Protective screen for jet-engine intake
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuation-in-part of my copending application Ser. No. 715,459, filed Aug. 18, 1976 and now abandoned. 
    
    
     FIELD OF THE INVENTION 
     My present invention relates to a protective screen for the air intake of a jet engine mounted in a nacelle of an aircraft. 
     BACKGROUND OF THE INVENTION 
     Flying objects, including birds, have frequently been the cause of malfunction of the power plants of jet aircraft by being drawn into the intake ends of their engines. To prevent such malfunctions and possible accidents resulting therefrom, the use of protective devices for the intake ends of such jet engines has already been proposed. Known devices of this type generally are in the form of curved screens with relatively small meshes formed by intersecting wires. The transverse wire loops of these screens form a rather tight array when projected onto a plane perpendicular to the engine axis, thus presenting an elevated resistance to the in-flight aspiration of air by the engine. Also, the limited relative mobility of the wires and their rather close juxtaposition are conducive to the deposition of the ice particles on the screen surface, thus requiring special measures such as electric heating for de-icing. 
     OBJECTS OF THE INVENTION 
     The general object of my present invention, therefore, is to provide a protective screen for the purpose set forth which is structurally stable, has a low air resistance and minimizes the problem of ice formation. 
     An ancillary object is to provide simple de-icing means for a screen of this nature. 
     SUMMARY OF THE INVENTION 
     The protective screen according to my present invention comprises a frustoconical array of a multiplicity of straight resilient metal rods, e.g. of stainless steel, surrounding the front end of the nacelle to form a cage-like structure, the rods converging forwardly from that front end and having their forward ends held together by a pointed tip lying substantially in line with the nacelle axis. 
     In a preferred embodiment, the rods are further interconnected at not more than two other points, namely at the base of the conical cage structure by a mounting ring secured to the nacelle and at an intermediate location--about midway of their length--by a retaining ring. Thus, the rods are free to vibrate in flight over large portions of their length (or even over their full length if the retaining ring is omitted) so as to shake off ice particles which might adhere to them. Their vibrations, moreover, increase their effectiveness in fending off birds or debris without significantly impeding the access of air to the jet-engine intake, even with a relatively wide separation at their rear extremities. Their constant convergence angle, which is preferably not more than about 30° on either side of the nacelle axis, lets them easily deflect oncoming objects impinging anywhere upon the cage. 
     Pursuant to a further feature of my invention, a small fraction of the exhaust gases generated by the jet engine is fed back by one or more conduits--preferably a single external pipe--from the rear end of the nacelle to the interior of the screen to help with the de-icing of the rods. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The above and other features of my invention will now be described in detail with reference to the accompanying drawing in which: 
     FIG. 1 is a side-elevational view of a jet-engine nacelle of an aircraft provided with a protective screen according to my invention; 
     FIG. 2 is an end view of the screen taken on the line II--II of FIG. 1; and 
     FIG. 3 is a longitudinal sectional view, drawn to a larger scale, of the forward end of the screen encompassed by a circle III in FIG. 1. 
    
    
     SPECIFIC DESCRIPTION 
     In FIG. 1 I have shown a power plant 10 of an aircraft, not further illustrated, comprising a jet engine 11 in a nacelle 12 which may be mounted on a wing of the craft and is open at an intake end 13 and an exhaust end 14. The nacelle and its engine are centered on an axis O oriented in the direction of flight which has been indicated by an arrow F. 
     A protective screen 15 embodying my invention, also shown in FIG. 2, comprises a frustoconical array of straight, resilient and therefore vibratile metal rods 2 whose rear extremities are held together by a mounting ring 3 having inwardly projecting lugs 4 by which it is bolted to the intake end 13 of the nacelle 12. The forward ends of the rods 2 are fixedly secured, as by welding, to a pointed tip 1 also centered on axis O; the rods are shown to include with this axis an acute angle of less than 30°. A retaining ring 5 inside the cage-like screen 15 interconnects the rods 2 in a transverse plane about halfway between the base and the vertex of the cone, the rods being otherwise free to oscillate transversely at their natural frequency. Certain of these rods are foreshortened at their rear extremities to form a port 6&#39; in the vicinity of the intake end 13, this port serving as an access opening allowing a mechanic to reach into the interior of the screen for tightening or loosening the nonillustrated mounting bolts which traverse the lugs 4. The port 6&#39; is normally closed by a door 6 in the form of a sliding cover which is guided by a pair of parallel rails 6&#34; on opposite sides of the opening. The door 6, provided with a handle, may be held in its closure position by a latch not shown. 
     The tip 1 at the vertex of the conical structure is hollow, as best seen in FIG. 3, and forms a mouth 1&#39; open toward the cage 15. Its conical peripheral wall 1&#34; has an aperture 17 communicating with a pipe 16 which feeds back some of the exhaust gases, issuing from the rear end 14 of nacelle 12, to the interior of the cage. Pipe 16 extends along the exterior of the nacelle, advantageously at a sheltered location near the body of the aircraft, and is held in position by a strap 19 welded to mounting ring 3 and a further strap 20 bolted to the nacelle. A conical insert 18 within tip 1, supported by radial webs 18&#39;, directs the hot exhaust gases from pipe 16 to the inner rod surfaces for preventing the formation of ice thereon. These gases will thus be most effective in an area of the screen remote from the jet engine 11 where the risk of icing is greatest. The free end 16&#39; of the pipe 16 is shown to have an inlet 16&#34; slightly spaced from the discharge end 14 of the nacelle; this facilitates the mounting and demounting of the assembly 15, 16.