Ralph C. Fenn

Terfenol-D driven flaps for helicopter vibration reduction

The utility of helicopter aviation is limited by the high vibration levels caused by the interaction of each rotor blade with the wake of preceding blades. Existing full-blade actuation using a swashplate has various problems such as insufficient bandwidth, limitations in the number of harmonics controlled, high maintenance, and lack of spanwise lift variation. These problems are avoided by the proposed flap operated, individual blade control system, which uses magnetostrictive actuation technology. Terfenol-D actuation has many advantages over competing technologies such as hydraulic systems, electric motors, and piezoelectric elements. These benefits include all-electric operation, simplicity and reliability, low mass, low voltage, and insensitivity to centripetal acceleration. A blade mounted Terfenol-D actuator was developed for the high-weight-penalty helicopter application. The optimum coil to Terfenol-D volume ratio was derived that gives the highest mechanical power output for a small actuator envelope and mass. A fixed ability to dissipate coil resistive losses is assumed. The magnetostrictive actuation system will weigh less than 1% of gross vehicle weight, and use only 0.7% of cruise power. Other required subsystems of the vibration reduction system are available from commercial sources or are described in the literature. Helicopter vibration reduction greater than 90% is predicted because of superior actuator performance and individual blade control. This magnetostrictive actuator technology will also produce future helicopter systems having lower noise and higher performance. Such advances will significantly improve the utility and competitiveness of helicopters for civilian and military transportation.

Passive damping and velocity sensing using magnetostrictive transduction

Magnetostrictive Terfenol-D transducers are an attractive alternative to viscoelastic dampers, and electrodynamic and piezoelectric actuators for damping and self-sensing. These advantages include high stiffness and primary load carrying capability, high power density, low voltages, and low temperature sensitivity. Terfenol-D converts 50 percent of the transducer strain energy into magnetic field energy. Because the Terfenol-D transducer is a primary load carrying member, large amounts of structural energy are converted into magnetic field energy. This magnetic field energy is converted into electric energy by a surrounding coil and dissipated in a resistor to provide damping. The voltage developed in the surrounding coil is proportional to the strain rate of the magnetostrictive material, thus producing a velocity signal. This velocity signal can be used for colocated active damping by controlling coil current based on coil voltage induced by transducer velocity. Experiments using a Terfenol-D actuator capable of 65 microns motion and 1,000 N force showed modal loss factors to 0.22 (relative damping to 0.11) and velocity sensing scale factors to 183 volts/(meter/sec). Room temperature tests of a transducer designed for 77 degree(s)K use showed only 20 percent reductions in damping and velocity signals. Magnetic modeling supports the damping and sensing observations.

Terfenol-D-driven flaps for helicopter vibration reduction

The utility of helicopter aviation is limited by the high vibration levels caused by interaction of each rotor blade with the wake of preceding blades. Existing full blade actuation using a swashplate has various problems such as insufficient bandwidth, limitations in the number of harmonics controlled, high maintenance, and lack of spanwise lift variation. These problems are avoided by the proposed flap operated, individual blade control system, which uses magnetostrictive actuation technology. Terfenol-D actuation has many advantages over competing technologies such as hydraulic systems, electric motors, and piezoelectric elements. These benefits include all-electric operation, simplicity and reliability, low mass, low voltage, and insensitivity to centripetal acceleration.

Low-cost active anti-gravity suspension system

Recently, SatCon Technology Corporation has successfully demonstrated a novel anti-gravity suspension for NASA Langley. This approach consists of a passive gravity-unload mechanism enhanced with an active inertia-controller. The passive gravity-unload is achieved by supporting the suspended body with a counterbalanced cable system. The suspension is unique because it has essentially zero stiffness and zero damping relative to conventional approaches. The effect of suspension stiffness on the dynamics of the suspended article is essentially eliminated. During this phase, a hardware demonstration of this concept providing a vertical anti-gravity suspension using low-cost, off-the-shelf components was developed. The results achieved are compared with the capabilities of available mechanical suspensions systems to attain zero-gravity environments. Finally, a discussion is provided on extending this concept to three dimensions using an actively-controlled translational table.

High force-to-volume Terfenol-D reaction mass actuator: modeling and design

A high force to volume ratio magnetostrictive reaction mass actuator has been designed and developed. The actuator operates as a resonant device allowing the stored strain energy to be utilized. A discussion of the design issues associated with this actuator are presented. In addition, preliminary data is presented for this actuator. This data includes a linear analysis, evidence of parameter variation, and preliminary small signal tests intended to explore this behavior.

Integrated actuation system for individual control of helicopter rotor blades

The unique configuration of the rotorcraft generates problems unknown to fixed wing aircraft. These problems include high vibration and noise levels. This paper presents the development and test results of a Terfenol-D based actuator designed to operate in an individual blade control system in order to reduce vibration and noise and increase performance on Army UH- 60A helicopter. The full-scale, magnetostrictive, Terfenol-D based actuator was tested on a specially designed testbed that simulated operational conditions of a helicopter blade in the laboratory. Tests of actuator performance (strike, force moment, bandwidth, fatigue life under operational loading) were performed.

Magnetostrictive structural elements fabricated from metallic glass

Magnetostrictive adaptive materials have many benefits over competing materials such as piezoelectric types. These advantages include very low power and voltage, high toughness and strength, and the ease of composite manufacture. The amorphous metal Metglas was chosen for fabrication of tubular and bimorph samples of magnetostrictive composites. Metglas composites produced magnetostrictive strains greater than 50 ppm in tests. The composite Youngs modulus was 7.8 X 106 psi, which is 78 percent of aluminum. Specific stiffness is 48 X 106 in, which is 47 percent of aluminum. This specific stiffness is favorable because the composite replaces heavy actuator components, such as high density piezoelectric materials, as well as supplying primary load carrying capability. Very low power requirements are anticipated because of the 90 percent conversion efficiency from magnetic to mechanical energy.