Small body dynamics control method

A projectile including an ejectable aft fin housing assembly. The aft fin housing assembly includes aft fins that increase a distance between a center of gravity and a center of pressure of the projectile, improving passive stabilization of the projectile. Once the projectile has been passively stabilized, the aft fin housing assembly is ejected, decreasing a distance between the center of gravity and the center of pressure, improving active stabilization of the projectile.

TECHNICAL FIELD

The present disclosure relates generally to projectiles and more particularly to stabilization of small form factor aero-bodies.

BACKGROUND

Missiles use active stabilization systems to reduce pitch rate and enable greater control during flight. Small form factor aero-bodies (SFFA) are lower cost, lighter, and smaller compared to traditional missiles. Exemplary SFFA include drones, drone deployables, swarming MAV, precision taggant delivery, precision marking, precision sensor placement, and fireworks. Due to size and cost constraints, the active stabilization systems available to traditional missiles are not possible for SFFA.

SUMMARY

Improved passive deployment stabilization (also referred to as passive stabilization) of small form factor aero-bodies (SFFA) is needed to complement the reduced capabilities of active stabilization available to SFFA (e.g., due to size and cost limitations). Further driving this need is that (compared to traditional missiles) SFFA typically have a high angle of attack, making passive stabilization more difficult.

Passive stabilization of SFFA differs from passive stabilization of traditional missiles. For example, missiles have a length to diameter ratio (LD ratio) of approximately 20 to 1, while SFFA have a LD ratio of approximately 4 to 1. Also, missiles are considerably heavier (e.g., over 9 kg (20 pounds) for missiles as compared to 0.45-2.5 kg (1-5 pounds) for SFFA).

In both missiles and SFFA, stabilization is determined based on the center of pressure (CP) to center of gravity (CG) relationship. Center of pressure is a point where resultant aerodynamic force act on the projectile. Center of gravity is a point where the weight of the body is considered to act. If center of pressure and center of gravity coincide along a length of the projectile, then the net pitching moment produced about the center of gravity due to aerodynamic force is zero.

The above described differences between traditional missiles and SFFA result in different stabilization forces being dominant during passive stabilization. In missiles, passive stabilization is driven by Ma. Conversely, passive stabilization in SFFAs is driven by lateral inertia (Iyy). When launched at a high angle of attack (i.e., an angle of launch relative to a direction of travel at a time of launch), these differences result in traditional missiles having a passive stabilization time of approximately 500 milliseconds (ms) and traditional SFFA having a passive stabilization time of approximately 5 seconds. In one embodiment, a high angle of attack is an angle of 60° or greater. In another embodiment, a high angle of attack is an angle of 75° or greater.

This invention provides a novel, low cost, faster passive stabilization method. This solution is particularly useful with SFFA launched at high angles of attack, where the low cost and small form factor of SFFA drives the need for passive stabilization, because active stabilization may not be cost effective.

The present disclosure provides a projectile including an ejectable aft fin housing assembly that alters a center of pressure (1) to improve passive stabilization of the projectile before ejection and (2) to improve active stabilization of the projectile after ejection.

According to one aspect, a projectile is provided. The projectile includes a body and an aft fin housing assembly. The body includes a forward positioned nose. The aft fin housing assembly including aft fins, the aft fin housing assembly coupled to the body with a center of pressure of the projectile being aft of a center of gravity of the projectile, and the projectile being passively stabilized by the aft fins such that a pitch rate of the projectile is reduced below a capture pitch rate. The center of gravity is located closer to the nose than to a center point of a length of the projectile. The aft fin housing assembly is ejectable such that the aft fin housing assembly is no longer mechanically coupled to the body, and the center of gravity and the center of pressure of the projectile shift towards the nose.

Alternatively or additionally, the projectile also includes a control action system including maneuvering fins and maneuvering motors that alter an orientation of the maneuvering fins. The control action system is configured to actively stabilize the projectile when the pitch rate of the projectile is below the capture pitch rate by altering the orientation of the maneuvering fins when the projectile is in flight in an atmosphere, such that the pitch rate of the projectile is reduced to a stabilized pitch rate.

Alternatively or additionally, a diameter of the maneuvering fins is smaller than a diameter of the aft fins. When the aft fin housing assembly is mechanically coupled to the body, the maneuvering fins are fixed relative to the aft fins, such that the aft fins mechanically stabilize the maneuvering fins.

Alternatively or additionally, the maneuvering fins are mechanically fixed relative to the aft fins when the aft fin housing assembly is mechanically coupled to the body, such that a load caused by the atmosphere on the maneuvering fins is taken by the aft fins.

Alternatively or additionally, a passive capture rate of the projectile comprises a duration of time from launch until the pitch rate of the projectile decreases below the capture pitch rate. When an angle of attack relative to a direction of travel at a time of launch is greater than 60°, the passive capture rate is less than four seconds.

Alternatively or additionally, a length to diameter ratio of the projectile is at most ten-to-one. The length of the projectile is from a forward point of the body to an aft most point of the aft fin housing assembly. A diameter of the projectile is a diameter of the body.

Alternatively or additionally, the projectile has a weight of less than 2.3 kg (five pounds).

Alternatively or additionally, the aft fins are fixed to the aft fin housing assembly during the passive stabilization.

Alternatively or additionally, the projectile is configured to be launched into the atmosphere. Before being launched into the atmosphere, the aft fins are positioned, such that the aft fins have a diameter less than or equal to a diameter of the maneuvering fins. After being launched into the atmosphere, the aft fins are re-oriented such that the aft fins have a diameter greater than the diameter of the maneuvering fins.

Alternatively or additionally, when the aft fin housing assembly is mechanically coupled to body, the center of pressure of the projectile is additionally aft of a center point of a length of the projectile.

Alternatively or additionally, the aft fin housing assembly is ejected when the pitch rate of the projectile is reduced below the capture pitch rate.

Alternatively or additionally, the projectile also includes circuitry configured to control ejection of the aft fin housing assembly.

According to another aspect, a method of stabilizing a projectile with an aft fin housing assembly is provided. The method includes measuring a pitch rate of the projectile. The method also compares the pitch rate of the projectile to a capture pitch rate. The method further includes passively stabilizing the projectile, when the pitch rate is greater than the capture pitch rate, using aft fins of the aft fin housing assembly. The aft fins are configured to cause a center of pressure of the projectile to be aft of both a center point of a length of the projectile and a center of gravity of a projectile. The method additionally ejects the aft fin housing assembly, when the pitch rate of the projectile is less than the capture pitch rate, such that the aft fin housing assembly is no longer mechanically coupled to a body of the projectile, and the center of gravity and the center of pressure of the projectile shifts towards a nose of the projectile.

Alternatively or additionally, when the pitch rate of the projectile is less than or equal to the capture pitch rate, actively stabilizing the projectile by altering an orientation of maneuvering fins of a control action system using maneuvering motors of the control action system, such that a pitch rate of the projectile is reduced to a stabilized pitch rate.

Alternatively or additionally, when the pitch rate of the projectile is greater than the capture pitch rate, the maneuvering fins of the control action system are stabilized by fixing a position of the maneuvering fins relative to the aft fins.

Alternatively or additionally, the maneuvering fins are mechanically fixed relative to the aft fins when the aft fin housing assembly is mechanically coupled to the body, such that an aerodynamic load on the maneuvering fins is transferred to the aft fins.

Alternatively or additionally, the passive stabilization of the projectile is performed in less than four seconds from a launch of the projectile into an atmosphere until a pitch rate of the projectile decreases below the capture rate.

Alternatively or additionally, a length to diameter ratio of the projectile is at most five-to-one, A length of the projectile is from a forward point of the body to an aft most point of the aft fin housing assembly. A diameter of the projectile is the diameter of the body.

Alternatively or additionally, the aft fins are fixed to the aft fin housing assembly during the passive stabilization.

Alternatively or additionally, prior to passively stabilizing the projectile: launching the projectile into an atmosphere with the aft fins positioned such that the aft fins have a diameter less than or equal to a diameter of the maneuvering fins; and after being launched into the atmosphere, re-orienting the aft fins, such that the aft fins have a diameter greater than the diameter of the maneuvering fins.

While a number of features are described herein with respect to embodiments of the invention; features described with respect to a given embodiment also may be employed in connection with other embodiments. The following description and the annexed drawings set forth certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features according to aspects of the invention will become apparent from the following detailed description when considered in conjunction with the drawings.

The present invention is now described in detail with reference to the drawings. In the drawings, each element with a reference number is similar to other elements with the same reference number independent of any letter designation following the reference number. In the text, a reference number with a specific letter designation following the reference number refers to the specific element with the number and letter designation and a reference number without a specific letter designation refers to all elements with the same reference number independent of any letter designation following the reference number in the drawings.

DETAILED DESCRIPTION

A projectile includes an ejectable aft fin housing assembly. The aft fin housing assembly includes aft fins that increase a distance between a center of gravity and a center of pressure of the projectile, improving passive stabilization of the projectile. Once the projectile has been passively stabilized, the aft fin housing assembly is ejected, shifting the center of gravity and the center of pressure towards the nose, improving active stabilization of the projectile.

Turning toFIG.1, a projectile10including a body12and an aft fin housing assembly14is shown. The body12includes a forward positioned nose16and the aft fin housing assembly14includes aft fins18. The aft fin housing assembly14is mechanically coupled to the body12.

The body12is configured such that the center of gravity22is located closer to the nose16than to a center point24of a length28of the projectile. In an embodiment, the body12includes a skin, an airframe, and a forward ballast (also referred to as a nose ballast). The airframe is located inside of the skin and the skin protects internal components of the projectile10from an atmosphere (e.g., a liquid or gas) that the projectile10is passing through. A weight and position of the forward ballast is chosen based on a desired location of a center of gravity (CG)22of the projectile10. (As is described in further detail below, the position of the center of gravity affects stabilization of the projectile.) In an embodiment, the ballast is positioned adjacent a nose16of the projectile10.

In another embodiment, the body12does not include a forward ballast, but instead a composition of the skin, airframe, and other components of the projectile is chosen based on the desired location of the center of gravity22. For example, the nose16may include shielding and/or a portion of the airframe nearer the nose16may be made of a heavier material than a different portion of the airframe nearer the aft of the projectile10.

In an embodiment, a length28to diameter60ratio (LD ratio) of the projectile is at most five-to-one. In another embodiment, the LD ratio is at most 10-to-one. In still another embodiment, the LD ratio is between 4-to-1 and 8-to-1. The length28of the projectile10is from a forward point of the body to an aft most point of the aft fin housing assembly14. A diameter60of the projectile10is the diameter of the body12of the projectile.

In the embodiment depicted inFIG.1, the length28of the projectile is not affected by ejection of the aft fin housing assembly14. In this embodiment, the aft fin housing assembly14may be a torus that fits around the body12. Alternatively, in another embodiment, the length28of the projectile is affected by ejection of the aft fin housing assembly14. In this embodiment, the aft fin housing assembly14may be placed in line with the body12, such that the length28of the projectile is reduced by ejection of the aft fin housing assembly14.

In an embodiment, the projectile10has a weight of less than 1.4 kg (three pounds). In another embodiment, the projectile has a weight of less than 2.3 kg (five pounds).

As described above, the aft fin housing assembly14includes aft fins18. The aft fins18affect a center of pressure (CP)20of the projectile10. As shown inFIG.2, the aft fin housing assembly14is also ejectable, such that the aft fin housing assembly14is no longer mechanically coupled to the body12after being ejected. By ejecting the aft fin housing assembly14, the center of pressure20of the projectile10is altered by removal of the aft fins18. In an embodiment, the projectile10additionally includes circuitry62that controls ejection of the aft fin housing assembly14. In another embodiment, a deterministic charge is used to separate the aft fin housing assembly14from the body12.

In the embodiment shown inFIGS.1and2, the projectile10is shown along with the relative positions of the center of pressure20and the center of gravity22. InFIG.1, the presence of the aft fins18affects the center of pressure20, such that the center of pressure is located aft of the center point24along the length28of the projectile10. InFIG.2, the aft fin housing assembly14has been ejected so that it is no longer mechanically coupled to the body12. Due to the lack of the aft fins18and the loss of the mass of the aft fin housing assembly14, ejecting the aft fin housing assembly14shifts the center of pressure20and the center of gravity22of the projectile10towards the nose16. Ejecting the aft fin housing assembly14may decrease a distance30between the center of gravity22and the center of pressure20. Alternatively, ejecting the aft fin housing assembly14may increase the distance30between the center of gravity22and the center of pressure20or may have no effect on the distance30.

Properties of the aft fins18(e.g., material, size, position, etc.) are chosen, such that a position of the center of pressure20is located at a preferred location when the aft fin housing assembly14is mechanically coupled to the body12. In particular, when the aft fin housing assembly14is mechanically coupled to body12, the center of pressure20of the projectile10is aft of a center of gravity22of the projectile. In the embodiment shown inFIG.1, the center of pressure20of the projectile is additionally aft of a center point24of a length28of the projectile10.

Properties of the aft fin housing assembly14(e.g., materials, size, position, etc.) are chosen such that the center of gravity22is both located at a first desired location before ejection of the aft fin housing assembly14and is located at a second desired location after ejection of the aft fin housing assembly14. In one embodiment, the mass of the aft fin housing assembly14is minimized to increase the distance between the center of pressure20and the center of gravity22during passive stabilization (i.e., when the aft fin housing assembly14is mechanically coupled to the body12).

In an embodiment, the aft fin housing assembly14includes a fixation structure for maintaining a position of the aft fins18relative to the body12. In one embodiment, the fixation structure is an extension of the body12, such that the length28of the projectile10decreases when the aft fin housing assembly14is ejected. The aft fins18are mechanically attached to the fixation structure such that ejecting the fixation structure also ejects the aft fins18.

When the aft fin housing assembly14is mechanically coupled to the body12, the projectile10is passively stabilized by the aft fins18, such that a pitch rate of the projectile10is reduced below a capture pitch rate.

In an embodiment, the projectile10also includes a control action system40. The control action system40includes maneuvering fins42, and maneuvering motors44that alter an orientation of the maneuvering fins42. When the pitch rate of the projectile10is below the capture pitch rate, the control action system40actively stabilizes the projectile10by altering the orientation of the maneuvering fins42, such that the pitch rate of the projectile10is reduced to a stabilized pitch rate. In this embodiment, the capture pitch rate is determined based upon capabilities of the control action system40. That is, the capture pitch rate is determined as a pitch rate that the control action system40is capable of actively stabilizing to the stabilized pitch rate. Similarly, the stabilized pitch rate may be determined based on capabilities of a guidance system of the projectile10. In an embodiment, the stabilized pitch rate is determined based on a maximum pitch rate that the guidance system can actively guide the projectile10to a defined location when the projectile is experiencing the maximum pitch rate. The maximum pitch rate may be a pitch rate of approximately 0 degrees per second.

Returning toFIG.1, the center of pressure20is located aft of center of gravity22and at a distance30from the center of gravity22to provide for nose-forward flight. When the aft fin housing assembly14is mechanically coupled to the body12(FIG.1), an increased distance30between the center of pressure20and the center of gravity22enables faster passive stabilization of the projectile10. When the aft fin housing assembly14is ejected (FIG.2), the distance30between the center of pressure20and the center of gravity22may decrease. A decreased distance30may enable the control action system40to use smaller maneuvering fins42and less powerful and less expensive maneuvering motors44to stabilize flight of the projectile10(i.e., reduce the pitch rate to enable guided flight). Consequently, the projectile10has improved passive stabilization when the aft fin housing assembly14is mechanically coupled to the body12, followed by improved active control when the aft fin housing assembly14has been ejected.

In one embodiment, the aft fin housing assembly14is ejected when the pitch rate of the projectile10is reduced below the capture pitch rate. As described above, ejecting the aft fin housing assembly14shifts center of pressure20forward toward the nose16, enabling the maneuvering fins42to actively stabilize the projectile10.

Including the ejectable aft fin housing assembly14improves passive stabilization of the projectile10(also referred to as a passive capture rate). The passive capture rate of the projectile10is a duration of time from launch of the projectile10until the pitch rate of the projectile10decreases below the capture pitch rate. In one embodiment, when an angle of attack relative to a direction of travel at a time of launch is greater than 60°, the passive capture rate of the projectile is less than four seconds.

In the embodiment shown inFIG.1, a diameter46of the maneuvering fins42is smaller than a diameter48of the aft fins18. When the aft fin housing14assembly is mechanically coupled to the body12, the maneuvering fins42are fixed relative to the aft fins18, such that the aft fins18mechanically stabilize the maneuvering fins42. In an embodiment, the aft fins18are fixed to the aft fin housing assembly14during passive stabilization (i.e., while the aft fin housing assembly14is mechanically coupled to the body12).

In one embodiment, the maneuvering fins42are supported by the aft fin housing assembly14. In an embodiment, the maneuvering fins42are mechanically fixed relative to the aft fins18when the aft fin housing assembly14is mechanically coupled to the body12, such that a load caused by the fluid (e.g., the atmosphere that the projectile is passing through) on the maneuvering fins42is taken by the aft fins18. In one embodiment, the aft fins18include a notch that mechanically couples the maneuvering fins42and the aft fins18. In this way, the maneuvering fins may be shielded from mechanical loads at higher pitch rates that could, e.g., cause damage to the maneuvering fins and/or maneuvering motors.

In the embodiment shown inFIG.3, before being launched into the atmosphere, the aft fins18are positioned, such that the aft fins18have a diameter less than or equal to a diameter of the maneuvering fins42. After being launched into the atmosphere, the aft fins18are re-oriented such that the aft fins18have a diameter48greater than the diameter of the maneuvering fins46. In this embodiment, the increased diameter of the aft fins18post deployment pulls the center of pressure20aft.

In an embodiment, multiple projectiles10may be placed in a launching platform. The projectiles10may be ejected at odd angles (e.g., having a high angle of attack compared with typical missiles) from the launching platform due to the projectiles10being placed into the ejection platform at positions and angles designed to maximize the number of projectiles that can be fit into the launching platform. (Angle of attack refers to the angle between a central axis of the projectile along its length and a direction of travel of the projectile.) When ejected with a high angle of attack, passive stabilization is important to ensure that the pitch rate is reduced below the capture pitch rate of the control action system40to enable delivery of the projectile10to an identified location.

In an embodiment, the projectile10includes guidance for controlling a flight path of the projectile10to ensure that the projectile10is delivered to a determined identified location. In an embodiment, the guidance is part of the circuitry62.

The circuitry62may have various implementations. For example, the circuitry62may include any suitable device, such as a processor (e.g., CPU), programmable circuit, integrated circuit, memory and I/O circuits, an application specific integrated circuit, microcontroller, complex programmable logic device, other programmable circuits, or the like. The circuitry62may also include a non-transitory computer readable medium, such as random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), or any other suitable medium. Instructions for performing the method described below may be stored in the non-transitory computer readable medium and executed by the circuitry62. The circuitry62may be communicatively coupled to the computer readable medium through a system bus, mother board, or using any other suitable structure known in the art.

While the projectile is shown in the figures having a shape similar to a missile, the projectile10is not limited to being a missile. For example, the projectile10may be a drone, drone deployable, swarming MAV, precision taggant delivery, precision marking, precision sensor placement, missile, firework, unmanned aerial vehicle (UAV), etc.

Turning toFIG.4, a method100for stabilizing a projectile in flight in an atmosphere is shown. In decision block102, a pitch rate of the projectile10is compared to the capture pitch rate. If the pitch rate is greater than the capture pitch rate, then the method progresses to process block104. If the pitch rate is less than or equal to the capture pitch rate, then the method progresses to process block106.

In process block104, the projectile is passively stabilized using aft fins18of the aft fin housing assembly14. As described above, the aft fins18are configured to cause a center of pressure20of the projectile10to be aft of both the center point24of the length28of the projectile and the center of gravity22of the projectile.

In process block106, the aft fin housing assembly14is ejected, such that the aft fin housing assembly is no longer mechanically coupled to the body. Ejecting the aft fin housing assembly14causes the center of gravity22and the center of pressure20of the projectile to shift towards the nose16of the projectile. Ejecting the aft fin housing assembly14may also cause a distance30between the center of gravity22and the center of pressure20to decrease. Alternatively, ejecting the aft fin housing assembly14may increase the distance30between the center of gravity22and the center of pressure20or may have no effect on the distance30.

In an embodiment, the method moves from process block106to process block108. In process block108, the control action system40actively stabilizes the projectile10by altering an orientation of maneuvering fins42the using maneuvering motors44, such that a pitch rate of the projectile is reduced to a stabilized pitch rate.

In an embodiment, when the pitch rate of the projectile is greater than the capture pitch rate, processing moves from process block104to process block110. In process block110, the maneuvering motors44of the control action system40are stabilized by fixing a position of maneuvering fins42of the control action system40relative to the aft fins18.

In one embodiment of process block110, the maneuvering fins42are mechanically fixed relative to the aft fins18when the aft fin housing assembly14is mechanically coupled to the body12, such that a load caused by the atmosphere on the maneuvering fins42is taken by the aft fins18.

In an embodiment, the passive stabilization of the projectile10is performed in less than four seconds from a launch of the projectile into the atmosphere until a pitch rate of the projectile decreases below the capture rate.

In an embodiment, the method100may include process block112before decision block102. In process block112, the projectile10is launched into an atmosphere with the aft fins18positioned such that the aft fins18have a diameter48less than or equal to a diameter46of the maneuvering fins42. After being launched into the atmosphere in process block112, the aft fins18are re-oriented in process block114, such that the aft fins18have a diameter48greater than the diameter46of the maneuvering fins44.

Throughout this disclosure, when referring to both passive and active stabilization of the projectile, the projectile is assumed to be moving (e.g., in flight, falling, etc.) in an atmosphere.

All ranges and ratio limits disclosed in the specification and claims may be combined in any manner. Unless specifically stated otherwise, references to “a,” “an,” and/or “the” may include one or more than one, and that reference to an item in the singular may also include the item in the plural.