Geoffrey Frost

Control Authority of a Projectile Equipped With an Internal Unbalanced Part

A key technical challenge for smart weapon developers is the design of appropriate control mechanisms that provide sufficient control authority to enable correction of typical trajectory errors while not excessively burdening the overall weapon design. The work reported here considers a rotating mass unbalance control mechanism, created by radial orientation of an internal part. To investigate the potential of this control mechanism, a seven degree-of-freedom flight dynamic model of a projectile, equipped with an internal part is defined. Using this dynamic model it is shown that by holding the internal part fixed with respect to a nonrolling reference frame, predictable trajectory changes are generated including predictable impact point changes. As expected, when unbalance-offset distance, or mass is increased, control authority increases proportionally. This control mechanism creates impact point changes that are the same order of magnitude as dispersion caused by errors induced at launch and in flight. Control authority is significantly altered with changing projectile characteristics, such as, the mass center location, pitch inertia, yaw inertia, aerodynamic drag, and aerodynamic normal force.

Linear theory of a rotating internal part projectile configuration in atmospheric flight

Dynamic modeling of the atmospheric flight mechanics of a projectile equipped with an internal rotating disk is investigated, and a modified projectile linear theory is established for this configuration. To model this type of projectile requires alteration of several of the coefficients of the epicyclic dynamics leading to changes in the fast and slow epicyclic modes. A study of the frequency and damping properties of the epicyclic modes is conducted by the systematic variation of disk orientation, location, mass, and rotational speed. It is shown that the presence of an internal rotating disk can causes substantial changes in the epicyclic dynamics, including instability, in some configurations.

Improved Deployment Characteristics of a Tether-Connected Munition System

This study investigates theeffectofa tetherreel resistancemechanism intended to improve theunreeling process of a tether line connected to two projectiles comprising a munition system. The munition system considered is released from an aircraft at altitude and falls toward a target on the ground. Reel resistance models, based on feasiblemechanisms,aregeneratedasfunctionsofdropspeed,projectilemass,dragcoefe cientratio,andtetherline stiffness. Reel cone gurations are determined to decrease tether line loads, maximum acceleration on the follower projectile, time to reach a steady-state condition, and terminal miss distance. Reel resistance based on either the tetherlinepay outorthetetherpay outrateprovidesa powerful meansto improvesystem performance.Resistance as a function of tether line pay out yields theoverall best performance; however, resistancebased on tetherline pay out rate provides suitable performance over a wider band of drop speeds, mass ratios, and drag coefe cient ratios. Nomenclature An = projected area of the follower object Awi = wetted area of the ith element CDn = coefe cient of drag for the follower object Cfp = coefe cient of the e at-plate drag Csf = coefe cient of the skin-friction drag ci = damping coefe cient for the ith element Fr = resistance force of the reel FTj = magnitude of the elastic line force for the jth element Ir = mass moment of inertia for the reel i = bead index j = line element index ki = stiffness coefe cient for the ith element li = unstretched length of the ith element m j = mass of the jth bead ml = tether line mass per unit length mr = mass of the reel n = number of the follower object r = effective radius of the tether reel ri = directional vector of the ith element s = total length of tether line unspooled from the tether reel

Holistic mechanical engineering education with a mechatronic platform for learning/sup /spl trade//

A new platform for learning has been developed for mechanical engineering programs at Oregon State University with great success. This new platform provides hands-on experience, encourages innovation, and presents the means for a more holistic education of mechanical engineering graduates. By combining experiences in electronics, programming and a heavy dose of mechanical theory and practice students can use the platform to build exciting projects and test benches.

Two projectiles connected by a flexible tether dropped in the atmosphere

Abstract : This study investigates the atmospheric flight dynamics of a munition system that is released from an aircraft at altitude and drops toward a target on the ground. The munition system consists of two projectiles connected by a tether line. Initially, the two projectiles are rigidly attached. At a specified time, the projectiles separate and subsequently unreel the tether line. After the tether line is fully payed out, the system settles toward a steady state as it approaches the ground. It is shown that while projectile position results converge for a relatively low number of tether line elements, the maximum tether loads require a significantly larger number of elements. For a low follower-to-lead projectile mass ratio, the tether line unreeling process is predominantly due to the follower and lead projectile separation. Conversely, for a high follower-to-lead projectile mass ratio, the tether line tends to billow and subsequently unreel itself, independent of the lead and follower projectile motion.

Bomb damage assessment using a dispensed sensor projectile

The problem of obtaining images of a target site after munition impact is approached by releasing a small projectile equipped with a camera from a dropped munition. A ballute is deployed from the sensor projectile shortly after release from the munition. This type of system is capable of viewing munition impact and subsequent target effects over a wide variety of conditions and offers the possibility of real-time battle damage assessment (BDA). However, fundamental limits exist on the duration that the camera is able to view the target after impact for a particular required separation distance between the sensor projectile and the target at impact and the field of regard (FOR) of the camera. Munition release altitude and velocity significantly affect these fundamental limits. Optimal performance is attained under high altitude and low speed munition drop conditions. Basic characteristics of the camera projectile also significantly influence system performance. Maximum target view time is attained with a low weight high drag configuration., To reduce the maximum acceleration experienced by the sensor projectile, a small delay time between the release of the small sensor projectile from the munition and inflation of ballute is required.

Simulation of a Mortar Launched, Parachute Deployed Battlefield Imaging System

Flight behavior of a mortar launched, parachute deployed imaging system is examined with particular attention to characterizing the quantity and quality of recorded image data. Coverage area of the imager, blur due to motion of the imager, and view time are evaluated for different system configurations allowing important design parameters to be identified. It is shown that proper tailoring of the dynamic characteristics of the system greatly improves gathered image data quantity and quality. Coning of the canister is an important system characteristic that largely drives total ground coverage. Canister coning is influenced in a complex manner by system geometric parameters. Mounting the parachute riser to the canister in such a way that the connection is off the axis of symmetry of the canister is a powerful technique to increase coning of the canister. Likewise, increasing riser length also yields increased coning. Increasing spin rate of the canister leads to a proportional increase in image blur, which is largest toward the edge of the image. Also, increased canister weight tends to increase the descent rate, which reduces total view time. At the same time, increased descent rate increases the spin rate for cross type parachutes, leading to increased image blur. @DOI: 10.1115/1.1789974#

SIMULATION OF TWO PROJECTILES CONNECTED BY A FLEXIBLE TETHER

Abstract : This report investigates the atmospheric flight mechanics of two projectiles connected by a flexible tether. Both projectiles are individually modeled with six degrees of freedom. The projectile aerodynamic model depends on angle of attack and Mach number and includes unsteady roll, pitch, and yaw aerodynamic damping. The tether is split into a finite number, of beads, with each bead possessing three translation degrees of freedom. Forces acting on the beads include weight, line stiffness, line damping, and aerodynamic drag. The tether aerodynamic drag force is dependent on the tether line angle of attack and Mach number. The tether line deployment process is modeled with a single degree of freedom that permits unreeling resistance to be incorporated. The effect of follower-to-lead projectile mass ratio and drag coefficient ratio on system response are investigated.