Abstract:
An ejection seat arm flail injury prevention apparatus comprises a pair of rigid support arms on each side of the ejection seat that deploy outwardly to support a semi-rigid backstop substantially behind the ejection seat occupant. When the ejection seat is propelled out of the aircraft and is subjected to the windblast, the occupant&#39;s arms are allowed to flail in a rearward direction in the windblast until the occupant&#39;s arms impact the semi-rigid backstop. The backstop is semi-rigid in that it deforms sufficiently to enable the rearward motion of the occupant&#39;s arms to be arrested without impact injury, yet is sufficiently rigid to prevent the occupant&#39;s arms from rebounding off the backstop or striking the rigid support arms.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of provisional application No. 61/261,055 filed Nov. 13, 2009. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to aircraft interior equipment, and more particularly, to aircraft ejection seats. 
     When a pilot or other aircraft occupant ejects from an aircraft moving at high speed, the occupant is subjected to various aerodynamic forces which, if not properly controlled, may lead to injury. One area of concern is the occupant&#39;s arms, which can be severely injured if allowed to flail uncontrollably in the windblast. 
     Various methods and devices have been proposed to restrain an ejection seat occupant&#39;s arms to prevent windblast flailing injuries. U.S. Pat. No. 3,074,669 to Bohlin teaches a plurality of tethers attached to the occupant&#39;s arms. As the ejection seat is propelled from the aircraft, the tethers draw the occupant&#39;s arms inward and restrain them to prevent windblast flailing. Although satisfactory in operation, the restraints taught by Bohlin are “active” in that they require the occupant to attach the tethers upon entering the aircraft. A significant disadvantage of all “active” systems is that they impose additional tasks on crewmembers in order for them to be readied, and may be improperly attached or ignored entirely by the crewmember, rendering them ineffective. 
     U.S. Pat. No. 4,592,523 to Herndon discloses a “passive” restraint system that includes a plurality of nets that deploy forward and inward to form a curtain surrounding the occupant. The restraint system disclosed in Herndon requires the added complexity of a pyrotechnic actuator to deploy the system and, because it wraps around the occupant, may interfere with the occupant&#39;s separation from the ejection seat after deployment. 
     U.S. Pat. No. 4,081,156 to Ideskar discloses a passive restraint system that includes a plurality of side curtains that deploy forward to form a cage around the occupant. Although the side curtains of Ideskar restrict the occupant&#39;s arms from moving outward, they do not prevent the occupant&#39;s arms from flailing upward and possibly over the leading edge of the side curtains. 
     What is needed is a passive restraint system that reliably prevents arm flail injuries without the disadvantages of the prior art passive restraints. 
     SUMMARY OF THE INVENTION 
     The present invention comprises an apparatus for preventing arm flail injuries to the occupant of an aircraft ejection seat. According to an embodiment of the invention, the arm flail injury prevention apparatus comprises a plurality of rigid outwardly-extending support arms that support a semi-rigid backstop deployed substantially behind the ejection seat occupant. When the ejection seat is propelled out of the aircraft and is subjected to the windblast, the occupant&#39;s arms are allowed to flail in a rearward direction in the windblast until the occupant&#39;s arms impact the semi-rigid backstop. The backstop is semi-rigid in that it deforms sufficiently to enable the rearward motion of the occupant&#39;s arms to be arrested without impact injury, yet is sufficiently rigid to prevent the occupant&#39;s arms from rebounding off the backstop or striking the rigid support arms. Once the backstop arrests the rearward motion of the occupant&#39;s arms, the windblast forces themselves press the occupant&#39;s arms safely against the backstop to prevent flailing. Because the backstop is completely passive, it requires no action on the part of the occupant to hook-in or otherwise ready the apparatus for use prior to takeoff. Additionally, because the backstop is deployed substantially behind the ejection seat occupant, it does not interfere with the occupant&#39;s separation from the ejection seat when the parachute is deployed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       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: 
         FIG. 1  is a front perspective view of an ejection seat incorporating features of the present invention; 
         FIG. 2  is simplified drawing showing the ejection seat of  FIG. 1  with the arm flail injury prevention apparatus in the stowed position; 
         FIG. 3  is a simplified perspective view of the ejection seat of  FIG. 1  with the arm flail injury prevention apparatus in the partially deployed position; and 
         FIG. 4  is a simplified perspective view of the ejection seat of  FIG. 1  with the arm flail injury prevention apparatus fully deployed. 
     
    
    
     DETAILED DESCRIPTION 
     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 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. 
     With reference to the drawing figures and with particular reference to  FIG. 1 , ejection seat  10  comprises a seat frame  12  having a seat pan portion  14  and a seat back portion  16 . Seat frame  12  is formed of any suitable material including aluminum alloys, titanium alloys and/or composite materials but in the embodiment of  FIG. 1  is composed of aluminum alloy. Ejection seat  10  is launched conventionally by means of a catapult and a solid rocket motor which propels ejection seat  10  out of the aircraft along launch rail  18 . A lower support arm  20  is attached to frame  12  by means of a ratcheting hinge  24 , the purpose of which will be explained more fully herein after. Lower support arm  22  is similarly attached to frame  12  by means of a ratcheting hinge (not shown). An upper support arm  26  is attached to frame  12  with a conventional non-ratcheting hinge  30 . Upper support arm  28  is similarly attached to frame  12  by means of a non-ratcheting hinge (not shown). Upper and lower support arms  20 ,  22 ,  26 ,  28  may be formed of any suitably strong, rigid and lightweight material such as carbon fiber, titanium or aluminum alloy but in the illustrative embodiment of  FIG. 1 , arms  20 ,  22 ,  26  and  28  are formed of high-strength aluminum alloy having an I-beam cross section to maximize the area moment of inertia of the arms. 
     A primary cable  32  is secured at its upper end  34  to seat frame  12 . The lower end  36  of primary cable  32  is spliced to a lower support cable  38  which is secured at its ends  40 ,  41  to seat frame  12 . Primary cable  42  is similarly secured to seat frame  12  at its upper end  44  and is secured at its lower end  46  to a lower support cable  48  which is secured at its ends to seat frame  12 . Primary cable  32  is routed through an eye at the free end  50  of lower support arm  20  and through an eye located at the free end  52  of upper support arm  26 . Primary cable  42  is similarly routed through eyes in the free ends  54 ,  56  of lower support arm  22  and upper support arm  28 , respectively. A secondary cable  60  is attached to frame  12  at an upper end  62 . The lower end  64  of secondary cable  60  is attached to one of a plurality of tertiary cables  66  that run between frame  12  and a plurality of eyes located at free end  50  of lower support arm  20 . Secondary cable  68  is of substantially identical construction as secondary cable  60  and therefore will not be discussed in detail herein. As can be determined from an inspection of  FIG. 1 , the cables discussed hereinbefore form a net-like backstop  70 ,  72  composed of a plurality of shrouds having very little frontal area that would cause wind resistance as compared with the area contained within the perimeter of primary cables  32  and  42 . 
     The cables forming backstops  70  and  72  may be of any suitable material having sufficiently low elongation such that the force of the occupant&#39;s arm striking the backstop does not deform the backstop a sufficient distance for the occupant&#39;s arms to impact the support arms  20 ,  22 ,  26 ,  28 . In the embodiment of  FIG. 1 , the cables comprise a woven aramid fiber having an elongation of approximately five percent (5%). The length of the cables are chosen such that as the arms deploy, the cables are tensioned to approximately 200 lbs. such that upon impact with a 90 th  percentile occupant&#39;s arms at 600 knots, the backstop deforms and recovers no more than 3 inches, preferably between 1-2 inches and most preferably approximately one inch at its maximum deflection. 
       FIGS. 2-4  show the operation of ejection  10 . With reference to  FIG. 2 , backstop  70  is shown in its undeployed condition with arms  20 , 22 , 26 , 28  folded against seat back  16  within container  74 . Attenuator  78  is attached via deployment cable  80  which is attached to anchor  82  secured to the aircraft frame. As shown in  FIG. 3 , as ejection seat  10  is propelled out of the aircraft, attenuator  78  pulls lower support arm  20  out of container  74  and along with it primary cable  32  and the remaining components of backstop  70 . A splice, cable stop or similar device  84  is attached to primary cable  32  at a predetermined location. As lower support arm  20  is deployed by attenuator  78  cable stop  84  deploys upper support arm  26  to its deployed position. This method of deployment causes primary cable  22  and lower support cable  38  to tension before secondary cable  60 . Thus, the section below lower support arm  20  is fully tensioned when lower support arm  20  is at an angle 10 degrees above horizontal while the section above lower support arm  20  is fully tensioned when lower support arm  20  is about 20 degrees below horizontal (relative to the seat back). The function of cable stop  86  acting on upper support arm  28  is substantially identical and therefore will not be discussed in detail herein. Attenuator  88  acts in a similar manner as attenuator  78  to deploy lower support arm  22 . 
     As show in  FIG. 4 , as ejection seat  10  exits the aircraft, deployment cable  80  continues to pull lower support arm  20  downward thereby tensioning the cables that form backstop  70 . At a predetermined tension, a rip stitch in attenuator  78  fractures allowing deployment cable  80  to separate from attenuator  78 . The ratcheting hinge  24  attaching lower support arm  20  to frame  12  then locks lower support arm  20  in position against the tension of primary, secondary and tertiary cables,  32 ,  60 ,  66 . Lower support arm  22  is similarly locked in position by means of its ratcheting hinge. As ejection seat  10  enters the windblast, the occupant&#39;s arms flail backwards until they impact backstops  70 ,  72 , which safely arrest the rearward motion of the occupant&#39;s arms. Because the frontal area of backstop  70  and  72  is less than ten percent (10%), preferably less than five percent (5%) of the area contained within the perimeter of primary cables  32 ,  42 , the windblast itself safely holds the occupant&#39;s arms against the backstop until the ejection seat has slowed to a speed enabling safe separation from the seat. 
     As can be determined from an inspection of  FIG. 1 , although backstops  70  and  72  deploy outward, they do not deploy perpendicular to the forward direction of ejection seat  10  but are deployed forward approximately 15 degrees from perpendicular. Accordingly, the invention is not intended to be limited to a backstop in which the entirety of the structure is rearward of the occupant. Any structure in which the occupant&#39;s arms are allowed to intentionally flail backwards until the rearward motion is arrested by a backstop with the occupant&#39;s arms at a sufficiently oblique angle to the windblast that the windblast itself holds the occupant&#39;s arms safely against the backstop is considered within the scope of the invention. Accordingly, although in the illustrative embodiment the forward angle of the backstop is approximately 15 degrees, a forward deployment of zero up to 30, 35 or even 40 degrees forward of perpendicular is considered within the scope of the invention as is any angle of deployment in which the entirely of the structure is rearward of the occupant&#39;s elbows at the moment of initiation of the ejection sequence. 
     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 invention. Accordingly, it is intended that the invention should be limited only to the extent required by the appended claims and the rules and principles of applicable law. Additionally, as used herein, unless otherwise specifically defined, the terms “substantially” or “generally” when used with mathematical concepts or measurements mean within ±10 degrees of angle or within 10 percent of the measurement, whichever is greater.