Abstract:
According to the invention, fresh air at the turboprop outlet is captured and mixed with the warm airflow created by said turboprop to lower the temperature, via a device having a tubular sleeve able to slide into the tubular duct while hot gases flow therethrough and which can switch from an inner position to a projecting position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a §371 national stage entry of International Application No. PCT/FR2009/000273, filed Mar. 16, 2009, which claims priority to French Patent Application 0801538, filed Mar. 20, 2008, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     This invention relates to a device for reducing the infrared signature of a turboprop nozzle for aircraft. 
     BACKGROUND OF THE INVENTION 
     It is known that, in some turboprops, the outlet of the hot gas flow generated by the nozzle has, within said turboprop, a duct which extends downwardly from the nozzle and through which said hot gases flow. Such duct is generally tilted at an angle of 15 to 20 degrees with respect to the horizontal and enables a portion of the residual thrust of the turboprop to be recovered. 
     SUMMARY OF THE INVENTION 
     This invention is particularly suitable for such a turboprop. 
     According to the invention, a device for reducing infrared emissions at the outlet of a turboprop mounted to an aircraft, said outlet having, within said turboprop, a tubular duct which extends downwardly from a nozzle of said turboprop and through which hot gases flow off said nozzle, is remarkable in that it has a tubular sleeve which is able to slide into said tubular duct while said hot gases flow therethrough and which can switch:
         from an inner position, in which said tubular sleeve is entirely accommodated inside said tubular duct,   to a projecting position, in which said tubular sleeve projects outwardly from said tubular duct and is able to collect, in the same way as a scoop, a flow of outside fresh air in the vicinity of said turboprop and to mix said flow of outside fresh air thus collected with said hot gases flow from the turbine, in order to lower the temperature of the latter flow before it is discharged outside by said tubular sleeve.       

     Thus, thanks to this invention, hot gases flowing off the nozzle are diluted by outside fresh air, which enables the infrared signature of said turboprop to be reduced. 
     For taking in outside fresh air, said tubular sleeve has a side opening directed to the front of said aircraft and provided, in a projecting position of said tubular sleeve, in the vicinity of said turboprop. In one advantageous embodiment, said side opening results from the end of said tubular sleeve directed towards the nozzle being truncated slantwise. 
     In order to guide the sliding of said sleeve inside said tubular duct, it is advantageous to provide cooperating slides between these two elements. 
     Preferably, said tubular sleeve is removably added into said tubular duct. It is then advantageous for said inner position of the sleeve in the duct to be labelled by first latching means with automatic latching and controllable unlatching, integral with said tubular sleeve. Thus, on the ground when said turboprop is shut down, said sleeve can be loaded into said duct, through the free lower end thereof, and then it can be pushed into said duct until said first latching means automatically latch it in the inner position. On the contrary, when, during a flight, it is required to switch said sleeve from the inner position to the projecting position thereof, said first latching means are controlled to unlatch said sleeve. Therefore, it can, under the combined action of gravity and the hot gases flow generated by the nozzle, slide to said projecting position. 
     It is advantageous for said projecting position of the tubular sleeve to be labelled by second latching means with automatic latching, integral with said tubular duct. Thus, when said sleeve slides from the inner position to the projecting position thereof, said second latching means will latch it into the latter position. Moreover, it is preferable for said second latching means to be of the controllable unlatching type. Indeed, said sleeve can be released during a flight, in order for the aircraft to recover full aerodynamic performance, when using said sleeve is no longer required. 
     Preferably, both said first and said second latching means are of the electromagnet-controlled latch finger type, wherein said latch finger is elastically mounted with respect to said electromagnet. 
     Preferably, said first and second latching means act at said cooperating slides of the sleeve and the inner duct. 
     This invention further relates to a turboprop, wherein the inner duct has slides able to cooperate with the slides mounted to the tubular sleeve and/or latching means for labelling at least one of said positions of said sleeve inside said duct. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The figures of the appended drawing will help better understand how the invention can be implemented. In these figures, identical references designate similar elements. 
         FIG. 1  schematically shows, in a perspective bottom view, an airplane provided with turboprops. 
         FIG. 2  schematically shows, in a partial broken view, one of the turboprops of the airplane of  FIG. 1 . 
         FIG. 3  schematically illustrates installing a tubular sleeve according to the invention into one of the turboprops. 
         FIGS. 4 and 5  illustrate, in a partial bottom perspective view, the inner and projecting positions, respectively, of the sleeve inside one of the turboprops. 
         FIG. 6  shows, in a partial cross-section view, the cooperating slide system between said tubular sleeve and the hot flow discharge duct of the turboprop nozzle. 
         FIG. 7  shows, in a partial section at line VII-VII of  FIG. 6 , the latching means in position of said sleeve inside said duct. 
     
    
    
     DETAILED DESCRIPTION 
     The airplane  1 , schematically illustrated in a bottom perspective view on  FIG. 1 , has wings  2  bearing turboprops  3 . 
     Usually (see  FIG. 2 ), each turboprop  3  has a propeller  4  (partially illustrated on  FIG. 2 ) and a turbine (not illustrated on  FIG. 2 ) provided with a nozzle  5  for discharging to the outside the flow of hot gases F generated by said turbine. As shown on  FIG. 2 , the nozzle  5  extends outwardly through a tubular duct  6 , downwardly tilted and through which said hot flow F passes. The tubular duct  6  emerges outside through the lower end  7  thereof. 
     As schematically illustrated on  FIG. 2 , inside the tubular duct  6  is provided a tubular sleeve  8  (see also  FIG. 3 ) which is able to slide into the tubular duct  6  while said hot gas flow F passes therethrough. 
     As shown in solid line on  FIG. 2 , the tubular sleeve  8  can assume, in the tubular duct  6 , an inner position in which it is entirely accommodated inside the duct (see also  FIG. 4 ). 
     The tubular sleeve  8  can also assume, as illustrated in dotted lines on  FIG. 2  and in perspective on  FIG. 5 , a projecting position in which it projects outwardly from said duct  6 . In this projecting position, as illustrated by arrow E on  FIGS. 2 and 5 , the tubular sleeve  8  collects, when the plane is flying, a flow of outside fresh air in the vicinity of the turboprop  3  and mixes it with the hot flow F, so that, at the outlet of the sleeve  8 , the mix being achieved has a temperature lower than that of said hot flow F. 
     As can be seen on  FIGS. 2 and 3 , the sleeve  8  has a whistle cut at its end  9  directed towards the nozzle  5 . Thus, in a projecting position, a side opening  10  appears, directed to the front of the airplane  1 , between the lower end  7  of the duct  6  and the slanted end  9  of the sleeve  8 . This opening  10  acts in the same way as a scoop for introducing the outside fresh flow E inside the sleeve  8  and mixing the same with the hot flow F therein. 
     Thanks to the cooperating longitudinal slides  11  and  12 , mounted in the duct  6  and to the sleeve  8 , respectively, the latter is slidably guided inside said duct (see in particular  FIG. 6 ). 
     The sleeve  8 , for example made of stainless steel sheet, can be loaded into the duct  6  in the manner illustrated on  FIG. 6 , by having the slides  12  of sleeve  8  cooperating with slides  11  of duct  6  and by pushing said sleeve  8  into said duct until latching means  14  automatically latch sleeve  8  into the inner position ( FIG. 4 ). 
     The latching means  14  have a latch finger  15  actuated by an electromagnet  16  and elastically mounted with respect thereto through a compression spring  17  ( FIG. 7 ). 
     Optionally, the front end of the slide  12  of the sleeve  8  has a bevel cut  18 . 
     Thus, when loading the sleeve  8  into the duct  6 , the bevel  18  reaches the latch finger  15 , it pushed it back against the action of the spring  17 , until the latter makes said latch finger  15  penetrate a notch  19  of said slide  12 . Sleeve  8  is then latched into the inner position ( FIG. 4 ) in the duct  6 . 
     When, during a flight, it is useful to reduce the infrared signature of turboprop  3 , the electromagnet  16  is controlled and retracts the latch finger  15  by making it come out the notch  19 . Sleeve  8  can then switch from its inner position ( FIG. 4 ) to its projecting position ( FIG. 5 ) thanks to the combined action of gravity and the hot flow F. 
     Provided on the duct  6  are second latching means identical to first means  14  for automatically latching the sleeve  8  into the projecting position thereof, which is then labelled by a latch finger (identical to the finger  15 ) cooperating with a notch of the slide  12  (identical to the notch  19 ). For that purpose, the rear end of slide  12  can have a bevel similar to the bevel  18 . 
     If, as schematically illustrated on  FIG. 1 , it is desired to release the sleeves  8  during a flight, the electromagnet of the second latching means is consequently controlled so as to retract the latch fingers thereof. The sleeves  8  can then slide down until they entirely come out of the ducts  6 .