Patent GB-945646-A (GB)
Title: Improvements in or relating to ground aviation trainers
Inventor: BRINKMANN KLAUS HERMANN
IPC: G09B9/20
Filed: 1960-08-26
Abstract: 945,646. Non-linear amplifier circuits; relay operating circuits. GENERAL PRECISION SYSTEMS Ltd. Aug. 28, 1961 [Aug. 26, 1960], No. 29618/60. Headings H3P and H3W. [Also in Divisions B7 and G4] An electronic summing amplifier is arranged to deliver at a point in its output circuit a signal which varies with the difference between two input signals representing aircraft and terrain altitude respectively, the output signal exhibiting a sudden increase or decrease in value when said difference changes sign. The Figure shows part of a grounded flight trainer computer, wherein a simulated rate of climb or descent Za signal is fed to amplifier A 11  through summing resistor R 12  and contact TD 1  of a relay TD. The amplifier energizes a height servomotor HS driving a potentiometer P 1  and a tachometer generator G providing a feedback signal through summing resistor R 11  and contact TD/1, so that the servo shaft position represents the simulated aircraft altitude Za. Potentiometer P 1  derives a D.C. signal representing Za, fed to a high internal gain D.C. amplifier A 1  over summing resistor R 2 . A potentiometer P 2  is set manually to a given terrain altitude Zg, so that the total external input to amplifier A 1  is the normally positive terrain clearance Za-Zg. The output at point Y of the amplifier is thus normally negative, and a feedback path comprising rectifier D 1  and resistor R 1  is conductive, to reduce the amplifier gain to, say, unity. If now Za-Zg goes negative, simulating touch down, the point Y goes positive, and the feedback path D 1 , R 1  becomes non-conductive, so that amplifier A 1  exhibits its full internal gain, say 10<SP>6</SP>, resulting in a sudden high potential rise at the point Y. This is limited to the value at which the tap of a potential divider R 4 , R 5  connected to a negative D.C. source, goes positive, whereupon a feedback path comprising rectifier D 2  and resistor R 1  becomes conductive, to limit the amplifier gain. The high positive potential at point Y energizes a relay C through rectifier D 3 . Its contact C 1  energizes relays E and TD, the latter holding itself on by contact TD 3 . Contact TD 1  is changed over, removing the Za signal from amplifier A 11  and substituting a positional answer signal from potentiometer P 1  over resistors R 2 , R 1  and R 13 , whereby the height servo is locked in a position representing Zg. A damping rate feedback signal is applied over resistors R 14 . A negative Za signal is still available on touchdown, and to simulate the taking up of the aircraft weight by the landing gear, this signal is fed to amplifier A 21 . In flight, the output of this amplifier is held at substantially zero by a very low feedback resistor R 21 . This path is opened, however, on touchdown by contact E/1 of relay E, so that the operative feedback path comprises resistor R 23  and capacitor C 21 , so that the amplifier integrates, and produces a rising positive output, fed over contact TD 2  of relay TD to the flight computer as a ground reaction force signal. This brings about a reduction of Za to zero, and thus a constant ground reaction force, when the latter equals the aircraft weight. On simulated take-off, a positive Za signal is produced, so that the positive output signal of amplifier A 21  decreases, and eventually goes negative, simulating lift-off. A diode D 22  then conducts and shorts out the amplifier feedback path, so that its full internal gain is employed, and the negative output suddenly becomes high. This energizes a relay B through rectifier D 21 , and its contact B 1  breaks the holding circuit of relay TD. Contact TD/2 removes the ground reaction force signal (now negative) from the flight computer, and contact TD/1 charges to the full line position, so that the height servo HS commences integration of Za with initial integrand value Zg. Za-Zg thus goes positive, and the point Y goes negative, so that feedback path D 1 , R 1  of amplifier A 1  conducts, and relay C is de-energized. Its contact C/1 de-energizes relay E, and contact E 1  restores the feedback path R 21  to amplifier A 21 , so that its output returns to substantially zero.