Abstract:
The thrust reverser is used with an aircraft gas turbine engine and includes upper and lower doors pivotable between a stowed position and a deployed position. When deployed, the doors redirect a portion of the efflux to generate a nose-down pitching moment on an aircraft to improve handling during thrust reversing on a runway.

Description:
TECHNICAL FIELD 
     The invention relates to thrust reversers for gas turbine engines. 
     BACKGROUND 
     It is generally desired to assist wheel braking using aerodynamic decelerating means on aircrafts equipped with gas turbine engines because of the high landing speeds of these aircrafts. The aerodynamic decelerating means are especially useful on wet or icy runways to enhance the stopping capability of aircrafts. A thrust reverser is one example of such aerodynamic decelerating means. A thrust reverser deflects at least a portion of the efflux from a gas turbine engine to create a braking force slowing down the aircraft. 
     Many different models of thrust reversers have been suggested since they exist. However, it always remains desirable to, among other things, improve the design of the thrust reversers so as to obtain additional benefits during their operation, one example being an improved handling of the aircraft on the ground during braking. 
     SUMMARY 
     In one aspect, the present concept provides a thrust reverser for a nacelle of a gas turbine engine, the thrust reverser comprising an upper reverser door and a lower reverser door defining a portion of an aft section of the nacelle, the doors having a respective trailing edge adjacent to a propulsive jet outlet of the nacelle, the doors being pivotable together between respective stowed and a deployed positions, the trailing edge of the upper door being positioned behind the trailing edge of the lower door in the deployed position, the trailing edges of the doors in the deployed position delimiting a rear opening that is generally oriented aft and downwardly relative to the engine, the rear opening communicating in use with a portion of thrust generated by the engine. 
     In another aspect, the present concept provides thrust reverser for a gas turbine engine of an aircraft, the thrust reverser comprising an upper door and a lower door pivotable between a stowed position and a deployed position, the doors configured and disposed in the deployed position to redirect a first portion of an engine thrust forwardly to create a braking force and a second portion of the engine thrust downwardly to create a nose-down pitching moment on the aircraft. 
     In another aspect, the present concept provides a method of thrust reversing an aircraft on a runway, the aircraft having at least one gas turbine engine producing an efflux, the method comprising the steps of: (a) generating a braking force by redirecting a first portion of the efflux; and (b) generating a nose-down pitching moment on the aircraft by redirecting a second portion of the efflux at a rear of the engine. 
     Further details of these and other aspects of the improvements presented herein will be apparent from the detailed description and appended figures. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a side view of an example of a nacelle provided with a thrust reverser according to the present description, its doors being shown in a stowed position; 
         FIG. 2  is a schematic view showing an example of the present thrust reverser doors in a deployed position; 
         FIG. 3  is a rear view of  FIG. 2 ; and 
         FIG. 4  is a side view showing an example of an aircraft with thrust reversers applying the new concept. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , there is shown an example of a nacelle  20  including a target/bucket door type thrust reverser  22  in the aft section  20   a  of the nacelle  20 . The turbofan gas turbine engine is located within the nacelle  20  and the nacelle  20  is attached under the wings or on the fuselage of the aircraft using an appropriate arrangement (not shown). The thrust reverser  22  comprises two opposite pivoting doors  24 ,  26  forming most of the propulsive jet outlet of the nacelle  20  when they are in their stowed position. One door  24  is at the upper side and the other door  26  is at the bottom side. The doors  24 ,  26  have trailing edges which are generally semi-circular. The centerline C 1  of the thrust reverser is preferably collinear with the centerline E 1  of the engine. This permits forward thrust produced by the engine to be substantially unaffected by the thrust reverser installation, as will be discussed below. 
     Each door  24 ,  26  has a trailing edge  24   a ,  26   a  adjacent to the propulsive jet outlet  28 . The arrows A 1  in  FIG. 1  show the direct thrust operation of the engine. The thrust reverser  22  is then inactive. As additionally shown in  FIG. 2 , the trailing edges  24   a ,  26   a  cooperate with the trailing edge of side arms  32  of a jet pipe  30  located inside the aft section  20   a  of the nacelle  20  and to which the doors  24 ,  26  are pivotally connected. The leading edges  24   b ,  26   b  of the doors  24 ,  26  and their outer wall form a smooth continuity with the upstream parts of the nacelle  20  when the doors  24 ,  26  are in the closed position. 
     The side arms  32  are shown in  FIG. 2 , which figure schematically shows an example of the interior side of the thrust reverser  22 . The jet pipe  30  is concealed inside the aft section  20   a  of nacelle  20  when the doors  24 ,  26  are in their stowed position, as in  FIG. 1 . 
     The engine is in a thrust reversal mode in  FIG. 2 . This mode is generally used immediately after landing an aircraft on a runway. The doors  24 ,  26  are pivoted to that position simultaneously using actuators (not shown). The arrows A 2 , A 3  in  FIG. 2  indicate the main flow path of the efflux coming out of the engine when operated during the thrust reversal. As can be seen, a large portion of the gases coming out of the engine are deviated substantially toward the front. The gases exit the doors  24 ,  26  in the vicinity of their leading edges  24   b ,  26   b . These edges are located at the front of the doors  24 ,  26  and are referred to as “leading” edges with reference to the travel path of the aircraft. The deviation of the gases creates a resulting horizontal retarding force opposing the forward movement of the aircraft. Increasing the output thrust generated by the engine creates an increased aerodynamic decelerating force, thus more braking. 
       FIGS. 2 and 3  show that the trailing edge  24   a  of the upper door  24  is pivoted behind the trailing edge  26   a  of the lower door  26  when the doors  24 ,  26  are deployed. This can be achieved, for example, from an asymmetrical positioning of the door pivots with reference to the horizontal center plane of the jet pipe  30 , such as is disclosed in applicant&#39;s co-pending application Ser. No. 11/534,202, filed Sep. 21, 2006.  FIG. 3  shows a rear view of the doors of  FIG. 2 . 
       FIG. 3  shows that a portion of the efflux exits through a crescent-shaped rear opening  40  defined between the trailing edges  24   a ,  26   a  of the doors  24 ,  26 , as shown by the small arrow A 4  in  FIG. 2 . The rear opening  40  is generally oriented downwards, as the plane of the opening  40  faces the rear and has a downward orientation. The flow of gas out of the rear opening  40  is then oriented toward the rear bottom. It generates a resulting force creating a nose down pitching moment on the aircraft because the force has an upward vertical component and that it is at the rear of the engine. This force also has a horizontal component opposing the braking force on the aircraft but its magnitude is much smaller than the braking force and consequently the overall retarding force produced by the thrust reverser is substantially unaffected. The nose down pitching moment during aircraft landing with the reverser deployed improves the controllability of the aircraft on the ground, but when the reverser is in its stowed configuration, the forward thrust produced by the engine is not affected as the centerlines of the engine and of the reverser are collinear. In other words, the configuration of the present thrust reverser does not require modification of the angle of the thrust vector produced by the engine when the reverser is in its stowed position. Also, when the reverser is in its deployed position, it generates a nose down pitching moment to the aircraft without substantially affecting the overall retarding force produced by the thrust reverser. 
       FIG. 4  shows an example of an aircraft  100  during braking on a runway and with an engine having deployed thrust reverser  22 , incorporating the present concept, being provided on each side of the aircraft&#39;s tail. As can be seen, the efflux A 4  coming out through the rear opening creates a force vector acting on the center of gravity CG of the aircraft  100 . The force on the lever-arm L generates a nose-down pitching moment M around the center of gravity CG of the aircraft  100 , which lever-arm L is relatively long when the engines are tail-mounted. The moment M induces a downward vertical force F on the front landing gear  102 . This force F improves controllability of the aircraft  100  and is proportional to the output thrust of the engine. 
     The value of the moment M produced by the efflux A 4  can be tailored through the adjustment of the opening angle of the upper door  24 . For instance decreasing the opening angle of the upper door  24  will decrease the vertical component of the efflux A 4  and consequently will decrease the value of the moment M. Increasing the upper door opening angle will increase the moment M. 
     The above description is meant to be exemplary only, and one skilled in the art will recognize that many changes may also be made to the embodiments described without departing from the inventions disclosed. For instance, the exact shape of the illustrated elements (nacelle, doors, etc.) may be different. The aircraft illustrated in  FIG. 4  is only an example and the nacelle  20  can also be provided under the wings or within the tail of the aircraft, for instance. The rear opening  40  can have another shape, depending on the shape of the trailing edges  24   a ,  26   a  and the relative position of the doors  24 ,  26 . Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.