: The goal of this study was to better understand the flight of spin-stabilized projectiles at high angle of attack for improved delivery accuracy of indirect fires. Experiments successfully captured flight motions over 40 angle of attack around Mach 0.8 using advanced spark range techniques. Flight analysis validated analytical expressions, kinematics, and dynamics with mass asymmetries, aerodynamic modeling, and parameter estimation algorithms. Significant nonlinearities in angle of attack were quantified in the axial force and Magnus moment with more-linear behavior found in the normal force and pitching moment. Stability analysis indicated that this vehicle does not fly below 3 angle of attack and likely suffers instabilities around 3 angle of attack. These results ultimately improve impact point prediction for applications such as high-arcing, spin-stabilized munitions.

: The goal of this study is to improve understanding of maneuvering flight and reduce aerodynamic uncertainty of guided munitions to compress the iterative design cycle and realize enhanced maneuverability vehicles. To accomplish this, novel dynamic wind tunnel and spark range flight experiments were performed. An actively controlled vehicle was mounted on a 3 degree-of-freedom gimbal in a wind tunnel with balance, Euler angle, and canard deflection instrumentation. Free-flight spark range firings were conducted with various configurations to isolate control aerodynamics and induce a spectra of angle of attack. An aerodynamic model was postulated to capture high maneuver phenomena such as flow separation and vortex interactions, which were encountered during experiments. This aerodynamic model was used with the experimental data in a parameter estimation algorithm to obtain static and dynamic aerodynamics. Results confirm the novel experimental and aerodynamic modeling approaches and provide validation data for computations.

Actively controlled gun-launched projectiles require a means of modifying the projectile flight trajectory. While numerous potential mechanisms exist, microspoiler devices have been shown to be a promising control actuator for fin-stabilized projectiles in supersonic flight. These devices induce a trim force and moment generated by the boundary layer–shock interaction between the projectile body, rear stabilizing fins, and microspoilers. Previous investigations of microspoiler mechanisms have established estimates of baseline control authority, but experimental results have been restricted to cases in which the mechanism was statically deployed. This paper details the design and flight testing of a projectile equipped with a set of active microspoilers. A mechanical actuator is proposed that exhibits unique advantages in terms of robustness, simplicity, gun-launch survivability, and bandwidth compared to other projectile actuator mechanisms considered to date. A set of integrated test projectiles is constructed using this actuator design, and flight experiments are performed in which the microspoilers are oscillated near the projectile roll frequency. Data obtained from these flight tests are used in parameter estimation studies to experimentally characterize the aerodynamic effects of actively oscillating microspoilers. These predictions compare favorably with estimates obtained from computational fluid dynamics (CFD). Overall, the results presented here demonstrate that actively controlled microspoilers can generate reasonably high levels of lateral acceleration suitable for trajectory modification in many smart-weapons applications.

The maneuvers required for guided flight are often obtained through inducing aerodynamic asymmetries. The goal of this study is better understanding of the behavior of asymmetric flight bodies for enhanced control authority and more accurate aerodynamic characterization to improve guidance algorithm design and component (for example, actuator and feedback sensor) selection. The configuration considered is a missile featuring a pair of canards representative of a class of rolling airframes with a single plane of actuating control surfaces. Free-flight experiments are conducted on this body, which demonstrates a means of collecting high-quality experimental data on guided airframes using roll-yaw resonance. Characterization of the asymmetric aerodynamics are obtained from spark range and computational fluid dynamics techniques. Aerodynamic coefficients compare favorably between spark range, computational fluid dynamics, and onboard sensor techniques. Experiments also validate linearized theory of the amplification factor due to roll-yaw resonance. Lastly, the aerodynamic uncertainty quantified during this study enables the maneuverability design margin to be assessed for asymmetric, rolling airframes.

: The maneuvers required for guided flight are often obtained through inducing aerodynamic asymmetries. The goal of this study is to understand the flight behavior of asymmetric flight bodies. The configuration considered was a fin-stabilized projectile featuring a pair of canards representative of a class of rolling airframes with a single plane of actuating control surfaces that have recently undergone successful guided flight demonstrations. In addition to this aerodynamic asymmetry, an asymmetric mass was placed within the body. This internal asymmetry creates a trim moment and angle of attack that is amplified during free-flight as the roll rate of the body increases from zero at launch and passes through the natural yawing frequency of the projectile. Increasing the angle of attack amplitude in this manner enables analysis of a rich set of flight behaviors. Free-flight experiments were conducted on this flight body in the spark range at the Transonic Experimental Facility at the US Army Research Laboratory. Aerodynamic parameter estimation was performed on the spark range measurements using a maximum likelihood method with a body-fixed 6-degrees-of-freedom flight model. Nonlinear aerodynamic models including asymmetries in the pitching moment, normal force, and dynamic derivatives were accommodated in these techniques. Aerodynamics were compared to results obtained using computational fluid dynamics and onboard sensor techniques. Experiments also permitted analysis of the amplification factor due to roll-yaw resonance and provide a means of more easily collecting high-quality experimental data on guided projectile configurations in the future.

This paper examines the problem of enhancing maneuverability of gun-launched munitions utilizing low cost technologies. Two ideas are proposed for reducing cost: (1) designing algorithms that reduce the sensor or actuator burden, and (2) performing high fidelity modeling and simulation of the entire system with realistic data input. The fundamental theory underpinning guided projectile flight systems, including nonlinear equations of motion for projectile flight, aerodynamic modeling, actuator dynamics, and measurement modeling, is outlined. Manipulation of these nonlinear models into linear system models enables airframe stability investigation and flight control design. A basic framework for low cost guidance, navigation, and control (GNC) of high maneuverability projectiles is formulated. Theory was implemented in simulation and exercised for a guided projectile system. Results support the hypothesis that algorithms can compensate for poor actuator performance and identified critical trade study parameters. Monte Carlo analysis indicated that the cost associated with measurements of a threshold accuracy rather than actuation technologies prescribes guided system performance.

Abstract : A recent gun launch experimental program required that the pusher assembly of the launch package be diverted so that it would not follow behind the projectile being evaluated. Initial experiments showed that a subscale launch package fired from a 2-inch (51-mm)-diameter air gun exhibited similar sabot discard performance to the full-size projectile. The subscale launch package was assembled from parts built from plastic via rapid prototyping (3-dimensional printing). Subsequent evaluation of several sabot concepts revealed that the best design had one of the 4 sabot petals firmly attached to the pusher assembly so that the discarding sabot petal pulled the pusher assembly off of the line of fire. The modified assembly was fabricated and fired from the full-scale 8-inch (203-mm) gun. Sabot discard and pusher diversion occurred as expected, allowing the experimental program to proceed. The launch package modifications are described, and a simple analysis of basic equations of force and motion illustrates why a low-speed, subscale simulation can be used for first order evaluations of sabot discard phenomena.

Future enhanced lethal effects at the infantry squad level likely include precision guided technologies. The focus of this study is maneuvering projectiles launched from man-portable weapon systems. Anovel guided projectile concept is proposed for achieving control authority requirements in the challenging environment of low-dynamic pressure, small size, high launch loads, spin stabilization, and low cost. This new maneuver concept is based on a rotating wing actuator. Experimental and advanced computational aerodynamics techniques were applied. Aerodynamic models and projectile flight mechanics were derived to enable flight simulation. Assessment of ballistic delivery accuracy, based on physics-based models of the delivery process, was undertaken to quantify control authority requirements. Maneuvering flight simulations demonstrated that this concept affords enough course correction to compensate for ballistic delivery errors.

A recent test program required firing a saboted projectile through a spark shadowgraph range. The sabot design included a pusher assembly that would follow directly behind the projectile in the early portion of the flight. Initial testing showed that a subscale launch package assembled from parts built from plastic via rapid prototyping (3-D printing) and fired from a 2 '' diameter air gun exhibited similar sabot discard performance to the full-size projectile. Subsequent evaluation of several sabot concepts revealed that the best design had one of the four sabot petals firmly attached to the pusher assembly using an aluminum rod (stripper pole), so that the discarding sabot petal pulled the pusher assembly off of the line of fire. The modified assembly was fabricated and successfully tested in the full-scale 8 '' gun.

Future enhanced lethal effects at the squad level likely include precision guided technologies. The focus of this study is maneuvering projectiles launched from man portable weapon systems. A novel guided projectile concept is proposed for achieving control authority requirements in the challenging environment of low dynamic pressure, small size, high launch loads, spin-stabilization, and low cost. This new maneuver concept is based on a rotating wing actuator. Experimental and advanced computational aerodynamics techniques were applied to enable flight simulation. Maneuvering flight simulations demonstrated that this concept may afford enough course correction to compensate for ballistic delivery errors.

The US Army Research Laboratory is conducting research to explore technologies that may be suitable for maneuvering man-portable munitions. Current research is focused on the use of rotary actuators with spin-stabilized munitions. A rotary actuator holds the potential of providing a low-power solution for guidance of a spinning projectile. This is in contrast to a linear (reciprocating) actuator which would need to constantly change direction, resulting in large accelerations which in turn would require large forces, thereby driving up the actuator power. A rotational actuator would be operating at a fairly constant rotation rate once it is up to speed, resulting in much lower power requirements. Actuator experiments conducted over a variety of conditions validate the dynamic models of the actuator and supply the data necessary for model parameter estimation. Actuator performance metrics of spin rate response, friction, and power requirements were derived from the data. This study indicates that this class of maneuver concepts can be driven with these actuators. These results enable actuator design and multi-disciplinary simulation of refined maneuver concepts for a specific application.

T HE overarchingmotivation for this work is to provide capability for gun-launched munitions to engage targets that require high maneuverability. Past efforts resulted in precision indirect fire for stationary targets [1,2]. This Note represents a component of a program focused on general development of this enhanced maneuverability for application to relevant systems such as artillery, mortars, and shoulder-launched munitions. The approach to achieve a low-cost gun-hard skid-to-turn maneuver control system outlined in this Note is to leverage commercial-off-the-shelf (COTS) technology for the high-levels-ofacceleration (high-G) environment and develop control algorithms that rely on a high-fidelity characterization of the aerodynamics and flight mechanics. Servomechanisms used by remotecontrolled aircraft hobbyists feature low costs due to high-volume manufacturing; however, components must withstand the high structural loadings during gun launch [3]. A canted fin-stabilized canard-controlled projectile flying in a skid-to-turn configuration was selected. This configuration complicates the aerodynamic characterization due to flow interactions; however, mature computational [4] and experimental [5] methods may be applied. Vortices generated by canard deflections are swept downstream and impact the stabilizing fins, sometimes reversing the fin roll moment [6–8]. Packaging constraints for gun tube launch require deploying stabilizing and control surfaces. The skid-to-turn configuration was chosen for the high bandwidth since the time of flight for some applications of interest may only be 1 s. Classical and modern control techniques have been applied to the roll control problem for missiles [9,10]. The approach herein is to formulate these techniques in the simplest manner possible for the unique projectile environment by including effects like fin cant and canard–fin interactions. The goal of this Note is to develop and demonstrate roll control performance of a low-cost gun-hard skid-to-turn maneuver system. The contribution of this work lies in leveraging COTS devices to reduce cost, ensuring structural integrity, and using high-fidelity flight characterization methods in the control strategy for the gun launch environment. A wide variety of technical disciplines have been successfully synthesized to develop this technology using theory, nonlinear simulation, and experiments.

Abstract : The next generation of precision munitions is likely to use a non-rolling airframe with 4 independent canards to increase maneuverability of the munition such that it can engage moving as well as stationary targets. The design of such a precision munition requires increased understanding of the airframe, of maneuver technology, and of guidance and flight control. Prior to engaging in the research on the high maneuverability airframe and maneuver system, a demonstration platform needed to be selected. The focus of this study was to design an airframe that would meet stability, range, and maneuverability requirements, while remaining simple enough so that quality research in other areas could be engaged. Advanced computational aerodynamic techniques found that the initial airframe design did not meet stability requirements as a consequence of excluding the canard-fin interaction effects. Using an updated aerodynamic coefficient database, an airframe was designed using optimization parameters and realistic mass properties. An aerodynamic coefficient database and the associated flight dynamics were derived on the second configuration to enable flight simulation. Maneuvering flight simulations demonstrated that this airframe design will meet the stability, range, and maneuverability requirements.