The design of the mortar bomb

The cast of the trench plaster peltIt is important to do studies on existing information regarding the design of the mortar die. This exit help in giving a diminutive review ab expose the subject in this study which is the ammunition for 81mm mortar. This chapter will discuss about the discovers of the mortar flunk, types of 81mm mortar ammunition, b wholeistic of mortar, dismantleation of the miscarry, silky mights and piece acting, bomb stableness and softwargon utilise for simulation. From the research, all information will be the guideline in developing this study. This chapter will also increase the understanding of this study in order to check success at the end of the second semester.2.1.1 Background of howitzer trench mortars started to be developed when tactical trench lines came into use in the World struggle I. The objective was to bring casualty into the enemy trenches. The early idea and Byzantine design was the German mine launcher, Minenwerfer exc ept the archetype of a mortar was the British Stokes design in 1915 which was a simple tube with a fixed firing pin at the bottom end, where a bomb was dropped and extravasated to launch the bomb out from the pose to the score. Basically, mortar is a stumpy tube intentional to fire a missile at an angle higher than 45 degrees tho lower than 85 degrees so that it falls on the enemy territory. examine 2.1 (a) Minenwerfer (www.landships.freeservers.com) propose 2.1 (b) Stokes trench mortar (www.landships.freeservers.com)2.1.2 Types of MortarThere are no precise definitions in categorising the mortar. Therefore it is steadying to group them as light, medium or ponderous.2.1.2.1 Light MortarsMortars of approximately 50 to 70mm size of calibre which are laid by hand subject matter they adjudge no demonstrateplate or bipod and have truly simple spy systems. They are generally carried at platoon level.Figure 2.2 Light mortar (www.flamesofwar.com)2.1.2.2 modal(a) MortarsAll ot her conventional man portable mortars, with calibres sizing up to approximately 110mm. They are usually pooled in specialist support sections at company or battalion level. They have base plate, bipods, and sophisticated comprehend system.Figure 2.3 Medium mortar (www.gosfordhobbies.com.au)2.1.2.3 Heavy MortarsMortars which are too heavy to be carried and which are and then vehicle attach or towed, although it should be noted that light and medium mortars are frequently vehicle mounted for tactical fifty-fifty though they may be man portable.Figure 2.4 Heavy mortar (www.missing-linx.com)2.1.3 Mortar AmmunitionIt is the mortar bomb, a aerodynamic metal shell having stabilising vanes at the tush which is ordinarily change with explosives. The mortar bomb gained its overgorge by dint of the burning of an amount dynamic charge placed in the tube. The size of mortar bomb varies depending on the national diameter of the mortar. Mortar ammunition can be categorized depending o n their fillings and usanced asi. High Explosive (HE) is use for fragmentation and blast. It causes muckle casualties and damage to light material.ii. Red Phosphorus (RP), White Phosphorus (WP) smoke. It is use to screen, signal, and act as an incendiary.iii. Illumination. Used to illuminate, signal, and mark.iv. Training Practice (TP). Training items are completely inert. Practice items may or may not arrest explosive sections such as propellant charges or spotting charges.2.2 Mortar Bomb PartsThe construction of a mortar bomb is normally consists of fuze, causa with obturation baffles, cartridge and fin. Every part mentioned has different purpose on the bomb.Figure 2.5 A typical mortar bomb2.2.1 FuzeThe purpose of a fuze is to initiate a projectile when it strikes a target or at an appropriate point in its flight. It cannot be circumstantially initiated in storage, transportation, or in the weapon when it is fired. Fuze used on mortar bomb is the honker fuze type, a simple r hythm section fuzes which form when the nose of the shell is crushed on impact with the target. This type of fuze is normally fitted to High explosives (HE) and white phosphorus smoke ammunition. Those used with HE shells often incorporate an optional delay setting which allows the projectile to penetrate the target before functioning.Figure 2.6 Projectiles with nose fuze (www.globalsecurity.org)2.2.2 grammatical caseThe display case carries fillings which determine the purpose of the ammunition. For HE fillings, it is designed to provide supreme fragmentation during explosion when detonated by the fuze. The material used in presidential term the casing is normally forged steel and cast iron.Figure 2.7 Cut-section of the casing2.2.3 ObturationThe diameter of a mortar bomb must(prenominal)(prenominal) be slight than that of the tube from which it is to be fired or otherwise it could not be loaded. For the bomb to drop straight to the bottom of the barrel without being suppor t on a cushion of ventilate there must be a gap between the outer wall of the bomb and the inner wall of the tube. This gap is known as windage. Windage allows expanding propellant gases to scat past the bomb and vent into the atmosphere and thus lower the thrust of the bomb when it is launched. Obturation provides a close dash off to this gap.2.2.3.1 Obturating BafflesTo prevent the excessive freeing of gas on firing is to machine series of baffles around the widest part of the casing. The baffles create turbulence in the windage gap between the bomb and the internal surface of the barrel, and thus prevent the gases from flowing freely upwards.Figure 2.8 Obturating baffles system (Cranfield make of Technology)2.2.3.2 Obturating RingOne of the most significant advances in modern mortar bomb design was the invention of the plastic obturating ring, an expanding transgress ring sitting in a single groove in the bomb casing. This system provides excellent obturation.Figure 2.9 Obt urating ring system (Cranfield Institute of Technology)2.2.4 CartridgeCartridge carries propellants. Upon firing, a pin strikes the primer at the base of the cartridge and ignites the propellant powder, which burns rapidly and generates expanding gases. The gases are pull backd down the length of the barrel, pushing the projectile in front of them and eventually out of the barrel.2.2.4.1 Primary CartridgeThe primary cartridge carries the initiating system and the first growing of the propelling charge. It fits into the central channel in the spigot of the tail section. When the propellant in the primary cartridge is ignited, the cartridge ruptures at point similar to the holes in the tail spigot. The flames which come from the tail spigot and then ignite the augmenting cartridges, which are fitted around the tail of the bomb.2.2.4.2 Augmenting CartridgeMost mortar bombs have augmenting cartridges which are ignited by the primary cartridge and which provide the abundant charge f or achieving maximum range. For firing at shorter range, increments can be aloof quickly and discarded.Figure 2.10 Primary and augmenting cartridge (Royal Ordnance)2.2.5 FinFin provides stability to the projectile. Attached fin projectile does not need some miscellany of rifling bore to be launched since it does not require spinning in order to gain stability in flight.2.3 ballistic of MortarBallistic is characteristic for the gesture of objects moving under their own momentum and the force of gravity. Mortars operate at low insistency compared to guns. It is possible to increase the imperativeness generated in the bore on firing but this requires a stronger, and heavier barrel and a bigger baseplate. Such solutions are possible for vehicle-mounted or towed equipments, but not for manportable mortars.All the work done by the expanding propellant gases in accelerating the bomb to its maximum amphetamine is achieved in the short distance traveled in the bore by the widest part o f the bomb, which carries the obturating ring or baffles. aft(prenominal) this part of the bomb has emerged from the muzzle the expanding gases continue to accelerate through the increase gap into the atmosphere. In a typical mortar the distance traveled in the bore by the obturating part of the bomb is less then one meter. Any increase in this distance would arrive a higher muzzle swiftness and thus increased range, but this would be at the expense of portability.The muzzle velocity of typical 81-mm mortar bomb fired at maximum charged is around 300 m/s and this produces a maximum range in the region of 5000-6000 m. The tactical need for the infantry to engaged targets beyond this range is not so great as to outweigh the advantages of current weapon systems, with their portability, flexibility and induceing into and out of action.Most mortar fire bomb at subsonic velocities and this avoids the ballistic complication of the transonic and supersonic zones. It is called subsonic if all the reanimates considered are less than the speed of sound, transonic if speeds both below and above the speed of sound are present, supersonic when the flow speed is great than the speed of sound. In the past the transonic zone presented a barrier through which mortar bomb could not fly without becoming catastrophically unstable, but this was largely the consequence of crude manufacture and assembly which resulted in asymmetrical and inherently unstable ammunition. Modern mortar bomb are manufacture to close tolerance and they are thus more stable in flight an can be fired at supersonic velocities if greater ranges are required. Tampella long-barrelled 81-mm, 120-mm and 160-mm mortars fire bombs at muzzle velocities of up to 400 m/s.2.4 FragmentationThe act of fragments scattering after the bomb is detonate. Fragmentation process is controlled by fragment mass, fragment velocity and payload.2.4.1 Fragment MassFactors organization fragment mass arei. material properties of the casingii. thickness of casing walliii. quantity of explosivesiv. detonation velocity of explosivesThe material of the casing must be neither excessively ductile nor excessively brittle.2.4.2 Fragment swiftnessFactors governing fragment velocity arei. Quantity of explosive at bottom casingii. Energy of the explosivesiii. Density of casing materialTo calculate fragment velocity, Gurney Formula is usedV = (2E) . (C/M) (1+C/2M) WhereV is the fragment velocityE is the Gurney explosives constantC is the mass of explosives per unit lengthM mass of casing per unit lengthVariations in the parameters would lead to a combination of fragment size and velocity which could be optimised for particular applications. In the case of mortar casing, the constraints imposed on the shape by aerodynamic considerations and on both shape and material choice by morphologic considerations will mitigate against an ideal fragmentation performance.2.4.3 PayloadIt is usually preferred to carry the ma ximum high explosives payload to the target. Such considerations can therefore have a substantial effect on the design of blanket(a) range projectiles solutions may include using an extended length of nose cone to reduce tail or use a sub-calibre round or to use base bleed. These solutions compromise the payload carrying capacity.2.5 Aerodynamic Forces and Moment playing On the BombThe aerodynamic forces and moments which have measurable effect on a finned type projectile are the drag force, lift force, and lurch moment. Once the projectile leaves the muzzle, its trajectory is determined by many forces. Primarily, gravity exerts a constant pull on the embody and acts through the summation of gravity which is determined by the distribution of weight throughout the body. graveness always produces a uniform vertical acceleration of about 9.8 m/s2.Figure 2.11 Forces and moment during flight (Arrow Tech)2.5.1 Centre of GravityAn unspin projectile must have its centerfield of gra vity well forward so that it travels nose first. This governs the shape of the typical mortar bomb, which is wide at the nose and tapers toward the tail. The tail assembly must be as light as possible, and in modern designs this is achieved by making of lightweight aluminium alloy. If the bomb body is roughly cylindrical, as in a bomb used as a carrier for an ejecting payload such as smoke canisters or bomblets, the centre of gravity can be moved forward in intercourse to the overall length of the complete bomb by accommodation a long tail boom.2.5.2 Centre of PressureThe centre of pressure is the point at which wind forces exert no turning moment, and in any unspun projectile this point must be merchantman the centre of gravity. The lift generated by the fins of a mortar bomb provides a force the move the centre of pressure towards the rear, behind the centre of gravity. This generates a restoring moment that rotates the projectile through its centre of gravity towards the direc tion of its trajectory, thus more and more reducing yaw.2.5.3 Drag ForceDrag force opposes the forward velocity of the bomb. Drag forces act at the centre of pressure which is a function of the bodys shape and are in the opposite direction as the motion of the bomb. There are three types of drag force that apply, which arei. pare down drag- friction on the outer surface as it moves through the bloodii. Shape drag- caused by low pressure behind the body repayable to the flow of air around its shape.iii. Wave drag a breathing out of energy that is put into acoustic waves as the body passes through the air. particularly strong near the speed of sound in air.Drag coefficient is in the first place dependent on the shape of the bomb. In addition to this shape-related coefficient, the aerodynamic drag also depends on the frontal area of bomb, the air density, and the square of the sexual congress air speed. The relationship between drag and these factors can be expressed byDrag = WhereA is the frontal areais the density of the airis the speed of the bomb relative to the air2.6 Stability of the BombMortar bomb obtain stability through the use of fins located at the aft end of the bomb. Normally, six, eight, ten or twelve fins are employed. additive stability is obtained by imparting some spin to the bomb by canting the leading edge of the fins. Fin-stabilized projectiles are very often sub-calibre. A sabot, woods or metal fitted around the projectile, is used to centre the projectile in the bore and provide a gas seal. Such projectiles vary from 101 to 151 in length-to-diameter ratio. Fin-stabilized projectiles are advantageous because they sweep up the trajectory very well at high-launch angles, and they can be designed with very low drag thereby increasing range and/or terminal velocity. However, fin-stabilized projectiles are disadvantageous because the extra length of the projectile must be accommodated and the payload volume is comparatively low in re lation to the projectile length. For projectiles fired without spin or only with a minuscular spin the stabilising influences must be created by aerodynamic forces. For the bomb to be stable, the center of pressure location is required to be behind the center of gravity location when measured from nose.2.7 PRODASSimulation software is very important in order to simulate data and to see the doings of the projectile. Utilisation of simulation software reduces the cost and the probability of failure for this study. In this study, simulation is the main method determining the projectile behaviour in term of ballistic theory generally, external ballistic theory specifically.PRODAS is produce by the Aero Tech, an Engineering Consulting business with a focus on the defending team industry. This software is focuses in advance weapon design with the standard worldly concern integrated weapon design tool. Simulation tools provided by PRODAS arei. clay sculpture Build a model from a draw ing or even a picture.ii. Aerodynamics Compare aerodynamic coefficients from multiple aero estimators.iii. Launch dynamics Interior ballistics, balloting and jump.iv. Trajectories Fly 4DOF, 6DOF and Body Fixed and Guided Trajectories.v. terminal figure Effects Estimate penetration of KE projectiles and lethality of fragmenting or shaped charge warheads.20