Abstract:
An electro-magnetic landing gear up-lock includes at least one electro-magnet mounted to the aircraft structure positioned adjacent the landing gear trunion. When the at least one electro-magnet is energized, magnetically responsive material in the landing gear positioned adjacent to the electro-magnet is attracted to the electro-magnet with sufficient force to hold the landing gear in a retracted. De-energizing the electro-magnet causes the electro-magnet to release the landing gear to allow the landing gear to extend.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional patent application No. 60/963,119 filed Aug. 2, 2007, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to aircraft with a retractable landing gear and more particularly to a landing gear up-lock system which employs at least one electro-magnet for retaining the landing gear in a fully retracted position. 
     BACKGROUND OF THE INVENTION 
     In a conventional retractable landing gear assembly the gear retracts into the wheel well after takeoff or extends to a down and locked position prior to landing. The extension and retraction force is provided by a double acting hydraulic actuator connected between the movable trunion and fixed aircraft structure. Once the landing gear is in a retracted position, a mechanical up-lock hook is automatically engaged and hydraulic power is subsequently removed from the hydraulic actuator by a position sensing and control system. In order to extend the landing gear, hydraulic power is sequenced to first disengage the mechanical up-lock device. When the up-lock device is fully disengaged, hydraulic power is then directed to the double acting hydraulic actuator to extend the landing gear to a down and locked position. Once the landing gear achieves a down and locked position, a position sensing and control system removes hydraulic power from the double acting hydraulic actuator. 
     In the event of a failure in the normal gear extension system, a redundant means of extending the landing gear must be provided. This may consist of a purely mechanical system consisting of cables, pulleys, and brackets that connect the mechanical up-lock hook to a manual handle in the cockpit. Significant manual input force may be required to manually release the landing gear up-lock. This activity increases the flight crew&#39;s workload during critical phases of flight. 
     A disadvantage inherent in existing mechanical landing gear up-lock systems is that the various linkages and components of a mechanical system must be installed and properly adjusted such that the desired release of the landing gear prior to landing gear extension actually occurs. In some cases, because of improper adjustment or installation, the above described up-lock hook has failed to disengage rendering it impossible to extend landing gear for a landing. Such a landing gear extension failure is an extremely disruptive event that results in significant danger to passengers and crew and at best, significant damage to the aircraft as a gear-up landing is executed. What is needed is a simpler landing gear up-lock system that also reduces flight crew workload in the event that the normal extension system has failed. A simpler landing gear up-lock system would also reduce the time required to install the system and reduce the maintenance activity required to inspect and maintain the mechanical backup system. 
     SUMMARY OF THE INVENTION 
     The above described need is met by an electro-magnetic landing gear up-lock for retractable landing gear. The electro-magnetic landing gear up-lock may include at least one electro-magnet and preferably includes two electro-magnets mounted to the aircraft structure positioned adjacent to the landing gear trunion. When the electro-magnets are energized using switched aircraft electrical bus power, magnetically responsive material in the landing gear positioned adjacent to the electro-magnets is attracted to the electro-magnets with sufficient force to hold the landing gear in a retracted position. De-energizing the electro-magnets causes the electro-magnets to release the landing gear to allow the landing gear to extend. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic of a prior art mechanical landing gear up-lock system. 
         FIG. 2  is a schematic of an electro-magnetic landing gear up-lock system. 
         FIG. 3  is a perspective view of a prior art mechanical landing gear up-lock system with the landing gear in the retracted position. 
         FIG. 4  is a perspective view of a prior art mechanical landing gear up-lock system with the landing gear in the extended position. 
         FIG. 5  is a perspective view of an electro-magnetic landing gear up-lock system with the landing gear in the retracted position. 
         FIG. 6  is a perspective view of an electro-magnetic landing gear up-lock system with the landing gear in the extended position 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 ,  3  and  4  illustrate a typical prior art landing gear up-lock mechanism  10 A. Landing gear up-lock mechanism  10 A is associated with a retractable main wheel landing gear assembly  100 . Main wheel retractable landing gear assembly  100  is an example of a typical retractable main wheel landing gear assembly as may be found on a multi-engine passenger aircraft designed to carry between six and nineteen passengers. The skilled reader should appreciate that the general arrangement of landing gear assembly  100  may scaled down to accommodate smaller retractable landing gear equipped aircraft or scaled up to accommodate larger retractable landing gear equipped aircraft and that the magnetic landing gear up-lock mechanism described below may also be scaled for smaller or larger aircraft. 
     Landing gear assembly  100  is shown in  FIGS. 3-6 . Landing gear assembly  100  is shown in a retracted position in  FIGS. 3 and 5  and in an extended position in  FIGS. 4 and 6 .  FIGS. 3 and 4  show landing gear assembly with a prior art gear up-lock mechanism  10 A as will be described in greater detail below.  FIGS. 5 and 6  show landing gear assembly with the present electro-magnetic gear up-lock mechanism  10  as will also be described in greater detail below. Landing gear assembly  100  is a trailing link landing gear assembly for a main wheel. Landing gear assembly  100  includes a trunion  105 , a trailing link  110 , a shock strut  120 , a double acting hydraulic cylinder  125 , a wheel axle  130  and a wheel  140 . Trunion  105  is pivotably mounted to the aircraft frame for rotation around an axis of gear rotation  100 L. A double acting hydraulic cylinder  125  shown in phantom in  FIGS. 3-6  connects between the aircraft frame and trunion  105 . When hydraulic cylinder  125  extends landing gear assembly  100  pivots about axis  100 L from the retracted position shown in  FIGS. 3 and 5  to the extended position shown in  FIGS. 4 and 6 . 
     As noted above, when landing gear  100  is in the retracted position shown in  FIGS. 3 and 5 , it is important that landing gear  100  stay in the retracted position until such time landing gear assembly  100  must be extended for landing and ground operations. In the prior art, a mechanical hook and linkage mechanism is employed to secure landing gear  100  in the up and locked position. A typical prior art system is diagrammed in  FIG. 1 . The prior art up-lock system  10 A includes an up-lock sequence actuator assembly  12 A which is connected by a mechanical linkage  13 C to a landing gear up-lock hook  13 A. The landing gear up-lock hook  13 A engages a corresponding up-lock lug  13 B fixed to a trailing link  110  as shown in  FIG. 3 . 
     Such a mechanical up-lock mechanism as diagrammed in  FIGS. 1 ,  3  and  4 , is highly effective for retaining landing gear in an up-locked position. However, care must be taken that mechanical linkage  13 C and back-up hook release  13 D are properly adjusted to insure proper engagement and disengagement of up-lock hook  13 A. It is particularly important that up-lock hook  13 A disengages up-lock lug  13 B prior to the deployment of the landing gear. A significant misalignment of mechanical linkage  13 C may cause up-lock hook  13 A to fail to disengage prior to landing gear. A manual cable release  13 D connected to up-lock hook  13 A is available for manually release up-lock hook  13 A if up-lock hook fails to release automatically. The manual cable release  13 D must also be adjusted for proper operation. Other examples of such up-lock mechanisms may be found in U.S. Pat. No. 5,288,037 by Derrien and in US patent Publication US2003/0164421 by Collet et al. 
     The electro-magnetic landing gear up-lock system  10  of the present application is schematically diagrammed in  FIG. 2  and is illustrated in  FIGS. 5 and 6 . 
     As can be seen in  FIG. 2 , electro-magnetic landing gear up-lock system  10  includes electro magnets  12  and  14  and magnetic plate  22 . Electro magnets  12  and  14  are mounted to the aircraft structure by bracket  16  shown in  FIG. 5 . Magnetic plate  22  is fixed to trunion  105 . 
     As can be seen in  FIG. 2 , each electro-magnets  12  and  14  are connected to two identical energizing circuits  41  and  45  respectively. Energizing circuit  41  includes a power source  42 , an override switch  44 A, a circuit breaker  46  and electro-magnet  12 . Energizing circuit  45  includes an override switch  44 B, circuit breaker  47  and electro-magnet  14 . Circuit breakers  46  and  47  are connected with the landing gear actuator system via a line  32 , so that electro-magnets  12  and  14  are energized when trunion  105  is retracted and de-energized when trunion  105  is extended. 
     The landing gear control system for controlling hydraulic cylinder  125  associated with the landing gear is schematically represented in both  FIGS. 1 and 2  and should be understood by the skilled reader as conventional and well known in the art with the exception of the interface between controller  50  and electro-magnetic landing gear up-lock system  10  shown in  FIG. 2 . As shown in  FIG. 2 , in electro-magnetic gear up-lock system  10 , controller  50  of the landing gear actuator system sends a signal via line  32  to close circuit breakers  46  and  47  when landing gear control handle output signal  82  indicates an UP command. Conversely, controller  50  of the landing gear actuator system sends a signal via line  32  to open circuit breakers  46  and  47  when landing gear control handle output signal  82  indicates a DOWN command. In the unlikely event that landing gear extension is commanded to a DOWN position by landing gear control handle output signal  82  and the uplock system continues to retain the landing gear, then the pilot may use manual override switches  44 A and  44 B to release the gear. 
     In  FIG. 2 , a controller  50  controls the operation of electromagnets  12  and  14  as well as a hydraulic control valve  52  which controls the extension and retraction of hydraulic cylinder  125 . As can be seen in  FIGS. 1 and 2 , the hydraulic system includes a normal hydraulic power source  62  as well as a back up power source  72  and a shuttle valve  74  which is controlled by hydraulic control valve  52 . Hydraulic control valve  52  is, in turn, controlled by controller  50 . Controller  50  receives inputs from the landing gear control handle  82  which commands the gear to an up or a down position. Additionally, the system includes gear position sensors  84  and  86 . Gear up position sensor  84  indicate a gear up condition when the gear is up and locked. Gear down position sensor  86  indicates a gear down condition when the gear is down and locked. When neither position sensor is activated, then the landing gear is in transition. The absence of a gear up indication from gear up position sensor  84  in combination with a landing gear up condition in landing gear control handle output  82  indicates the gear is unlocked but should be up and locked and thus should be returned to an up and locked condition. Such a condition is normal when the gear is in the process of being retracted but such a condition might also occur after a large vertical acceleration causes magnetic plate  22  to disengage from both magnets  12  and  14 . This condition causes controller  50  to activate hydraulic control valve  52  and thus activate cylinder  125  to retract the landing gear so that magnetic plate  22  comes back into contact with energized magnets  12  and  14 . Thus, a temporary, unwanted disengagement of electro-magnetic gear up-lock system  10  is corrected by the normal operation of the landing gear control system. 
     The use of two electro-magnets  12  and  14  and two associated circuits provides a reliable, redundant system. If either circuit fails, either one of electro-magnets  12  or  14  is preferably sufficiently powerful to hold trunion  105  in a retracted position. Passenger aircraft are typically approved for flight loads ranging generally between −1.5 G and +3.8 G. Both electro-magnets  12  and  14  acting in unison are preferably sized to provide enough support to hold trunion  105  when the aircraft experiences vertical accelerations occurring within the above described flight load range. A disengagement of trunion  105  from electro-magnets  12  and  14  under very high loading conditions is not a serious incident. A position sensor associated with the landing gear hydraulic system provides a signal is preferably arranged to cause the hydraulic system to retract trunion  105 . This action brings magnetic plate  22  into proximity with electro-magnets  12  and  14  thus allowing electro-magnets  12  and  14  to reengage magnetic plate  22 . 
     An electrical analog to the manual cable release  13 D described above is also present in this system. Mechanical override switches  44 A and  44 B may be used to open both circuits for electro-magnets  12  and  14  should the system fail to disengage prior to landing gear extension. Opening mechanical override switches  44 A and  44 B interrupts the flow of current to electro-magnets  12  and  14  and thus causes electro-magnetic landing gear up-lock system  10  to disengage. 
     Electro-magnetic landing gear up-lock system  10  provides several important advantages. Even with the presence of relatively heavy electro-magnets, the total weight of the gear up-lock system may be reduced by 5 to 10 lbs. per aircraft for an aircraft under 15000 lbs. maximum takeoff weight. Electro-magnetic landing gear up-lock system  10  is simpler, has fewer parts and is therefore much easier to fabricate and install than a conventional mechanical up-lock system. Accordingly, electro-magnetic landing gear up-lock system  10  fulfills the above stated need for an effective landing gear up-lock system which is simple and which does not require the precise alignment and adjustment of mechanical components. Electro-magnetic landing gear up-lock system  10  significantly reduces flight crew workload in the event of a failure in the normal gear extension system. 
     It is to be understood that while certain forms of this invention have been illustrated and described, it is not limited thereto, except in so far as such limitations are included in the following claims and allowable equivalents thereof.