Abstract:
The invention provides a method of reducing the cooling time for disks of a brake ( 5 ) of an aircraft wheel ( 1 ) fitted with a heat screen ( 10 ) extending between the wheel and the disks of the brake, and mounted to rotate on aircraft landing gear about an axis of rotation, the method comprising making perforations ( 11, 12, 13 ) through the heat screen to allow air heated by the disks to pass through the heat screen towards the wheel, the perforations being provided with obstacles to block any radiation from passing directly from the disks towards the wheel.

Description:
[0001]    The invention relates to a method of limiting the cooling time for disks of an aircraft wheel brake, and to an aircraft wheel heat screen constituting an application of the method. 
       BACKGROUND OF THE INVENTION 
       [0002]    Certain aircraft wheels are associated with a brake comprising a stack of disks housed at least in part inside the wheel. It is known to place a heat screen between the disks and the wheel so as to protect the wheel and its tire from radiation from the hot disks. In particular, it is important to avoid any zones of the wheel that are in contact with the tire reaching a temperature higher than 200 degrees Celsius. 
         [0003]    Nevertheless, such screens do not enable the heat accumulated in the brake during landing and during taxiing of the aircraft from the runway to a terminal. It turns out that the temperature of the brake is a criterion having a major influence on the aircraft. For example, takeoffs are authorized only if the temperature of the brake is less than 400 degrees. Unfortunately, it takes the brake a certain amount of time to cool, which can prevent the aircraft taking off again quickly after it has stopped at the terminal. 
         [0004]    Various means have been proposed to reduce this cooling time, in particular by using a cooling fan. Nevertheless, such equipment is not used by all airlines. 
       OBJECT OF THE INVENTION 
       [0005]    The invention seeks to propose a method for reducing the time required for cooling the disks of an aircraft wheel brake that makes it possible to improve operating conditions for the aircraft. 
       SUMMARY OF THE INVENTION 
       [0006]    In order to achieve this object, there is provided a method of reducing the cooling time for disks of a brake of an aircraft wheel fitted with a heat screen extending between the wheel and the disks of the brake, and mounted to rotate on aircraft landing gear about an axis of rotation, the method comprising making perforations through the heat screen to allow air heated by the disks to pass through the heat screen towards the wheel, the perforations being provided with obstacles to block any radiation from passing directly from the disks towards the wheel. 
         [0007]    Thus, the perforations enable a convective stream to be set up through the perforations, thereby facilitating discharge of the heat produced by the brake disks. The air heated by the disks can thus escape more quickly to the outside without having to go round the heat screen via its end deepest inside the wheel. 
         [0008]    The presence of obstacles nevertheless prevents radiation from the disks impacting against the wheel directly, which would contribute to heating it quickly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention can be better understood in the light of the following description of non-limiting embodiments of the invention given with reference to the figures of the accompanying drawings, in which: 
           [0010]      FIG. 1  is a fragmentary section view of an aircraft wheel fitted with a brake and provided with a heat screen; 
           [0011]      FIG. 2  is a perspective view of one petal of the heat screen provided with perforations in a first embodiment of the invention; 
           [0012]      FIG. 3  is a longitudinal section view of the heat screen petal of  FIG. 2 ; 
           [0013]      FIG. 4  is a view similar to the view of  FIG. 3  showing a variant embodiment of the invention; 
           [0014]      FIG. 5  is a perspective view of a heat screen petal provided with perforations in a second embodiment of the invention; 
           [0015]      FIG. 6  is a longitudinal section view of a heat screen petal in a third embodiment of the invention; and 
           [0016]      FIGS. 7 a  to 7 c    are longitudinal section views of heat screen petals in several variants of a fourth embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    With reference to  FIG. 1 , the invention applies to an aircraft wheel  1 , in this example comprising two half-wheels  1   a  and  1   b  that are connected together by bolts  2  in order to carry a tire  3 . The wheel is provided with bearings (not shown) for mounting it to rotate on an axle of aircraft landing gear, about an axis of rotation that is substantially horizontal. The half-wheel  1   a  is hollow and receives the disks of a brake  5 , having rotor disks  5   a  that are driven in rotation about the axis of rotation of the wheel by bars  6  that are formed in the half-wheel  1   a,  and stator disks  5   b  that are engaged on a torque take-up tube of the brake (not shown), which prevents them from rotating. A heat screen  10  made up in this example of a plurality of petals, each extending between two bars  6 , is arranged between the rim of the wheel  1  and the disks  5   a,    5   b  in order to protect the wheel from radiation from the hot disks. This well known and is recalled merely to situate the invention. 
         [0018]    In the invention, the heat screen  10  is provided with perforations enabling air heated by the disks to pass through the shield in order to be discharged to the outside, while preventing direct radiation going from the disks to the wheel. In the figures below, the convective stream is represented by thick arrows, while radiation is represented by fine arrows. 
         [0019]    In a first embodiment of the invention shown in  FIG. 2 , each petal of the heat screen  10  is made from three superposed sheets  10   a,    10   b,  and  10   c  with only the outer sheet  10   a  being visible in  FIG. 2  with scoops  11  extending in a direction perpendicular to an axial direction (the axial direction being the direction parallel to the axis of rotation of the wheel). In 
         [0020]      FIG. 3 , it can be seen that the scoops  11  on the outer sheet  10   a  are associated with similar scoops  12  that are oriented in the opposite direction and made in the inner sheet  10   c,  while being mutually offset, so that two associated scoops are not in register with each other. 
         [0021]    Orifices  13  are made in the intermediate sheet  10   b  between the scoops  11  and  12  in order to allow air to pass through the screen. The perforation in the heat screen enables a convective stream of air heated by the disks to be set up through the heat screen, with the offset between the scoops enabling the intermediate sheet to form an obstacle blocking radiation from passing directly from the disks to the wheel. Indirect radiation that has been subjected to multiple reflections, and that is thus necessarily attenuated, may nevertheless pass through the perforations. 
         [0022]    In a variant shown in  FIG. 4 , the scoops  11  and  12  may be open towards the inside of the heat screen instead of towards the outside of the heat screen. Naturally, it is possible to mix these two variants, e.g. providing for the outer sheet to have outwardly open scoops and the inner sheet to have inwardly open scoops. 
         [0023]    In a second embodiment, as shown in  FIG. 5 , the scoops  14  extend axially both in the outer sheet, as can be seen in the figure, and in the inner sheet, while still being offset. As above, associated orifices are made in the intermediate sheet between two scoops so as to co-operate with the scoops to form perforations allowing hot air to pass through the heat screen, with the intermediate sheet forming an obstacle blocking radiation from passing directly from the disks to the wheel. Indirect radiation that has been subjected to multiple reflections, and that is thus necessarily attenuated, may nevertheless pass through the perforations. 
         [0024]    Under all circumstances, when the scoops allow pollution (external dust, carbon from the disks, . . . ) to penetrate into the inside of the heat screen, provision is made in the heat screen for discharge orifices that are regularly arranged so that when the wheels are being cleaned, cleaning liquid can easily remove and carry away the pollution, regardless of the angular position of the wheel. 
         [0025]    In a third embodiment shown in  FIG. 6 , the heat screen  10  is provided with perforations at a location where the three sheets  10   a,    10   b,  and  10   c  are contiguous. Superposed scoops  15  and  16  are made in the outer and inner sheets  10   a  and  10   b  so as to open towards the same side, while the intermediate sheet  10   b  is pierced between the scoops  15  and  16 , so as to leave a portion  17  of the intermediate sheet that extends facing the openings of the scoops  15  and  16  so as to form an obstacle blocking any radiation from passing directly from the disks towards the wheel. Indirect radiation that has been subjected to multiple reflections, and that is therefore necessarily attenuated, may nevertheless pass through the perforations. 
         [0026]    In a fourth embodiment as shown in  FIGS. 7 a  to 7 c   , perforations made in the heat screen, and the heat screen is provided with shields covering the perforations so as to block any radiation from passing directly from the disks towards the wheel, while still leaving openings for passing hot air. The examples shown relate to single-sheet heat screens. However, if the heat screen has a plurality of sheets, the shield should preferably be fastened to the outer sheet. 
         [0027]    As can be seen in  FIG. 7 a   , the sheet constituting the heat screen  10  has a perforation  18  for allowing air heated by the disks to pass to the outside, but the perforation is provided with a shield  19  that is fitted to the heat screen so as to project from an outer face thereof. The shield  19 , which is fastened by folding in this example, covers the perforation  18  so as to form an obstacle blocking any radiation from passing directly from the disks towards the wheel, while allowing an opening to remain for passing air. In this example, the shield  19  extends well beyond the perforation so as to encourage repeated reflections of radiation passing through the perforation between the shield  18  and the outside face of the heat screen, in order to attenuate its intensity. 
         [0028]      FIG. 7 b    shows a variant of a shield  20  that covers a perforation in the heat screen  10  by being fitted on fastener tabs  21  that are fastened to the heat screen  10  at the perforation. As shown in  FIG. 7 c   , the shield  20  advantageously has a peripheral dropped edge  22  for limiting the passage of radiation towards the wheel. 
         [0029]    The invention is not limited to the above description, but on the contrary covers any variant coming within the ambit defined by the claims.