Projectile

About: Projectile is a research topic. Over the lifetime, 13047 publications have been published within this topic receiving 115563 citations.

Angular motion of a spinning projectile with a viscous liquid payload

Abstract: : Liquid payload motion can have a significant effect on the stability of a spinning projectile. A general definition of the liquid moment is developed and expressions are obtained for the frequencies and damping rates of the projectile's angular motion. An expression for the liquid pressure moment is derived without the unnecessary mathematical approximations of the Stewartson- Wedemeyer theory, and wall shear effects are added to this improved SW pressure moment to obtain the total liquid moment. This moment expression applies to cavities that are fully filled, partially filled or fully filled with a central rod. The improved theory shows that as the Reynolds number decreases, (a) the eigenfrequency-related side moment peaks decrease steadily in size but that (b) the average side moment level first increases and then decreases. This latter predicted behavior is in good qualitative agreement with the D'Amico-Miller conjecture that relates the liquid spin-down moment to the liquid side moment. Good agreement is also obtained between the theory and all available published data from liquid- filled gyroscope experiments.

Computations of projectile Magnus effect at transonic velocities

Abstract: : The Magnus effect has long been the nemesis of shell designers. Although very small in magnitude, on the order of 1/10th the normal force, this spin-induced side moment has a significant destabilizing effect on projectiles. A combined computational and experimental research program has been ongoing at BRL in recent years to develop a predictive capability for the Magnus effect in particular and for projectile aerodynamics in general. This effort has been very successful in the supersonic regime. The research to be reported in this paper is an extension of this effort into the transonic regime. Utilizing the time marching, thin-layer Navier-Stokes computational technique developed at NASA ames Research Center, solutions have been obtained for a spinning, 6-caliber long, ogive-cylinder-boattail shape at Mach = 0.91 and angle of attack = 2degrees. The computed results predict the correct development of the Magnus force along the body, and comparisons between the computation and experiment are very favorable. Details of the flow field solution such as turbulent boundary- layer velocity profiles and surface pressure distributions are presented. The components which contribute to the Magnus effect are determined and presented as a function of axial position. A complete set of aerodynamic coefficients have been determined from the flow field solutions. Those to be presented here and compared with experimental data include the normal force and Magnus force coefficients. The computations for this research effort were obtained both on a CDC 7600 computer and Cray 1S. (etc.)

Some progress in the study of the water entry phenomenon

Abstract: This paper reports on progress in the study of the water entry phenomenon. First, an experiment conducted measuring the velocity of the projectile after water entry. An empirical formula was obtained describing the change of the velocity of an underwater projectile with water depth. From the formula, the velocity decay coefficient β=0.5ρw A o C d/m, was determined, where ρw is the water density, A o is the projection area of the projectile, C d is the drag coefficient and m is the mass of the projectile. A theoretical model was then presented to describe the motion of the projectile during entry. Based on the obtained value of β, when the projectile was treated equivalently as a sphere, the theoretical water depth for deep closure of the cavity was predicted.

A Scenario for a Future European Shipboard Railgun

Abstract: Railguns can convert large quantities of electrical energy into kinetic energy of the projectile. This was demonstrated by the 33-MJ muzzle energy shot performed in 2010 in the framework of the Office of Naval Research electromagnetic railgun program. Since then, railguns have been a prime candidate for the future long-range artillery systems. In this scenario, a heavy projectile (several kilograms) is accelerated to approximately 2.5-km/s muzzle velocity. While the primary interest for such a hypersonic projectile is the bombardment of targets hundreds of kilometers away, they can also be used to counter airplane attacks or in other direct fire scenarios. In these cases, the large initial velocity significantly reduces the time to impact the target. In this paper, we investigate a scenario, where a future shipboard railgun installation delivers the same kinetic energy to a target as the explosive round of a contemporary European ship artillery system. At the same time, the railgun outperforms the current artillery systems in range. For this scenario, a first draft for the parameters of a railgun system was derived. For the flight path of the projectile, trajectories for different launch angles were simulated and the aerothermodynamic heating was estimated using engineering tools developed within the German Aerospace Center (DLR). This enables the assessment of the feasibility of the different strike scenarios, as well as the identification of the limits of the technology. It is envisioned that this baseline design can be used as a helpful starting point for discussion of a possible electrical weaponization of the future European warships.