Morphing aircraft structures using tendon actuated compliant cellular truss.

摘要

The research described in this thesis aims to develop a structural concept capable of achieving continuous stable deformations over a large range of aircraft shapes. The basic concept underlying the approach is a compliant cellular truss, with tendons used as active elements. The members of the truss are connected through compliant joints such that only modest bending moments may be transmitted from one member to another. Actuation is achieved by pulling on one set of cables while controlling the release of another, so that the stability of the structure is maintained in any intermediate position. The tendon-actuated compliant truss can be made to behave locally, and temporarily, as a compliant mechanism, by releasing appropriate cables. As a result, in the absence of aerodynamic forces, the structure can be morphed using relatively low forces.; A six-noded octahedral unit cell with diagonal tendon actuation was obtained for a bending type deformation of the NASA HECS wing. Initial cell geometry and orientation is determined by "strain matching" to the local morphing deformation required by the application. The cell size is dictated by the available space, the morphing strain, and discretization errors in approximating a smooth desired shape. A finite element analysis is performed on a wing made of these unit cells and sized for a representative vehicle weighing 3000 lbs (1360 kg). The weight of the truss wing (without the skin and actuators) was comparable to a conventional stiffened skin construction although its deflections are larger. Aeroelastic concerns of flutter and divergence can perhaps be addressed through the use of active control.; An analysis on the scaling of actuator requirements with aircraft size showed that, if actuation of the aircraft structure involves the morphing of the wing against the lift forces or if the actuators are in the load path, then the weight of the aircraft can be limited to something in the range of a few kilograms to a few thousands of kilograms. (Abstract shortened by UMI.)