Kevin Massey

Mechanical Actuators for Guidance of a Supersonic Projectile

*† ‡ In this paper, the results of a series of experiments funded by DARPA to determine the feasibility of using small actuators to provide directional control for a supersonic projectile are presented. Controlling the flight of the projectile was accomplished by taking advantage of complex shock-boundary layer interactions produced by mechanical devices. Experimental tests were conducted at GTRI to screen several control concepts and actuator locations. Further experiments were conducted on a scale projectile in a supersonic stream to investigate the rise time of the forces. Several different mechanical actuators were tested which served to provide guidance for future actuator designs. CFD results were also used to predict the results in flight as well as gain insights into the fluid mechanics involved.

Optimized Guidance of a Supersonic Projectile using Pin Based Actuators

6-DOF simulations were used to investigate various control schemes for a guided supersonic projectile. The 6-DOF simulation results were compared with actual range data acquired at ARL. Very favorable comparisons were made between predicted and actual performance of the projectile. After verifying the 6-DOF tool, projectile guidance schemes were developed based on the pin based actuators developed by GTRI that have been described in a companion paper. Pitch oscillations of the projectile were predicted using the 6-DOF tool and it was also shown that these oscillations could be controlled by appropriate deployment of the pins. Deployment schemes were developed that greatly reduced the oscillations in pitch. For a notional projectile that was undergoing a roll, multiple control schemes were developed that steered the projectile in a single direction. These control schemes were compared on two figures of merit and the optimal pin based guidance control scheme was determined.

Noise Scaling for Unheated Low Aspect Ratio Rectangular Jets

A unique set of acoustic and fluid dynamic data was obtained for three converging rectangular jets of aspect ratios 1.5, 4.0, and 8.0 and a round nozzle. All four nozzles had the same exit area and were tested in the same facility for static and unheated conditions for a range of subsonic and slightly supersonic Mach numbers. Farfield noise measurements were made for polar angles ranging from 40° to 110° with respect to the jet axis and for azimuthal angles that corresponded to both a flyover and a sideline condition. On a spectral basis, it was found that the rectangular jets were typically louder in the high frequency range and quieter in the low frequency range. Attempts were made to collapse the acoustic data for all of the jets on a non-dimensional basis and thus determine the functional dependency of the noise upon the nozzle geometry. The process of collapsing the acoustic data mirrored a previously performed collapse for round jets. Upon discovering that existing methods for scaling round jet noise would not be sufficient to collapse the rectangular jet noise, additional scaling laws were adopted. Physical justification for the these scaling laws are provided.

Testing the Maneuvering Performance of a Mach 4 Projectile

*† The results from a series of range tests designed to demonstrate the divert of a Mach 4 projectile are presented. These tests were conducted at the Army Research Lab’s Transonic Experimental Facility in Aberdeen, MD. This work was a continuation of laboratory measurements and 6-degree of freedom simulations that demonstrated the feasibility of using guidance pins to divert a supersonic projectile. The test results clearly show that it is possible to generate the forces required to maneuver a medium caliber projectile traveling at Mach 4 using guidance pins. The tests also demonstrate that the hardware to enable maneuvering flight can be fabricated and survive the high G-forces of a gun launch.

Force Measurements and Flow Visualization for a Flexible Flapping Wing Mechanism

This paper describes a series of experiments using a flapping wing mechanism. Force measurements were combined with high speed photography for two sets of flexible wings. The aerodynamic forces generated by flexible membrane type wings were measured using a two degree of freedom force balance constructed during the course of these experiments which measured the aerodynamic forces of lift and thrust. Lift and thrust measurements were acquired as the mechanism flapped the flexible wings for multiple cases, and the two most interesting conditions were explored in more detail. These two conditions consisted of a zero velocity free stream condition and a forward flight condition of 5 m/s. For these two conditions, high-speed video of the flapping wing was taken. The images from the video were also correlated with cycle averaged aerodynamic forces produced by the mechanism. Several observations were made regarding the behavior of flexible flapping wings that should aid in the design of future flexible flapping wing vehicles. In addition, flow visualization images were taken of the flapping wing under forward flight condition and flow field velocity vectors were calculated.

Integrated Numerical and Experimental Investigation of Actuator Performance for Guidance of Supersonic Projectiles

Abstract : A recent study showed that the complex 3-D shock/boundary layer interaction of a pin placed next to a fin produces an asymmetric lift force that can be utilized for flight control of a projectile. The current study was completed to validate this new technology. A similar projectile was modeled, using high performance fluid dynamic computations and six degree-of-freedom trajectory simulations, to determine the projectiles flight characteristics prior to being flown in the US Army Research Laboratorys Aerodynamic Experimental Facility. A flight test was designed using this asymmetric lift to produce roll torque. Analysis of the flight data determined that the projectiles with pins developed the expected rolling moments. Computations were completed after the range test on the experimental model for computational validation.

Noise Measurements of Tactical UAVs

This paper describes several noise measurement activities of GTRI to measure and understand the noise produced by tactical UAVs. As UAVs in the tactical class have begun to see much more use in the battlefield, it has become apparent that the noise produced by these aircraft affects their utility in certain roles. GTRI has thus undertaken to measure the noise of several UAVs through a series of static ground measurements, flyover measurements, and measurements taken in an anechoic chamber. The results indicate that propeller noise and engine exhaust noise are generally of equal importance for typical UAVs. The difficulties in measuring flyover noise are also discussed as are methods for extracting noise buried in back ground noise. Finally some discussions on UAV noise relative to UAV detection is provided along with some concepts which would serve to reduce UAV noise and thus reduce detectability.

Mechanical and Jet Actuators for Guiding a Small Caliber Subsonic Projectile

Multiple actuator concepts for guiding a subsonic projectile were screened in a series of wind tunnel tests. Both mechanical protrusion type devices and jet based devices were tested at various subsonic Mach numbers. Pressure measurements were made on an instrumented double scale model representative of a 25 mm grenade. Each of the devices changed the flow field around the model projectile in the wind tunnel which in turn changed the surface pressure distribution. The measured surface pressures were used to estimate the forces and moments developed as a result of the actuator. In addition, actuation times for several devices to were measured in a series of bench tests in order to assess their relative utility on an actual round. Particular emphasis was placed on developing fast actuators that could be used for spin stabilized rounds. The results indicate that it is possible to generate forces that can be used to guide subsonic rounds, however, developing actuators with sub millisecond response times remains a challenge.

Investigation of Explosive Charge Driven Actuators for Guided Projectiles

In this paper the use of multiple squib charges as actuators for the guidance of transonic projectiles is explored. A series of experiments were developed to simulate squib explosions and these were compared with a limited set of measurements from actual squibs. The rapid release of high pressure gas was used to both generate thrust directly and to actuate a small guidance pin. The thrust developed, chamber pressure, drain time, as well as the rise and fall time of the pin were studied over a range of several pressures and configurations. Experimental tests were conducted at the Georgia Tech Research Institute and the Army Research Lab. Force and pressure measurements, impact response, and high-speed video captures were acquired for analysis and comparison. The results show that it is both possible to create a sub-millisecond thruster and to actuate a mechanical pin into an oncoming flow in less than a millisecond. However, further experimentation is needed to refine the experimental setup and obtain the smallest possible actuation times.

Forward Flight Effects on the Internal Noise of an Ejector Nozzle

The effect of forward flight upon the noise internal to an ejector was investigated in a series of experiments. A nozzle system that simulated a mixer/ejector nozzle was designed and tested under both heated and unheated conditions in GTRI’s Anechoic Free-jet Flight-simulation Facility. The nozzle system consisted of a round nozzle surrounded by an ejector that was fed through a series of pipes. The round nozzle system was tested in both a baseline configuration and with a spoiler in the exit plane of the round nozzle that served to vastly increase the internal noise. By using the spoiler, it was insured that the noise in the far field was dominated by internal mixing noise over a majority of the frequency range. Source location measurements were made to provide further confidence that the noise under consideration was generated inside the ejector. It was found that the measured internal noise radiation pattern has a very distinctive lobe that is centered near an emission angle of 60°. It was also found that the effect of forward flight upon the internal noise was minimal at polar angles near the exit plane of the ejector. In the forward arc the internal noise increased with forward flight. The measurements made in this study can be used to increase the accuracy of flight noise predictions of a future aero-engine system that are based upon static ground tests for mixer/ejector nozzles.