Patent Application
20100212529
Not Applicable
Not Applicable.
Not Applicable
1. Field of the Invention
This invention relates to the field of projectile delivery systems. More specifically, the invention comprises an improved projectile assembly having a gas generator in its aft end. The gas generator injects gas into the projectile's wake, thereby reducing the projectile's base drag.
2. Description of the Related Art
Although the present invention can be applied to many different types of projectiles, it was primarily developed as part of a propulsion system for launching 40 mm grenades (such as the U.S. Army's M433). The invention incorporates many features described in greater detail in prior U.S. Pat. No. 7,004,074 to Van Stratum (2006), which is hereby expressly incorporated by reference.
Metallic cartridges have been used to encapsulate solid propellants for many years. In recent years other materials have been substituted for the traditional brass, but the principles of operation remain the same: A projectile is seated in the open mouth of a cartridge case containing solid propellant. Ignition of the propellant is provided by percussive or electrical means. The burning propellant generates pressurized gas which forces the projectile out of the mouth of the case and then typically down a rifled bore.
The launching of a 40 mm grenade involves the same principles. The main difference, however, is the size and mass of the projectile. A typical shoulder-fired military weapon launches a projectile weighing less than 30 grams at a relatively high velocity (700-1,000 meters per second). In contrast, a 40 mm grenade weapon launches a projectile weighing over 200 grams at a relatively low velocity (70-80 meters per second). Thus, while the operating principles between the two types of weapons are the same, they can be said to operate in different regimes.
Since the human operator can only withstand a fixed amount of recoil, one cannot merely scale up the cartridge of a shoulder-fired rifle and create a useable weapon for launching 40 mm grenades. The design considerations are different. The incorporated U.S. Pat. No. 7,004,074 illustrates and describes an effective approach to the problem of launching large masses at low velocities. The '074 invention uses a high-pressure cartridge embedded within a low-pressure larger cartridge. A burst cup metering system is used to meter propellant gases from the high pressure cartridge into the low pressure cartridge, thereby accelerating the projectile in a smooth and controlled fashion. This approach helps to reduce the peak recoil loads experienced by a user. The high pressure found within the high pressure cartridge also ensures the reliable ignition and combustion of the propellant it contains.
Once the projectile is free of the rifled bore, it flies along a ballistic path until it strikes its target. The velocity of the projectile diminishes continuously due to aerodynamic drag. One of the significant components of the aerodynamic drag is the “base drag,” which refers to the drag induced by the turbulent wake region immediately behind the projectile. The present invention seeks to reduce the base drag, thereby extending the projectile's range using a given amount of powder. As an alternative, the invention also allows a smaller amount of powder to be used while achieving the same range as a prior art projectile. The smaller amount of powder means reduced recoil for the person firing the weapon.
The present invention is a modified cartridge assembly including a projectile having a gas generator proximate its aft end.
The gas generating assembly can be used with a variety of projectile payloads. Examples include smoke rounds, marker flares, and high explosive rounds. Some of the specific details are preferably altered to suit each different type of projectile payload, but the operating principles remain the same. The reduction in base drag increases the projectile's range for a given amount of propellant. Alternatively, a reduced amount of propellant can be used while maintaining the same range as a prior art projectile. The reduction in propellant reduces recoil forces when the weapon is fired.
Propellant assembly 18 is a high/low pressure launch system, as described more particularly in the incorporated U.S. Pat. No. 7,004,074 to Van Stratum (2006). High pressure cartridge 42 contains propellant 36 (housed within high pressure chamber 31). High pressure chamber 31 is separated from low pressure chamber 30 by a rupturable burst cup 46 (The burst cup is labeled in a non-sectioned view of the high pressure cartridge shown in the right hand portion of
Low pressure case 12 includes base 24, which opens into high pressure cartridge receiver 26. The base also includes a conventional extraction flange 22, which is used to remove the spent casing from the firing chamber. Charge casing 28 preferably surrounds and reinforces the high pressure cartridge. It includes charge vent hole 52, which lies directly over the high pressure cartridge. The round is ignited by striking percussion primer 34. This action ignites the propellant and ruptures burst cup 46. Hot propellant gases are then metered from high pressure chamber 31 to low pressure chamber 30. The gases force the projectile assembly away from the propellant assembly and accelerate it down the rifled bore of the firing weapon.
The use of the high pressure cartridge with charge vent hole 52 is particularly advantageous for the present invention. When the burst cup ruptures, a stream of hot propellant gas is directed up through the charge vent hole and against the aft portion of the projectile. This directed stream of hot propellant gas serves to ignite components placed in the aft end of the projectile, as will be described subsequently.
Cavity 58 is filled with several layers of material. Black powder layer 62 covers the aft extreme. Just forward of the black powder layer is a layer of ignition material 64. The rest of cavity 58 is filled with gas generating material 66. Igniter charge 68 fills output opening 70. Those skilled in the art will know that some of these materials are granular. A good example would be the black powder layer, which is composed of very fine grains of black powder. Binding agents are used to adhere the granules together and possibly to adhere the layers together. One or more mechanical interference features such as annular recesses 74 are also preferably provided in cavity 58's side wall. These annular recesses create a mechanical interference with the materials contained within the cavity, thereby holding them in position. Other mechanical interference features could be used, such as steps in the cavity's diameter or threads. The contents of the cavity are typically pressed into place so that voids are eliminated.
The example of
When projectile assembly 14 is launched via the ignition of propellant assembly 18, a sequence of ignition events transpires. First, the hot gases produced by the propellant assembly impinge upon black powder layer 62, which readily ignites. Black powder layer 62 ignites ignition material 64, which provides a uniformly combusting layer. Ignition material 64 then ignites gas generating material 66. Gas generating material 66 produces a steady volume of gas, which is ejected from the rear of the projectile (primarily during the projectile's flight).
When the gas generating material is nearly consumed, it ignites ignition charge 68. Ignition charge 68 ignites ignition material 54, which in turn ignites smoke material 48. The smoke produced by the smoke material is then vented back through output opening 70. This sequence will be described with respect to the projectile's flight momentarily.
In
Those skilled in the art will know that air flow around such a projectile produces turbulent wake and resulting base drag. The base drag is actually produced by a region of relatively low pressure immediately behind the projectile in flight. This base drag slows down the projectile. However, in the case of the present invention, propellant gas 80 produced by gas generating material 66 is spewed into the low pressure region, thereby raising the pressure. Base drag is significantly reduced. The artificial pressurization of the wake region produces a sort of streamlined “tail” for the projectile, which is labeled as effective extension 84 in the view. In this context the term “effective” is used to indicate that the artificial pressurization has an effect similar to placing a streamlined “boat tail” shape on the rear of the projectile.
The gas generating material preferably continues to burn through the projectile's flight. In
The reader will thereby understand that the present invention includes a gas generating component in the base of a projectile. The gas generating component is integrated into an ignition sequence including several other components. In the case of an ignitable payload (such as a marker flare, illumination flare, or smoke round), the gas generating component is part of the sequence that ultimately ignites the payload.
The inclusion of the gas generating component creates several performance advantages. For a given payload, it significantly reduces the propulsion energy needed to reach a given range. The reduction in propulsion energy also reduces the launch impulse (“kick”) experienced by the shooter. The cartridge pressure loads applied to the firing weapon are also reduced. The hardware illustrated is preferably made interchangeable with other prior art components, such as standard M433 propellant assemblies.
The reader may wish to know some typical properties of projectiles using the proposed invention. A typical prior art projectile assembly weighs 205 grams. 1000 mg of M9 flake propellant is used in the high pressure cartridge to propel such a projectile assembly to a range of 800 m. With the addition of the gas generating material in the projectile's base, the same range can be achieved using only 700 mg of M9 flake propellant. On the other hand, if 1000 mg of M9 is used with the gas generating approach, the projectile's range is extended to approximately 1000 meters.
As disclosed previously, the present invention can be used with many different types of projectiles. Some hardware modifications are preferable in order to optimize the invention for each type of round.
The illuminant composition burns intensely, producing a brilliant flare. So much gas is produced that output opening 70 is insufficient for adequate venting. The escaping flame also passes through the array of secondary vents 90. As the illuminant composition continues to burn, the secondary vents and output opening may in fact merge into a single large hole—the intervening webs having been eroded away. This allows the brightly burning flare gases to escape the round and illuminate an area or brightly designate a fixed point.
A similar aft closure assembly can be used for explosive rounds, though the inclusion of an output opening 70 is unnecessary. The payload of an explosive round is typically ignited by impact, so the contents of the aft closure would not be used in an ignition sequence leading to such a payload.
Although the preceding description contains significant detail, it should not be construed as limiting the scope of the invention but rather as providing illustrations of the preferred embodiments of the invention. As an example, the physical characteristics of the ft closure could be modified substantially while still providing the injection of pressurized gas into the projectile's wake region. Thus, the scope of the invention should be fixed by the following claims, rather than by the examples given.
