Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to EP 13382253.6 filed Jun. 28, 2013, the entire content of which is hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to in-flight refueling operations with a boom device and more particularly to communication methods between a tanker aircraft and a receiver aircraft which facilitate the in-flight refueling operation. 
     BACKGROUND 
     A usual method of in-flight refueling operations, illustrated in  FIG. 1 , is based on the use of a boom device  15  to interconnect the tanker aircraft  11  with the receiver aircraft  13 . The boom  15  is basically an extensible or telescoping tube attached to the bottom of the tanker aircraft  11  by means of a mechanical articulation which provides the passage of fuel from the tanker aircraft  11  to the receiver aircraft  13 . 
     In the tanker aircraft  11 , the operator monitors visually all steps and procedures to carry out a safe refueling operation. In particular, the operator controls the movement of the boom  15  until it is physically connected to the receptacle  19  of the approaching receiver aircraft  13 . After completion of the refueling operation in a given session the boom  15  is retracted to its safety position in the tanker aircraft  11 . 
     Refueling operations are very sensitive and must be performed in a very precise and accurate way due to security reasons. 
     Currently, communications between the tanker aircraft and the receiver aircraft are performed by means of visual signals transmitted from the tanker aircraft and voice communications between the boom operator in the tanker aircraft and the pilot of the receiver aircraft. 
     For transmitting visual signals to the receiver pilot to facilitate the approaching operation the tanker aircraft includes several Pilot Director Lights (PDL) at its bottom with conventional symbols. 
     For voice communication radio system are used and, in radio silence environments, an audio transmission system in an intercom mode between the tanker aircraft  11  and the receiver aircraft  13  through an electro-magnetic connection between the tanker aircraft and the receiver aircraft available when both aircraft are coupled is used. In  FIG. 2 , which represents a known nozzle  16  of a boom device  15 , a coil  17  that allows establishing said electro-magnetic connection together with another coil in the receptacle  19  of the receiver aircraft  13  can be seen. 
     These communication means do not meet all the communication needs between the tanker and the receiver aircraft and the present invention is directed to solving that problem. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide communication methods of data messages between the tanker aircraft and the receiver aircraft to improve the in-flight refueling operations in, particularly, radio silence environments. 
     This and other objects are met by a method of transmitting data messages through the electro-magnetic connection which is used for contact and disconnection detection and audio communications in radio silence environment between the tanker aircraft and the receiver aircraft comprising the following steps: 
     a) providing in the aircraft that emits the message a digital data frame containing a data message and a control signal for its sending; 
     b) converting in the aircraft that emits the message said digital data frame into a digital data signal and transforming this signal into an analog data signal conditioned to a suitable voltage level for its transmission to the target aircraft of the message; 
     c) transmitting the signal obtained in the previous step to the target aircraft via said electro-magnetic connection; 
     d) transforming in the target aircraft the received analog data signal into a digital data signal and converting this signal into a digital data frame. 
     The method comprises the simultaneous transmission of a data message from the tanker aircraft to the receiver aircraft and of a data message from the receiver aircraft to the tanker aircraft. 
     The method may comprise the transmission of messages that include data messages and voice messages. In such case, the method also comprises
         in step a), providing in the aircraft that emits the message an analog audio signal containing the voice message and a control signal for its sending;   in step b), converting in the aircraft that emits the message the analog audio signal into a second analog audio signal conditioned to a suitable voltage level for its transmission to the target aircraft and filtered to remove frequencies above a predetermined frequency f1 and mixing the second analog audio signal with the analog data signal for obtaining an analog audio and data signal;   in step d), separating the analog data signal and the analog audio signal contained in the analog audio and data signal received in the target aircraft.       

     In one embodiment of the method comprising the transmission of data messages and voice messages is contemplated that:
         in step b), the transformation of the digital data signal into an analog data signal is performed by means of a Frequency-Shift Keying modulation process obtaining a modulated signal in two frequencies f2, f3 for the logic levels 0 and 1, being f2 lesser than f3 and being f2 greater than f1;   in step d) the separation of the analog data signal and the audio data signal is made filtering in parallel the analog audio and data signal to eliminate, respectively, the frequencies below f2 and the frequencies above f1.       

     Other desirable features and advantages of the invention will become apparent from the subsequent detailed description of the invention and the appended claims, in relation with the enclosed drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of an in-flight refueling operation between a tanker aircraft and a receiver aircraft using a boom device. 
         FIG. 2  is a perspective view of a known nozzle of a boom device. 
         FIG. 3  is a block diagram illustrating the communication method of the invention for transmitting data messages between the tanker aircraft and the receiver aircraft. 
         FIG. 4  is a block diagram illustrating the communication method of the invention for the simultaneous transmission of data messages and voice messages between the tanker aircraft and receiver aircraft. 
         FIG. 5  is a block diagram illustrating the communication method of the invention for the transmission of data messages and voice messages from the tanker aircraft to the receiver aircraft. 
         FIG. 6  is a block diagram illustrating the communication method of the invention for the transmission of voice messages from the tanker aircraft to the receiver aircraft for the transmission of data messages from the receiver aircraft to the tanker aircraft. 
         FIG. 7  is a block diagram illustrating the communication method of the invention for the transmission of voice messages from the receiver aircraft to the tanker aircraft and for the transmission of data messages from the tanker aircraft to the receiver aircraft. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The method of the present invention comprises any kind of transmission of messages via the electro-magnetic connection between the coils  17 ,  18  of, respectively, the nozzle  16  of the boom device  15  of the tanker aircraft  11  and the receptacle  19  of the receiver aircraft  13 , comprising the simultaneous transmission of a voice message and a data message or the transmission of a data message from the tanker aircraft  11  to the receiver aircraft  13  and/or from the receiver aircraft  13  to the tanker aircraft  11 . 
     A detailed description of the method of the invention for different transmissions of messages between the tanker aircraft  11  and the receiver aircraft  13  follows. 
     Transmission of Data Messages Between the Tanker Aircraft and Receiver Aircraft (See  FIG. 3 ) 
     A digital data frame  24  generated by a device of the tanker aircraft  11  (indicating, for example, the remaining time to complete the ongoing refueling operation) is converted into a digital data signal  25  at step  35 . That signal is conditioned to a suitable voltage level for its transmission to the receiver aircraft  13  in step  37  and is subjected to a modulation process in step  39  to obtain an analog data signal  26 . 
     Preferably, the modulation process of step  39  is a Frequency-Shift Keying (FSK) modulation process that generates two fixed frequencies f2, f3 corresponding respectively to the logic levels 0 and 1. 
     Other modulation processes, particularly the Amplitude-Shift Keying (ASK) or the Phase-Shift Keying (PSK) modulation processes can also be used in step  39 . 
     The transmission of the analog data signal  26  to the next step is controlled by a switch  41  according to the content of the Request to Send (RTS) signal  29  of the data message. 
     The analog data signal  26  is injected into the coil  17  of the nozzle  16  of the boom device  15  and transmitted to the receiver aircraft  13  through the electro-magnetic connection with the coil  18  of the receptacle  19  of the receiver aircraft  13 . 
     In the receiver aircraft  13  the switch  75  controls the reception of the analog data signal  26 . In step  79  said signal is de-modulated to obtain the digital data signal  25  and in step  81  is converted in the digital data frame  24  to be sent to its destination. 
     Similarly a digital data frame  94  generated by a device of the receiver aircraft  13  (indicating, for example, the pressure of the received fuel) is converted in step  65  into a digital data signal  95 , is conditioned to an appropriate voltage level for its transmission to the tanker aircraft  11  in step  67  and is subjected to a modulation process in step  69  to obtain an analog data signal  96 . 
     The transmission of the analog data signal  96  to the next step is controlled by a switch  71  according to the content of the RTS control signal  99  of the data message. 
     The analog data signal  96  is injected into the coil  18  of the receptacle  19  of the receiver aircraft  13  and transmitted to the tanker aircraft  11  through the electro-magnetic connection with the coil  17  of the nozzle  16  of the boom device  15 . 
     In the tanker aircraft  11  the switch  45  controls the reception of the analog data signal  96 . In step  49  said signal is de-modulated to obtain the digital data signal and in step  51  is converted in the digital data frame  94  for being sent to its destination. 
     Simultaneous Transmission of Data Messages and Voice Messages Between the Tanker Aircraft and the Receiver Aircraft (See  FIG. 4 ) 
     An analog audio signal  21 , generated by the equipment of the boom device operator or of another crewman of the tanker aircraft  11  when a voice message directed the pilot of the receiver aircraft  13  is issued (informing him, for example, about the start of the refueling operation), is conditioned to a suitable voltage level for its transmission to the receiver aircraft  13  and filtered to remove frequencies above a predetermined frequency f1 to eliminate treble tones (preferably f1=5 KHz) in step  31  obtaining a second analog audio signal  22 . The transmission of the analog audio signal  21  to the next step is controlled by a switch  33  according to the activation/deactivation of the Push to Talk (PTT) signal  23  of the voice message. 
     A digital data frame  24  generated by a device of the tanker aircraft  11  (indicating, for example, the remaining time to complete the ongoing refueling operation) is converted into a digital data signal  25  at step  35 . That signal is conditioned to a suitable voltage level for its transmission to the receiver aircraft  13  in step  37  and is subjected to a modulation process in step  39  to obtain an analog data signal  26 . 
     In case of using a Frequency-Shift Keying modulation, the two frequencies f2 and f3 of the analog data signal  26  should be greater than the above-mentioned frequency f1. Suitable values for these frequencies f2 and f3 are, for example, 15 KHz and 20 KHz respectively, which are greater than the frequency of the voice message to allow simultaneous transmission of a voice message and a data message. 
     The transmission of the analog data signal  26  to the next step is controlled by a switch  41  according to the content of the Request to Send (RTS) signal  29  of the data message. 
     In step  43  the second analog audio signal  22  and the analog data signal  26  are mixed for its simultaneous transmission and the mixed signal is amplified. The resultant signal  27  that thus contains a voice message and a data message is injected into the coil  17  of the nozzle  16  of the boom device  15  and transmitted to the receiver aircraft  13 , through the electro-magnetic connection with the coil  18  of the receptacle  19  of the receiver aircraft  13 , resulting the signal  28 . 
     In the receiver aircraft  13  switches  75  and  83  allow receiving the signal  28 . 
     In step  77  the signal  28  is filtered to pass only the analog data signal  26  that is de-modulated in step  79  to obtain the digital data signal  25  that is converted in step  81  in the digital data frame  24  to be sent to its destination. 
     The signal  28  is also filtered in step  85  to pass only the analog audio signal  22  to be sent to its destination. 
     Likewise an analog audio signal  91 , generated by the equipment of the pilot of the receiver aircraft when emits a voice message directed to the operator of the tanker aircraft  11  (informing him, for example, about the fuel volume needed) is conditioned to a suitable voltage level for its transmission to the tanker aircraft  11  and filtered to remove frequencies above a predetermined frequency f1 to eliminate treble tones in step  61  obtaining a second analog audio signal  92 . The transmission of the second analog audio signal  92  to the next step is controlled by a switch  63  according to the activation/deactivation of the PTT signal  93  of the voice message. 
     A digital data frame  94  generated by a device of the receiver aircraft  13  (indicating, for example, the pressure of the received fuel) is converted into a digital data signal  95  at step  65 . That signal is conditioned to a suitable voltage level for its transmission to the tanker aircraft  11  in step  67  and is subjected to a modulation process in step  69  to obtain an analog data signal  96 . 
     The transmission of the analog data signal  96  to the next step is controlled by a switch  71  according to the content of the Request to Send (RTS) signal  99  of the data message. 
     In step  73  the second analog audio signal  92  and the analog data signal  96  are mixed for simultaneous transmission and the mixed signal is amplified. The resultant signal  97  that thus contains a voice message and a data message is injected into the coil  18  of the receptacle  19  of the receiver aircraft  13  and transmitted to the receiver aircraft  13  through the electro-magnetic connection with the coil  17  of the nozzle  16  of the boom device  15  resulting the signal  98 . 
     In the tanker aircraft  11  switches  45  and  53  allow receiving the signal  98 . 
     In step  47  the signal  98  is filtered to pass only the analog data signal  96  that is de-modulated in step  49  to obtain the digital data signal  95  that is converted in step  51  in the digital data frame  94  to be sent to its destination. 
     The signal  98  is also filtered in step  55  to pass only the analog audio signal  92  to be sent to its destination. 
     Simultaneous Transmission of Data Messages and Voice Messages from the Tanker Aircraft to the Receiver Aircraft (See  FIG. 5 ) 
     This is a particular case of the above in which communication occurs in one direction only. 
     Transmission of Voice Messages from the Tanker Aircraft to the Receiver Aircraft and of Data Messages from the Receiver Aircraft to the Tanker Aircraft (See  FIG. 6 ) 
     It is a particular case of that illustrated in  FIG. 4  in which communication occurs in two directions for different types of messages. 
     Transmission of Voice Messages from the Receiver Aircraft to the Tanker Aircraft and of Data Messages from the Tanker Aircraft to the Receiver Aircraft (See  FIG. 7 ) 
     As in the above is a particular case of that illustrated in  FIG. 4  in which communication occurs in two directions for different types of messages. 
     An advantage of the method of the present invention is that it enables the establishment of a digital communication channel between a tanker aircraft  11  and a receiver aircraft  13  through the electro-magnetic connection between the coil  17  of the nozzle  16  of the boom device  15  and the coil  18  of the receptacle  19  of the receiver aircraft  13 . 
     Another advantage of the method of the present invention is its utility for refueling systems of unmanned receiver aircraft requiring the exchange of data messages with the tanker aircraft. 
     Another advantage of the method of the present invention is that it enables the establishment of a redundant system for detecting contact between the tanker aircraft and the receiver aircraft. 
     Although the present invention has been described in connection with various embodiments, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made, and are within the scope of the invention.

Technology Category: h