In order for rotorcraft to accomplish this, they must be engineered with durability and maneuverability in mind. A rotorcraft’s fuselage or structure must be strong and light weight while its flight controls agile and reliable. The type of rotor system designed is very important as well. There are two types commonly found on rotary-wing aircraft today. They are a fully articulated or semi-rigid under slung see saw type rotor system. Both have their own advantages and dis-advantages over the other. The fully articulated rotor system is complex by design, it has excellent control authority in the pitch and roll axis.
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It also typically has more than two rotor blades which reduces sound signature and increases control authority in the pitch and roll axis controlled by the cyclic due to its solidity ratio. The semi-rigid rotor system is a much simpler design thus, it cost significantly less to maintain but control authority in the pitch and roll axis is sluggish compared to the fully articulated rotor system due to its lower solidity ratio. Rotorcraft structures normally consist of three sections; the forward, intermediate, and tail boom sections.
Each of these sections is composed of different materials used to strengthen the frame, eliminate excessive weight, and create flexibility in the structure where required. The forward section of a rotorcraft consist of the nose, cockpit, and cabin areas of the aircraft, most designs are composed of a honey comb sandwich panel semi-monocoque design. “Semi-monocoque fuselage design may use any combination of longerons, stringers, bulkheads, and frames to reinforce the skin and maintain the cross-sectional shape of the fuselage. ” (http://aviationglossary. com/monocoque-fuselage-design/) The intermediate ection houses the avionics compartment, electrical shelf, and turbine engine compartment when it is a single engine type design. This section utilizes both semi-monocoque and monocoque design elements. The last section of the structure is the tail boom section. It begins just aft of the intermediate section at the tail boom attachment point and runs the length of the tail boom where it ends at the tail rotor. It is a fully monocoque design. “Monocoque fuselage design relies on the strength of the skin (also known as the shell or covering) to carry the various loads.
True monocoque construction does not use formers, frame assemblies, or bulkheads to give shape to the fuselage. ” http://aviationglossary. com/monocoque-fuselage-design/) The flight control system on most rotary-winged aircraft consist of the cyclic, collective, ant-torque pedals, hydraulic servo actuators, mechanical linkage and mixing units, swash plates (rotating and non-rotating), pitch pull tubes or PC links. These components are connected to the rotor system which controls the aerodynamic change in pitch to the rotor system allowing an aircraft to maneuver about the pitch, roll, and yaw axis. The cyclic pitch control system provides the means of controlling the forward, aft, and lateral movements of the helicopter. Movement of the pilot’s or co-pilot’s cyclic stick transmits through control rods and bell cranks. This movement is sent to the auxiliary servo cylinders, the mixing unit, and three primary servo cylinders. These primary servo cylinders control movement of the rotary-wing blades. ” (http://www. tpub. com/air/10-4. htm) The cyclic controls aerodynamic change in the pitch and roll axis. “The collective pitch control system provides vertical control of the helicopter.
Movement of the collective pitch control stick is sent through control rods and bell cranks to the appropriate auxiliary servo cylinder. Movement is sent from the servo cylinder to the mixing unit. At the mixing unit, all vertical movements of the collective sticks are sent to the primary servo cylinders and the rotary-wing swash plate. At this point, the pitch of all blades increases or decreases equally and simultaneously. ” (http://www. tpub. com/air/10-4. htm) When the collective lever is increased, it corresponds to an increase in the angle of attack of the blades which increase lift causing the helicopter to rise vertically.
It is the opposite aerodynamic reaction when the collective lever is decreased. While in a hover, an increase in torque to raise the aircraft vertically also requires an increase in tail rotor thrust to counteract the torque effect of the main rotor. This is a great example of Newton’s third law of action and reaction. “The rotary rudder control system controls the pitch of the rotary rudder blades. The blades control the heading of the helicopter. The pedals control the system through a series of control rods and bell cranks.
These units connect to the directional bank of the auxiliary servo cylinder and the mixing unit. ” (http://www. tpub. com/air/10-4. htm) Pitch changes to the tail rotor blades occur about the vertical axis resulting in a yawing moment of the aircraft. In summary, rotary-wing aircraft possess unique capabilities enabling them to support diverse operations throughout the aviation spectrum. Engineers design their structures to be strong and light weight by using composite materials. A rotorcraft’s rotor system can be either fully articulated or semi-rigid and there are advantages and dis-advantages with both.
Flight controls are comprised of mechanical linkage, hydraulic servos, bell cranks and mixing units which are controlled by the cyclic, collective, and anti-torque pedals located in the cockpit. When the pilot manipulates these controls it corresponds to aerodynamic change in the rotor system allowing a rotary-winged aircraft to change direction. References Accessed on 03 February 2012 from http://aviationglossary. com/monocoque-fuselage-design/ Accessed on 03 February 2012 from http://www. tpub. com/air/10-4. htm