Patent Document

CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is the U.S. national phase entry under 35 U.S.C. §371 of International PCT Application No. PCT/FR2014/050775, filed on Apr. 1, 2014, which claims priority to French Patent Application No. FR 1352953, filed on Apr. 2, 2013, the entireties of each of which are incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to generating electrical energy in aircraft by recovering kinetic energy and potential energy. 
     When an airplane gains on altitude and speed, it increases its kinetic energy Ec and its potential energy Ep, which can be calculated respectively from the following formulas:
 
 Ec= ½ mv   2  
 
 Ep=mgh  
 
where m is the mass of the airplane, v is the speed of the airplane, g is acceleration due to gravity (9.81 m/s 2 ) and h is the height of the airplane relative to the ground.
 
     During a stage of climbing, the airplane increases its speed so as to go from a takeoff speed of about 230 kilometers per hour (km/h) to a cruising speed lying in the range approximately 500 km/h to 800 km/h (Mach 0.82 to 0.84), thereby enabling it to accumulate a very large amount of kinetic energy. Concerning potential energy, present airplanes cruise at an altitude of about 12,000 meters (m). 
     During a stage of descent, because of the kinetic energy and the potential energy that has been accumulated, the pilot needs to control the speed of the airplane so as to avoid exceeding a critical speed or limiting Mach number referred to as the maximum operating limit speed or Mach number (VMO/MMO) beyond which the airplane can suffer major damage. 
     Nevertheless, and paradoxically, during stages of descent, the pilot is often obliged to increase engine speed in order to have sufficient energy for pressurizing and conditioning cabin air and also for running electrical devices on board. Under such circumstances, the pilot increases engine speed in order to cover demands for electrical and pneumatic energy while deploying air brakes in order to avoid exceeding the maximum operating limit speed or Mach number (VMO/MMO). That solution is not satisfactory since it leads to excessive fuel consumption in the engines even though they are operating at low speed during this stage of flight (descent). 
     Consequently, there exists a need to have a source of energy in an aircraft that is suitable for supplying electrical energy, and of doing so independently of engine speed. This need is particularly important since proposals are presently being made to replace the hydraulic means used by most functions of an airplane (e.g. extending landing gear, braking, etc.) with means that are entirely electrical, in particular for the purpose of lightening the overall weight of the airplane. 
     It is also known to fit the wing tips of airplanes with shells that are substantially in the shape of wing tip tanks in order to reduce the negative effects of wing tip turbulence (vortices), which shells serve to limit drag, and consequently to limit wing tip energy losses. 
     OBJECT AND SUMMARY OF THE INVENTION 
     To this end, the invention provides an electrical energy generator system for an aircraft, the system comprising a shell having the shape of a wingtip tank and containing at least one turbine housed in the front portion of the shell and an electrical energy generator connected to said turbine, the front portion of the shell being fitted with air admission means that are movable between an open position in which the turbine is exposed to the outside stream of air, and a closed position in which the turbine is masked inside the shell, the air admission means comprising flaps or slats that are movably fastened between the nose and the body of the shell. 
     Thus, an aircraft having at least one such system has a source of energy that is suitable for supplying additional electrical energy independently of the energy being supplied by the engine. Respective systems of the invention may be mounted for example at the tips of an airplane&#39;s wings and/or at the ends of one or more portions of its tail unit. 
     When the air admission means of the system of the invention are in the closed position, the system of the invention is totally streamlined and does not give rise to any longitudinal drag during stages of takeoff, climbing, and cruising. During the stage of descent, the air admission means of the system are placed in the open position so as to enable outside air to drive the turbine and the associated generator to produce electricity by recovering the kinetic and potential energy of the aircraft. The air admission means may also be placed in the open position during stages of takeoff, climbing, and cruising, should that be necessary, e.g. in the event of a failure of one or more engines or of their generators. 
     With the electrical energy generator system of the invention, there is no longer any need to increase engine speed above its normal speed during the stage of descent, thus making it possible on each flight to save 1% to 3% of fuel consumption, depending on the level reached and the speed at the end of cruising. 
     According to a first characteristic of the system of the invention, the air admission means comprise flaps fastened in hinged manner to the nose of the shell, the flaps being lowered in the open position of the air admission means and being held in alignment with the body of the shell in the closed position of the air admission means. 
     According to a second characteristic of the system of the invention, the air admission means comprise slats or butterfly members pivotally fastened between the nose and the body of the shell, the slats extending perpendicularly relative to the surface of the shell in the open position of the air admission means and being held parallel with the surface of the shell in the closed position of the air admission means. 
     In both circumstances, the air admission elements are totally integrated in the shell of the system when they are in the closed position, thereby not increasing drag as a result of local turbulence. 
     According to a third characteristic of the system of the invention, it further comprises storage means for storing the electrical energy produced by the electrical energy generator. Thus, some or all of the electrical energy produced by the system of the invention can be stored and used subsequently on demand. The electrical energy storage means may be selected from at least one electrical energy storage means selected from at least one of the following means: battery; supercapacitor; and flywheel. 
     According to a fourth characteristic of the invention, the system includes openings in the rear portion of the shell enabling the air stream flowing inside the shell to be exhausted and cooling the power electronics associated with the electricity generator and also cooling the electrical energy storage means, in particular when they are constituted by batteries that may heat up while they are being charged. 
     According to a fifth characteristic of the invention, the turbine has variable pitch blades, thus making it possible to control the speed of rotation of the turbine as a function of the speed of the air stream striking the turbine, and thus making it possible to regulate the frequency of the electricity generator. 
     The invention also provides an aircraft including at least one system of the invention. The aircraft may in particular correspond to an airplane having a respective system of the invention at the end of each of its wings and/or at the ends of one or more portions of its tail unit. 
     In a first aspect of the aircraft of the invention, it includes a control device “C” for causing the air admission means to open automatically, at least during a stage of the aircraft descending. The aircraft may thus have an additional source of electrical energy available during stages of descent without needing to increase engine speed as is commonly done during such a stage. 
     In a second aspect of the aircraft of the invention, it includes a control device “C” for automatically causing the air admission means to open in the event of the failure of at least one engine of the aircraft, and/or of a generator of at least one engine of the aircraft. 
     In a third aspect of the aircraft of the invention, the electrical energy generator systems may also be controlled manually by means of a control button or switch “S” placed in the cockpit of the airplane. The pilot or the copilot can thus act manually to cause the air admission means to open, and can thus consequently cause electrical energy to be produced when so desired, in particular in the event of an emergency (total failure of one or more of the main engines or loss of electricity generation in one or more of the engines) or in an electric airplane emergency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics and advantages of the invention appear from the following description of particular embodiments of the invention given as non-limiting examples and with reference to the accompanying drawings, in which: 
         FIG. 1  is a diagrammatic perspective view of an airplane fitted with electrical energy generator systems in an embodiment of the invention; 
         FIG. 2  is a diagrammatic section view of a  FIG. 1  electrical energy generator system in the closed position in accordance with an embodiment of the invention; 
         FIG. 3  is a diagrammatic section view of a  FIG. 1  electrical energy generator system in an open position in accordance with an embodiment of the invention; 
         FIGS. 4A and 4B  are diagrammatic section views showing an electrical energy generator system in a closed portion, and  FIG. 4C  is an end view of a blade of a turbine, in accordance with another embodiment of the invention; and 
         FIGS. 5A and 5B  are diagrammatic section views showing an electrical energy generator system in an open position in accordance with another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 1  shows an airplane  10  that includes, in accordance with an embodiment of the invention, two electrical energy generator systems  20  placed respectively at the ends of wings  11  and  12 . Each system  20  comprises a streamlined fairing  21  corresponding in this example to a shell having the shape of a wing tip tank and of the same type as those fitted to the ends of airplane or missile wings in order to reduce or “break” turbulence (vortices) at the wing tip and reduce the interfering aerodynamic drag due to such turbulence. The shape of the fairing is essentially that of a wing tip tank or an ovoid that is tapered to a greater or lesser extent depending on the size and the shape of the wing on which the system of the invention is to be mounted. Any other shape serving to reduce aerodynamic drag could be used. In addition, or instead of two electrical energy generator systems  20  placed at the ends of wings, the airplane could also have one or more systems  20  placed at the ends of portions of the airplane tail unit, as shown in  FIG. 1 . 
     As shown in  FIG. 2 , inside its fairing  21 , each system  20  contains a turbine  22  having its shaft  220  connected to the rotor (not shown) of an electricity generator  23 . The electricity generator  23  is a rotary machine, e.g. an alternator. In the presently-described example, the shaft  220  is connected to the electricity generator  23  via stepdown gearing  231 . 
     Since the speed of the turbine can vary significantly depending on variations in the speed of the airplane, the system  20  also has a regulator  24  connected to the output  230  of the electricity generator. The regulator  24  serves to convert the alternating voltage at varying amplitude produced by the generator into an alternating voltage at constant amplitude and/or a direct current (DC) voltage. In the presently-described example, the regulator  24  performs both of these functions, and for this purpose it has a first output  241  delivering an alternating voltage at constant amplitude that is used for injecting directly into the primary electricity power supply network  13  of the airplane, and a second output  242  delivering DC and for use in recharging electrical energy storage elements  25 , specifically batteries that may be constituted by nickel cadmium or lithium ion storage batteries. In variant embodiments, the electrical energy storage elements may also be formed by supercapacitors or by flywheels. The electrical energy stored in the element  25  is injected on demand via an output  251  into the secondary electrical power supply network  14  of the airplane. 
     The electrical energy immediately available from the output  241  of the regulator or the energy previously stored in the storage elements  25  and available at the output  251 , can be used during stages of descent in order to power numerous devices of the airplane, such as in particular:
         pressurizing the cabin of the airplane;   air conditioning the cabin;   de-icing mats for heating the leading edges of the wings;   an electrical system for extending landing gear;   electrical braking.       

     Each electrical energy generator system  20  also has air admission means in the front portion  21   a  of the fairing  21 , which air admission means are movable between an open position in which the turbine  22  is exposed to the stream of air outside the fairing ( FIG. 3 ), and a closed position in which the turbine is masked inside the fairing ( FIG. 2 ). 
     In the presently-described embodiment, the air admission means are constituted by flaps or lids  26  of curved shape that are arranged between the nose  210  and the body  211  of the fairing  21 . The upstream end  261  of each flap  26  is fastened to the nose  210  via a hinge connection  262 , while the downstream end  263  of each flap  26  is free. The downstream end  263  presents a portion  2630  of curved shape that presses against the upstream end  2110  of the body  211  when the flaps  26  are in the closed position, as shown in  FIG. 2 . In order to reduce potential drag due to turbulence created at the clearance present between the flaps and the fairing, an upstream annular sealing gasket  264  is arranged in the portion present between the nose  210  and the upstream end  261  of the flaps  26 , and a downstream annular sealing gasket  265  is arranged between the upstream end  2110  of the body  211  and the downstream ends  263  of the flaps  26 . 
     In the presently-described example, the flaps  26  are held and moved between a closed position and an open position by actuators  27 , each secured at one end to the inside wall of the fairing  21  and at the other end to a flap  26  via a linkage  28 . In the closing position of the air admission means as shown in  FIG. 2 , the actuators  27  exert thrust on the shaft  281  of the linkage  28  so as to hold the flaps  26  in the closed position via hinged arms  282  connected to the opposite end of the shaft  281 . In the closing position of the air admission means as shown in  FIG. 3 , the actuators  27  exert traction on the shaft  281  in order to cause it to retract downstream and lower the flaps  26 . 
     In the embodiment shown in  FIGS. 2 and 3 , the shaft  281  of the linkage  28  passes through the center of the turbine  22 . The shaft  281  is supported by an internal portion  212  of the fairing that is of axisymmetric shape for the purpose of directing the outside air stream penetrating into the fairing  21  towards the blades of the turbine  22 . The internal fairing portion  212  also supports a ball bearing  213  for the turbine  22 . On its rear portion, the turbine  22  includes a gearwheel  221  that is engaged with the shaft  220  of the turbine  22  and that is offset relative to its axis. 
     By acting on the actuators  27 , it is possible to cause the flaps to open and close, and consequently to generate or not generate electrical energy by means of the system  20 . Thus, when the air admission means are put into the open position, as shown in  FIG. 3 , the flaps  26  are lowered into the inside of the fairing  21 , thereby enabling the outside air stream F flowing over the fairing  21  to enter into the inside of the fairing and drive the turbine  22  in rotation, which by virtue of its coupling with the electricity generator  23 , enables electrical energy to be produced. When there is no need to generate electrical energy by means of the system  20  and/or during stages of takeoff, climbing, or cruising, the flaps  26  are held in the closed position for the air admission means, as shown in  FIG. 2 , in order to reduce aerodynamic drag. In this position, the flaps are placed in alignment with the streamlined shape of the fairing  21 , thereby totally masking the turbine  22  inside the fairing, together with all of the other elements used for generating and storing electrical energy. Consequently, in the closed position of the air admission means, the flaps  26  do not create longitudinal drag, with the system  20  then acting fully to reduce wing tip turbulence. 
     The rear portion  21   b  of the fairing  21  has openings that are formed in this example by louvers or vents  29  enabling the stream of air admitted into the inside of the fairing  21  to escape therefrom when the air admission means are open. This avoids raising pressure inside the fairing  21 . In addition, the stream of air flowing in this way inside the fairing  21  serves to cool the power electronics associated with the electricity generator and also to cool the electrical energy storage means, in particular when they are constituted by batteries that may heat up during charging. The openings may be permanent or they may be closable on command. 
     In a variant embodiment of an electrical energy generator system  120  in accordance with the invention, as shown in  FIGS. 4A, 4B, 5A, and 5B , the air admission means may be constituted by slats or butterfly members  126  extending between the nose  1210  and the body  1211  of the fairing  121 . More precisely, the upstream and downstream ends  1261  and  1262  of each slat  126  are fastened respectively to the nose  1210  and to the body  1211  via pivot connections  1212  and  1213 . In the presently-described example, each slat is connected to a pivot shaft  1281  by a link  1282 . Pivoting of the shaft  1281 , and consequently pivoting of the slat  126 , is driven by an actuator  127  connected at one of its ends to the opposite free end of the shaft  1281  and at its other end to the inside wall of the fairing  121 . The other portions of the electrical energy generator system  120  are identical to those of the above-described system  20  and are not described again, for simplification purposes. 
     By acting on the actuator  127 , it is possible to open and close the flaps, and consequently to generate or not generate electrical energy by means of the system  120 . Thus, when the air admission means are put into the open position as shown in  FIGS. 5A and 5B , the actuator  127  is actuated to pivot the shaft  1281 , and consequently to pivot the shafts of the slats  126  so that they occupy the position shown in  FIG. 5B . This position of the slats  126  enables the outside stream of air F flowing over the fairing  121  to enter into the inside of the fairing and drive the turbine  122  in rotation, which by means of its shaft  1220  coupled to an electricity generator (not shown in  FIG. 5A ), serves to produce electrical energy. In  FIG. 5B , it can be seen that the slats  126  present good aerodynamic transparency (i.e. low drag) when they are in their open position. 
     When there is no need for electrical energy to be generated by the system  120 , and/or during stages of takeoff, climbing, or cruising, the slats  126  are held in the closed position of the air admission means, as shown in  FIGS. 4A and 4B . In this position, the slats are placed in alignment with the streamlined shape of the fairing  121 , thereby totally masking the turbine  122  inside the fairing, together with all of the other elements used for generating and storing electrical energy. Consequently, in the closed position of the air admission means, the slats  126  do not create longitudinal drag, with the system  120  then acting fully to reduce wing tip turbulence. 
     In order to control the speed of rotation of the turbine in the electrical energy generator system of the invention as a function of the speed of the air stream entering the turbine, and as shown in  FIG. 4C , the turbine may have variable pitch blades  123 , with the pitch of the blades  123  being increased when the speed of the air stream is high, and reduced when the speed of the air stream is lower. 
     The electrical energy generator system(s) of the invention may be controlled automatically by the control system (onboard computer) of the airplane. The airplane control system may be programmed in particular to:
         cause the air admission means to open automatically at least during a stage of the aircraft descending;   cause the air admission means to open automatically in the event of at least one engine of the aircraft failing; and   to cause the air admission means to open automatically in the event of a failure of a generator of at least one engine of the aircraft.       

     The electrical energy generator system(s) may also be controlled manually by means of a control button or switch “S” placed in the cockpit of the airplane. The pilot or the copilot can thus act manually to open the air admission means, and consequently to produce electrical energy, whenever they so desire, and in particular in the event of an emergency (total failure of one or more of the main engines or loss of electricity generator from one or more of said engines), or in an electric airplane emergency. 
     Thus, the electrical energy generator system of the invention advantageously replaces the emergency ram air turbines (RAT) that exist on present airplanes and that in addition to being heavy and expensive, sometimes present problems of reliability. 
     In addition to the above-mentioned advantages, the electrical energy generator system is placed at locations of the aircraft that are easily accessible, thereby greatly simplify maintenance, in particular maintenance of the power electronics and of the energy storage means, since they are immediately accessible, while being isolated from the inside space of the airplane that is occupied by passengers, thereby preventing possible harmful gases, e.g. generated in the event of thermal runaway of one or more batteries, reaching the cabin of the airplane.

Technology Category: 7