Abstract:
An ejection seat having pitch, roll, and yaw control provided by three separate rocket motors where each rocket motor has a fixed nozzle and the entire rocket motor is rotated about a single axis corresponding to the minimum principal moment of inertia of the rocket. Actuation for each rocket motor is by means of a hydraulic rack and pinion actuator. Power for the hydraulic actuators is provided by a unique hydro-pneumatic amplifier that converts stored gas energy into pressurized hydraulic fluid. The high pressure hydraulic fluid is directed through conventional servo valves into the appropriate actuators to provide main, roll, pitch, and yaw thrust as required to achieve upright orientation and vertical flight.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to aircraft escape systems, in particular to aircraft ejection seats. 
         [0002]    Ejection seats in high performance military aircraft must be capable of safely removing the pilot or other occupant from the stricken aircraft across a wide variety of aircraft speed regimes, altitudes and aircraft attitudes. The most difficult ejection occurs when the aircraft is at low altitude and at an inverted or other non-upright orientation. Approximately 50% of the United States Air Force fighter aircraft ejection fatalities occur due to insufficient altitude at the time of ejection. Without sufficient altitude, the occupant&#39;s recovery parachute cannot fully deploy to bring the occupant safely to the ground. 
         [0003]    It has long been recognized that an aircraft ejection seat having the capability of assuming an upright orientation irrespective of the aircraft attitude and thereafter gaining sufficient altitude for a safe parachute deployment would be desirable for reducing ejection fatalities. U.S. Pat. No. 4,216,928 to Hooper, et al. discloses a microwave radiometric attitude reference system that uses microwave radiometry to sense the orientation of the ejection seat. Pitch and roll of the ejection seat are controlled by a linear pitch servo actuator and a linear roll servo actuator that move a single gimbal-mounted rocket motor. 
         [0004]    U.S. Pat. No. 4,303,212 to Stone, et al. discloses an aircraft ejection seat that includes an attitude control processor, which processes signals from three attitude sensors and uses those signals to control a pair of servo valves. The servo valves actuate a linear pitch servo and a linear roll servo that act on a gimbal-mounted spherical rocket motor. 
         [0005]    U.S. Pat. No. 4,721,273 to Trikha discloses an aircraft ejection seat in which the main thrusters have steerable nozzles for the purpose of changing the direction of the thrust axis. The ejection seat also includes a pair of fixed, opposed roll control thrusters and a pair of fixed pitch control thrusters that operate together to maintain the ejection seat in an upright orientation. 
         [0006]    U.S. Pat. No. 4,236,687 discloses an aircraft ejection seating having pitch, roll and yaw control. The ejection seat includes two spherical gimbal-mounted rocket motors each of which is acted on by two linear hydraulic actuators. Pitch and roll are controlled by varying the position of the two rocket motors in unison. Yaw control is accomplished by positioning the rocket motors so that the thrust vectors are not parallel, which produces a torque about the yaw axis of the ejection seat. 
         [0007]    Although linear actuators acting on large spherical rocket motors could theoretically accomplish the desired pitch, roll and yaw control, in practice the large moment of inertia of the spherical rocket motor necessitates very large and powerful linear actuators to move the rocket motors to maintain stable flight. Large powerful hydro-pneumatic actuators, in turn, are heavy and require substantial power to operate, which leads to a heavier ejection seat which requires a larger rocket motor, necessitating more powerful hydro-pneumatic actuators and so on. Accordingly, what is needed is an ejection seat with pitch, roll and yaw control that incorporates low moment of inertia rockets and actuators in order to meet the size and weight constraints as well as reaction times necessary for the ejection seat to achieve upright stable flight. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention comprises a maneuvering ejection seat for an aircraft in which the rocket motor has a fixed nozzle and the entire motor is rotated about a single axis. According to an illustrative embodiment of the invention, the main rocket motor is substantially cylindrical in shape and terminates at a fixed nozzle that is canted relative to the longitudinal axis of the rocket motor. The rocket motor is mounted with its longitudinal axis substantially vertical along the seat back portion of the ejection seat. The upper end of the rocket motor is supported by a thrust bearing that allows the main rocket motor to be pivoted about its longitudinal axis. A hydraulic rack-and-pinion actuator pivots the main rocket about its longitudinal axis. Pivoting of the main rocket about its longitudinal axis provides yaw control as well as vertical thrust. 
         [0009]    In addition to the main rocket, the illustrative ejection seat has a pitch control rocket and a roll control rocket. The pitch control rocket comprises a substantially cylindrical rocket motor with a fixed nozzle that has a thrust axis substantially orthogonal to the longitudinal axis of the rocket motor. The pitch control rocket is mounted with its longitudinal axis substantially orthogonal to the forward-facing direction of the seat. The pitch-control rocket is also pivoted about its longitudinal axis by a hydraulic rack-and-pinion actuator. 
         [0010]    Finally, in addition to the main rocket and the pitch control rocket, the illustrative ejection seat has a roll control rocket. The roll control rocket comprises a substantially cylindrical rocket motor with a fixed nozzle orthogonal to the longitudinal axis the rocket motor. The roll control rocket is mounted to the ejection seat with its longitudinal axis oriented along the forward facing direction of the ejection seat. In a preferred embodiment, because of space constraints, the roll control rocket may comprise two smaller rocket motors with parallel nozzles. As with the main rocket and the pitch control rocket, the roll control rockets are pivoted about their longitudinal axes by means of a hydraulic rack-and-pinion actuator. Power for the hydraulic actuators is provided by a unique hydro-pneumatic pressure source. The pressure source comprises a pressure vessel containing a pressurized gas such as helium or nitrogen with a pyrotechnically actuated valve. Upon initiation, the pressurized gas flows from the pressure vessel into the input end of a hydro-pneumatic amplifier. The hydro-pneumatic amplifier consists of a free-floating piston contained in a bore separating a supply of hydraulic fluid from the pressurized gas. Depending on the shape of the piston, the hydraulic fluid can be pressurized to a pressure greater than, equal to, or less than the gas pressure. The high pressure hydraulic fluid is directed through conventional servo valves into the appropriate hydraulic rack-and-pinion actuators to provide the appropriate main, roll, pitch, and yaw thrust as required to achieve upright orientation and vertical flight. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0011]    The present invention will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying drawing figures in which like references designate like elements and, in which: 
           [0012]      FIG. 1  is a perspective view of an ejection seat incorporating features of the present invention; 
           [0013]      FIG. 2  is a perspective view of the pitch and roll control motor assembly on the ejection seat of  FIG. 1 ; 
           [0014]      FIG. 3  is a bottom view, partially cut away of the pitch and roll control rocket motor assembly of  FIG. 2 ; 
           [0015]      FIG. 4  is an enlarged view of the upper portion of the ejection seat encircled in  FIG. 1 , partially cut away; and 
           [0016]      FIG. 5  is an exploded, perspective view of the yaw actuator shown in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The drawing figures are intended to illustrate the general manner of construction and are not necessarily to scale. In the detailed description and in the drawing figures, specific illustrative examples are shown and herein described in detail. It should be understood, however, that the drawing the figures and detailed description are not intended to limit the invention to the particular form disclosed, but are merely illustrative and intended to teach one of ordinary skill how to make and/or use the invention claimed herein and for setting forth the best mode for carrying out the invention. 
         [0018]    With reference to  FIG. 1 , an ejection seat  10  comprises a seat frame  12  supporting a back portion  14  and a seat portion  16  for supporting an aircraft occupant (not shown). Ejection seat  10  includes a main rocket motor  20 , a pitch control rocket motor  22 , and a pair of tandem roll control rocket motors  24  and  26 . In the illustrative embodiment of  FIG. 1 , main rocket motor  20  comprises a conventional United Air Force CKU-5 rocket catapult motor. 
         [0019]    With additional reference to  FIGS. 2 and 3 , the pitch and roll control unit  28  comprises pitch control motor  22  and roll control motors  24 ,  26  supported by a frame  30  which is mounted to seat portion  16  of ejection seat  10 . Pitch control rocket motor  22  comprises a conventional solid propellant rocket grain contained within a cylindrical housing  32 . Pitch control rocket motor  22  further comprises nozzles  34  and  36  located at opposite ends of cylindrical housing  32 . Nozzles  34  and  36  have thrust axes that are orthogonal to the longitudinal axis  38  of pitch control rocket motor  22 . Pitch control motor  22  is supported by low friction bearings  40 ,  42  located at either end of pitch control rocket motor  22 . Low friction bearings  40 ,  42  enable pitch control rocket motor  22  to be pivoted quickly about its longitudinal axis  38 . Pitch control rocket motor  22  is pivoted about it longitudinal axis by means of a pinion gear  44  attached to one end of cylindrical housing  32  which is driven by a rack gear  46  in a manner more fully described hereinafter. A position sensor  48 , which comprises a conventional potentiometer, optical encoder or similar device provides position feedback to the ejection seat avionics (not shown). 
         [0020]    Pitch and roll control unit  28  further comprises a pressure vessel  50  which is connected via a manifold  52  to hydro-pneumatic amplifiers  54  and  56 . Hydro-pneumatic amplifier  54  comprises a piston  58  which separates inlet port  60  from a quantity of hydraulic fluid  62  contained within the bore  64  of hydro-pneumatic amplifier  54 . Similarly, hydro-pneumatic amplifier  56  comprises a piston  68  separating inlet port  70  from a quantity of hydraulic fluid  72  contained within bore  74  of hydro-pneumatic amplifier  56 . Pressure vessel  50  is charged with high pressure gas such as nitrogen or helium to a pressure of 5000 psi. The stored energy available in the pressurized gas is sufficient to operate the servo mechanisms for the duration of the ejection seat flight. 
         [0021]    In operation, upon receipt of a signal to eject, as the main rocket motor  20  is firing, pyrotechnic valve  76  opens to release the pressurized gas into manifold  52  where it acts against piston  58  causing piston  58  to pressurize hydraulic fluid  62  to an equal pressure. Note that although in the illustrative embodiment the gain of hydro-pneumatic amplifier is one, by using a stepped bore and a piston having two diameters, the gain of hydro-pneumatic amplifier  54  can be greater than or less than one depending on the application desired. Pressurized hydraulic fluid  62  then flows out of hydro-pneumatic amplifier  54  into inlet port  80  of servo valve  82 . Servo valve  82  then directs the high pressure fluid to one of two outlet ports  84 ,  86 , which causes the high pressure fluid to act on piston  88  of actuator  90  to move rack gear  46  in and out of bore  92  of actuator  90 . The linear motion of rack gear  46  is transformed into rotary motion of pitch control rocket motor  22  by interaction of rack gear  46  with pinion  44 . In the preferred embodiment, the hydraulic fluid  62  is a conventional MIL-H-5606G hydraulic fluid. The servo valve  82  is preferable a high frequency hydraulic servo valve such as a HR Textron model  25 A servo valve. The pressure vessel  50  is preferably a welded high pressure vessel such as manufactured by Conax Florida. 
         [0022]    Because of fore-aft space constraints, rather than a single roll control rocket motor, a pair of roll control rocket motors  24 ,  26  are used in the illustrative embodiment. As with pitch control rocket motor  22 , roll control rocket motors  24 ,  26  are supported by low friction bearings to enable them to pivot about their longitudinal axes  96  and  98  respectively. As with pitch control rocket motor  22 , when pyrotechnic valve  76  opens, high pressure gas in manifold  52  acts on piston  68  of hydro-pneumatic amplifier  56  pressurizing hydraulic fluid  72  contained therein. High pressure hydraulic fluid  72  then enters inlet port  100  of servo valve (shown schematically as reference  94 ) which directs it to one of two outlet ports  102 ,  104  to act on a double acting piston  106  which moves a pair of rack gears  108 ,  110 . Rack gears  108 ,  110 , in turn act on corresponding pinion gears  112 ,  114  to rotate roll control rocket motors  24 ,  26  in unison. Position feedback is provided by position sensors  116  and  118  which comprise conventional potentiometers optical encoders or the like. 
         [0023]    With reference to  FIGS. 4-6 , yaw control is provided by a yaw control module  120  located near the upper end of back portion  14  of ejection seat  10 .  FIG. 4  is an enlarged view of the portion of  FIG. 1  circled with reference numeral  4  cutaway to show the detail of yaw control module  120 . Yaw control module  120  comprises a thrust collar  122  which attaches rigidly to upper portion  124  of main rocket motor  20 . Thrust collar  122  is supported by a low friction thrust bearing  126 . A pinion gear  128  is integral to thrust collar  122 . Pinion  128  comprises two sector gears  130 ,  132  for reasons discussed more fully hereinafter. 
         [0024]    In operation, when pyrotechnic valve  76  opens, a portion of the high pressure gas entering manifold  52  is directed through tube  134  into the inlet port of hydro-pneumatic amplifier  136 . Piston  138  of hydro-pneumatic amplifier  136  then compresses a quantity of hydraulic fluid (not shown) within the bore  140  of hydro-pneumatic amplifier  136 . The high pressure fluid is then directed via servo valve  142  to either end  144 ,  146  of a piston-rack combination  148  which meshes with sector  130  of pinion gear  128 . The linear motion of piston-rack combination  148  is converted into rotary motion of thrust collar  132  by interaction of piston rack  148  and pinion gear  128 . Because the nozzle  150  of main rocket motor  20  is canted at an oblique angle to the longitudinal axis  152  of main rocket motor  20 , main rocket motor has both a vertical and horizontal component to its thrust vector. Accordingly, rotating main rocket motor  20  about its axis provides a torque about the yaw axis of ejection seat  10 . Position feedback of main rocket motor  20  is provided by position sensor  48  which also comprises a conventional position sensor such as a potentiometer optical encoder or the like which meshes with sector  132  of pinion gear  128 . 
         [0025]    Because the rocket motors of the present invention are rotated about their longitudinal axes, the moment inertia of the rocket motors is minimized, which in combination of the high pressure hydraulic actuators, enables the rocket motors to pivot with a 20-25 Hertz response time. With a 20-25 Hertz response time for each of the rocket motors in the ejection seat of the present invention, the present invention is capable of assuming and maintaining stable flight in spite of the inherent aerodynamic instability of the ejection seat itself. 
         [0026]    Although certain illustrative embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods may be made without departing from the spirit and scope of the invention. For example, although the present invention uses a hydro-pneumatic amplifier with a gain of one to supply high pressure hydraulic fluid, a conventional accumulator with a flexible diaphragm is also considered within the scope of the present invention. Additionally, although the present invention utilizes cylindrical rocket motors, any substantially cylindrical rocket motor including tapered, conical, or other body of revolution or prism shapes are considered within the scope of the present invention provided the body has a principal axis of inertia that is less than the other two axis of inertia and the smaller principal axis defines the longitudinal axis about which the rocket motor is pivoted. Accordingly, it is intended that the invention shall be limited only to the extent required by the appended claims and the rules and principals of applicable law.