Abstract:
Two sensors spaced at a known separation produce signal pulses when activated by the wheels of a taxiing aircraft. The signals are transmitted to a processor in which the wheelbase of the aircraft can readily be calculated. Since specific aircraft types have unique wheelbase dimensions and characteristics, the type of aircraft passing the sensors is determined in a processor. Also, the time, direction, and speed of the aircraft can be determined and logged by the processor.

Description:
BACKGROUND OF THE INVENTION 
     A basic problem exists in obtaining accurate statistics of aircraft types using specific runways at airports. Such information is used for optimizing runway utilization and to make projections for future plans. Presently, this type of information is obtained by human observers manually noting the aircraft types using runways for arrivals or departures and to determine the taxi-and-hold times between two given locations for various aircraft types. 
     There is also need to assist ground controllers at airports when there is heavy traffic or poor visibility in tracking the location of aircraft and in knowing the types of aircraft involved with a minimum of communication between the control tower and aircraft. 
     At airports with aircraft noise monitoring systems there is a need to automatically classify the type of aircraft causing excessive noise after take-off or before landing. Such aircraft type identification is presently accomplished by observers or by reconstruction using the play-back of recordings of radio communications between the control tower and aircraft. 
     Automatic aircraft noise monitoring systems also require more reliable means to detect the aircraft traffic pattern at the airport in order to optimize system tracking and noise classification parameters. Presently automatic traffic pattern detection is accomplished by wind velocity sensors and acoustic sensors which are often unreliable in light fluky winds or due to false noise events respectively. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method to automatically classify the type of aircraft as well as its speed and direction while passing a sensor set at a given location on a runway or taxiway. By judiciously locating the sensor sets and by recording the time of the aircraft passing as well as the location, reliable data for the following may be automatically obtained with respect to aircraft type: (1) runway and taxiway usage statistics, (2) taxi-and-hold times between two locations, (3) the location of aircraft in specified sectors of runways or taxiways, (4) the classification of aircraft type causing noise exceedance, and (5) the determination of the aircraft pattern (direction of runway usage). 
     The method comprises the following components: a sensor set with its output signal conditioning device, a data transmission link to the input signal conditioning device for the processor, the processor with its input signal conditioning device, and a data read-out device. 
     The sensor set comprises two sensors spaced with a known separation along a runway or taxiway which produce signals when activated by the presence of the individual wheels of a passing aircraft. The time intervals between the transient signals caused by the individual wheels of the aircraft activating the two sensors systems are utilized by the processor to calculate the aircraft wheelbase, that is, the distance between the main landing gear and either the nose or tail wheels. The same time intervals are used to determine the speed and direction of the aircraft. The processor contains a look-up table relating aircraft types to the calculated aircraft wheelbase and the number of wheels in the main landing gear assembly if necessary. The processor also stores data from each aircraft passing event; e.g. the aircraft type with the time of the event, the direction of travel, and location of the event; allowing long-term statistics of runway or taxiway usage to be accumulated; the development and accumulation of taxi-and-hold times; the localization of aircraft in given sectors of the airport; and the post facto identification of the aircraft type causing excessive noise in the airport environs. The data read-out device is actuated by the processor as required for the statistical data, excessive noise events, or the real time display of aircraft types localized in airport sectors. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the drawing: 
     FIG. 1 is a plan view of a sensor set on a runway or taxiway with an aircraft approaching the sensor set; 
     FIG. 2 is the resulting sequence of signal pulses generated by the sensors as the aircraft passes by the sensor set; 
     FIG. 3 is an isometric of the remaining components of the invention located in an airport facility where the data is utilized. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates an aircraft 10 taxiing at speed V on a runway 11 approaching a sensor set 12. The nominal wheelbase of the aircraft 10 is the distance D between the nose wheel 13 at location a on the aircraft and the front wheel 14 at location b of the main landing gear. The sensor set 12 comprises two sensor systems 15 and 16 shown at locations 1 and 2 respectively with a separation of distance ι along the runway 11. Each sensor system 15 and 16 could be comprised of light beams 17 emanating from light sources 18 and being received by photocell units 19. When the wheels of the aircraft 10 break the light beams 17, electric signals are transmitted from the photocell units 19 via cables 20 to the output signal conditioning device 21 which, in turn, transmits signals over the data transmission link 22. 
     FIG. 2 illustrates the sequence of signal pulses generated at output cables 20 in sensor set 12 as the aircraft 10 passes by the sensor set 12. The time t of occurrence of the pulses are characterized by the first subscript designating the sensor set involved and the second subscript the wheel of the aircraft involved. For example, the pulse at time 1a is caused by sensor system 15 at location 1 on the runway 11 being actuated by the nose wheel 13 at location a on the aircraft 10. 
     The speed of the aircraft can be calculated utilizing the measured time interval, e.g. (t 2a  -t 1a ), between the pulses from the sensor systems caused by actuation from a given wheel at a single location on the aircraft, e.g. location a: 
     
         V=ι/(t.sub.2a -t.sub.1a). 
    
     The nominal wheelbase dimension D can then be calculated by utilizing the measured time interval, e.g. (t 1b  -t 1a ), between the pulses from a given sensor system location, e.g. location 1, caused by actuation of the wheels at the two different locations on the aircraft, e.g. locations a and b: 
     
         D=V(t.sub.1b -t.sub.1a). 
    
     Using these two relationships the nominal wheelbase D can be expressed as the product of the known distance ι and the ratio of the two measured time intervals: ##EQU1## To account for the aircraft taxiing at other than constant velocity V as it passes by the sensor set, the other combination of pulse time intervals can be used to improve the accuracy and to obtain the average velocity or the average calculated wheelbase D: 
     
         (d=d+d&#39;)/2 
    
     where ##EQU2## Since the nominal orientation of the runway is known, the direction of travel of the aircraft can be expressed in degrees, e.g. 90°, if the first pulse arrives from sensor system 15 and can be expressed in the supplement direction, e.g. 270°, if the first pulse arrives from sensor system 16. 
     The raw signal pulses from the sensor systems 15 and 16 as shown in FIG. 2 may be sent over the data transmission link 22 or preprocessing may be accomplished in the signal conditioning device 21 to transmit data in the form of time intervals or ratios of time intervals. In either case, the data is transmitted to the input signal conditioning device 23 in the vicinity of the processor 24 as illustrated in FIG. 3. If raw signal pulses are transmitted, then all processing of the calculations is accomplished in the processor 24 illustrated in FIG. 3. The processor obtains the following typical information: the measured and calculated wheelbase D resulting from the aircraft passing the sensor set at location A at time t 1a  in direction X°. 
     The processor contains a look-up table of wheelbase dimensions and the characteristics of the landing gear for various aircraft types and identifies the wheelbase bin (or range of values) into which the calculated wheelbase value D belongs. Following is a typical table of wheelbase bins for common commercial jet aircraft: 
     
         __________________________________________________________________________  Wheelbase D in feetAircraft Type  39    41      43        45          47            49              51                53                  55                    57                      59                        61                          63                            65                              67                                69                                  71                                    73__________________________________________________________________________737-Mod 200  XDC-9 Mod 20  XDC-9-Mod 40            X707-Mod 320                XDC-10                                    X727-Mod 200                      X__________________________________________________________________________ 
    
     The processor 24 actuates a read-out device which may be in the form of a printer 25 or a real-time display board 26. If desired, the printer could document each aircraft movement event at all sensor set locations, e.g.: 
     
         ______________________________________Location   Aircraft Type              Time      Direction                                Speed______________________________________A       707-B      1803:15    90°                                20 mphB       747        1803:18   270°                                20 mphD       DC-9       1804:00   270°                                15 mph______________________________________ 
    
     The processor 24 could contain a memory bank and obtain long term statistics on runway and taxiway usage by aircraft types, e.g.: 
     
         ______________________________________Takeoffs from Runway 09 for Month of March 1977Aircraft Type        Peak Hours   Off Peak Hours______________________________________747          130          70707          110          62DC-9         140          83______________________________________ 
    
     Similarly the processor 24 could accumulate taxi-and-hold times between two sensor set locations, e.g.: 
     
         ______________________________________Average Taxi-and-Hold Times Between D and A in MinutesAircraft Type        Peak Hours   Off Peak Hours______________________________________747          8            2707          10           3DC-9         7            5______________________________________ 
    
     The processor could be integrated with an automated noise monitoring system and when excessive aircraft noise is measured in the airport environs by the noise monitoring system, typical print-outs are: 
     
         ______________________________________              Decibels at Microphone              LocationAircraft Type      Departure Time A                    1      2    3    4______________________________________707        19:08         105    98   87   67747        20:13          92    88   71   60______________________________________ 
    
     Statistics showing which aircraft types cause excessive noise levels above given noise thresholds can be automatically developed, e.g.: 
     
         ______________________________________Noise Exceedances at Microphones1 Through 4 During March 1977Aircraft Type       Day        Night      Total______________________________________747         3          9          12707         11         15         26DC-9        8          2          10______________________________________ 
    
     Typical options other than the optical system used above as the example for the sensor-systems are vibration sensors, inductance sensors, and magnetic sensors. The primary constraints on acceptable sensor types are: technical constraints, e.g. short signal pulse rise times, commonly in the region of 1 millisecond, in order to provide acceptable classification between aircraft types with similar landing gear characteristics; environmental constraints due to temperature, moisture, corrosion, and optical transparency; and aircraft operational constraints such as minimum intrusion into critical airspace, maximum resistance to injestion by jet engine intakes, and durability under jet exhaust blasts. 
     Typical options for the data transmission link 22 are common voice grade telephone lines with output and input signal conditioning devices 21 and 23 containing tone burst generators and receivers respectively or containing analog to digital conversion devices; or the data transmission link 22 may be via radio or optical transmission with signal conditioning devices 21 and 23 containing compatible transmitters and receivers respectively.