The spar consists of filament-wound or pultruded carbon tow running spanwise. It therefor has very high resistance to bending in the out-of-plane and the inplane directions, but it has low resistance to twisting about the feathering axis. A braided sleeve with diagonal bi-directional (45º/-45º) tapes or threads is bonded over the pultruded spar. These diagonal tapes are capable of reducing their length when subjected to an electrical stimulus. By applying current to the clockwise and/or the counterclockwise wound tapes, the twist of the blade can be actively changed during flight. An alternatively to the braided sleeve is to one or more pairs of layers with unidirectional tows. One layer would have a 45º bias and the next layer would have a -45º bias. To enhance torsional rigidity about the feathering axis, electrical power might be constantly applied to the 45º bias and to the -45º bias windings. Electrical changes to the two and between the two would determine the amount of twist and the torsional rigidity. The numerous advantages of applying active blade twist (ABT) to a helicopter's rotor can be seen at OTHER: Rotor Concept - Active Blade Twist (ABT) ~ Advantages The range of pitch amplitude and frequency can be seen at OTHER: Rotor Concept - Active Blade Twist (ABT) ~ Range. This page is an electromechanical alternative to the mechanical and aerodynamic ones on OTHER: Rotor Concept - Independent Root & Tip (IRAT)

An additional advantage will be the ability to actively vary the blade pitch; by element as well as by azimuth at rates considerably higher than 1/rev. This should significantly reduce vibration and noise, while it is improving lift/drag ratio.

The pultruded portion of the spar could be manufactured with a mean twist. [For information on the spar construction, see UniCopter_Blade_NACA00xx.html ]. The clockwise braids of the sleeve will actively twist the spar in one direction and the counterclockwise braids will actively twist the spar in the opposite direction. Smaller Rotorhub: If all or some of the mechanical flight-control components are removed from the rotorhub then this hub might be smaller. This should represent less parasitic drag and less downwash from the blades of the other rotor. In addition, the final right angle gearing located under the rotorhub could be reduced to 1:1, which will result in an additional reduction of parasitic drag. This could be an even bigger advantage for the interleaved configuration then for the intermeshing configuration. Triple Redundancy: The threads in a braid could be assigned to three groups. Each group would have separate electrical controls. Therefor a failure will only effect one third of the threads. The remaining two thirds may be able to have their forces increased to temporarily overcome this loss of partial pitch control. Segmenting the Twist: (more than just Independent Root and Tip) If the braided wires, which run the length of the blade, were to be segmented into smaller lengths and these segments (elements) were to be independently powered then the twist and therefor the pitch of the blade could be varied by blade radius, as well as by blade azimuth.

Electro- and Magneto-rheological Fluids: Forget

Shape-Memory Alloy: Forget.

Piezoelectric: Tutorial Transducer: A substance or device, such as a piezoelectric crystal, microphone, or photoelectric cell, that converts input energy of one form into output energy of another. Electrolyte - a nonmetallic conductor of electricity usually consisting of a liquid or paste in which the flow of electricity is by ions. A substance which forms ions in an aqueous (water) solution. Magnetostrictive: Deformation of a ferromagnetic material subjected to a magnetic field. Magnetostriction is a property of ferromagnetic materials to undergo a change of their physical dimensions when subjected to a magnetic field. This effect was first identified in 1842 by James Joule when observing a sample of nickel. This property, which allow magnetostrictive materials to convert magnetic energy into kinetic energy and conversely, is used for the building of both actuation and sensing devices. It is often quantified by the magnetostrictive coefficient, L, which is the fractional change in length as the magnetization of the material increases from zero to the saturation value. The effect is responsible for the familliar 120Hz "electric hum" which can be heard near transformers and high power electrical devices. The reciprocal effect, the change of the susceptibility of a material when subjected to a mechanical stress, is called the Villari effect. Two other effects are related to magnetostriction: the Matteucci effect is the creation of a helical magnetic field by a magnetostrictive material when subjected to a torque and the Wiedemann effect is the twisting of these materials when an helical magnetic filed is applied to them. Ferromagnetic: Refers to a material, such as iron and nickel, that can be easily magnetized.

Helicoidal bimorph piezoelectric actuator: http://www.google.com/search?q=ha_kwangtae_200512_phd.pdf&sourceid=ie7&rls=com.microsoft:en-US&ie=utf8&oe=utf8 See Chapter 3. I have file on E-drive under the name ha_kwangtae_200512_phd.pdf