How Does A Blowpipe Work English Language Essay

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CHAPTER 2

The blowpipe sometimes also called a blowgun or blow tube has a long but not necessarily well documented history [6]. A blowpipe is a primitive weapon that has its origins in ancient history. The weapon is constructed out of a narrow, hollow lightweight tube. By blowing air into one end of the blowpipe, a small dart or other projectile is fired from the weapon at several hundred meter per second. Although very simple, the blowpipe has been used for centuries as an effective hunting weapon around the world. The most common projectile fired by

a blowpipe is the dart. Some hunters use a poison dart since the blowpipe is not guaranteed to make a kill with one shot.

2.1.1 How does a Blowpipe Work

The hunter simply placed a dart into one end of the gun, placed his mouth over the opposite end, took aim, and blew [8]. A strong blow of air forced the dart through the tube, hopefully to capacitate a small bird or animal. The velocity of the dart was dependent upon the length of the tube and one's lung capacity.

Indigenous tribes in South America and parts of Asia were especially skilful in the use of the blowpipe. Blowpipes do not possess the killing power of a rifle, but their extremely sharp darts can easily pierce skin [8]. Thus, blowpipes were typically a tool for hunting small game. To take larger game, many of the tribes coated their darts with poisons. Via this technique the blowpipe was effective against larger animals and even against humans during times of battle and warfare.

2.1.2 The Advantages and the Capabilities of the Traditional Blowpipe

Tactically, the blowpipe offers a number of significant advantages over other weapon. One distinct advantage is its quietness [7]. With the exception of hand thrown weapon, no other projectile weapon is as quite as a blowpipe. From distances of more than a few meters, the blowpipe can hardly be heard at all.

Historian accounts tell of natives who could shoot hummingbirds in flight with their blowpipe or kill a deer with a poisoned dart at 100 yards [7]. While these stories may be exaggerated, historians writing about witnessing native blowgunners in action invariably regard them with awe. One of the first considerations of any projectile weapon is the velocity with which it delivers its projectiles. Velocity not only affects the power with which a dart or pellet hits, it also determines the practical accuracy of the weapon. Chronograph test have revealed that, when shot by average shooters, dart can easily approach or exceed velocities of 300 feet per second [7]. This of course varies with the length of the blowpipe, the weight of the dart, and the lung power of the shooters, but it represents a good average. With this velocity, a short ranges steel dart will easily penetrate 3/8 - inch plywood. (Refer Figure 2.1)

Figure 2.1: Steel dart easily penetrate 3/8 inch plywood

( Source: Janich, Michael D,' Blowguns - The Breath of Death')

2.2 Pneumatic System

2.2.1 Check valve

A check valve (sometimes called clack valve, non-return valve or one-way valve) is a mechanical device, a valve, which normally allows fluid (liquid or gas) to flow through it in only one direction [9].

Check valves are two-port valves, meaning they have two openings in the body, one for fluid to enter and the other for fluid to leave. There are various types of check valves used in a wide variety of applications. Check valves are often part of common household items. Although they are available in a wide range of sizes and costs, check valves generally are very small, simple, and/or cheap. Check valves work automatically and most are not controlled by a person or any external control; accordingly, most do not have any valve handle or stem. The bodies (external shells) of most check valves are made of plastic or metal.

An important concept in check valves is the cracking pressure which is the minimum upstream pressure at which the valve will operate. Typically the check valve is designed for and can therefore be specified for a specific cracking pressure.

B

A

Figure 2.2: Check Valve A) A closed ball check valve and B) An open ball check valve.

2.2.2 Regulator

The air enters the regulator from the reservoir, travels through the piston and into the firing valve chamber. As the pressure increases so does the force on the large end of the piston. As the force increases on the piston the spring behind the piston begins to compress. This process continues until the shaft of the piston contacts the Teflon seat and shuts the flow of air off. When the shot is fired the air pressure in the firing valve chamber drops and the spring lifts the piston off its seat allowing high pressure air to flow into the valve chamber once again and the cycle is repeated.

Figure 2.3: Regulator

Source: (Amir,2009)

The pressure in the firing valve chamber is determined by the size of the piston head and the strength of the spring. These dimensions will vary between manufactures, among all the airgun regulators available today none has the same dimensions as another. There are, however, several regulators available that use this basic design.

2.2.3 Pressure Reservoirs

Pressure reservoir is used to store air compressed in pneumatic blowpipe. It will discharge to firing chamber by a regulator. The way to compressed air into the reservoir is by hand pump or compressor. Figure 2.4 shows the pressure versus stroke in the reservoir.

aircomp6

Figure 2.4: Pressure versus Stroke in Pneumatic Cylinder

(Source: Amir,2009.)

2.2.4 Barrel

Basically, barrel has two types, smoothbore and rifling. Usually, the smoothbore barrel is used for fin-stabilized projectile.

Figure 2.5: Rifled Versus Smoothbore Barrels

(Source: Amir, 2009)

The purpose of rifling is to stabilize the bullet and increase its accuracy. This is called spin stabilizing, and works because of gyroscopic forces acting on the spinning bullet during flight.

There are various ways to rifle a barrel. The old way was to cut the rifling one groove at a time on a rifling machine. A more modern method is to pull a gang of broaches through the barrel, which cuts the all the grooves into the bore simultaneously. Another is to insert a very hard mandrel, which bears the reverse of the intended rifling pattern, into an oversize bore; then the outside of the barrel is "hammer forged" (or beaten) to impress the rifling into the bore. A fourth method is to pull a very hot rifling "button" through the bore, turning it as it progresses, which irons (melts) the rifling into the barrel. All of these methods are entirely satisfactory if done properly.

Rifle barrels are usually made from steel alloys called ordinance steel, nickel steel, chrome-molybdenum steel, or stainless steel, depending upon the requirements of the cartridge for which they are chambered (Geoffrey Kolbe, September 1991). The higher the pressure and velocity of a cartridge (pressure and velocity usually go up together), the faster it will wear out a barrel.

The rate of twist, expressed as one turn in so many inches (i.e. 1 in 10"), is designed to stabilize the range of bullets normally used in a particular caliber. It takes less twist to stabilize a given bullet at high velocity than at low velocity. At the same velocity in the same caliber, longer (pointed) bullets require faster twist rates than shorter (round nose) bullets of the same weight and heavier bullets require faster twist rates than lighter bullets of the same shape. It is undesirable to spin a bullet a great deal faster than necessary, as this can degrade accuracy. A fast twist increases pressure and also the strain on the bullet jacket.

2.3 Projectile

A projectile is a body which is propelled with various initial velocities, and then allowed to be acted upon by the forces of gravity and possible drag [10]. Figure 2.6 show that the maximum upward distance h reached by the projectile is called the height, the horizontal distance travelled x the range (or sometimes distance), and the path of the object is called its trajectory[11]. If a body is allowed to free-fall under gravity and is acted upon by the drag of air resistance, it reaches a maximum downward velocity known as the terminal velocity. The study of the motion of projectiles is called ballistics [11].

http://scienceworld.wolfram.com/physics/pimg465.gif

Figure 2.6: Motion of Projectile

In ballistics, the easiest way to describe a trajectory is by its x- and z-components, with the z component being affected by local gravity. Ignoring air resistance, a particle that is fired from the origin at time t = 0, where is the initial velocity and is the initial angle made with the x-axis, the trajectory of a particle is described by

(1)

(2)

Where t is the elapsed time and g is the gravitational acceleration, and its velocity components are

(3)

(4)

2.3.1 Bullet

Bullets are composed of a casing containing an explosive powder charge, which, on striking, forces the end projectile element out at speeds of up to 1500 metres/second, depending upon the ammunition and the type of gun used [12]. The word "bullet" is sometimes used to refer to ammunition generally, or to a cartridge, which is a combination of the bullet, case/shell, powder, and primer.

2.3.2 Design

Generally, bullet shapes are a compromise between aerodynamics, interior ballistic necessities, and terminal ballistics requirements.

Table 2.1: Effect bullet design at ballistic

Types of Ballistic

Details

Internal Ballistic

They must first form a seal with the gun's bore.

If a strong seal is not achieved, gas from the propellant charge leaks past the bullet, reducing efficiency.

The bullet must also engage the rifling without damaging the gun's bore.

Bullets must have a surface which will form this seal without causing excessive friction.

Bullets must be produced to a high standard, as surface imperfections can affect firing accuracy.

External Ballistic

The primary factors affecting the aerodynamics of a bullet in flight are the bullet's shape and the rotation imparted by the rifling of the gun barrel.

Rotational forces stabilize the bullet gyroscopically as well as aerodynamically.

Any asymmetry in the bullet is largely cancelled as it spins.

With smooth-bore firearms, a spherical shape was optimum because no matter how it was oriented, it presented a uniform front.

Unstable bullets tumbled erratically and provided only moderate accuracy.

Method of stabilization is for the center of mass of the bullet to be as far forward as is practical as in the shuttlecock.

This allows the bullet to fly front-forward by means of aerodynamics.

Terminal Ballistic

The outcome of the impact is determined by the composition and density of the target material, the angle of incidence, and the velocity and physical characteristics of the bullet itself.

Bullets are generally designed to penetrate, deform, and/or break apart.

For a given material and bullet, the strike velocity is the primary factor determining which outcome is achieved.

2.3.3 Common Bullet Types

2.3.3.1 Hollow Point Bullets

Figure 2.7: Cut-through of a hollow-point bullet.

(Source: www.Wikipedia.com)

Expansion, or hollow point, bullets are specialised bullets designed to deform upon impact because of a collapsible space within the projectile tip. The result is that a single projectile will inflict greater overall damage to a target, allowing an increased transfer of kinetic energy compared with a standard bullet. The "benefits" include a decreased risk of ricochet because the overall penetration distance is reduced. However, some of the older ammunition failed to expand on impact as a result of pieces of clothing obstructing the cavity.

Hollow point bullets, characterized by a small hollow cavity in the nose. Hollow-point bullets are often used in hunting ammunition to provide a clean and humane kill, reducing crippling. Their use in law enforcement and personal defense ammunition is to enhance the stopping effect and reduce the danger of over-penetration.

Despite recent claims, hollow-point bullets are not specifically designed to cause more injury to victims. Rather, they are designed to transfer energy from the bullet to the target to maximize the stopping effect and minimize the unintended consequences if someone must regrettably fire a bullet at another human being in self-defense. When such a course of action becomes necessary, the private citizen, law enforcement agent or soldier needs to have the appropriate ammunition. It is simply not possible to design handgun ammunition that adequately does its job under appropriate circumstances that cannot be misused by violent felons to their own end.

2.3.3.2 Full Metal Jacket

Figure 2.8: An example of FMJ bullets in their usual shapes: pointed ("spitzer") for the 7.62x39mm rifle and round-nosed for the 7.62x25mm pistol cartridges.

(Source www.Wikipedia.com)

Manufactured to military specifications, such bullets are generally not as accurate as civilian rifle ammunition but are optimized toward the reliable functioning of the firearms for which they are designed [13]. Therefore, they are loaded to moderate operating pressure and are usually equipped with a "full metal jacket" completely enclosing their lead core [13]. The unique requirements of military use, where the wounding of an enemy combatant may be a desirable goal, mandate that military handgun ammunition is, paradoxically, not the best choice for personal defense. This fact is illustrated by the almost universal use of semi jacketed handgun ammunition by all federal and state agencies and police departments that use defensive handguns full metal jacketed ammunition simply offers too much possibility of over-penetration through the target, resulting in the danger of injury to innocent bystanders beyond the intended target. Ricochets may also occur since, if such a bullet hits a hard surface, it does not immediately deform and break up as lead or semi-jacketed ammunition usually does.

2.4 Basic Ballistic Theory

Ballistics is the study of the firing, flight, and effects of projectiles [14]. It is the science of how a projectile shot from a weapon behaves [15]. The field of ballistic can be broadly classified into three major disciplines:-

Internal ballistics concerns what happen between the cartridges being fired and the projectile leaving the muzzle

External ballistics is concerned with the flight of the projectile from the muzzle to the target and what happens during the bullet's flight.

Terminal ballistic describes what happen when the projectile strikes the target.

2.4.1 Internal Ballistic

Internal ballistics studies the events inside the weapon when the primer is detonated igniting the propellant [16]. From the terminal ballistic aspect it is relevant to know the internal ballistic factors affecting the bullet velocity. Every powder type has its characteristic burning velocity. Burning is actually controlled explosion since no external oxygen is required [16].

From the terminal ballistic and tactical point of view it is important that the powder and primer are as insensitive to external temperature as possible and thus contribute to consistent performance. A combination of the amount of powder, its burning velocity, burning volume and bullet resistance in the barrel give a pressure curve depicting how fast and how high the pressure builds up and how fast it subsides. An ideal powder charge burns almost completely before the bullet exits the muzzle. Shortening the barrel will reduce the Vo when the same cartridge is used [16]. Reducing the powder charge also will naturally do that too. Figure 2.9 shows an example of the relationship between pressure, barrel length and bullet velocity.

Figure 2.9: An example of the relationship between chamber pressure, barrel length and bullet velocity of a 5.56x45 mm cartridge calculated using Broemel QuickLoad software.

When the pressure increases sufficiently high, it pushes the bullet into the barrel. The forces involved cause radial expansion and torsional twist of the barrel as the bullet is forced into the helical rifling.

2.4.1.1 Basic Requirement for a High-speed Gun

The basic factor determining the speed of a projectile propelled from the rifle may be simply obtained by applying Newton's force equation to the projectile. From the calculation, we can see how long the barrel needs to accelerate the projectile. For this calculation, below is the schematic of projectile during travel in the gun barrel.

Figure 2.10: Diagram of Barrel

(Source: Arnol E. Seigel "The Theory of High Speed Guns")

The projectile mass is denoted by M, the length of barrel by L, and the cross-sectional area of the barrel by A. the propellant pressure at the back end of the projectile is denoted by Pp. At any instant of time Newton's Law applied to the projectile given

Where

The equation above is integrated becomes

The partial average propelling pressure defined as

Then projectile velocity becomes

Figure 2.11: Graph Pressure versus Length of Barrel

(Source: Arnol E. Seigel "The Theory of High Speed Guns")

From the Figure 2.11, pressure behind the projectile in the conventional gun is plotted as a function as its travel. The rise in pressure from zero to peak pressure PM results from the burning of propellant. Then the rapid pressure decrease thereafter results mainly from the propellant inertia as the propellant gas accelerates to push the projectile. It is evident from the figure above that the average pressure, is considerably below the peak PM for the conventional propellant.

2.4.2 External ballistics

Once the bullet exits the barrel, it decelerates and faces the effects of atmospheric drag [14]. This area of ballistics is known as external. Here, it is subjected to the force of the pressure of the atmosphere that it is flying through, the force induced by its spin, and the force due to the acceleration of gravity [18].

The two factors are determined the external ballistics of a projectile [17]:

Muzzle velocity - velocity with which the bullet exits the barrel.

Ballistic coefficient

2.4.2.1 Ballistic Coefficient

The rate at which velocity decays is a measure of penetration; it is often referred to by means of a quantity called the ballistic coefficient [19]. The ballistic coefficient is significant because it determines the rate of which the projectile slows down, and in conjunction with the muzzle velocity this decides the maximum range (at given elevation) and the time of flight to any particular distance [20]. The time of flight in turn decides the amount by which the projectile drops downwards as this happen at a constant rate due to gravity. This is incorporated into the ballistic coefficient, BC as [19]:

It follows that the deceleration of the projectile is given by [21]:

2.4.3 Terminal Ballistic

Once the target is penetrated, the study is categorized as terminal ballistics. Terminal ballistics is the study of the penetration of a medium denser than air. In other words, it is the scientific study of injuries caused by projectiles and the behavior of these projectiles within human biological tissue [16]. This thesis project will solely focus on terminal ballistics. There are several factors that affect the terminal ballistic result that call injury assessment which are:

Type of the bullet.

Stopping Power

Energy Transfer/ Kinetic Energy

Hydrostatic Shock/ Shock Wave

Taylor Knock Out Theory (KO)

Relative Stopping Power (RSP)

Stopping Power (StP)

2.4.3.1 Wound Ballistics

Wound ballistics is the area of terminal ballistics that studies the injury pattern of a particular bullet. The characteristics of a bullet wound include the depth penetration, the permanent cavity diameter, temporary cavity diameter, and bullet fragmentation. Wound ballistics analyzes the potential of a bullet to incapacitate and the underlying mechanisms.

2.4.3.2 Mechanic of Projectile Wounding

In order to predict the possibility of incapacitation with any firearm bullet, an understanding of the mechanic of wounding is required. There are four components of projectile wounding [22]. There are:

Penetration - The tissue through which the projectile passes and which disrupts or destroy.

Permanent Cavity - The volume of space once occupied by tissue that has been destroyed by the passage of the projectile. This is the function of penetration and the frontal area of the projectile. Quite simply, it is the hole left by the passage of the bullet.

Temporary Cavity - The expansion of the permanent cavity by stretching due to the transfer of kinetic energy during the projectile's passage. A missile's ability to produce a temporary cavity is considered an important component in wound production and degree of destruction [35]. Most researchers agree that the wounding effect of the cavitations phenomenon is only significant in velocities surpassing 300 meter per second [34]. When a missile enters the body, the kinetic energy imparted on the surrounding tissues forces them forward and radially producing a temporary cavity or temporary displacement of tissues [33]. The temporary cavity may be considerably larger than the diameter of the bullet, and rarely lasts longer than a few milliseconds before collapsing into the permanent cavity or wound (bullet) track (Kirkpatrick, 1988).

Fragmentation - Projectile pieces or secondary fragments of bone which are impelled outward from the permanents cavity and may sever muscle tissue, blood vessel, apart from the permanents cavity[23]. Fragmentation is not necessarily present in every projectile round. It may, or may not occur and can be consider a secondary effect [24].

Projectile incapacitate by damaging or destroying the nervous system, or by causing lethal blood loss. To extend the wound components cause or increase the effects of these two mechanisms, the likelihood of incapacitation increases.

2.4.3.3 Energy Transfer

The energy transfer hypothesis states that the more energy that is transferred to the target, the greater the destructive potential. In terminal ballistics, energy is a function of mass and the square of velocity which is related to the kinetic energy equation. Bullet weight and velocity determine the kinetic energy possessed by a projectile with velocity being the most critical component [31]. A variety of factors are responsible for the amount of kinetic energy lost in the body: "...amount of kinetic energy possessed by the bullet at the time of impact..." (Di Maio, 1985:46), mass, yaw (deviation of the missile from its flight path), caliber or size of bullet, shape, deformation, and density of the tissue being struck [32].

Double the mass will double the value of kinetic energy and double the velocity will give the value of kinetic energy four times greater.

It is the aim of the shooter to deliver an enough amount of energy to the target through the projectiles. Projectiles such as rifle bullets and high velocity handgun bullets can over-penetrate. Projectiles such as handgun bullets and shot-gun can under-penetrate. Projectiles that reach the target with too low velocity may not penetrate at all. All the above conditions affect energy transfer.

Furthermore, over-penetration is one of the factors to stopping power regards to energy. This is because a bullet that passes throughout the target does not transfer all of its energy to the target. Although it's decreased tissue damage due to loss of transferred energy on an over-penetrating shot, the resulting exit wound would cause increased blood loss and therefore a decrease in blood pressure in the victim.

The Swiss delegation to the Expert Meeting of the International Committee of the Red Cross presented a Draft Protocol on Small Calibre Weapon Systems (1994) (Prokosch,1995). Recognising that not only bullet expansion but also other factors cause tissue injury, it proposes a limit for the amount of kinetic energy that is released. It suggests prohibiting the use of 'arms and ammunition with a calibre of less than 12.7 millimetres which from a firing distance of at least 25 meters release more than 20 joules of energy per centimetre during the first 15 centimetres of their trajectory within the human body'.

Under-penetration is also one of the factors to stopping power. Projectile/s that does not transfer enough energy to the target may fail to create a fatal wound cavity. Also vital organs may not be reached, thereby limiting the amount of tissue damage, blood loss, and/or loss of blood pressure.

2.4.3.4 Hydrostatic Shock

Hydrostatic shock can be describes the observation that a penetrating projectile can produce remote wounding and incapacitating effects in living targets, in addition to local effects in tissue caused by direct impact, through a hydraulic effect in liquid-filled tissues.

The term also can be described as ballistic pressure wave which is the force per unit area created by a ballistic impact. The hypothesis from Michael Courtney states that bullets producing larger pressure waves incapacitate more rapidly than bullets producing smaller pressure waves.

The origin of the pressure wave is Newton's third law. The bullet slows down in tissue due to the force the tissue applies to the bullet. By Newton's third law, the bullet exerts an equal and opposite force on the tissue. When a force is applied to a fluid or a viscous-elastic material such as tissue or ballistic gelatine, a pressure wave radiates outward in all directions from the location where the force is applied [27].

The instantaneous magnitude of the force, F, between the bullet and the tissue is given by

Where E = is the instantaneous kinetic energy of the bullet, and x is the instantaneous penetration distance.

Courtney and Courtney believe that remote neural effects only begin to make significant contributions to rapid incapacitation for ballistic pressure wave levels above 3,400 kPa corresponds to transferring roughly 410 J in 30 cm of penetration and become easily observable above 6,900 kPa corresponds to transferring roughly 810 J in 30 cm of penetration [28]. Dave Ehrig expresses the view that hydrostatic shock depends on impact velocities above 340 meter per second.

2.4.3.5 Relative Stopping Power (RSP)

As the objective of the Armed Forces is to stop life endangering activity of an offender quickly and effectively the incapacitation or "stopping power" approach has certain validity. General J.S. Hatcher presented the concept of stopping power in his book "Pistols and Revolvers and their use" in 1927 and later "relative stopping power" (RSP) (Hatcher 1935). According to Hatcher the incapacitation potential of a projectile was proportional to impact momentum times the bullet's cross-sectional area [29].

Where A is the cross-sectional area of the bullet and the form factor U.S. Army expanded Hatcher's theory by hypothesizing that incapacitation "stopping power" (StP ) was a function of kinetic energy deposited in 15 cm of gelatine tissue stimulant (Sturdivan 1969 referred to in Bruchey and Frank 1983a). DiMaio expanded the theory in 1974 on handgun effectiveness (DiMaio 1974 referred to in Bruchey and Frank 1983a and Sellier and Kneubuehl 1994, Kneubuehl 1999).

Which are form factor, Ff o r m :-

0.70   Fully Jacketed Pointed

0.90   Fully Jacketed Round Nose

1.05   Fully Jacketed Flat Point

1.10   Fully Jacketed Flat Point (Large flat)

1.05   Lead Flat Point

1.10   Lead Flat Point (Large Flat)

1.35   Jacketed Softpoint (expanded) 

1.25   Lead Semi-wadcutter

1.10   Hollow Point (unexpanded)

1.35   Hollow Point (expanded)

2.4.3.6 Taylor Knockout Theory (KO)

J. Taylor, a british big-game hunter developed a "Knockout value" (KO) in 1948 to describe the effectiveness of hunting ammunition [30].

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