What Is the Basic Structure of a Helicopter?
Helicopters are designed with unique flight characteristics that provide them with the efficiency and speed they currently possess. Considered rotary-wing aircraft, helicopters are equipped with rotors, or rotating airfoils, that produce lift in a similar way wings provide lift on fixed-wing aircraft. Regarding helicopters, the air flows at a faster rate over the curved, upper surface of the rotors, creating a negative pressure that lifts the aircraft.
By changing the angle of attack, the rotating blades increase or decrease lift which either raises or lowers the helicopter. Meanwhile, tilting the rotor’s plane of rotation allows the aircraft to move horizontally. To better understand the technicalities behind such maneuverability, this blog will outline a helicopter’s airframe structure by covering its major components.
Airframe
The fundamental structure within any aircraft is the airframe, and it is usually composed of metal, wood, or a combination of the two. Composite components are also used, those of which consist of many layers of fiber-impregnated resins that are bonded to create a smooth panel. Tubular and sheet metal are also suitable materials for substructures, with aluminum, stainless steel or titanium serving as the most commonly used for areas subject to higher stress and heat.
Fuselage
Similar to fixed-wing aircraft, helicopter fuselages and tail booms make use of truss-type or semimonocoque structures of stress-skin designs. For such assemblies, steel and aluminum tubing, formed aluminum, and aluminum skin are popularly used. Today, helicopters are manufactured using advanced composites, while firewalls and engine decks are usually made of stainless steel. The multidirectional nature of helicopters makes visibility from the cockpit paramount. As such, large, formed polycarbonate, glass, or plexiglass windscreens are common.
Landing Gear or Skids
In terms of landing gear, helicopters are usually equipped with a simple set of tubular metal skids. However, some helicopters may have landing gear with wheels that are retractable.
Powerplant and Transmission
The two most common types of engines used in helicopters are turbine engines and reciprocating engines. Turbine engines are recognized for having a tremendous amount of power for their size, but are expensive to operate. In these engines, the exhaust outlets release expended gasses and do not contribute to the forward propulsion of helicopters. Moreover, turbine engines are made up of a compressor, combustion chamber, turbine, and accessory gearbox assembly. Power is provided to the main rotor and tail rotor systems via the freewheeling unit which is affixed to the accessory gearbox power output gear shaft.
The transmission system is responsible for transferring power from the engine to the main rotor, tail rotor, and other apparatuses during normal flight conditions. The transmission system consists of the main rotor transmission, tail rotor drive system, clutch, and freewheeling unit. The freewheeling unit, or autorotative clutch, enables the rotor transmission to drive the tail rotor drive shaft during autorotation. It is important to note that helicopter transmissions are generally lubricated and cooled with their own oil supply, and a sight gauge is featured to check the oil level. Additionally, some transmissions may have chip detectors in the sump that warn the pilot if there is an internal problem.
Main Rotor System
The rotor system is the rotating part of the helicopter that generates lift and consists of a mast, hub, and rotor blades. They are typically classified by how the rotor blades are attached and move relative to the main rotor hub. These classifications include rigid, semirigid, or fully articulated systems.
Controls
Finally, like other aircraft, helicopters have many controls, most of which are operated by the pilot’s left hand. As a part of this collective assortment, you can find an engine throttle control, a cyclic control stick, and foot pedals. The engine throttle control is located on the hand grip and the cyclic control stick is positioned between the pilot’s legs.
Conclusion
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