Abstract:
A retractable deflector to deflect birds and debris from an air intake duct of an aircraft jet engine. The duct has a forward opening for air receipt. The deflector includes a plurality of elongate members disposed on the duct in spaced relation to each other, each member having two end segments and a central segment disposed between the two end segments; and a plurality of guiding members, each mounted for movement along the perimeter of the duct and coupled to one end segment of an elongate member. The central segment of each elongate member extends between a pair of guiding members such that the elongate member is movable by a respective pair of guiding members between a retracted position and a deployed position in front of the duct. When in the deployed position, the central segments are situated to impede the ingress of debris into the duct.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The subject matter of this application is related to, and claims priority from, the following provisional and utility applications: 
     1) Provisional Application No. 61/205,381 filed Jan. 16, 2009, and 2) Provisional Application No. 61/205,785 filed Jan. 22, 2009; and 
     2) U.S. patent application Ser. No. 12/689,554, filed Jan. 19, 2010 (now allowed), from which this application is a continuation-in-part.] 
    
    
     Large sized debris which enters the intake of a jet engine may have disastrous consequences, including engine damage, functional engine destruction, and, if all or most engines become non-functional, emergency termination of a flight. This is what occurred on Jan. 15, 2009 with a flight out of LaGuardia Airport which made an emergency landing in the Hudson River after both of its engines failed: The source of damage was a flock of birds some of which entered the air intake of the engines, and rendered both engines non-functional. 
     U.S. Pat. No. 4,354,346 to Wooding discloses an intake duct for a jet engine which is not retractable. The engine intake extension of the invention is long and expected to be aerodynamically very demanding. 
     U.S. Design Pat. No. 433,029 to Eidson comprises an non-retractable cowl. Because it is non-retractable, it will exert aerodynamic inefficiencies throughout a flight. 
     U.S. Pat. No. 5,385,612 to Li discloses a cleaning system which is intended to be useful for jet engine intake. However, the device is not retractable, and is not able to provide jet air intake without very substantial aerodynamic limitation. 
     U.S. Pat. Nos. 4,137,535; 5,102,375 and 5,139,464 all relate to mechanisms for extending a telescoping antenna. 
     The subject matter of these prior U.S. patents is incorporated herein by reference. 
     The invention herein discusses methods and apparatus for preventing birds and other debris from doing damage to a jet engine using two types of deployable/protractible apparatus with acceptable aerodynamic features. 
     SUMMARY OF THE INVENTION 
     It is a principal object of the present invention to provide protection to an operating jet engine against airborne birds and other debris which may damage the engine. 
     It is a further object of the present invention to provide such protection using retractable apparatus, so that the aerodynamic consequences of such an apparatus are minimized, with respect to duration of use. 
     The invention herein discusses methods and apparatus for preventing birds and other debris from damaging a jet engine. It entails the deployment of a radially distributed set of first elements in front of the engine air intake. During the process of deployment, the leading edges of these first elements converge as they are extended from the engine housing. In order to prevent these first elements from suffering damage or mal-positioning due to air turbulence, a second element, oriented transverse to the first elements, and positioned at the leading edge of the first elements, is also deployed. The second element features an adjustable circumference, allowing it to maintain the leading edges during the process of deployment, with the circumference changing as the length of the deployed portion of the first element changes. 
     The first elements are retractable into the housing of the engine, so that once the aircraft rises above the altitude where such a strike may occur, better aerodynamic performance may be attained. During the landing phase of the flight, the first elements may be re-deployed when the aircraft has descended to an altitude where such protection is needed. 
     There are a variety of possible first element configurations involving variations in (a) the shape of the first element (straight and curved), (b) the number of first elements, and (c) the structural details of the first elements (for example: rigid rod terminating in eyelet, rigid rod terminating in tubular structure, hollow rod terminating in T-shaped tubular structure, and cable terminating in eyelet). 
     There are a variety of possible second element configurations involving variations in (a) the quality of the second element material (elastic, spring, cable), and (b) the number of second elements. 
     In one preferred embodiment of the invention, electromagnetic coupling secures adjacent leading edges of first elements in the fully deployed state. 
     in another preferred embodiment, de-icing apparatus warms the first and/or second elements. 
     In yet another preferred embodiment, the entire deflector apparatus rotates about the longitudinal axis, to provide additional protection. 
     Another embodiment of the invention entails the deployment of elongate linear elements which are deployed across the air intake duct of the engine, oriented perpendicular to the longitudinal axis of the engine. In the retracted stated, these filter elements are moved to one or more sides of the intake duct, out of the incoming air stream. Guiding elements facilitate the deployment and retraction processes. 
     in a preferred embodiment of the invention, the elongate linear elements are a cable. 
     In another preferred embodiment of the invention more than one set of filter elements is deployed, with each set of elements having a different orientation. 
     In yet another preferred embodiment of the invention one or more sets of deflector elements rotates about a central longitudinal axis. 
     In yet another preferred embodiment of the invention a cleaning apparatus cleans the filter elements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view of a jet engine with a deployed deflector apparatus having multiple curved first elements and a single transverse second element. 
         FIG. 1B  is a perspective view of a jet engine with a deployed deflector apparatus having multiple straight first elements and a single transverse second element. 
         FIG. 1C  is a representational diagram of a jet engine indicating the storage of retracted first elements and a retracted second element. 
         FIG. 1D  is a representational diagram of a jet engine indicating the storage of telescoping first elements. 
         FIG. 1E  is a front view of the placement of first elements within an engine housing. 
         FIG. 2A  is a representational diagram showing a front view of a fully deployed deflector apparatus with 16 first elements arrayed in a radially symmetric configuration, and a second element. 
         FIG. 2B  is a representational diagram showing a front view of a partially deployed deflector apparatus with 16 first elements arrayed in a radially symmetric configuration, and a second element. 
         FIG. 2C  is a representational diagram showing another front view of a partially deployed deflector apparatus with 16 first elements arrayed in a radially symmetric configuration, and a second element, showing a lesser degree of deployment than that shown in  FIG. 2B . 
         FIG. 2D  is a representational diagram showing another front view of a partially deployed deflector apparatus with 16 first elements arrayed in a radially symmetric configuration, and a second element, showing a lesser degree of deployment than that shown in  FIG. 2C . 
         FIG. 2E  is a representational diagram showing a front view of the deflector apparatus of  FIG. 2D  in a fully retracted state. 
         FIG. 3A  shows a representational cross sectional diagram of a deflector apparatus with curved, telescoping first elements, and a second element, in a deployed position. 
         FIG. 3B  shows a representational cross sectional diagram of a deflector apparatus with curved, telescoping first elements, and a second element, in a retracted position. 
         FIG. 4A  shows a representational cross sectional diagram of a deflector apparatus with straight, telescoping first elements, and a second element, in a deployed position. 
         FIG. 4B  shows a representational cross sectional diagram of a deflector apparatus with straight, telescoping first elements, and a second element, in a retracted position. 
         FIG. 5A  shows a representation diagram of a deflector apparatus with four first elements, a second cable element, and a single winch for adjusting the length of the cable. 
         FIG. 5B  shows a representation diagram of a deflector apparatus with four first elements, two second cable elements, and two winches for adjusting the length of the cables. 
         FIG. 5C  shows a representation diagram of a deflector apparatus with four first elements, four second cable elements, and four winches for adjusting the length of the cables. 
         FIG. 5D  shows a representational diagram of a T-shaped leading end of a first element, showing apparatus to decrease the friction due to motion of a cable. 
         FIG. 6A  is a representational diagram showing a coiled second element, in a configuration corresponding to a fully deployed state. 
         FIG. 6B  is a representational diagram showing a coiled second element, in a configuration corresponding to a partially deployed state. 
         FIG. 6C  is a representational diagram showing a coiled second element, in a configuration corresponding to a partially deployed state, showing a lesser degree of deployment than that of  FIG. 6B . 
         FIG. 6D  is a representational diagram showing a coiled second element, in a configuration corresponding to a partially deployed state, showing a lesser degree of deployment than that of  FIG. 6C . 
         FIG. 6E  is a representational diagram showing a coiled second element, in a configuration corresponding to a fully retracted state. 
         FIG. 7A  is a representational diagram showing a coiled second element passing through the leading edge of each of two T-shaped first elements, in a deployed configuration. 
         FIG. 7B  is a representational diagram showing a coiled second element passing through the leading edge of each of two T-shaped first elements, in a retracted configuration. 
         FIG. 5A  is a perspective view of a jet engine with a deployed deflector apparatus having multiple curved first elements and two transverse second elements. 
         FIG. 5B  is a perspective view of a jet engine with a deployed deflector apparatus having multiple straight first elements and two transverse second elements. 
         FIG. 5C  is a representational diagram of a jet engine indicating the storage of retracted first elements and two retracted second elements. 
         FIG. 9A  is a representational diagram showing a front view of a fully deployed deflector apparatus with 16 first elements arrayed in a radially symmetric configuration, and two second elements. 
         FIG. 9B  is a representational diagram showing a front view of a partially deployed deflector apparatus with 16 first elements arrayed in a radially symmetric configuration, and two second elements. 
         FIG. 9C  is a representational diagram showing another front view of a partially deployed deflector apparatus with 16 first elements arrayed in a radially symmetric configuration, and two second elements, showing a lesser degree of deployment than that shown in  FIG. 9B . 
         FIG. 9D  is a representational diagram showing another front view of a partially deployed deflector apparatus with 16 first elements arrayed in a radially symmetric configuration, and two second elements, showing a lesser degree of deployment than that shown in  FIG. 9C . 
         FIG. 9E  is a representational diagram showing a front view of the deflector apparatus of  FIG. 9D  in a fully retracted state. 
         FIG. 10A  is a representational diagram showing a cross sectional view of a tubular T-shaped first element, with projections forming two pairs of second elements, containing cables. 
         FIG. 10B  shows a representation diagram of a deflector apparatus with four first elements, four second cable elements each located at the leading edge of the first elements, four additional second cable elements each located between the leading edge and the trailing edge of the first elements, and four winches for adjusting the length of the additional cables elements. 
         FIG. 10C  is a representational diagram of a jet engine indicating the storage of retracted first elements and two retracted second elements. 
         FIG. 11A  is a perspective view of a jet engine with a deployed deflector apparatus having multiple curved first elements and six transverse second elements. 
         FIG. 11B  is a perspective view of a jet engine with a deployed deflector apparatus having multiple straight first elements and six transverse second elements. 
         FIG. 12A  is a representational diagram showing a front view of a fully deployed deflector apparatus with 16 first elements arrayed in a radially symmetric configuration, and six second elements. 
         FIG. 12B  is a representational diagram showing a front view of a partially deployed deflector apparatus with 16 first elements arrayed in a radially symmetric configuration, and six second elements. 
         FIG. 12C  is a representational diagram showing another front view of a partially deployed deflector apparatus with 16 first elements arrayed in a radially symmetric configuration, and six second elements, showing a lesser degree of deployment than that shown in  FIG. 12B . 
         FIG. 12D  is a representational diagram showing another front view of a partially deployed deflector apparatus with 16 first elements arrayed in a radially symmetric configuration, and six second elements, showing a lesser degree of deployment than that shown in  FIG. 12C . 
         FIG. 12E  is a representational diagram showing a front view of the deflector apparatus of  FIG. 12D  in a fully retracted state. 
         FIG. 13  is a representational diagram of a deflector apparatus with 40 T-shaped first elements in a fully deployed configuration. 
         FIG. 14  is a representational diagram of two T-shaped first elements with electromagnetic apparatus at two adjacent projections. 
         FIG. 15A  is a representation diagram of a deflector apparatus with four cable-based first elements, four winches for adjusting the length of the respective cables, and a cable-based second element associated with a tubular T-shaped additional first element and with an additional associated winch. 
         FIG. 15B  is a perspective view of a jet engine with a deployed deflector having the apparatus shown in  FIG. 15A . 
         FIG. 16A  is a cross sectional view of a portion of a hinge and a hinge-controlling apparatus for attaching a first element to a jet engine, showing a deployed state of the first element. 
         FIG. 16B  as a cross sectional view of the hinge and hinge-controlling apparatus of  FIG. 16A , showing a transitional state between the deployed state and the retracted state. 
         FIG. 16C  is a cross sectional view of the hinge and hinge-controlling apparatus of  FIG. 16B , showing the retracted state. 
         FIG. 17  is a perspective view of a jet engine with a deployed deflector apparatus having multiple straight first elements and a single transverse second element, with the deflector apparatus showing rotational motion about the longitudinal axis of the engine. 
         FIG. 18A  shows a representational oblique view of a jet engine. 
         FIG. 18B  shows a representative oblique view of a jet engine with a fully deployed bird and debris filter comprising two sets of elements. 
         FIGS. 19A-19E  shows a schematic of the gradual deployment of a bird and debris filter with two groups of elements. 
         FIGS. 20A-20E  shows a schematic of the gradual deployment of a bird and debris filter with one group of elements. 
         FIGS. 20F-20J  shows a schematic view of a mechanism for providing filter elements with multiple orientations without the use of a second filter. 
         FIG. 21  shows another oblique view of a jet engine with a deployed set of two filters, with elements of one filter aligned in a different direction than that of the elements of the other filter. 
         FIGS. 22A and 22B  show a schematic frontal view of both filter elements and guiding elements, in the retracted and deployed states, respectively. 
         FIGS. 23A-23C  show schematic views of exemplary means for causing the positioning of the guiding elements of  FIGS. 22A and 22B . 
         FIGS. 24A-24C  show schematic views of exemplary means for causing the positioning of the guiding elements of  FIGS. 22A and 22B . 
         FIGS. 25A and 25B  show schematic views of means for releasing a portion of the filter elements during the process of deployment, and taking up a portion of the filter elements during the process of retraction; and show a cleaning apparatus. 
         FIG. 26  shows a schematic oblique diagram in which a group of filter elements is operative to rotate about an axis parallel to that of the long axis of the engine. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIGS. 1A and 1B  show two types of deflector apparatus for a jet engine.  FIG. 1A  shows  12  curved first elements  102  projecting from the air intake end of jet engine  100 .  FIG. 1B  shows  11  straight first elements  104  projecting from the air intake end of jet engine  101 . Many other configurations are possible. Both figures show first elements in a radially symmetric distribution. Configurations with a greater or lesser number of first elements are possible. 
     To stabilize the first elements during deployment, a second expandable element connects the leading end of the first elements, shown as  103  in  FIGS. 1A and 105  in  FIG. 1B . 
     Embodiments of the invention in which the first elements link at a point or a small area without an aperture (i.e. an opening at the most forward point) are possible. Embodiments of the invention in which the circular apparatus is substituted by an apparatus of another shape are possible. Elliptical shapes, hexagonal shapes, octagonal shapes, polygonal shapes (and any shape in which the number of sides to the central aperture is equal to the number of first elements) are possible. A shape which is identical to that of the engine housing, if not circular, is possible. 
       FIG. 1C  shows the first elements  108  in the fully retracted position (indicated in the figure as broken lines) within the housing of engine  106 . In the embodiment shown in  FIG. 1C , the first elements in the retracted state are stored inside the engine housing, and are not telescoped. The configuration shown in  FIG. 1C  would be suitable for straight first elements, and could also be used for curved first elements with a large radius of curvature. Curved first elements with a smaller radius of curvature (i.e. approximately the same radius of curvature as the engine housing) could be stored by rotating them 90 degrees so that they would, in the stored state, lie along the circumference of the engine. 
       FIG. 1D  shows the storage of telescoped first elements  110 . The advantage of telescoping is ease of storage in the retracted state. The telescoped configuration for the retracted state shown in  FIG. 1D  could also accommodate curved first elements (e.g. as shown in  FIGS. 3A and 3B ) with a smaller radius of curvature (without having to rotate 90 degrees for storage) than that of the engine housing of  FIG. 1C . 
       FIG. 1E  shows a front view of telescoped first elements  114  within compartments  112 , situated in engine housing  118 . The engine apparatus is situated centrally, in the location indicated by  116 . 
       FIGS. 2A through 2E  show front views of an engine with the first elements joined at the leading edge by a circular second element. During the deflector retraction process, the circular second element increases in circumference as shown in the sequence of  FIGS. 2A to 2E .  FIG. 25  shows the fully retracted state—where most or all of the first element apparatus has been withdrawn into the engine housing, as the radius of what was the central circular element is increased to the point that it equals approximately that of the engine housing. A 16 first element configuration is shown; configurations with fewer and larger numbers of first elements are possible. 
       FIGS. 3 and 4  show a side view of an embodiment of the apparatus, emphasizing a first element structure with a telescoping configuration.  FIG. 3  shows an apparatus with curved first elements, and  FIG. 4  shows an apparatus with straight first elements. Each figure shows that the first element structure consists of a series of cylindrical elements with a telescoping structure, much like a retractable automobile antenna.  FIG. 3A  shows the first elements  300 A fully extended, with circular stabilizing apparatus  310 A assuming a minimal circumference. In the fully retracted state shown in  FIG. 3B , the telescoping of concentric cylindrical first elements  300 B allows the first elements to fit inside the engine housing, while the circular apparatus  310 B expands (in a process described hereinbelow) so that it may also fit into the engine housing. Only two sets of first elements are shown for simplicity. Configurations with more sets of first elements are desirable to allow for greater stability and ease of retraction. Arrows above  FIGS. 3A and 3B  show the direction of air flow into the engine. Electrically controllable telescoping elements which are controlled by one or more electric motors, by hydraulic apparatus and by pneumatic apparatus are known. 
       FIG. 4A  shows the first elements  400 A fully extended, with circular stabilizing apparatus  410 A assuming a minimal circumference. In the fully retracted state shown in  FIG. 4B , the telescoping of concentric cylindrical first elements  400 B allows the first elements to fit inside the engine housing, while the circular apparatus  410 B expands (in a process described hereinbelow) so that it may also fit into the engine housing. Only two sets of first elements are shown for simplicity. Configurations with more sets of first elements are desirable to allow for greater stability and ease of retraction. Arrows above  FIGS. 4A and 4B  show the direction of air flow into the engine. 
       FIGS. 5A-5C  show a possible structure for controlling the configuration of the second element. Apparatus with only four first elements is shown for ease of interpretation. Referring to  FIG. 5A , as first elements  510 A-D are retracted (by movement which is radially outward in the figure), cable  512 , the second element, is gradually unspooled from spool  518  by motorized apparatus  516  in housing  514 , (The segment; of cable which lies between each of  510 A/B,  510 B/C,  510 C/D and  510 D/A is shown in a curved configuration, which would be the conceptual limiting case with an infinite number of first elements; In the case of a large number of first elements, a many-sided polygon would approximate the circle shown in the figure.) As shown in the figure, the terminal segment of each radial arm forms a curved cylindrical shape which allows the cable to pass through. When the first elements go from the retracted state to the deployed state, motor  516  causes cylinder  518  to take up cable slack as it becomes available. Embodiments of the invention in which  512  is a spring apparatus (see hereinbelow) are possible. 
       FIG. 5S  shows an apparatus similar to that of  5 A, except that there are two cables,  542 A and  542 B. The slack for one end of each of  542 A and  542 B is controlled by slack uptake and release apparatus  544 A and  544 B (each of which operate in similar fashion to that of  514 ). 
       FIG. 5C  shows an apparatus similar to that of  FIGS. 5A and 5B  except that there is one cable segment ( 572 A-D) for each pair of adjacent retractable arms, and one slack uptake and release apparatus ( 574 A-D) for one end of each pair of adjacent cable ends. For example, when the apparatus in  FIG. 5C  goes from the deployed to the retracted state:
           574 A unrolls appropriate portions of one end of cable  572 A and one end of cable  572 B;  574 B unrolls appropriate portions of one end of cable  572 B and one end of cable  572 C;     574 C unrolls appropriate portions of one end of cable  572 C and one end of cable  572 D; and  574 D unrolls appropriate portions of one end of cable  572 D and one end of cable  572 A.       

     Configurations of the invention with various friction reducing elements are possible.  FIG. 5D  shows a representational cross sectional view of the terminal protuberance of a first element in one embodiment of the invention. In order to minimize friction between the cable and the first element, one or more of friction reducing elements  592 A,  592 B,  594 A,  5948 ,  596 A,  596 B,  598 A, and  598 B are included. These may be flat rolling elements, or grooved wheels. In another embodiment of the invention,  592 A and B may be considered to be a cross-sectional representation of a circular bearing device which guides the cable with minimal friction; the same is true of the  594 A and B pair, the  596 A and B pair and the  598 A and B pair. Embodiments of the invention with either a greater or lesser number of guiding elements are possible. Embodiments of the invention in which the friction-reducing elements are actively lubricated, or are self-lubricating are possible. Many other friction reducing configurations will be apparent to those skilled in the art. 
       FIGS. 6A to 6E , shows a circular spring apparatus which provides the attractive force between adjacent distal ends of the first elements when they are deployed.  FIGS. 6A to 6E  correspond, respectively to the states of deployment/retraction shown in  FIGS. 2A to 2E , i.e., five states ranging from first elements fully deployed ( FIG. 6A ) to first elements fully retracted ( FIG. 6E ). 
       FIG. 7 , consisting of  FIGS. 7A and 7B  shows the circular spring apparatus of  FIG. 6  in conjunction with first elements in two different states of ret reaction/deployment: 
       FIG. 7A  corresponds to  FIGS. 2B and 6B ; while 
       FIG. 7B  corresponds to  FIGS. 2D and 6D . 
     Embodiments of the spring apparatus shown in  FIGS. 6 and 7  in which one end of the spring is anchored to a first element are possible. 
       FIGS. 8A and 8B  (analogous to  FIGS. 1A and 1B  respectively) show a configuration of the apparatus in which there are two transverse/second element supporting apparatus structures ( 810  and  820  for engine  815  in  FIG. 8A , and  830  and  840  for engine  835  in  FIG. 8B ). The mode of operation of the transverse apparatus shown in each of the two figures is similar to that of the configurations with one transverse supporting apparatus, i.e. in the case of two such apparatus, each is retractable as shown by  850  and  860  in  FIG. 5C . In  FIG. 5C , the engine is indicated by  855  and the first support elements are indicated by broken lines  870 . 
       FIGS. 9A-9E  (each showing two circular second elements) are analogous to  FIGS. 2A-2E  (each showing one circular second element). As indicated hereinabove, in many configurations the circle representing the second element in the figure represents the theoretical upper limit of a many-sided polygon. 
     In  FIG. 9A , the fully deployed configuration, the distal (i.e., nearest to the leading end) circular apparatus is  910 A and the proximal (i.e. nearest to the trailing edge) one is  920 A. In  FIG. 9B , the partially retracted configuration, the distal circular apparatus is  930 B and the proximal one is  940 B. In  FIGS. 9C-E , the proximal circular apparatus is retracted within the engine housing, so the appearance is identical to  FIGS. 2C-2E , respectively. 
       FIG. 10A  shows a representational view of a complex first element for a configuration with one distal transverse supporting apparatus and one transverse supporting apparatus in the mid-portion of the first element. In principle, such a complex element has features of both a first element (i.e. as it exits the engine housing, one section extends longitudinally) and a second element (has projections which, as they exit the housing, extend in a direction transverse to the longitudinal section). The entire apparatus of  FIG. 10A  is analogous to element  510 A in  FIG. 5A  (which is a first element without a transverse supporting apparatus in its midportion). Referring again to  FIG. 10A , cables  1000 A and  1000 B help to align and hold together the distal ends of the complex first elements; They are analogous to any of [a]  512  in  FIG. 5A ; [b]  542 A and  542  in  FIG. 5B ; and [c] any of (i)  572 A and  572 B, (ii)  572 B and  572 C, (iii)  572 C and  572 D, and (iv)  572 D and  572 A in  FIG. 5C . In addition, cables  10000  and  1000 D serve to anchor the midportion of each complex first element. 
     When the apparatus in  FIG. 10A  is utilized in a configuration analogous to that of  FIG. 5C  (i.e. an array of four of complex first element  1002 ), each cable segment analogous to  1000 C in  FIG. 10A  extends to the neighboring first element to the left (see  FIG. 10B ), enters its main shaft, and comprises the segment analogous to  1000 D in that left neighboring first element. Similarly, each cable segment analogous to  1000 D in  FIG. 10A  extends to the neighboring first element to the right (see  FIG. 10B ), enters its main shaft, and comprises the segment analogous to  1000 C in that right neighboring first element. 
     In a configuration analogous to that of  FIG. 5A , the cable segment  1000 C would extend from shaft  1002 , out through projection  1004 , and thence through the midportion of each first element (via projections analogous to each of  1004  and  1006 ), and ultimately return to first complex element  1002  via projection  1006  to form cable segment  1000 D. 
     In configurations analogous to that shown in  FIG. 5B , the cable segment  1000 C would extend from shaft  1002 , out through projection  1004 , through the midportions of two or more adjacent first elements, each first element (via projections analogous to each of  1004  and  1006 ), and ultimately enter another first element via a projection analogous to  1006 , and form a cable segment analogous to segment  1000 D in another first element. 
     In configurations analogous to that of  FIG. 5B , the cables within first elements traversed by transverse cable segment must be geometrically set up so that the transverse segment does not contact longitudinal segments analogous to  1000 A and  1000 B. Although  FIG. 10A  shows all four cable segments lying in the same plane (i.e. the plane of the figure), in three dimensions, the transverse segment could cross through the shaft either so that it does not contact either of the segments analogous to  1000 A or  1000 B (i.e. by crossing above or below the plane defined by  1000 A and  1000 B). 
     The advantage of projections  1004  and  1006  is that they help guide and secure the transverse cable in the midportion of the first element, and allow for a locking mechanism to further stabilize the apparatus. The disadvantage is that they add weight, they further restrict the open area in front of the engine, and they make retraction of the first element more complex. Embodiments of the invention in which each of projections  1004  and  1006  are absent, replaced by respective openings in the shaft of  1002  to accommodate respective cables  1000 C and  10000  are possible. 
     Though  FIG. 10A  shows projections  1004  and  1006  to be in the midportion of the first element, configurations are possible in which the junction is asymmetrically located, either proximally (i.e. nearer to the engine housing) or nearer to the distal end of the apparatus. 
     The proximal ends of each of  1000 C and  1000 D are linked to cable control apparatus which appropriately releases or takes in cable, as the situation may require. Such cable control apparatus is analogous to any of [a]  514 ,  516  and  518  shown in  FIG. 5A ; [b]  544 A and  544 B shown in  FIG. 5B ; and [c]  574 A,  574 B,  574 C and  574 D shown in  FIG. 5C . 
     Cables may be secured within  1002  by a variety of means and mechanisms including: 
     a) situating the cable within a non-moving sheath; b) grooves within  1002  for each cable; and/or c) one or more guiding wheels, rollers, or bearings along the length of the cable within  1001 ,  1002 ,  1003 ,  1004  and/or  1006 , analogous to that which is shown herein in conjunction with  FIG. 5D . 
       FIG. 10B  shows a deflector which includes an array of four of the complex first elements shown in  FIG. 10A . The apparatus shown in the figure is analogous to that shown in  FIG. 5C . However, the apparatus in  FIG. 10B  includes an additional transverse support group of structures. Cable take-up apparatus  1008  controls the length of cable segment  10000 , which passes through  1002 , exits through projection  1006  and enters the corresponding structure on the right side of the figure. Similarly, cable take-up apparatus  1008  controls the length of cable segment  1000 C, which passes through  1002 , exits through projection  1004  and enters the corresponding structure on the left side of the figure. The operation of  1008  and associated components is similar to that of  574 A-D in  FIG. 5C . These aforementioned structures link the midsection (which need not be located at the geometric middle) of the complex first elements (e.g.  1002 ). 
     The cable segments which forms the distal second element exit through projection  1003  as  1000 B, and then enters the corresponding structure indicated by elements on the right side of the figure; Another cable segment which forms the distal second element exit through projection  1001  as  1000 A, and then enters the corresponding structure indicated by elements on the left side of the figure. 
     The four cable take-up apparatus for the distal second elements is not shown in the figure, but is similar to that of  100 . 8 , and  574 A-D. Long broken lines in the figure indicate cable for the distal/leading edge second elements which are contained within  1002 . Although these cable segments extend into the proximal shaft of  1002  (as shown in  FIG. 10A ), these segments of cable are not shown in the figure, for clarity. Short broken lines indicate cable for the proximal/midportion second elements, which are shown in their full extent. 
       FIG. 10C , analogous to  FIG. 1D , shows a representational view of the retracted state, of an embodiment with (a) one transverse stabilizing cable  1020  in its midportion, and (b) collapsible/telescoping first elements  1022 . With embodiments of the invention with lateral protuberances in the midsection, there will be a limitation to the collapse above and below such midsection protuberances. An embodiment of the invention is also possible in which the midsection protuberances themselves are able to collapse/telescope. 
     The telescoped configuration for the retracted state shown in  FIG. 10C  could also accommodate curved first elements (e.g. as shown in  FIGS. 3A and 3B ), as discussed hereinabove in conjunction with  FIG. 1D . 
     Whereas the aforementioned embodiments contain either no transverse elements along the first elements, or one such element ( FIGS. 5A to 9E ),  FIG. 11A  shows a configuration with 5 transverse elements and curved first elements (analogous to  FIGS. 1A and 8A ) and  FIG. 11B  shows a configuration with 5 transverse elements and straight first elements (analogous to  FIGS. 1B and 8B ). Configurations with greater and lesser numbers of first elements are possible. More first elements result in a greater degree of first element stability and the ability to limit the maximum size of an object which may cross the barrier resulting from the deployment of the apparatus described herein. On the other hand, more first elements result in greater weight, greater resistance to air entry and more complex cable arrangements within first elements and more complex cable supporting apparatus. 
     FIGS.  12 A- 12 E—analogous to  FIGS. 2A-2E  and  9 A- 9 E—show a front view of some of the successive steps in the transition from a fully deployed apparatus ( FIG. 12A ) to a fully retracted one ( FIG. 12E ) for a configuration with five transverse elements,  1200 ,  1202 ,  1204 ,  1206  and  1208  (in addition to the distal transverse support common to all of the configurations hereinabove).  FIG. 12B  shows a state in which two of the five transverse elements have been retracted (and in which the non-retracted transverse elements and the distal supporting apparatus have each (i) been pulled back and (ii) undergone an increase in radius).  FIG. 12C  shows a state in which four of the five transverse elements have been retracted (and in which the one remaining non-retracted transverse element and the distal supporting apparatus have each (i) been further pulled back and (ii) undergone a further increase in radius).  FIG. 12D  shows a state in which all of the five transverse elements have been retracted (and in which the remaining non-retracted distal supporting apparatus has (i) been still further pulled back and (ii) undergone a still further increase in radius). 
       FIG. 13  shows a front view of a fully deployed engine protection device with 40 first elements ( 1300 A), in which first element has a terminal protuberance ( 1300 B) which is analogous to  1001  and  1003  of  FIG. 10A  herein. Cable or cables  1302 , analogous to the cable shown in any of the configurations of  FIGS. 5A ,  5 B and  5 C, serve to draw the protuberances together as the device is deployed, and to stabilize the protuberances as the device is retracted. In addition  1302  may secure each of the protuberances  1300 B so that they are in secure contact with each other. Another mechanism for securing each  1300  to its two adjacent neighboring  1300 Bs is to have the surface of each form a secure fit with its neighboring  1300 B, either because the surfaces are parallel, or because the surfaces have complementary extensions and depressions which promote such a fit. Furthermore, by making the projections and depressions cone-shaped rather than cylindrical, a non-perfect alignment of adjacent first elements during deployment may be corrected for. 
     In another embodiment of the invention, a magnetic attraction between adjacent protuberances may be used to promote their attraction during deployment. The magnetic mechanism may be from fixed elements (e.g. one side of each protuberance is a north magnetic pole, and the other side is a south pole, such that the arrangement is:
         . . . (N-S)-(N-S)-(N-S)-(N-S) . . .       

     Alternatively, the source of magnetism may be electromagnetic, as shown in  FIG. 14 , thereby allowing for a simple means of turning off the attractive mechanism.  FIG. 14  shows a coil of conducting wire  1404 A on one end of first element  1400 A for generating a magnetic field when a current is passed through it. The wires need not be on the surface of the object, and may be embedded beneath the surface. The ends of the coil  1404 B pass through the shaft of  1400 A to a power supply and control unit. There is corresponding apparatus  1406 A on the end of first element  1402 A for generating a magnetic field when a current is passed through it. The ends of the coil  1406 B pass through the shaft of  1402 A to a power supply and control unit. The orientation and winding of the coils is such that  1404 A attracts  1406 A when a current is passed through each. In a preferred embodiment, additional coils are placed symmetrically on each projection, i.e.  1400 B and  1402 B, to allow for the attraction to each of their respective neighboring projections. 
     In yet another embodiment of the invention, an active locking mechanism between adjacent protuberances is possible. Activation and deactivation of the locking mechanism may be electric or via one or more cables which traverse one or more of first elements with such a mechanism. 
       FIG. 15A  shows an embodiment of the invention in which the first elements are not composed of rigid rods. These first elements consist of cables  1502 A-D. At their respective proximal ends are cable take-up and release apparatus  1500 A-D; At their respective distal ends is an eyelet  1504 A-D, which allows each of  1502 A-D to be pulled during the deployment process. Deployment is caused when cable take-up  1506  winds in  1510 , causing the perimeter of this cable loop to decrease. As the decrease occurs cables  1502 A-D are pulled out of  1500 A-D. The tension on the loop  1510  exerted by each of  1500 A-D is adjusted to keep loop  1510  centered over the air intake. In one version of this embodiment of the invention, an apparatus  1520  (either electromechanical, hydraulic or pneumatic) pushes  1508  distally (toward the center of the air intake) during deployment. The retraction of the deflector involves active uptake of cables  1502 A-D by take-up apparatus  1500 A-D, with simultaneous spooling out of cable from  1506 . In the version which includes  1520 , it may be used to facilitate the retraction of  1508 . The tension of each of  1500 A-D on each respective one of  1502 A-D is adjusted, during the retraction process, to keep the deflector properly centered at all times. 
       FIG. 15B  shows a perspective view of a jet engine  1530 , and the first elements and second elements (with element numbers corresponding to those of  FIG. 15A ) which make up this embodiment. The embodiment shown in the figure contains no rigid support elements except for  1508 . It would therefore be situated at the mouth of the engine. 
     Versions of this embodiment with two or more sets of apparatus to shorten loop  1510  are possible. Versions are also possible in which each of  1502 A-D is a rigid telescoping rod, anchored to the engine housing, and deployed by the force exerted by cable take-up device  1506 . 
       FIGS. 16A-16C  show an embodiment of a hinge which anchors a first element  1600  to the engine housing, and is retractable. The first element is joined to one hinge component  1602 , and retraction rod  1608  is joined to the other hinge component  1606 .  1602  and  1606  pivot about  1604 .  1608  is moved in and out by apparatus  1610 , either mechanically or electromagnetically.  1608  is anchored to inner housing wall  1612  (anchoring not shown in figure), which is contiguous with  1614  which is the support apparatus for the engine. 
       FIG. 17  shows an embodiment of the invention in which the first and second elements apparatus rotate along the long axis of the engine, thereby to reduce the aerodynamic consequences of a fixed first element configuration, to reduce asymmetric engine wear, and to more efficiently deflect debris and/or birds. In the figure, the base of the deflector apparatus  1702  is contiguous with engine  1700 , but is able to rotate about the long axis of the engine. 
     Embodiments of the inventions hereinabove are possible in which: 
     1) There is more than one distal cable running around the circumference of the device, to impart additional stability; 2) There are two or more cables running in parallel through the transverse/non-distal second elements (one cable illustrated hereinabove); 3) The cable is replaced or supplemented by one or more ribbon shaped elements; 4) There are two tandem deflector apparatuses, each of which has the appearance of all of the protection elements shown in  FIG. 11A  (or  11 B,  1 A,  1 B,  8 A or  8 B). In a preferred embodiment of the invention, the first elements of the first apparatus are placed so that debris which passes through the outer apparatus is geometrically unlikely to pass through the second apparatus. The longitudinal first elements of the outer apparatus may have a different angular location than those of the inner apparatus, and/or the transverse elements of the outer apparatus may be situated in a more (or less) distal location than those of the inner apparatus. The outer apparatus may rotate (a) at a different speed than the inner one; and/or (b) in a different direction than the inner one; 5) The arrangement of first elements functions to (a) deflect airborne debris, and/or (b) break up airborne degree into smaller pieces. 6) Embodiments of the invention with other first element retraction and extension mechanism are possible. 7) Embodiments of the invention with other stabilizing mechanisms for the distal end of the first elements are possible. 8) Embodiments of the invention with a device, such as a device for passing electric current through the deflector elements, for maintaining the temperature of the elements above freezing, thereby to prevent formation of ice on the deflector. 
     The retractable bird and debris filter described heretofore consists of elements which project forwards from the jet engine. A second type of retractable bird and debris filter is comprised of elements largely confined to the vicinity of a plane defined by the forward opening of the engine, described hereinbelow. 
       FIGS. 18A and 18B  show a jet engine with such a bird and debris filter in the retracted, and in the deployed state, respectively. 
       FIG. 18A  shows a perspective view of a jet engine  1800 , with air intake shown on the right side of the figure. The filter is in the retracted state, and is not seen in the figure. 
       FIG. 18B  shows a perspective view of engine  1802 , with deployed filter  1804 A. The filter shown in the figure has two sets of parallel linear filter elements, with one set of elements  1804 B oriented perpendicular to the other set  1804 C. Embodiments of the invention with one set, and with three or more sets of filter elements are possible. Embodiments of the filter in which one filter element is neither perpendicular nor parallel to another filter element are possible. In the embodiment of the filter shown in the figure, the filter elements form a grid over the air intake of the engine. 
     Clearly, increasing either (a) the number of filter elements or (b) the thickness of the elements, the greater the impedance to engine air intake. On the other hand, small numbers of filter elements or excessively thin elements will decrease the effectiveness of the filtration process. 
     The filter elements may be metallic, may be composed of a non-metal, or may be a composite of metallic and non-metallic elements. Each filter element may comprise a single strand of material or multiple strands comprising a cable. The strands, if multiple, may or may not be twisted or braided. The filter elements may or may not have elastic properties. Other filter element configurations will be apparent to those skilled in the art. 
       FIGS. 19A-19E  show a schematic view of an example of the process of deployment of a set of vertically oriented filter elements, as seen looking into the engine from the air-intake side.  FIG. 19A  shows the retracted state of the filter, i.e. no filter elements are seen. The engine perimeter is indicated by  1920 . 
     In  FIG. 19B , the beginning of the filter element deployment process, one filter element  1900  extends, vertically oriented, across the left hand portion of the air intake, having moved from a storage location (not shown in this figure) at the extreme left of the figure. Another filter element  1901  extends, vertically oriented, across the right hand portion of the air intake, having moved from a storage location (not shown in this figure) at the extreme right of the figure. 
       FIG. 19C  shows further progression of the deployment process beyond that shown in  FIG. 19B :
         On the left side of the figure, tilter element  1900  has moved further to the right, and additional filter element  1902  has begun to traverse the intake opening; and   On the right side of the figure, filter element  1901  has moved further to the left, and additional filter element  1903  has begun to traverse the intake opening.       

       FIG. 19D  shows another step in the progression of the deployment process beyond that shown in  FIG. 19C :
         On the left side of the figure, filter elements  1900  and  1902  have moved still further to the right, and additional filter element  1904  has begun to traverse the intake opening; and   On the right side of the figure, filter elements  1901  and  1903  have moved still further to the left, and additional filter element  1905  has begun to traverse the intake opening.       

       FIG. 19E  shows yet another step in the progression of the deployment process, beyond that shown in  FIG. 19D :
         On the left side of the figure, filter elements  1900 ,  1902  and  1904  have each moved still further to the right, and additional filter element  1906  has moved to extend across a portion of the intake opening; and   On the right side of the figure, filter elements  1901 ,  1903  and  1905  have moved still further to the left, and additional filter element  1907  has moved to extend across a portion of the intake opening.       

     This exemplary figure shows a total of eight filter elements. Embodiments of the invention with a greater or lesser number of elements is possible. In the figure, in the deployed state, spacing between the elements is seen to be roughly equal. Embodiments of the invention in which the spacing is not equal are possible. The four step deployment process shown by  FIGS. 19A to 19E  is not intended to indicate that deployment is a step-wise process; it may be stepwise, or continuous; and if continuous the elements may move from the retracted to the deployed position at a constant or non-constant speed. 
     The relative width of the filter elements in the figure is not intended to indicate an actual relative width. The width may vary from element to element among an array of such elements. The width may vary along the length of an individual filter element. The vertical orientation of the filter elements is exemplary, and embodiment of the invention with horizontally oriented elements are possible, as well as embodiments in which the elements are neither vertical nor horizontal. Furthermore, embodiments of the invention are possible in which the filter elements are not parallel to each other—either during the process of deployment or in the fully deployed state. 
       FIGS. 20A-20E  show a schematic view of an example of the process of deployment of a set of vertically oriented filter elements, as seen looking into the engine from the air-intake side, in which all of the elements are stored in a single group ( FIGS. 19A-19E  having shown the case of two stored groups).  FIG. 20A  shows the retracted state of the filter, i.e. no filter elements are seen. The engine perimeter is indicated by  2020 . 
     In  FIG. 20B , the beginning of the filter element deployment process, two filter elements  2000  and  2001  extend, vertically oriented, across the right hand portion of the air intake, having moved from a storage location (not shown in this figure) at the extreme right of the figure. 
       FIG. 20C  shows further progression of the deployment process: Filter elements  2000  and  2001  have moved further to the left than their respective positions in  FIG. 20B , and additional filter elements  2002  and  2003  have begun to traverse the intake opening. 
       FIG. 20D  shows still further progression of the deployment process, beyond that shown in  FIG. 20C : Filter elements  2000 ,  2001 ,  2002  and  2003  have moved still further to the left than their respective positions in  FIG. 20C , and additional filter elements  2004  and  2005  have begun to traverse the intake opening. 
       FIG. 20E  shows still further progression of the deployment process, beyond that shown in  FIG. 20D : Filter elements  2000 ,  2001 ,  2002 ,  2003 ,  2004  and  2005  have moved still further to the left than their respective positions in  FIG. 200 , and additional filter elements  2006  and  2007  have begun to traverse the intake opening. 
     As with the apparatus of  FIGS. 19A to 19E , the exemplary set of  FIGS. 20A to 20E  shows a total of eight filter elements. Embodiments of the invention with a greater or lesser number of elements is possible. In the figure, in the deployed state, spacing between the elements is seen to be roughly equal. Embodiments of the invention in which the spacing is not equal are possible. The four step deployment process shown by  FIGS. 20A to 20E  is not intended to indicate that deployment is a step-wise process; it may be stepwise, or continuous; and if continuous, the elements may move from the retracted to the deployed position at a constant or non-constant speed. 
       FIGS. 20F-20J  show a schematic view of an example of the process of deployment of both a vertically-oriented ( 2032 ) and horizontally-oriented ( 2034 ) filter element for engine  2030 .  FIG. 20F  shows the fully retracted state;  FIGS. 20G through 20I  show gradual deployment and  FIG. 20J  shows full deployment. This mechanism can accommodate larger numbers of filter elements, and can accommodate filter elements with three or more orientations when fully deployed. 
     The relative width of the filter elements in the figures is not intended to indicate an actual relative width. The width may vary from element to element among an array of such elements. The width may vary along the length of an individual filter element. The vertical orientation of the filter elements is exemplary, and embodiment of the invention with horizontally oriented elements are possible, as well as embodiments in which the elements are neither vertical nor horizontal. Furthermore, embodiments of the invention are possible in which the filter elements are not parallel to each other—either during the process of deployment or in the fully deployed state. 
       FIG. 21  shows tandem filter arrays  2100  and  2102  at the front end of engine  2104 . The respective elements of  2100  and  2102  are oriented perpendicular to each other, but in other embodiments, may be at any angle. Embodiments of the invention with one or more additional arrays of filter elements (i.e. a third, fourth . . . array) are possible. The arrays need not be identical. 
       FIGS. 22A and 22B  show the placement of guiding elements for the respective filter elements in a retracted configuration and in a partially deployed configuration respectively. 
     Referring first to  FIG. 22B , a partially deployed array of filter elements is shown. The deployed elements include  2200  and  2210  (and two others); the non-deployed elements include  2208  and  2209 . Two guiding elements  2202  and  2207  are shown at each end of the line segment which represents filter element  2200 . These two guiding elements move  2200  between its deployed position (partially deployed position shown in  FIG. 22B ) and its retracted position (shown in  FIG. 22A ). 
     As discussed hereinbelow (in conjunction with  FIGS. 25A and 25B ), the guiding elements have structure which facilitates the deployment and take-up of the respective filter element. And as discussed hereinbelow (in conjunction with  FIGS. 23A-C  and  24 A-C) the guiding elements may move either passively (i.e. caused to move by another structure) or may have active means of locomotion. 
     As shown in  FIG. 22B , the guiding elements move between an inner housing  2218  and an outer housing  2216 . Also shown in  FIG. 22B  are filter element  2208  with respective guiding elements  2204  and  2205  in a minimally deployed position; partially deployed guiding element pair  2203  and  2206 ; partially deployed filter element  2210  with a respective pair of guiding elements  2212  and  2214 ; and minimally deployed filter element  2209 . 
       FIG. 22A  (in which the filter and guiding elements correspond to those with identical element numbers to those in  FIG. 22B ) shows the retracted state of the filter array. Guiding element pair  2204  and  2205  are shown in the most leftwards position of the figure, with a visible remnant of the filter element extending between them. Guiding element  2203  abuts  2204 , and its associated second guiding element  2206  abuts guiding element  2205 . Guiding element  2202  abuts  2203 , and its associated second guiding element  2207  abuts guiding element  2206 . Guiding element pair  2212  and  2214  are shown on the right side of the figure (along with two other pairs of guiding elements), all in the retracted position. 
       FIGS. 22A and 22B  are intended to be exemplary. Those skilled in the art will note many other possible embodiments and configurations, including those with a different number of filter elements; those in which all of the retracted elements are situated in a single group (e.g. on the left side of the figure); those in which retraction is not to the right or left side of the engine (e.g. top and bottom, or top only, or bottom only); those in which the housing configuration differs; those in which the housing shape is not circular; and those in which the guiding and filter elements are not restricted to a one-dimensional placement in the retracted state. 
     Apparatus corresponding to that shown in  FIGS. 22A and 22B  will accommodate the filter array shown schematically in  FIGS. 20F-20J  if the guiding elements for the horizontally oriented (when deployed) filter element(s) extend forward (schematically, above the plane of the figure) to a greater or lesser degree than the guiding elements of the vertically oriented (when deployed) filter element (s). This feature is necessary in filter arrays comprising filter elements with more than one orientation, to accommodate what would otherwise be a “crossing problem”—i.e. the intersection of filter elements if confined to a single plane. Thus the plane occupied by the filter elements of one orientation will differ from the plane occupied by filter elements of another orientation. Furthermore, the orientation of the aforementioned two planes need not be parallel, as long as no part of a filter element in one plane contacts a filter element of another plane, in the deployed state. 
     For filter arrays with three or more orientations of deployed filter elements, a similar increase in the number of guiding element protrusion amounts would be necessary. 
       FIGS. 23A-C  show schematic representations of a mechanism for causing the movement of guiding elements  2300 ,  2302 ,  2304 ,  2306 ,  2308  and  2310  in a passive manner—i.e. the guiding elements themselves do not possess an active source of propulsion. The propulsion source during deployment is deployment motors  2312  and  2314 . The propulsion source during retraction is retraction motor  2316 . Linkage  2318  links guiding element  2300  to deployment motor  2312 ; linkage  2320  links guiding element  2300  to guiding element  2302 ; linkage  2322  links guiding element  2302  to  2304 ; and linkage  2324  links retraction motor  2316  to guiding element  2304 . 
     During deployment,  2312  pulls  2300  via linkage  2318 . Guiding element  2302  is caused to move by the motion of  2300 , via linkage  2320 ; and guiding element  2304  is caused to move by the motion of  2302  via linkage element  2322 . Linkage control elements  2326 ,  2328  and  2330  associated with each guiding element control the length of the linkage between guiding elements. Thus, during deployment these lengths increase, and during retraction they decrease. The linkage control elements, in a preferred embodiment of the invention will comprises a motor or motors. 
     During retraction,  2316  pulls  2304  via linkage  2324 . Guiding element  2302  is caused to move by the motion of  2304 , via linkage  2322 ; and guiding element  2300  is caused to move by the motion of  2302  via linkage element  2320 . During the process of retraction, the length of the linkage elements between each adjacent pair of guiding elements decreases, under control of linkage control elements  2326 ,  2328  and  2330 . A variety of spring arrangements which will be obvious to those skilled in the mechanical arts may subsidize the retraction process. 
     The arrangement of linkage control elements need not be one per guiding element: For example, linkage control element(s) in guiding element  2300  could control (a) the length of the linkage between deployment motor  2312  and guiding element  2300  and (b) the length of the linkage between guiding element  2300  and guiding element  2302 . A similar dual function linkage control apparatus could be situated in association with guiding element  2304 . In the aforementioned arrangement, there would be no need for linkage control apparatus in guiding element  2302 . 
     The position of linkage motors in each of the drawings is not intended to indicate its relative position in the actual apparatus; such position will be obvious to those skilled in the art. The same is true of all of the other elements shown in the figures discussed hereinabove and hereinbelow. 
     The elements and their function in the lower right portion of the figure are analogous to those in the upper right portion. Furthermore, similar apparatus would be arranged on the left side of the apparatus. Such left sided apparatus could use deployment motors  2312  and  2314 , or a second set of deployment motors. 
     For the embodiment of the invention in which all of the filter elements are situated in one group in the retracted state, deployment motor(s) placement at the left side of the figure could be utilized. 
     The figure also shows a plurality of bearings, for example  2330 A-C for guiding element  2300 , to decrease friction during motion. Numerous possible arrangements of bearings are possible. A lubricating system to further decrease friction, not shown, will be desirable. 
     The figure also shows exemplary figure elements (e.g.  2332 ) and housing  2334 . 
       FIG. 23B  is similar to  FIG. 23A  except that two types of linkage elements are shown: linkage deployment elements  2338 ,  2340  and  2342 , utilized during the deployment process, and linkage retraction elements  2350 ,  2352  and  2354 . A single linkage control element ( 2356 ,  2358  and  2360 ) is shown in conjunction with each guiding element; configurations with (a) twice as many such elements [i.e. one per linkage element], (b) a larger number of linkage control elements and a smaller number of such elements are possible. 
       FIG. 23C  is analogous to  FIGS. 23A and 23B , except that in the configuration shown in  FIG. 23C  each guiding element (for example  2370 ) is associated with (a) a linkage element (e.g.  2372 ) which links it directly to deployment motor  2376 , and (b) a linkage element (e.g.  2374 ) which links it directly to retraction motor  2378 . In such a configuration, linkage control elements are not necessary; the deployment motor(s) and the retraction motor(s) perform this function. 
       FIG. 24A-24C  comprise apparatus analogous to that of  FIGS. 23A-C , but in  24 A-C the means for causing propulsion of the guiding elements is part of the guiding element, rather than a separate element. 
       FIG. 24A  shows a guiding element propulsion system in which each guiding element is propelled by a motorized apparatus (hereinabove and hereinbelow referred to as “motor”), indicated by hexagon shapes in figure contained in the guiding element apparatus. Filter element  2401  is shown to extend from guiding element  2400  with motor  2404  to guiding element  2402  with motor  2414 . Additional motors are shown (elements  2406 ,  2408 ,  2410  and  2412 , one each in association with each of the shown guiding elements. The engine housing is indicated by  2420 . 
       FIG. 24B  is similar to  24 A except:
         only the end guiding elements  2434  and  2436  have a respective motor ( 2430  and  2432 ); linkage elements  2438  and  2440  allow for the passive deployment of respective guiding elements  2446  and  2448  powered by motor  2430 ; and linkage elements  2444  and  2442  allow for the passive deployment of respective guiding elements  2450  and  2452  powered by motor  2432 .       

     Examples of two types of linkage control formats and elements are shown in  FIG. 24B . 
     In the first example, two linkage control elements are shown in association with guiding element  2446 : Linkage control element  2456  is for slack control and tension maintenance of linkage element  2438 ; and linkage control element  2458  is for slack control and tension maintenance of linkage element  2440 . 
     In the second example, one linkage control element is shown in association with guiding element  2450 : Linkage control element  2460  is for slack control and tension maintenance of each of linkage elements  2442  and  2444 . 
     Numerous other slack/tension maintenance arrangements are possible with zero to two linkage control elements in association with each guiding element. 
     The retraction process in  FIG. 24B  could be powered:
         By having motor  2430  cause a pushing action of guiding element  2434  in the direction of  2446 , and thence in the direction of  2448  (with a pulling motion away from these respective guiding elements have cause the deployment of these guiding elements); and by having motor  2432  cause a pushing action of guiding element  2436  in the direction of  2450 , and thence in the direction of  2452  (with a pulling motion away from these respective guiding elements have cause the deployment of these guiding elements);   By motors in the linkage control elements. For example motors  2456  and  2458  would cause guiding elements  2430  and  2448  to approach guiding element  2446 , and motor  2460  would cause guiding elements  2436  and  2452  to approach guiding element  2450 ; In such an example, at least one additional linkage control motor  2464  would be required to complete the retraction process. ( 2464  would cause the group of guiding elements  2434 - 2446 - 2448  to approach the group of guiding elements  2436 - 2450 - 2452 .)       

       FIG. 24C  shows another configuration for propulsion of guiding elements, in which
         “pulling motors”  2470  and  2472  cause deployment of the filter array, with each causing respective guiding elements  2474  and  2480  to move leftwards in the figure; The motion of  2474  during deployment passively causes the motion of guiding elements  2476  and  2478 , while the motion of  2480  during deployment passively causes the motion of guiding elements  2482  and  2484 ; and   “pulling motors”  2486  and  2488  cause retraction of the filter array, with each causing respective guiding elements  2478  and  2484  to move rightwards in the figure; The motion of  2478  during retraction passively causes the motion of guiding elements  2476  and  2474 , while the motion of  2484  during retraction passively causes the motion of guiding elements  2482  and  2480 .       

     Linkage control elements  248 S,  2490 ,  2492  and  2494  manage slack/tension control. Numerous other slack/tension control configurations are possible. 
     In addition, the management of deployment and retraction for filter element configurations in which the retracted state includes two or more groupings of filter elements (as shown for example in  FIG. 19 ) can be accomplished utilizing each of the concepts and mechanisms shown and discussed in conjunction with  FIGS. 23A-C  and  24 A-C. 
     Numerous other configurations for causing the movement of guiding elements and the management of linkages between them will be apparent to those skilled in the art. 
       FIG. 25A  shows one mechanism for allowing the length of a central segment  2500  of a deployed filter element to increase during the deployment process and decrease during the retraction process. The entire filter element consists of (a) a first end segment  2502  shown coiled around shaft  2506 , (b) central segment  2500 , and (c) a second end segment  2504  shown coiled around shaft  2508 . The control of shafts  2506  and  2508  may be either active (motor), passive (spring) or a combination of the two. In the case of a spring-based source of torque for the take-up of slack amounts of the filter element during retraction, the energy for release of additional amounts of filter element during deployment would be caused by the motion of the pair of respective guiding elements. 
       FIG. 25B  shows another configuration for making an increasing length of central segment available during filter array deployment, and stowage during filter array retraction. The filter element in the figure comprises:
         a first end segment comprising  2520 A (wound around shaft  2530 ) and unwound portion  2520 B, a central segment  2522 , and a second end segment comprising unwound portion  2524 B and wound portion  2524 A (around shaft  2532 ).       

     Exemplary bearings  2540  and  2542  are shown, intended to indicate a plurality of bearings with appropriate lubrication. 
     Whereas the shaft and supporting components of the apparatus shown in  FIG. 25A  are located approximately in the plane of the front of the engine, these items are located further toward the back of the engine in the  FIG. 25B  configuration. 
     Numerous other configurations for release and take-up of filter element material will be apparent to those skilled in the art. 
     Cleaning apparatus  2550  and  2552  are shown in proximity to the end segments. The cleaning apparatus removes, minimizes and/or consolidates debris that may become attached to the filter elements. It may comprise a nozzle and reservoir for application of a cleaning fluid to the filter element; it may comprise a nozzle and air compression device to apply a blast of air to the filter element; it may comprise warming apparatus to melt ice that may have accumulated on the filter element; it may comprise one or more brushes to mechanically clean the element. 
     In a preferred embodiment, a catchment apparatus will store accumulated debris. The apparatus may alternatively, or in addition be situated to clean the central segment of the filter element. 
       FIG. 26  shows an embodiment of the invention in which the array  2604  of filter elements  2602  rotates about the long axis of the engine  2600 , to increase the efficiency of bird and debris deflection. Dotted lines in the figure indicate that the filter array is attached to the engine. Embodiments of the invention in which two tandem filter arrays (e.g. as shown in  FIG. 21 ) both utilize such rotation are possible. In a preferred embodiment with tandem rotating filter arrays, the angular velocity and direction of rotation of the arrays would differ. 
     There has thus been shown and described novel retractable bird and debris deflector for an aircraft jet engine which fulfills all the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is to be limited only by the claims which follow.