Method to Develop a Control System for a Stable and Guidable Hybrid Projectile

A Hybrid Projectile (HP) is a munition that transforms into an unmanned aerial vehicle (UAV) after being launched from a tube. In many situations it is desirable for this type of projectile to change its point of impact and depart from its current ballistic trajectory similar to a UAV following a path. A method was created to utilize deflectable control surfaces in conjunction with a guidance system to ensure the HP was statically and dynamically stable and to maneuver the HP to a desired point of impact. Methods were devised to control heading and pitch using vertical and horizontal tail surfaces. Testing and tuning these control methods were done using the Six Degree of Freedom (6DoF) system in Simulink. A cruciform tail section was utilized so that the HP could be statically and dynamically stable. The simulation showed that the method devised was able to guide a 40 mm HP up to 6250 projectile diameters off of the line of fire and increase range by 25.8% while landing within 125 projectile diameters of the desired impact point

Pitch-Axis Identification for a Guided Projectile Using a Wind-Tunnel-Based Experimental Setup

International audienceThis paper details the identification of a pitchaxis model for an 80-mm fin-stabilized canard-guided projectilethrough a hardware-in-the-loop experimental setup. This setup is based on an autonomous functional projectileprototype installed in a subsonic wind tunnel by the means of a three-degree-of-freedom gimbal mount. A nonlinear dynamical model is first derived from flight mechanics principles;then, a linearized model is obtained through Taylorseries expansion. The a priori and a posteriori identifiabilityof the proposed linear model are assessed, and the associatedexperimental input signals are accordingly designed.The model parameters are then estimated using a numericaloptimization procedure, and the associated uncertainty isobtained through a boostrapping method. The results andtheir implication on the projectile flight control design arefinally discussed

Euler-Lagrange Optimal Control of Indirect Fire Symmetric Projectiles

An important aspect of controls engineering is the dynamic modeling and flight control of smart weapons. One division of this area involves the guidance, navigation, and control of smart projectiles. In recent decades, methods for controlling projectiles have become much more sophisticated. In this thesis, principles of optimal control are used to develop a controller for indirect fire symmetric projectiles, or high-launch projectiles. A plant model is created to simulate the flight of a 2.75-inch Hydra-70 rocket. Two pairs of forward-mounted controllable canards are used as actuators to modify the flight toward a downrange target. A linear optimal regulator is used to compute control inputs which minimize a cost function. Results are demonstrated through impact point dispersion plots which show both the effectiveness and robustness of the controller. Additionally, defining characteristics of the control method are explored and optimized

Projectile linear theory for aerodynamically asymmetric projectiles

Currently, there are few analytical tools within the ballistics community to aid in the design and performance evaluation of aerodynamically asymmetric projectiles. The scope of this thesis is to (1) create analytical tools that are capable of quantifying aerodynamically asymmetric projectile performance, (2) demonstrate the ability of these models to accurately account for aerodynamic asymmetries, and (3) gain insight into the flight mechanics of several aerodynamically asymmetric projectiles. First, a six-degree-of-freedom (6 DOF) flight dynamic model, which uses a point-force lifting-surface aerodynamic model, was developed to replicate flight characteristics observed from measured results of common projectiles. A quasi-linear flight dynamic model was then created using the machinery of Projectile Linear Theory (PLT). From this, flight dynamic stability models were developed for linear time-invariant (LTI) and linear time-periodic (LTP) systems. Dynamic simulation and stability trade studies were then conducted on asymmetric variants of 4-finned, 3-finned, 2-finned, and hybrid projectile configurations. First, stability of symmetric projectiles are validated and show that the classical and extended PLT model yielded identical results. Results show that aerodynamic asymmetries can sometimes cause instabilities and other times cause significant increase in dynamic mode damping and increase/decrease in mode frequency. Partially asymmetric (single plane) configurations were shown to cause epicyclic instabilities as the asymmetries became severe, while fully asymmetric (two plane) can grow unstable in either the epicyclic modes or the roll/yaw mode. Another significant result showed that the LTP stability model is able to capture aerodynamic lifting-surface periodic affects to evaluate dynamic stability requirements for asymmetric projectiles.MSCommittee Co-Chair: Dr. Ari Glezer; Committee Co-Chair: Dr. Mark Costello; Committee Member: Dr. Wayne Whitema

Predictive Control of a Munition Using Low-Speed Linear Theory

Modified linear theory provides reasonable impact predictions at high speeds. However, for typical small UAS mission speeds, less than 20-m/s impact errors were substantial due to large angles of attack and pitch rates. Low-speed linear theory was developed by including higher-order terms involving w and q that modified linear theory neglects. As a result, the angle of attack, pitch, and yaw predictions are significantly improved, leading to accurate impact predictions even at very low speeds. A predictive control scheme was developed to reduce dispersion using control surfaces near the tail. The predictive controller uses low-speed linear theory to rapidly predict the impact error using the current state and control. Based on the estimated impact error, the control is iteratively found to minimize the predicted-impact error. For an example munition, it was shown that the maximum number of iterations during the control solution only impacted the initial control estimates. Limiting the guidance algorithm to a single iteration had little impact on the final accuracy and permitted a rapid solution. It was shown for the example munition that the predictive guidance significantly reduced the CEP from 14.1 to 2.7 and 2.2 m when the maximum iterations were 1 and 10. Furthermore, for a typical high- explosive 40-mm grenade, the percentage of impacts within a lethal radius was increased from 10 to 78% when the maximum iterations were both 1 and 10. In practical applications, errors in the target location must beincluded when considering the probability of impact within a lethal range of a target

Guidance, navigation, and control for munitions

The United States Army is currently looking for new methods of guiding munitions, which would allow the military to employ guided munitions in place of traditional munitions. This will give the US Army an edge on the battle eld and also allow the use of munitions in areas where traditional mortars and artillery cannot be used, including dense urban environments where collateral damage is not acceptable.In this thesis, an innovative approach to Guidance, Navigation, and Control (GN&C) is developed for a spinning projectile that utilizes a single axis canard actuation system. Utilizing the projectiles spin, the controller can provide a full range of aerodynamic forces, over the 360o of rotation, that provides maneuverability using only one actuator. This technique minimizes the need for multiple actuators and maintains the inherent aerodynamic stability provided by the spin.The GN&C system design described in this thesis consists of a tracking regulator for sinusoidally oscillating the canard system, a nonlinear state estimator for attitude measurement, and a guidance law to guide the projectile to a target. By combining the three components, we can demonstrate a closed-loop guidance system that will hit a target accurately at distances normally not achieved by an unguided projectile.Ph.D., Mechanical Engineering -- Drexel University, 200

Improving rotorcraft survivability to RPG attack using inverse methods

This paper presents the results of a preliminary investigation of optimal threat evasion strategies for improving the survivability of rotorcraft under attack by rocket propelled grenades (RPGs). The basis of this approach is the application of inverse simulation techniques pioneered for simulation of aggressive helicopter manoeuvres to the RPG engagement problem. In this research, improvements in survivability are achieved by computing effective evasive manoeuvres. The first step in this process uses the missile approach warning system camera (MAWS) on the aircraft to provide angular information of the threat. Estimates of the RPG trajectory and impact point are then estimated. For the current flight state an appropriate evasion response is selected then realised via inverse simulation of the platform dynamics. Results are presented for several representative engagements showing the efficacy of the approach