Abstract:
Store ejector rack systems and methods having an improved fluid actuator assembly for sequencing the opening of the hooks from which the store is suspended and the pressurization of thrusters which force the store away from the aircraft are disclosed. In one embodiment, an actuator assembly includes a staged valve assembly including a primary valve for controlling the flow of high pressure fluid from an accumulator to the thrusters, and a slave piston independently movable with respect to the primary valve for actuating the hook release mechanism.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention generally relates to store ejector rack systems and methods for aircraft and, more particularly, to an improved fluid actuator for such racks.  
       BACKGROUND OF THE INVENTION  
       [0002]     An aircraft ejector rack is a device used to carry and release stores such as bombs and missiles from an aircraft in flight. These racks are typically mounted to the undersurfaces of aircraft wings and fuselages and incorporate both release and ejection features. The release features normally include bails or hooks from which stores may be suspended, and the ejection features normally include pneumatically operated thrusters for forcibly ejecting stores away from the aircraft to minimize the possibility of their colliding with the aircraft after release.  
         [0003]     A contemporary ejection rack system of the type described above incorporates an onboard pressurization capability, employing a single pressurization system capable of operating multiple release mechanisms and uses air to operate both the store release bails and thrusters. The system also includes a miniature compressor and a gas purification system which filters, dries, and stores ambient air as an energy medium. With the onboard compressor, pressure in the system can be maintained at the desired operating level regardless of system usage or temperature changes in the gas. The use of air eliminates the problems associated with the use of pyrotechnics to generate high pressure gasses, such as periodic cleaning required by the corrosives and moisture generated in such systems, and also eliminates the sealing problems commonly found in hydraulically operated ejector racks. An example of such a state-of-the-art pneumatically operated ejector rack system is seen in U.S. Pat. No. 5,583,312, which is incorporated herein by reference.  
         [0004]     It is common in the above-described prior art ejector rack systems to release a store by simultaneously pressurizing the hook release mechanism and the thrusters. The problem with such simultaneous pressurization is that it results in significant forces being applied to the store before the hook is fully opened, resulting in the transfer of those forces to the release mechanism. If those forces are sufficiently high, the release mechanism may jam or stall and the store may not be released. Secondly, the force required to open the hook may result in the excessive consumption of energy in the gas so that insufficient energy is available to power the thruster. One solution to this problem is proposed in U.S. Pat. No. 6,347,768, incorporated herein by reference, which discloses a fluid actuator for ejector rack systems which stages or sequences the operation of the hook release mechanisms and the thrusters.  FIG. 4  of that patent illustrates an actuator including a valve assembly which controls the flow of high pressure gas from an accumulator to the thrusters. The valve is also mechanically connected by a rod and a release ram to a hook release mechanism. The valve includes a cylindrical projection, referred to as a tab, which enters a bore in the valve seat when the valve is in its uppermost or closed position. Upon command, the valve moves downward, engaging the hook release mechanism when the valve is moved downward a predetermined distance. When the hook is fully opened, the tab on the valve head clears the valve seat, permitting high pressure air to pass to the thrusters. The problem encountered with this device is that because the tab is unsealed in the bore, it permits the leakage of high pressure air through the valve as soon as the primary valve is unseated which results in the loss of energy and the premature pressurization of the thruster.  
         [0005]     Accordingly, there is an unmet need in the prior art to provide for an aircraft stores ejector rack having a fluid actuator which pressurizes the hook release mechanism prior to the pressurization of the thrusters, thus avoiding the loss of fluid energy and jamming of the hook release mechanism.  
         [0006]     Moreover, there is a further unmet need in the prior art to provide for such a fluid actuator including a staged valve assembly connected to the hook release mechanism which permits passage of high pressure gas to the thruster only after the hook release mechanism has moved the hook to the open position.  
       SUMMARY OF THE INVENTION  
       [0007]     This invention can be broadly summarized as providing for stores ejector rack systems and methods for an aircraft. In one embodiment a rack includes a jacket having upper, middle, and lower chambers, and a primary valve for controlling fluid flow between the upper and middle chambers. The valve assembly also includes a slave piston which is movable independently of the primary valve in response to the pressure differential between the middle and lower chambers.  
         [0008]     In accordance with a more detailed aspect of the invention, the valve assembly includes a stem slidably mountable within the jacket and a primary valve slidably mountable on the stem. The valve assembly also includes a slave piston mounted to the stem for translation between upper and lower positions and engageable with a hook release mechanism. The valve assembly further includes a spring for biasing the valve toward its closed position, a second spring for biasing the slave piston towards its upper position, and a control valve for controlling fluid pressure in the lower chamber. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     Preferred and alternate embodiments of the present invention are described in detail below with reference to the following drawings.  
         [0010]      FIG. 1  is a side view of an aircraft in accordance with an embodiment of the invention;  
         [0011]      FIG. 2  is a perspective view of an injector rack constructed in accordance with an embodiment of the invention;  
         [0012]      FIG. 3  is a schematic side view of a fluid actuator assembly according to another embodiment of the present invention;  
         [0013]      FIG. 4  is a schematic front view of the actuator assembly of  FIG. 3 ;  
         [0014]      FIG. 5  is a second schematic side view of the actuator assembly of  FIG. 3 ;  
         [0015]      FIG. 6  is a schematic front view of the actuator assembly of  FIG. 5 ;  
         [0016]      FIG. 7  is a third schematic side view of the actuator assembly; and  
         [0017]      FIG. 8  is a schematic front view of the actuator assembly of  FIG. 7 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]     The present invention generally relates to systems and methods for separating stores from an aircraft. Many specific details of certain embodiments of the invention are set forth in the following description and  FIGS. 1 through 8  provide a thorough understanding of such embodiments. One skilled in the art, however, will understand that the present invention may have additional embodiments or that the present invention may be practiced without several of the details described in the following invention.  
         [0019]     It will be appreciated that embodiments of apparatus and methods in accordance with the present invention may be employed on a wide variety of aerospace vehicles. For example,  FIG. 1  is a side view of an aircraft generally designated by the numeral  10  in accordance with an embodiment of the invention. In this embodiment, aircraft  10  includes a fuselage  12 , a pair of wings  14 , and at least one engine  16 . Aircraft  10  further includes a pair of stores separation systems  18  in accordance with the present invention located on the lower surfaces of each of the wings  14 . In one particular embodiment, each of the systems  18  is of the type described above and shown in  FIGS. 2-8 . It will be appreciated that a variety of alternate embodiments of stores separation systems in accordance with the invention may be conceived. For example, a stores separation system in accordance with the present invention may be operatively coupled to the fuselage  12  rather than to the wings  14  (e.g. to eject a bomb, missile, drop tank, payload, etc), or to any other suitable portion of the aircraft  10 .  
         [0020]     Furthermore, although aircraft  10  shown in  FIG. 1  is representative of a well-known fighter aircraft, specifically, an F/A-18E Super Hornet manufactured by The Boeing Company, in alternate embodiments, virtually any other type or variety of military aircraft may be conceived that include apparatus and methods in accordance with the present invention. In alternate embodiments, for example, the aircraft may be a fighter aircraft, a rotary aircraft, a bomber aircraft, or any other suitable type of manned or unmanned aircraft, including those described, for example, in The Illustrated Encyclopedia of Military Aircraft by Enzo Angelucci, published by Book Sales Publishers, September 2001, and in Jane&#39;s All the World&#39;s Aircraft published by Jane&#39;s Information Group of Coulsdon, Surrey, United Kingdom, which texts are incorporated herein by reference.  
         [0021]     In  FIG. 2  illustrates a pneumatic ejector rack assembly  20  for forcibly ejecting a store from an aircraft in accordance with an embodiment of the present invention. Store  22  is suspended from the ejector rack assembly by carrier  24  which includes hooks  26  and hook actuating mechanisms  28 . The rack assembly also includes pneumatically actuated thrusters  30  and  32  which include rams  34  and  36  (not shown), each of which is disposed for reciprocating motion within its respective thruster. The purpose of the thruster is to forcibly eject store  22  downward and away from the aircraft after release of the store by carrier  24  to minimize the possibility of the store striking the aircraft after release.  FIG. 2  shows the rams in their fully retracted position and with hooks  26  in engagement with carrier  24 .  
         [0022]     Both the thrusters and the release mechanism are actuated by compressed air from a remotely located onboard pressurization unit (not shown) which supplies drive filtered and pressurized air to accumulator  50 . The accumulator  50  is in fluid communication with thrusters  30  and  32  by means of manifold  52  and feed conduits  54  and  56 , respectively. Upon command, high pressure air is provided for the accumulator  50  by means of a fluid actuator located within the accumulator  50  to activate hook release mechanism  28  and opening hooks  26  thereby releasing store  22 . High pressure air is also directed by the fluid actuator to thrusters  30  and  32  driving rams  34  and  36  downward and forcibly ejecting store  22  away from the aircraft. Store ejector racks of the type generally described above are known in the prior art as shown by U.S. Pat. Nos. 6,035,759 and 6,009,788 each of which is incorporated herein by reference.  
         [0023]      FIGS. 3 and 4  schematically illustrate an improved fluid actuator assembly  60  which provides for sequential pressurization of the hook release mechanisms and the thrusters to alleviate the problems encountered with simultaneous pressurization of those devices as described above. Actuator assembly  60  is largely disposed within accumulator  62  which is similar in construction to accumulator  50  referred to above except for important, inventive aspects described below. The actuator assembly  60  includes jacket  64  which defines upper chamber  66 , middle chamber  68 , and lower chamber  70 . The jacket  64  houses a valve assembly  80  which includes stem  82 , primary valve  84  which is slidably mounted on the stem, and slave piston  86  which is affixed to the stem and mounted for reciprocation within bore  88  of the jacket. Stem  82  is also sealably mounted for reciprocation in bore  108  formed in the jacket. Also affixed to the stem is hook release piston  90  which is operably engaged to a hook release mechanism which is not shown, but which is well described in the incorporated patents. In  FIGS. 3 and 4 , primary valve  84  is shown in the closed position where frusto-conical surface  92  of the valve sealably engages mating seat  94  formed in the jacket. Coil spring  96 , which extends between upper surface  98  of the slave piston and ledge  100  of the valve, biases the primary valve upward into the closed position. Likewise, coil spring  102 , which extends between base  104  of bore  88  and under surface  106  of the slave piston, biases the slave piston upward into an upper position as shown in  FIG. 4 .  
         [0024]     Actuator assembly  60  also includes control valve  120  which operates on command to open and close primary valve  84 . It does so by providing communication between lower chamber  70  and either the interior  122  of accumulator  62  or a source of fluid pressure, typically ambient pressure, which is lower than the pressure of fluid within accumulator  62 . The control valve includes body  124  and shaft  126  which is mounted for rotation within the valve body. In the operational position shown in  FIG. 4 , the control valve provides communication between the accumulator and lower chamber  70  via a first passage  130  in the valve body  124 , a second passage  132  in the valve shaft  126 , a third passage  134  in the valve body  124 , a fourth passage  136  in the jacket  64 . In that position, the pressure in lower chamber  70  is equal to the pressure of the fluid within accumulator  62 . Because middle chamber  68  is also in communication with interior  122  of the accumulator, the pressure of both sides of slave piston  86  is equal, so it is forced upward by spring  102  until primary valve  84  which rests atop the slave piston and engages seat  94 . When seated, primary valve  84  prevents high pressure fluid from entering upper chamber  66  which is in fluid communication with thrusters  30  and  32 . Details of the operation and construction of the control valve are well described in U.S. Pat. No. 6,347,768 which is incorporated herein by reference.  
         [0025]     When the command is given to eject store  22 , control valve  120  is activated, causing valve shaft  126  to be rotated into the position shown in  FIG. 6 . In that position lower chamber  70  is placed in fluid communication with a source of lower pressure, typically the atmosphere, via the passages  132 ,  134 ,  136 , and a fifth passage  140  in the valve body  124  and the accumulator  62 . When so positioned, the control valve  120  causes the pressurized fluid in lower chamber  70  to be vented to the atmosphere. As the pressure in lower chamber falls, slave piston  86  is exposed to an increasing pressure differential between the upper and middle chambers, causing it to move downward in bore  88 , as shown in  FIGS. 5 and 6 . As it does so, stem  82  and release piston  90  which are affixed to the slave piston also move downward, engaging and actuating the hook release mechanism (not shown). As the stem continues downward, retainer  150 , which is affixed to the stem, contacts upper surface  152  of valve  84 . At that point, hook release piston  90  has moved downward sufficiently that hooks  26  have fully opened and have released the store.  
         [0026]     Referring now to  FIGS. 7 and 8 , as stem  82  and slave piston  86  continue to move downward, primary valve  84  is forced further downward by retainer  150 , causing the valve to unseat and open. As it does so, high pressure fluid from accumulator  62  is permitted to flow into upper chamber  66  which is in fluid communication with thrusters  30  and  32  by means of feed conduits  54  and  56 , respectively. As they are pressurized, rams  34  and  36  are driven downward, ejecting the store from the aircraft. As the store is ejected, primary valve  84  and slave piston  86  will continue to move downward until they reach the positions shown in  FIG. 8  where primary valve  84  is fully opened and the slave piston  86  is in its lower most position. The cycle is completed by returning the valve shaft to the position shown in  FIG. 4 , thus equalizing the pressure between middle chamber  68  and lower chamber  70 . At that point, spring  102  forces slave piston  86  and valve  84  upward until the valve is closed.  
         [0027]     Embodiments of systems and methods in accordance with the present invention may provide significant advantages over the prior art. For example, because the thrusters are not pressurized until hooks  26  are fully opened, any potential jamming or binding of the hook release mechanisms is avoided. Also, because the fluid actuator pressurizes the hook release mechanism prior to the pressurization of the thrusters, the loss of fluid energy associated with the prior art is reduced or eliminated.  
         [0028]     While preferred and alternate embodiments of the invention have been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of these preferred and alternate embodiments. Instead, the invention should be determined entirely by reference to the claims that follow.