Helicopter blade control

A.J. Du Plessis, N. Hagood, Modeling and experimental testing of twist actuated single cell composite beams for helicopter blade control. Master s Thesis, Massachusetts Inst, of Tech. (1996)... 

Helicopter blades and shell control surfaces and floor beams (Boeing 767) F-16s horizontal stabilizer, skin, dorsal access panels and leading edge fairing, and vertical tail fin skins and louver fin leading edge and rudder... 

Igor Sikorsky is most often associated with the development of the helicopter and is called the father of the modern helicopter. Sikorsky s VS-300, the first operational helicopter, made its first free flight in 1940. It introduced the practical use of the tail rotor to the helicopter airframe. Its purpose was to counteract the action of torque on the body of the aircraft and keep it from spinning wildly out of control in the opposite direction of the blades overhead. 

Rotary-Wing Aircraft. Helicopters use the same principles, with two exceptions. The engine in the helicopter is usually hooked directly to the propeller or rotor. It is also hooked in sync with the shaft that turns the rear or tail rotor. The tail rotor is necessary for the directional control of the aircraft. When the collective, the control system that governs lift, is pulled up, it sends directions for the rotor blades to change their pitch and take a larger bite out of the air to lift the machine. Without the tail rotor, torque takes effect, and this causes the aircraft body to rotate in the opposite direction of the rotor blades. The pitch (or amount of bite into the air of the blades) of the tail rotor is controlled by the foot pedals. 

Computer Control. The Army s desire to test an all-purpose, multiaxis tape placement machine led to the next step forward, an automatic machine built in 1974 for helicopter rotor blades for the Army Aviation Systems Command (AVSCOM) (19). This was the first 6-axis minicomputer-controlled tape-laying... 

Solid-state actuation signifies the use of the induced-strain effect present in active materials to achieve actuation without any moving parts, i.e., in a solid-state manner. Already, solid-state actuation has found niche application in the aerospace industry. The aero-servo-elastic control of vibrations and flutter with solid-state actuated flaps, tabs, vanes, etc. for helicopter rotor blades and aircraft wings is currently being experimented on. 

Fig. 2.4. MD 900 helicopter hingeless blade displaying the planned trim tab for in-flight tracking and active control flap for noise and vibration reduction [10]...

Roglin, R.L. and Hanagud, S.V. A Helicopter with Adaptive Rotor Blades for Collective Control. Smart Mater. Struct., 5 (1996), pp. 76-88... 

Konstanzer, P. Decentralized Vibration Control for Active Helicopter Rotor Blades. Doctoral thesis Univ. Stuttgart, VDI Fortschrittsberichte, Reihe 8, Nr. 923, VDI-Verlag Diisseldorf/Germany (2001)... 

In order to achieve equal lift on the advancing and retreating side of the rotor in spite of the unsymmetric flow velocity distribution, the common helicopter concept makes use of a varying angle of attack. This is introduced with the necessary cycle duration of one revolution by the swash plate mechanism. The idea is to actively control the blade pitch, and cancel or reduce the appearing vibrations by superposition of an adequate signal. 

P. Konstanzer, Decentralized vibration control for active helicopter rotor blades. Ph.D. Thesis, Universitat Stuttgart, Stuttgart, Germany (2002)... 

Vibration is a major destmctive force in many types of machinery. Vibration can lead to wear and fatigue failure of rigid materials like alloys and plastic components. The helicopter benefits from the unique flexibility and vibration dampening characteristics of elastomeric adhesives. Elastomers are used to transfer torque to the rotor blades while providing flexibility and vibration control. Rubber tires are another example of elastomeric adhesive use. Consumers have enjoyed a steady increase in the useful life expectancy of rubber tires due to improvements in adhesion between the elastomer, tire cords, and the filler. The rubber tire industry has driven a great deal of the fundamental research on elastomeric materials in engineering design. 

For example, one type of smart system is used in helicopters to reduce aerodynamic cockpit noise created by the rotating rotor blades. Piezoelectric sensors inserted into the blades monitor blade stresses and deformations feedback signals from these sensors are fed into a computer-controlled adaptive device that generates noise-canceling antinoise. 

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