Patent GB-841852-A (GB)
Title: Improvements in and relating to navigation training apparatus
IPC: G09B9/24
Filed: 1956-08-24
Abstract: 841,852. Grounded aircraft trainers. LINK AVIATION Inc. Aug. 24, 1956 [Aug. 24, 1955], No. 26046/56. Class 4. In a grounded aircraft trainer, the indicated instantaneous heading is computed from two components, the first representing rate of turning of the aircraft about a vertical axis ignoring change of longitude, and the second representing the turning effect with respect to the instantaneous meridian due to simulated travel transverse to converging meridians. The invention is used for more accurate simulation of navigation near the poles, or on long range flight, when owing to the convergence of the meridians an aircraft flying on a " straight " i.e. great circle course, will undergo substantial changes in geographical or magnetic heading, although the aircraft is not turning about a vertical axis. Fig. 1 shows the face of a simulated instrument which acts either as a magnetically enslaved gyro-compass or as a free directional gyro. The rate of turn of the aircraft about a vertical axis is computed as re = (r cos Ï + q sin Ï)/cos #, where r = rate of yaw, q = rate of pitch, Ï = angle of bank, and # = angle of pitch. In the a.c. computer of Fig. 3, the rate of yaw servo of a conventional flight computer positions the wiper of a constantly energized potentiometer R-301, the derived signal energizing a cosine contoured potentiometer R-303 the wiper of which is positioned by the bank angle servo to derive a signal r cos Ï fed to a summing resistor R-304 of an amplifier U-301. The wiper of a constantly energized potentiometer R-302 is positioned by the rate of pitch servo, and derives a signal energizing a sine-contoured potentiometer R-305 the wiper of which is positioned by the bank angle servo to derive a signal q sin Ï fed to a summing resistor R-306 of amplifier U-301. The latter has a cosine contoured feed back potentiometer R-307, the wiper of which is positioned by the pitch angle servo, to divide the inputs to the amplifier by cos #, whereby the output is re, the rate of turn about a vertical axis, as defined above. A signal r# representing the rate of change of heading due to convergence of the meridians is computed as r# = Vt sin #t tan L, where Vt is the aircraft ground speed, #t is the ground track azimuth, and L is the latitude. This signal is computed as explained below, and fed to a summing resistor R-325 of an integrator servo I-304. The other summing resistor R-310 is fed with an re signal from amplifier U-301. An initial heading datum #o is added to the shaft output position of integrator servo 1-304 in a differential 306, whereby the angular position #x of shaft 310 represents the geographical heading. A magnetic variation signal v set by the instructor is added in a differential 308, thus the position of shaft 399 represents the simulated magnetic heading. The shaft 310 also forms one input to a differential 313, the other input being from the shaft of a horizontal component of side slip (e) servo. To energize this, a signal # cos Ï + α sin Ï, where # is the angle of side slip and a the angle of incidence, derived from the flight computer is applied to terminal 320 to energize a cosine contoured potentiometer R-327, the wiper of which is positioned by the flight path elevation angle (y) servo, to derive a signal (# cos Ï + α cos °)cos γ - e. This is fed to a summing resistor R-329 of the horizontal side slip angle servo, the shaft of which is rotated in accordance with e. The output of differential 313 thus represents #x + # - #p which is the track heading in still air. To simulate the effect of wind, the relative wind determined by the instructor is resolved into components along and perpendicular to the track in still air, and the true ground speed vt and angle of drift #a computed. The air speed (Vp) servo positions the wiper of a potentiometer R-311 deriving a signal energizing a cosine contoured potentiometer R-326 the wiper of which is positioned by the flight path elevation servo to derive a signal Vp cos y representing the ground speed in still air, which is fed to a summing resistor R-313 of amplifier U-302. The wiper of a constantly energized potentiometer R-321 is adjusted by the instructor's wind velocity control to derive a signal Vw energizing a cosine contoured potentiometer R-316, the wiper of which is positioned in accordance with #i, the angle between the wind and the ground track in still air, so that a signal V w  cos # 1  being the component of wind along the still air ground track is fed to a second summing resistor R-314 of amplifier U-302, the output of which energizes one coil of a resolver A-301. The other coil is energized from the wiper of a sine contoured potentiometer R-315 energized by the V w  signal from potentiometer R-321, the wiper being positioned in accordance with #1. The latter is derived by integrating r e  in an integrator servo I-306 fed from amplifier U-301, and adding to the output an instructor's wind direction signal in differential 314. The shaft rotations representing #1, and #p are added in a differential 398, the output of which is the heading of the wind relative to the points of the compass being indicated to the instructor on a scale I-RW. The two input coils of the resolver A-301 are thus energized in accordance with the total velocity along and perpendicular to the still air ground flight path. The signal picked up in one output coil L 1  is fed to a drift angle (#a) servo which rotates coil L 1  until it picks up a minimum signal. The angular position of the servo shaft then represents #a, and the signal picked up in coil L 2  which is at right angles to coil L 1  then represents the total ground speed V t . The shaft rotations #a and #p are added in a differential 302, the result #t being the true flight path heading. The Vt signal on coil L 2  is fed to a cosine contoured potentiometer R-322 the wiper of which is positioned by the #t output shaft of differential 302. The resulting V t  cos #t signal represents the North -South component of ground speed and is integrated in an integrator servo 1-301. An initial latitude datum Lo is added to differential 304, the shaft output of which represents the simulated latitude L, and is used to adjust the wiper of a tangent contoured potentiometer R-323 which is energized from the wiper of a sine contoured potentiometer R-321. The latter is energized by the V t  signal and its wiper is positioned by the #t shaft, thus potentiometer R-323 is energized by a V t  sin # t  signal and its wiper derives a signal V t  sin # t  tan L fed to summing resistor R-325 as described above. To simulate the precession of a free gyro due to rotation of the earth, the L shaft output of differential 304 positions the wiper of a constantly energized sine contoured potentiometer R-324, and the sin L signal derived is fed to an integrator servo I-302, the output p of which is scaled to represent a precession of the gyro at 15 degrees per hour times the sine of the latitude. This is added in a differential 305 to the re signal integrated by an integrator servo I-303. A. random gyro wander signal Wr derived from a potentiometer R-317 positioned by the instructor and an integrator servo I-305 is added in a differential 307, and thus the output on. shaft 311 represents the angular position of the simulated gyro. This is fed to a three phase resolver A-302 having outputs on terminals 401-2-3. The simulated magnetic heading on shaft 399 and the gyro heading on shaft 311 form the inputs to a differential 309, the output representing the sum of the gyro angular position and the magnetic heading and being fed to a three phase resolver A-303 having outputs at 404-5-6. Fig. 4 shows the circuit of the simulated heading indicator of Fig. 1. The signals on terminals 401-2-3 are fed to the three phase rotor coils of a resolver A-402, and the signals on terminals 404-5-6 are fed to the three phase stator coils of a resolver A-401. Any signal developed in the rotor coil of resolver A-401 is, while the contact a of relay K-401 is in the position shown, fed to an amplifier U-401 energizing a conventional positional split phase motor generator servo MG having a damping rate feed back. The servo shaft 413 rotates the rotor coil of the resolver A-401 until no signal is developed therein, when the angular position of the shaft 413 represents that of the output shaft of differential 309 in Fig. 3. Shaft 413 also rotates, through gears 415, 417, the three phase rotor coils of resolver A-402, so that the angular position of the field set up by these coils represents the difference of the gyro angular position and the magnetic heading plus the gyro angular position, that is, the magnetic heading. A single phase rotor coil of resolver A-402 follows up the field, and thus the heading pointer 11 coupled to the coil indicates the magnetic heading on the scale 12. The relay K-401 is de-energized by rotating a knob 13 to its extreme anticlockwise position, Fig. 1, whereupon a pointer 14 indicates OFF and switch S-401 is open. Knob 13 is placed in this position by the trainee to select the magnetically enslaved gyro mode of operation. When, for example in a simulated trans-polar flight, the trainee selects the free gyro mode of operation, knob 13 is turned from the OFF position, closing switch S-401 and energizing relay K-401. Contacts a and b are changed over, and amplifier U-401 is fed from the output of a resolver A-403, the single phase rotor coil of which is coupled to rotate with knob 13. The pointer 11 is governed by the gyro position signal on terminals 401-2-3, which includes precession due to the earth's rotation. The trainee turns knob 13 until pointer 14 indicates his simulated latitude, whereupon shaft 413 rotates the three phase rotor of resolver A-402 at a rate determined by the setting of knob 13 to cancel out the gyro precession effect, the only errors in the heading indicatio