Projectile with filler material between fins and fuselage

A projectile has filler material placed between an outer surface of its fuselage, and fins that are hingedly coupled to the fuselage. The filler material fills space that otherwise would be occupied by pressurized gases. Such pressurized gases could cause undesired outward force against the projectile fins during launch of the projectile from a launch tube or gun, such as when pressure outside the fins is suddenly removed, as in when the projectile passes a muzzle brake in the launch tube. The filler material may be any of a variety of lightweight solid materials, such as suitable plastics or closed cell foams. The filler material prevents pressurized gases from entering at least some of the space between the fins and the outer fuselage surface. When the fins deploy after the projectile emerges from the launch tube the filler material pieces fall away harmlessly.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is in the field of projectiles launched form launch tubes or guns.

2. Description of the Related Art

Launching a projectile from a launch tube or gun requires as a practical matter that the projectile fit into a circular cross section tube. This makes it difficult to provide the projectile with fins, for example to stabilize the flight of the projectile. Many solutions have been tried to accommodate finned projectiles in guns or launch tubes, but no solution has been completely effective.

SUMMARY OF THE INVENTION

According to an aspect of the invention, filler material is placed between fins of a projectile and a fuselage of the projectile.

According to another aspect of the invention, a method of configuring a projectile includes molding filler material between the fins of the projectile, and a fuselage of the projectile.

According to yet another aspect of the invention, a projectile includes: a fuselage have an outer surface; fins hingedly coupled to the outer surface of the fuselage; and fillers in spaces between the fins and the outer surface when the fins are in a compact configuration, close to the outer surface.

According to still another aspect of the invention, a method of projectile launching includes the steps of: providing an initial configuration of a projectile and a launcher, wherein the providing includes: providing the projectile with a fuselage having an outer surface, and fins hingedly coupled to the outer surface of the fuselage, providing the fins in a compact configuration with the fins close to the outer surface, providing filler material in spaces between the fins and the outer surface of the fuselage, and having the projectile located within the launcher; launching the projectile from the launcher; deploying the fins from the compact configuration to a deployed configuration; and separating the filler material from between the fins and the fuselage outer surface.

According to a further aspect of the invention, a method of configuring a projectile includes: providing the projectile with a fuselage and fins outside the fuselage and hingedly coupled to the fuselage, with the fins configured folded in toward the fuselage in a compact configuration; placing molds around spaces between the fins and an outer surface of the fuselage; and forming filler material blocks in the spaces. The forming includes: injecting a polymer material into the spaces; hardening the polymer material; and removing the molds.

DETAILED DESCRIPTION

A projectile has filler material placed between an outer surface of its fuselage, and fins that are hingedly coupled to the fuselage. The filler material fills space that otherwise would be occupied by pressurized gases. Such pressurized gases could cause undesired outward force against the projectile fins during launch of the projectile from a launch tube or gun, such as when pressure outside the fins is suddenly removed, as in when the projectile passes a muzzle brake in the launch tube. Such outward pressure forces may cause bending or breakage of the fins, and may cause the fins to contact walls of the launch tube, possibly resulting in damage to the fins. The filler material may be any of a variety of lightweight solid materials, such as suitable plastics or closed cell foams. The filler material prevents pressurized gases from entering at least some of the space between the fins and the outer fuselage surface. When the fins deploy after the projectile emerges from the launch tube the filler material pieces fall away harmlessly. The projectile continues on its flight with the fins in the deployed configuration.

Referring initially toFIGS. 1-3, a projectile10has a fuselage12and a series of fins14that are hingedly coupled to the fuselage12. The fins14may be in a compact configuration, shown inFIG. 2, in which the fins14are folded up against the fuselage12, with spaces16between the fins14and a local outer surface of the fuselage12. Filler material slabs or blocks18fill all or part of the spaces16. The compact configuration shown inFIG. 2allows the projectile10to fit into a launch tube or gun having a circular cross section. In the compact configuration the fins14may be substantially parallel to a tangent of the outer surface of the fuselage12. The outer surface is a smooth surface that is exposed to the airstream around the projectile10during flight of the projectile10. The outer surface is a surface on the aft portion of the fuselage12that may have any of a variety of suitable shapes. The outer surface may be substantially cylindrical, or may have any of a variety of other streamlined or drag-reducing shapes, including simple truncated cones or curved diameter reductions. In addition, it will be appreciated that the fuselage12may include provisions for fin attachments or propulsion systems, which may introduce special features in addition to the major structure shape. Upon exiting the launch tube or gun the fins14extend to the deployed or flight configuration shown inFIG. 3. In the deployed configuration the fins14may be substantially normal to the local outer surface of the fuselage12.

The fins14may be made of steel, or another suitable material. The fuselage12and other components in the fuselage12may be similar to those of prior projectile designs.

With reference now in addition toFIG. 4, the fins14are coupled to the fuselage12at a series of hinges20. The hinges20may be substantially parallel to an axis24of the projectile10, allowing the fins14to rotate from generally parallel to the fuselage12(the compact configuration) to generally perpendicular to the fuselage12(the deployed configuration). This rotation is about hinge axes that may be substantially parallel to the projectile axis24. (Or if a boattail shape is used, the rotation may be parallel to the local plane.) The hinges20may have a mechanism, for example a spring, that provides force to extend the fins14from the compact configuration to the deployed configuration. Alternatively the fins14may be deployed as result of forces on them during flight of the projectile10. For example spinning of the projectile10about its axis24may deploy the fins14by centrifugal forces.

The hinges20may have locks that secure the fins14in the deployed positions. The locks may be any of a variety of mechanisms, for example involving one or more pins that engage suitable holes or recesses when the fins14reach the deployed positions.

The filler material slabs or blocks18solve a problem that occurs during launch of the projectile10, where the fins14receive a sudden pressure difference across them.FIG. 5illustrates the beginning of a launch process for launching the projectile10from a launch tube or gun40. A propelling charge42at a closed end44of the launch tube or gun40ignites, producing pressurized gases that propel the projectile10away from the closed end44, in the direction of an open end of the launch tube40. The propelling charge may be separate from the projectile10, or may be attached to the projectile10. At this phase or step in the launch process, the pressure is near isobaric under and over the fins14.

FIG. 6shows a later time in the launch process, with the projectile10approaching an open end48of the launch tube40. The projectile10has an obturator54forward of the fins14. The obturator54is a ring of a relatively soft material, such as copper or plastic, that forms a seal against the wall of the launch tube40. This keeps pressurized gases behind the projectile10, providing more force on the projectile10. Use of an obturator can result in a 10% increase in exit velocity of a missile or other projectile.

A muzzle brake58is near the open end48of the launch tube40. The muzzle brake58is a series of openings60used to redirect some of the pressurized gasses outward and backwards. This reduces the recoil from the launch of the missile or other projectile10. At this phase or step in the launch, the inner and outer pressures on the surfaces of the fins14are still near isobaric.

Referring now toFIG. 7, once the obturator54passes the muzzle brake58pressurized gasses flow out from the launch tube40through the openings60. This reduces the pressure outside of the projectile10. If the filler material18were not present, some pressurized gas would be trapped as captive gas in the spaces16between fins14and the fuselage12. Although the trapping of pressurized gases in the spaces16would be only temporary, it would have the potential to cause serious undesirable effects. Trapped pressurized gases may lead to a significant pressure difference across the faces (major surfaces) of the fins14(in the absence of the filler material blocks18). To give example figures, the pressure difference may be from 13.8 MPa (2000 psi) to 68.9 MPa (10,000 psi) or even 82.7 MPa (12,000 psi). Such pressure differences exert considerable forces on the fins14. For example a fin having dimensions of 15.2 cm (6 inches) by 12.7 cm (5 inches) has an area of 193 cm2(300 in2). At a pressure difference of 68.9 MPa this results in a force of 1.33 MN (300,000 pounds).

Such a force could bend the fin14outward or cause the fin14to push outward, pivoting on the hinge20. This may bring the tip of the fin14into contact with the wall of the launch tube40. A particular hazard is contact between the fin14and the edges of the launch tube40surrounding the openings60of the muzzle brake58. The mechanical stresses on the fins14may cause other problems, such as mechanical failure (breakage) of parts of the fins14. The result may be damaged fins14that perform their function inadequately if at all. Damage to the fins14may cause complete loss of the projectile10. In addition, damage to the launch tube or gun40may result.

The filler material18provides a solution to the problem of trapped pressurized gases in the spaces16. By filling some or all of the volume of the spaces16, the filler material18at least greatly ameliorates the effect of a pressure difference on the fins14caused by captive or trapped gases. The filler material18eliminates the push of high pressure gas against the inner faces of the fins14by have filler material18in contact with the fin inner faces and relevant parts of surfaces of the projectile fuselages12. In addition, a smaller volume of trapped gas means that the pressure in the gas is more easily relieved. The gas pressure may be relieved by movement around the edges of the fins14, from the high pressure fin face to the region around the low pressure fin face. Also any deformation of the fins14will itself reduce the pressure by increasing the volume being filled by pressurized gases. If some of the space16is filled by the filler material18, the increase in volume underneath the fins caused by deformation of the fins14will itself result in more of a reduction in pressure. An as example, it will be appreciated that the ideal gas law, PV=nRT, where P is pressure, V is volume, T is temperature, n is the number of moles of gas, and R is a universal gas constant, indicates the energy in the system. If the free volume is reduced from 74 ml (4.5 in3) to 0.74 ml (0.045 in3) the total system energy is likewise reduced by a factor of 1000. The remaining 0.74 ml (0.045 in3) produce no significant pressure effect on the fins14.

As shown inFIG. 8, the filler material18may separate from the projectile10when the projectile10emerges from the launch tube40. The filler material18may fall away from the fins14as the fins14deploy from the compact configuration to the deployed configuration. Even if the filler material slabs or blocks18may be initially adhered to the fins14and/or the outer surface of the fuselage12, forces on the filler material slabs or blocks18caused by placing them in the airstream of the flying projectile10may be sufficient to dislodge the filler material slabs or blocks18. The separated filler material slabs or blocks18, being made of lightweight material, may fall away from the projectile10without being a serious threat to nearby personnel or equipment.

The filler material slabs or blocks18may be made of any of a variety of suitable materials. It is desirable for the filler material to be light weight, so as to decrease the mass that needs to be accelerated by the propelling charge42, so as to present less of hazard when separated from the other parts of the projectile10. The filler material18may be a suitable plastic, such as nylon. The filler material18alternatively or in addition may be a foam material, such as a closed-cell foam with a plastic (polymer) material continuous phase. It will be appreciated that other alternatives are possible, such as plastic blocks with hollow interiors.

As an example, a typical block would be the size of chord and span of the surface to be protected, with a depth the difference between the outside diameter of the body and the stowed diameter of the inner surface side. To give one example, a block might be about 7.1 cm (2.8 inches) in width by 20.3 cm (8 inches) long by 0.5 cm (0.2 inches), for a total volume of 74 ml (4.5 in3), weighing about 82 grams (0.18 lbs). In this example there would be 6 blocks for a combined weight of 0.49 kg (1.08 lbs). It will be appreciated that this is only a single example, and that a wide variety of sizes, shapes, number, and weight of blocks18may be employed.

The filler material slabs or blocks18may be formed first, and then placed in the spaces16between the fins14and the fuselage12. Alternatively, and as shown inFIG. 9, the filler material slabs or blocks18may be formed in place, by placing a mold70around each of the spaces16between the fins14and the outer surface of the fuselage12. Then liquid material or foam is introduced into the spaces16, such as being injected through an opening72in the mold70. The liquid material or foam is allowed to fill the spaces16, being constrained by the molds70, the fins14, and the fuselage12. It will be appreciated that foam materials may easily expand when injected into the space16, filling substantially all of the spaces16. Once the filler material has hardened the molds70may be removed, leaving filler material slabs or blocks18in place between the fins14and the fuselage12.

The filler material slabs or blocks18may fill substantially all of the volume of the spaces16. Alternatively the filler material may fill something less than 100% of the volume of the spaces16, for example filling at least 90% of the volume of the spaces16. It will be appreciated that the percentage required would depend on the strength of the fin material, the over pressure to be managed, and any constraints of how quickly the fin is permitted to open. The filler material slabs or blocks18may be in contact with and may be attached to either or both of the fins14and the fuselage12. The filler material18need not be in contact with both the fins14and the fuselage12, and may for example be attached to one or the other without being in contact with the other.

The use of the filler material18may be combined with other measures to reduce the effect of trapped pressurized gas on the fins14. For example spiracles (holes or other openings that allow passage of pressurized gases) may be provided in the fins14. A concurrently-filed application, “Projectile Having Fins With Spiracles,” Ser. No. 12/257,690,which is incorporated herein in its entirety, describes many possible configurations for spiracles in fins, with or without flaps or other covering structures.