Patent Application
20200300590
The present disclosure relates to a tail kit assembly for a guided munition and more particularly to a tail kit assembly for a guided munition having a system of low profile trimmable rudders for guiding the munition along a trajectory.
Many guided munitions are known to include systems and/or assemblies that function to guide and control the munition by making corrections to its trajectory. These guidance systems typically include subsystems that can communicate with a fire control system which can implement course corrections—up or down and left and right maneuvers to alter or rather correct the course of the munition while in flight. Based on determinations made by guidance algorithms at the fire control system and communicated to the munition, different mechanical components of the munition can be activated or adjusted so as to control the flight path of the munition. These components are often generically referred to as “control surfaces” and can include wings, fins, strakes and rudders that, during flight, interact with the airstream to change the aeronautical characteristics and flight path of the munition.
Gun-fired, medium caliber munitions known in the art are constructed to have a general overall profile that provides a low degree of air resistance and facilitates rotation of the munition. A typical munition defines a longitudinal axis and may be formed with a conical leading end having a pointed or rounded tip, a central body section that is at least partially cylindrical, and a trailing end that may slope or taper radially inwardly from the central body section rearward.
The trailing end of the gun-fired munition may include a tail kit assembly coupled thereto that communicates with a guidance system as described above. Known tail kit assemblies can comprise a base coupled to the trailing end of the munition. In some cases, strakes and rudders are fixed to and extend outwardly from the surface of the base to stabilize the munition when in flight. When a guidance system is utilized in a gun-fired munition, controlling the trajectory of the munition is often problematic because the tail kit assembly needs to de-roll using strakes and place the rudder in the direction of the course correction. Gun-fired munitions can spin at a rotational rate of about 20,000 rpm causing the attached tail kit assembly to rotate, thus making calculation of its rotational orientation, which is essential for effectively guiding the munition, quite difficult and processor intensive.
To overcome this drawback, in some instances the base of the tail kit assembly is substantially rotationally decoupled from the munition such that the munition can spin at one rate of rotation due to the rifling of the barrel while the base spins at another slower rate of rotation. The strakes that are fixed to such a tail kit assembly can be angled or curved relative to the longitudinal axis, which generally corresponds to the direction of flight, so as to generate a rotational force on the base that is counter to rotation of the munition. To “de-spin” the base or, rather, to reduce or eliminate rotation of the tail kit assembly using the strakes simplifies determining the rotational orientation of the assembly and facilitates controlling the trajectory of the munition by way of the fixed rudder.
Conventionally, rudders and strakes are fixed to the surface of the base of the tail kit assembly and function to reduce the rotation of the assembly and guide or control the trajectory of the munition. When the munition is fired, shot, or launched from the ordinance the strakes and rudder project into the airstream as the munition travels along its direction of flight F or, in other words, the air resistance of the strakes and rudder produce counter rotation and transverse forces on the tail end of the munition in a desired manner thereby guiding or controlling the flight of the munition through the air. As is known in such aerodynamic components, the leading ends of the strakes and rudders are flush with the surface of the tail assembly base and progressively project further into the airstream along the axial length of the tail assembly. Due to the high rates of rotation, e.g., about 20,000 RPM of small munitions (25-30 mm) it is necessary for strakes to have a high or rather large profile such that their interaction with the airflow is significant enough in order to sufficiently counter the high rotational rates of the munitions enabling determination of the rotational position of the munition. Typical strakes of small munitions have a profile that is matched to the flight profile velocity, and coupled with the strakes projected area generate dynamic pressure to de-roll the tail kit. The size and shape of the strakes needs to be sufficient to overcome the bearing friction between the front of the munition and the base of the tail kit assembly. In addition, if the positioning of the tail kit is required to aide control guidance, the dynamics of the control actuator surface with the inertia of the tail kit needs to be considered in the sizing of the strakes. Since the typical control feature is a singular drag feature acting as a rudder in the air stream, roll placement of the rudder relative to the direction of travel is crucial for effectively controlling the trajectory of the munition. This results in aggressive strakes having a large surface area which interacts with the airstream to generate the needed control dynamics, thereby generating a significant amount of drag. Although the strakes and rudders as described above are beneficial for their intended purposes, because their fixed geometry on the outer surface of the base, the turning and drag forces caused thereby are constant. Such drag forces have a substantial negative effect on the velocity of the round and leads to a significant reduction in the effective range of such a guided munition. For example, it is common for a typical 30 mm×173 mm round to have a muzzle velocity of approximately Mach 3 (1,029 msec) and has a maximum range of about 5 km, but when a tail kit assembly, as described above, is utilized on the same round, because of the drag forces introduced thereby, the maximum range of the round decreases to about 3.5 km. While known tail kit assemblies facilitate guidance of such a round, the approximately 30% drop in the effective range of the round is undesirable.
Wherefore it is an object of the present disclosure to overcome the above-mentioned shortcomings and drawbacks associated with the conventional tail kit assemblies of guided munitions and more specifically with the tail kit assemblies of gun-fired, medium caliber guided munitions.
One aspect of the disclosure is a tail kit assembly of a guided munition having a tail kit base that is connected, relative to a direction of flight, to a trailing end of a projectile body. The tail kit base can rotate about a longitudinal axis relative to the projectile body. At least one trimmable control surface, rudder, flap or tab has, relative to the direction of flight, forward and rearward ends. The forward end is coupled to the tail kit base, such that the at least one trimmable control surface, rudder, flap or tab can be biased, moved, flexed or pivoted relative to the tail kit base, between a retracted orientation and an extended orientation. The at least one actuator is fixed between the tail kit base and the rearward end of the at least one trimmable control surface, rudder, flap or tab and can be electrically coupled to an onboard guidance system. The onboard guidance system can control actuation of the at least one actuator so as to bias, move, flex or pivot the trimmable control surface, rudder, flap or tab between the retracted orientation and the extended orientation.
One further aspect of the present disclosure is a system comprising a tail kit assembly equipped with multiple, trimmable control surfaces, rudders, flaps or tabs that allow the strakes of the tail kit assembly, which reduce spin from 20,000 RPM to between 0 to 12,000 RPM, to be far less aggressive than strakes of known tail kit assemblies thereby substantially reducing the overall drag on the projectile. The trimmable control surfaces, rudders, flaps or tabs can be modulated up to 50 to 200 Hz depending on the actuator used for modulating the trimmable control surfaces, rudders, flaps or tabs. Modulation of the trimmable control surfaces, rudders, flaps or tabs allows the tail kit base to continue to rotate in the original rotational direction of the projectile body. For example, a typical 30 mm projectile leaves the muzzle of a cannon rotating at 20,000 RPM or 333 Hz. The trimmable control surfaces, rudders, flaps or tabs feature of the current disclosure can be actuated from zero to full rudder by the actuator which is modulated up to 50 to 200 Hz, such that de-spinning the tail kit base requires only 133 Hz of strake compensation. This allows the strake dynamic pressure to be reduced by approximately 3:1 (reduced bearing friction) relative to the dynamic pressure of known strakes. Further reduction is realized by removing the dynamic coupling of the control dynamics and active positioning of the tail kit in the direction of the correction. While the tail kit is spinning, independent modulation of four control surfaces, rudders, flaps or tabs at 200 Hz can be activated when at least one specific control surface is pointed, i.e., oriented in the direction of the needed course correction, thereby removing the need to control the positioning of the tail kit directly by means of strakes. This reduces drag even further and additionally increases the range of the projectile and overall mission effectiveness.
In one embodiment of the system the trimmable rudder can comprise one, two, three or four control surfaces, rudders, flaps or tabs. Each of the control surfaces, rudders, flaps or tabs provides variable course correction when in the course correction direction while the tail kit base spins. The course correction or the measure of the course correction is variable and is based on a current airspeed of the munition.
These aspects of the disclosure are not meant to be exclusive and other features, aspects, and advantages of the present disclosure will be readily apparent to those of ordinary skill in the art when read in conjunction with the following description, appended claims, and accompanying drawings.
The foregoing and other objects, features, and advantages of the disclosure will be apparent from the following description of particular embodiments of the disclosure, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the disclosure.
Still referring to
The tail kit assembly 6 functions to direct, control or guide the munition 2 as it travels along a trajectory towards an intended target. The tail kit assembly 6 can be joined to the trailing end 14 of the front body 4 by way of bearings 16, e.g., ball, needle, or roller bearings in such a manner that a tail kit base 18 of the tail kit assembly 6 is rotationally decoupled from the front body 4. Because of this coupling, when the munition 2 is fired, shot, or launched out of a barrel, the front body 4 can spin about the longitudinal axis 8 at one rotational rate, e.g., 20,000 RPM while the tail kit base 18 can spin at different rotational rate or may not spin at all. The difference between the rotational speeds of the front body 4 and the tail kit base 18 is referred to below as the differential rotation speed. It is to be appreciated that the differential rotation speed can depend on a number of factors such as for example, the barrel rifling; the coupling between the front body 4 and the tail kit base 18; and the profile, i.e., form, size, and alignment of strakes 20 attached to an outer surface 22 of the tail kit base 18.
In certain embodiments of the present disclosure, the tail kit base 18 has, with respect to the direction of flight F, leading and trailing ends 24, 26. The outer surface 22 of the tail kit base 18 tapers inwardly along the longitudinal axis 8 from the leading end 24 to the trailing end 26. Although the general shape of the tail kit base 18 is a conical frustum, it is to be appreciated that the tail kit base 18 can have other profiles such as that of a cylinder or a prismatic cone for example. That is to say, from an axial point of view the outer surface 22 of the tail kit base 18 can have profile that is circular, as shown in
A number of control surfaces, hereinafter referred to as strakes 20, are secured to the outer surface 22 about the circumference of the tail kit base 18. The tail kit assembly 6 preferably has two to six strakes 20 and more preferably the tail kit assembly 6 has four strakes 20 as shown in
In certain embodiments, it is also possible for the strakes 20 to be secured to the tail kit base 18 in such manner that they can be arranged in a stowed position, when the munition 2 is secured within a casing and passes through the barrel, and can move to a deployed position when the munition 2 exits the muzzle of the barrel. It is also possible for a profile of the strakes 20 to be adjustable thereby enabling control the influence of the strake 20 on the rotation of the tail kit base 18, i.e., the differential rotational speed. For example, as shown in
The tail kit assembly 6, according to the disclosure, includes one or more trimmable control surfaces, rudders, flaps or tabs 34, each of which has forward and rearward ends 36, 38 and side edges 40. Hereinafter the one or more control surfaces, rudders, flaps or tabs will be referred to as trimmable rudders. With regard to
The embodiment of the tail kit assembly 6 shown in
The trimmable rudders 34 are made from a material that is lightweight and resilient such that the trimmable rudders 34 have a minimal effect on the overall weight of the munition 2 and are capable of maintaining their shape and profile when subjected to the stresses placed thereon by the airstream while in their extended orientation. The trimmable rudders 34 can be made from materials including one or more of: aluminum, steel, composites, i.e., carbon fibers, polyetherimide for example. Preferably the trimmable rudders 34 are made from aluminum. These materials can be in the form of thin plates, sheets, injection molded (both composites and metals), stamped films or foils such that the trimmable rudders 34 can be made to have a material thickness of between 0.003 to 0.015 in, preferably the trimmable rudders 34 are made to have a material thickness of approximately 0.010 in. Due to the minimal thickness, weight and rigidity along their length, the trimmable rudders 34 can provide desired aerodynamic characteristics in a minimal amount of space.
As shown in
Alternatively, as shown in
To bias the trimmable rudder 34 between the retracted and extended orientations, a synthetic muscle 50 is arranged within a cavity 51 in the pocket 42 of the outer surface 22 at the rearward end 38 of the trimmable rudder 34. The inner end 53 of the flexible muscle 50 is secured to the bottom surface of the cavity 51 while the opposite outer end 55 of the flexible muscle 50 is fixed to the inner facing surface of the trimmable rudder 34. The synthetic muscle 50 can be formed, for example, from a polymer or a carbon fiber based material that contracts or expands when a low voltage is applied thereto by the onboard guidance control system 54 via an electrical lead 52. One such synthetic muscle 50 is made from carbon fiber-reinforced siloxane rubber. A synthetic muscle of this type having a 0.4 mm diameter is able to lift 1.89 kg by 1.4 inches with a 0.172 V/cm applied voltage.
It is to be appreciated that in alternate embodiment, the trimmable rudder 34 can be biased between the retracted and extended orientations by means of a piezo actuator 50′ that is arranged within the cavity 51 of the pocket 42 at the rearward end 38 of the trimmable rudder 34. The piezo actuator 50′ contracts or expands when a voltage is applied by the onboard guidance control system 54 via an electrical lead 52. It is to be appreciated that due to its smaller more compact size, the synthetic muscle 50 is suited for use in smaller munitions, e.g., 25 to 30 mm, and simplifies actuator insertion therein. On the other hand, the piezo actuator 50′ is generally larger than the synthetic muscle 50 but it can sustain higher loadings and therefore maybe more appropriate for use in the large munitions, e.g., 40 to 57 mm Although the trimmable rudder 34 can be biased by one or the other of the synthetic muscle 50 or the piezo actuator 50′, the description below merely refers to the synthetic muscle 50 for biasing the trimmable rudder 34.
As shown in
A method of guiding the munition 2 along a trajectory with the trimmable rudders 34 will now be described with reference to the flowchart of
When a voltage is applied to the synthetic muscle 50 it can bias the bias the rearward end 38 of the trimmable rudder 34 laterally away from the outer surface 22 of the tail kit base 18 and into the airstream by a distance up to 4 mm, preferably the synthetic muscle 50 biases the trimmable rudder 34 into the airstream approximately 2 mm. It is noted that the distance by which the synthetic muscle 50 biases the trimmable rudder 34 into the airstream can be continuously adjusted based on the amount of voltage applied to the synthetic muscle 50 by the guidance control system 54.
Trimmable tail kit rudders 34 according to the present disclosure are advantageous for a number of reasons. For example, in their retracted orientation, the trimmable rudders 34 are flush with the outer surface 22 of the tail kit base 18 and produce no drag on the munition 2. As a result and in contrast to projectiles having rudders that are fixed in the airstream, the effective range of the munition 2 having trimmable rudders 34 is significantly enhanced.
The trimmable feature of the rudder 34 also enable adapting the orientation of the rudder 34 to the variable air speed (0.5 to 3.0 Mach) and providing the correct amount of rudder trim for the present air speed for the course correction needed.
In addition, although a tail kit assembly 6 having a single trimmable rudder 34 according to the disclosure can be utilized for controlling or guiding the direction of flight F of the munition 2 in an advantageous manner it is recognized that such control is limited, since the single trimmable rudder 34 needs to be properly radially aligned when it is activated in order to deflect the munition 2 in the desired manner. In the case of a single trimmable rudder 34 on the tail kit assembly 6, it is necessary for the tail kit base 18 to rotate about the longitudinal axis 8 so that the radial position of the trimmable rudder 34 can change thus enabling the munition 2 to be deflected in any lateral direction. However, due to rotation of the tail kit base 18, it is necessary for the trimmable rudder 34 to be activated and deactivated rapidly, such that the trimmable rudder 34 is extended only when in the desired radial orientation.
In an advantageous embodiment, the tail kit assembly 6 can have four trimmable rudders 34 that are located at 90 degree intervals from each other about the circumference of the tail kit base 18. A tail kit assembly 6 having four orthogonal trimmable rudders 34 that can be actuated individually or in different combinations to deflect the munition 2 reduces the need for the tail kit base 18 to roll to the correct radial orientation before the trimmable rudder 34 is biased to the extended position. This reduces the amount of time it takes for actuating the trimmable rudders 34 thereby enhancing the responsiveness of the tail kit assembly 6 and making changes in the direction of flight F of the munition 2 more rapid. The synthetic muscles 50 used in certain embodiments of the present disclosure can be deactivated and activated to bias the one or more trimmable rudders 34 between their fully retracted and fully extended orientations at a 200 Hz bandwidth response thus making it possible to leave the tail kit base 18 rotating about the longitudinal axis 8. That is to say, by utilizing the synthetic muscles 50 to rapidly trim the four trimmable rudders 34 it is not necessary to fully eliminate rotation of the tail kit base 18 in order to control or guide the flight of the munition 2. Due to the above, it is possible to reduce the size of the strakes 20 even further so as to have a yet lower interface with the airstream, thereby additionally reducing drag or air resistance caused by the strakes 20 and increasing the effective range of the munition 2. In contrast to strakes of known tail kit assemblies, the strakes 20 of the tail kit assembly 6 according to the disclosure have a reduced/smaller profile. Depending on the actuators 50 employed and the resulting modulation frequencies of the control surface, the strakes 20 according to the disclosure are reduced by more than 3:1 over known strakes. The reduced/smaller strakes 20 of the tail kit assembly 6 reduce the spin of the tail kit base 18 from 20,000 RPM to between 0 to 10,000 or 12,000 RPM and to reduce drag.
The tail kit assembly 6 with the trimmable rudders 34 is capable of generating power, via an alternator, which can be used for powering the onboard guidance control system 54. Using the difference of the rotational speeds (typically 10,000 to 20,000 RPM) of the tail kit assembly 6 and the front body 4, more than ample power, can be generated via a simple alternator, i.e., 100s of watts.
While the principles of the disclosure have been described herein, it is to be understood by those skilled in the art that this description is made only by way of example and not as a limitation as to the scope of the disclosure. Other embodiments are contemplated within the scope of the present disclosure in addition to the exemplary embodiments shown and described herein. Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present disclosure.
