innanzitutto vi ringrazio per la partecipazione
quello che inizialmente non avevo capito è che il tracking e quindi la regolazione dei tabs si fa a terra ed inoltre una sola volta, salvo complicazioni. direi che questo è in linea con quanto avevo letto , visto che si parlava di progetti futiri che impiegassero leghe a mamoria di forma per poter effettuare il tracking anche in volo ed in maniera automatica, visto che credo sia improponibile che un pilota si metta ad operare di continuo sui tabs. questo comferma quanto dice Flaggy. inoltre cosa che probabilmente avrei dovuto fare prima vi posto il pezzo di articolo citato:
Smart materials and adaptive structures are now common terms and large government supported programs
are underway to develop and utilize them in aeronautical and space structures. A number of international
meetings on smart materials take place every year under the aegis of SPIE and ASME. One major effort has
been to develop smart rotors for helicopters to minimize the problems of noise and vibration. Helicopters
have never reached their full commercial potential because of environmental noise problems, the high
maintenance resulting from their vibration, and passenger comfort. The principal source of noise and
vibrations blade vortex interaction which is the result of the blade impacting the vortex thrown off by the
blade in front. A second source of vibration is due to small differences in blade geometry resulting from
the manufacturing process. This requires each blade be adjusted so that it tracks in the same plane as the
other blades which when properly carried-out minimizes vibration. To date this tracking adjustment has
required the manual bending of small tabs in the trailing edge of the helicopter blade which causes the
blade to fly higher or lower. A SMA tracking control which makes it possible for the pilot to adjust
trailing edge tabs from the cockpit has been developed utilizing twin tubular NiTi torsion actuators [11].
When heated the tubes twist to move the tab through a linkage with a motion of ± 7.5o with an accuracy of
± 0.25o. Critical in the design of this actuator for a smart helicopter was weight and volume which
recommended the use of SMA because of the high force and strain output. The actuator system shown in
Figure 15 weighs only 440 gm and is 2.5cmx2.5cmx16.5cm, including all electronic controls.
The control of blade vortex interaction is more complicated requiring that the blade tips move at the
rotational speed of the blades, approximately 600 rpm, or 10Hz, far to rapid for SMAs. The newly
discovered magnetically activated shape memory effect in Ni2MnGa alloys may potentially lead to the
effective use of SMAs at higher frequency; experiments have shown that shape change frequencies as high
as 400 Hz have been observed.
For the control of aerodynamic performance in different regions of the flight envelope, particularly for
planes capable of supersonic speeds, a number of studies [12,13] are evaluating methods for embedding or
attaching to an aircraft wing structure SMA wires and tendons which can change the wing contour in flight.
A barrier to this goal is the fact that two very opposite requirements are involved, the wing must be stiff to
provide flight control and yet must be flexible in order to change contour. A variety of flexible ribs and
spars have been studied to solve this dilemma. Another technique which has been tested for flight control
is to provide wing twist using a large torsion tube actuator. The required angle of twist to alter the flight
characteristics is quite small and quarter scale wings with SMA actuation have been successfully tested.
Programs in adaptive structures have also been carried out to control the performance of hydrofoils such as
the control surfaces on submarines.
il pezzo è tratto da
INDUSTRIAL APPLICATIONS FOR SHAPE MEMORY ALLOYS di Ming H. Wu and L. McD. Schetky
