELLER DESIGN...

BASIC HELICOPTER & PROPELLER DESIGN MAJOR COMPONENTs and rotor system Prepared By Engr. Shiara Denise M. Valencia The rotors are rotating airfoils that provide lift similar to the way wings provide lift on a fixed-wing aircraft Air flows faster over the curved upper surface of the rotors, causing a negative pressure and thus, lifting the aircraft Major components Helicopters come in a variety of sizes and shapes, but most share the same major components. Major Components 1 AIRFRAME A helicopter can be made of: Tubular and sheet metal metal substructures are usually made of: wood composite materials combination of metal and aluminum wood composite materials stainless steel many layers of fiber- titanium impregnated resins Airframe design encompasses engineering, aerodynamics, materials technology, and manufacturing methods to achieve favorable balances of performance, reliability, and cost. AIRFRAME 2 FUSELAGE The fuselage, the outer core of the airframe, is an aircraft’s main body section that houses the cabin that holds the crew, passengers, and cargo. The fuselage also houses the engine, the transmission, avionics, flight controls, and the powerplant. FUSELAGE Helicopter fuselages and tail booms are often truss-type or semi monocoque structures of stress-skin design Steel and aluminum tubing Formed aluminum Aluminum skin Advanced composites Helicopter fuselages vary widely from those with a truss frame, two seats, no doors, and a monocoque shell flight compartment to those with fully enclosed airplane-style cabins as found on larger twin-engine helicopters. The multidirectional nature of helicopter flight makes wide-range visibility from the cockpit essential. 3 MAIN ROTOR SYSTEM The rotor system is the rotating part of a helicopter which generates lift. The rotor consists of a mast, hub, and rotor blades. MAIN ROTOR SYSTEM Mast is a hollow cylindrical metal shaft which extends upwards from and is driven and sometimes supported by the transmission. At the top of the mast is the attachment point for the rotor blades called the hub. The rotor blades are then attached to the hub by several different methods MAIN ROTOR SYSTEM Main rotor systems are classified according to how the main rotor blades are attached and move relative to the main rotor hub. rigid semirigid fully articulated 4 TAIL ROTOR Aka ANTI-TORQUE SYSTEM Pilots vary the thrust of the antitorque system to maintain directional control whenever the main rotor torque changes, or to make heading changes while hovering. Most helicopters drive the tail rotor shaft from the transmission to ensure tail rotor rotation (and hence control) in the event that the engine quits. TAIL ROTOR Fenestron Another form of antitorque system is the Fenestron or “fan-in-tail” design. This system uses a series of rotating blades shrouded within a vertical tail. Because the blades are located within a circular duct, they are less likely to come into contact with people or objects. TAIL ROTOR notar antitorque system provides safe, quiet, responsive, foreign object damage (FOD) resistant directional control. The enclosed variable-pitch composite blade fan produces a low pressure, high volume of ambient air to pressurize the composite tailboom TAIL ROTOR notar antitorque system provides safe, quiet, responsive, foreign object damage (FOD) resistant directional control. The air is expelled through two slots which run the length of the tailboom on the right side, causing a boundary-layer control called the Coanda effect. TAIL ROTOR 5 ENGINE / POWERPLANT Most commonly used engines: – reciprocating engine (piston engine) Generally used in small helicopters Simple and inexpensive to operate – turbine engine Turbine engines are more powerful and are used in a wide variety of helicopters They produce a tremendous amount of power for their size but are generally more expensive to operate ENGINE Turbine engines In most applications, the exhaust outlets simply release expended gases and do not contribute to the forward motion of the helicopter. Because the airflow is not a straight-line pass through as in jet engines and is not used for propulsion, the cooling effect of the air is limited. The gas turbine engine mounted on most helicopters is made up of a compressor, combustion chamber, turbine, and accessory gearbox assembly. ENGINE Turbine engines ENGINE Turbine engines 1. The compressor draws filtered air into the plenum chamber and compresses it 2. The compressed air is directed to the combustion section through discharge tubes where atomized fuel is injected into it. The fuel/air mixture is ignited and allowed to expand. 3. This combustion gas is then forced through a series of turbine wheels causing them to turn. These turbine wheels provide power to both the engine compressor and the accessory gearbox. 4. Power is provided to the main rotor and tail rotor systems through the freewheeling unit which is attached to the accessory gearbox power output gear shaft. 5. The combustion gas is finally expelled through an exhaust outlet. ENGINE Turbine engines On most turbine assemblies used in helicopters, the first stage and second stage turbines are not mechanically connected to each other. Rather, they are mounted on independent shafts, one inside the other, and can turn freely with respect to each other. This is referred to as a “free turbine.” When a free turbine engine is running, The combustion gases pass through the first stage turbine to drive the compressor and other components, and then past the independent second stage turbine. which turns the power and accessory gearbox to drive the output shaft, as well as other miscellaneous components. 6 TRANSMISSION The transmission system transfers power from the engine to the main rotor, tail rotor, and other accessories during normal flight conditions. main components of the transmission system are the main rotor transmission, tail rotor drive system, clutch, and freewheeling unit. TRANSMISSION TRANSMISSION 7 LANDING GEAR A helicopter’s landing gear can be simply a set of tubular metal skids. Many helicopters do have landing gear with wheels, some retractable.