Robert T. Ruggeri

Full-scale Flight Tests of Aircraft Morphing Structures using SMA Actuators

In August of 2005 The Boeing Company conducted a full-scale flight test utilizing Shape Memory Alloy (SMA) actuators to morph an engines fan exhaust to correlate exhaust geometry with jet noise reduction. The test was conducted on a 777-300ER with GE-115B engines. The presence of chevrons, serrated aerodynamic surfaces mounted at the trailing edge of the thrust reverser, have been shown to greatly reduce jet noise by encouraging advantageous mixing of the free, and fan streams. The morphing, or Variable Geometry Chevrons (VGC), utilized compact, light weight, and robust SMA actuators to morph the chevron shape to optimize the noise reduction or meet acoustic test objectives. The VGC system was designed for two modes of operation. The entirely autonomous operation utilized changes in the ambient temperature from take-off to cruise to activate the chevron shape change. It required no internal heaters, wiring, control system, or sensing. By design this provided one tip immersion at the warmer take-off temperatures to reduce community noise and another during the cooler cruise state for more efficient engine operation, i.e. reduced specific fuel consumption. For the flight tests a powered mode was added where internal heaters were used to individually control the VGC temperatures. This enabled us to vary the immersions and test a variety of chevron configurations. The flight test demonstrated the value of SMA actuators to solve a real world aerospace problem, validated that the technology could be safely integrated into the airplanes structure and flight system, and represented a large step forward in the realization of SMA actuators for production applications. In this paper the authors describe the development of the actuator system, the steps required to integrate the morphing structure into the thrust reverser, and the analysis and testing that was required to gain approval for flight. Issues related to material strength, thermal environment, vibration, electrical power, controls, data acquisition, and engine operability are discussed. Furthermore the authors layout a road map for the next stage of development of SMA aerospace actuators. A detailed look at the requirements and specifications that may define a production SMA actuator and the technology development required to meet them are presented. A path for meeting production requirements and achieving the next level of technology readiness for both autonomous and controlled SMA actuators is proposed. This path relies strongly on cross functional and organizational teaming including industry, academia, and government.

Shape memory actuator systems and the use of thermoelectric modules

Thermally activated shape memory materials have been employed as actuators fora number of years. They are generally activated by electrical resistance heaters, or sometimes by direct electrical resistance. Thermoelectric modules can also provide activation energy, and they provide several unique advantages over the more conventional heating methods. Antagonistic Shape Memory Actuator systems, the utilization of thermoelectric modules as heaters, and the advantages and practical approaches for utilizing actuators employing thermoelectrics are discussed.

Shape control of a morphing structure (rotor blade) using a shape memory alloy actuator system

Development and test results of a rotor blade twist control system that utilizes a thermo-mechanical shape memory alloy (SMA) are presented. The actuation system controls the blade shape during flight operations allowing the blade to be configured for greater lift during takeoff and landing. SMA actuators provided an excellent solution because of their very high torque output to weight ratio and suitability to the dynamic environment of a rotor blade. Several challenges related to the behavior of the SMA material are overcome by innovative control system design. Thermoelectric modules (TEMs) are used to actively transfer heat between SMA tubes and other heat conductor and radiator components. Modeling and system identification techniques and a non-trivial solution to nonlinear and coupled thermal response equations are used to insure effective use of the TEMs and to improve control during SMA phase transition.

Development of a ¼-scale NiTinol actuator for reconfigurable structures

Wind Tunnel tests of a NiTinol based actuator have been conducted for the reconfigurable rotor blade program. The purpose of the test was to demonstrate the potential to improve rotorcraft performance by optimizing the configuration of major structures in flight. The actuator is integrated into the rotor blade as a structural element controlling blade twist. A three-blade scale rotor was tested in a Boeing wind tunnel. The tests validated actuator design and performance by demonstrating simultaneous blade twist and control of twist position over the entire test matrix. A description of system requirements and compromises associated with the actuator and its integration into the rotor blade are provided and discussed. Test results showed that the RRB actuators were able to successfully twist the blade, control the twist between one twist state and the other, and simultaneously control three rotor blades to change state within two seconds of each other despite unanticipated electrical noise in the system.

Mechanical strain energy shuttle for aircraft morphing via wing twist or structural deformation

Direct structural deformation to achieve aerodynamic benefit is difficult because large actuators must supply energy for structural strain and aerodynamic loads. This ppaer presents a mechanism that allows most of the energy required to twist or deform a wing to be stored in descrete springs. When this device is used, only sufficient energy is provided to control the position of the wing. This concept allows lightweight actuators to perform wing twisting and other structural distortions, and it reduces the onboard mass of the wing-twist system. The energy shuttle can be used with any actuator and it has been adapted for used with shape memory alloy, piezoelectric, and electromagnetic actuators.

Spray forming of NiTi and NiTiPd shape-memory alloys

In the work to be presented, vacuum plasma spray forming has been used as a process to deposit and consolidate prealloyed NiTi and NiTiPd powders into near net shape actuators. Testing showed that excellent shape memory behavior could be developed in the deposited materials and the investigation proved that VPS forming could be a means to directly form a wide range of shape memory alloy components. The results of DSC characterization and actual actuation test results will be presented demonstrating the behavior of a Nitinol 55 alloy and a higher transition temperature NiTiPd alloy in the form of torque tube actuators that could be used in aircraft and aerospace controls.

CORRELATION OF LOCAL HEAT TRANSFER COEFFICIENTS AND PRESSURE ON AN AIRFOIL

Local heat transfer coefficients and pressure measurements are essential for investigating ice accretion on airfoils that can change airfoil shape, add weight to airplanes and degrade performance. This manuscript reports measurements of local heat transfer coefficients (Frossling Number) around an airfoil from –90% (pressure side) to +90% (suction side). Measurements were conducted at constant wall temperature for 5 different angles of attack and 3 Mach numbers. Simultaneously, static pressures were measured at the same operating conditions. The results show that the heat transfer coefficient is high at the stagnation point, decreases with the developing laminar boundary layer, and then increases through a region of transition to a peak at the onset of the turbulent boundary layer. Thereafter, the heat transfer coefficient slowly decreases as the thickness of the turbulent boundary layer increases. The location of the onset of turbulence moves toward the leading edge on the suction side and toward the trailing edge on the pressure side with increasing angle of attack in a range from –8.5° to 19.5° at a constant Reynolds number. The measured surface static pressure coefficients show that a positive pressure gradient favors the flow transition from laminar to turbulent and the initiation point of the negative pressure gradient matches the location of transition as indicated by the abrupt jump in the Frossling number.