Patent GB-809608-A (GB)
Title: Improved aircraft static pressure simulating system
IPC: G09B9/16
Filed: 1956-04-17
Abstract: 809,608. Grounded aircraft trainers. CURTISS-WRIGHT CORPORATION. April 17, 1956 [April 22, 1955], No. 11684/56. Class 4. An aircraft simulator comprises computing means for controlling the indication of flight instruments whose reading depends on the simulated static and dynamic pressures, in which means are provided for affecting the instrument readings on simulated selection of alternative sources of static pressure, e.g. one in a pilot head, and one inside the simulated aircraft. The computer comprises conventional true airspeed VT height h, and side slip # systems 133, 16, and 125. The indicators affected are the height, rate of climb, and indicated airspeed Vi indicators 13, 20 and 43. The readings of these instruments are affected by operation of a static source selector switch 62, a static leak switch 82, an icing condition switch 101, a static source icing switch 115, a pilot heater switch 109 a pilot heater failure switch 114, a turbulent air control 141<SP>1</SP> and the angle of side slip. The height system 16 comprises a summing amplifier 15<SP>1</SP> controlling a conventional bi-phase motor-generator combination with velocity feedback. The motor drives, through a transmission 17, the slider 14 of a potentiometer 15 energized by an A.C. voltage-E of negative reference phase. The derived signal simulating height is fed over line 18 to an indicated height (hIND) system 1 driving the indicator 13. This system has a velocity feedback (FDBK) from the generator winding 12 and an answer feedback (ANS) derived from slider 6 and potentiometer 5. The velocity feedback signal in the height system 16 is a measure of the rate of climb hÀ, and is fed over lines 25<SP>1</SP> and 26, a normally closed contact 27a of relay 28, line 29, a normally closed contact 30a of relay 31, lines 32 and 32<SP>1</SP>, a normally closed contact 33a of relay 34 and line 35 to the indicated rate of climb (hÀIND) system 19 driving the indicator 20. With switch 62 in the normal position shown, representing selection of the pilot head static source, relay 31 is de-energized and contact 30a is closed. Contact 27a of relay 28 is also closed unless the relay 28 is energized by closing contact 103b of the icing condition switch 101 and contact 116b of the static source icing switch 115, whereupon the hÀ signal is cut off from system 19 and the indicated rate of climb is zero. If, however, the alternative static source is chosen by closing contact 63b of switch 62, relay 31 is energized closing contact 30b, and the hÀ signal is fed over lines 25<SP>1</SP> and 36 and contact 30b to line 32 and reaches system 19, by-passing relay 28. As described above, the signal passes from line 32 to line 35 through contact 33a. If, however, relay 34 is energized by closing contact 83b of the static leak switch 82, contact 33a is opened and contact 33b closed, and a diminished signal is fed from line 32 through a potential divider 37, line 38, and contact 33b to line 35. A stabilizing hÀ signal is also fed to the hIND system 1 over lines 25<SP>1</SP> and 200. The V summing amplifier 135 feeds a transformer the secondary of which is connected over line 131<SP>1</SP> to energize a potentiometer 129, the slider 1291 of which is driven by the height system 16. The derived signal representing computed indicated air speed Vi is fed over line 131 to the Vi2 system 61. A potentiometer 60 has a slider 59 driven by this system and connected over line 58 to an amplifier 57 coupled to a transformer, the secondary 54 of which is connected over line 56 to the indicated air speed (ASI) system 39 controlling indicator 43. This system omits the generator, and derives feedback signals from an answer potentiometer 42 and the summing amplifier 40. The effect of switching from one static source to the other on indicated height is simulated by connection + Vl<SP>2</SP> and-Vi<SP>2</SP> signals from the transformer secondary 54 over line 65 and resistor 56, and line 68, to contacts 64a and 64b respectively of relay 31. Changing over switch 62 thus reverses the reference phase of the signal on line 67, connected to the hIND system 1. A transient fluctuation of the rate of climb indication is also produced as follows. Two contact makers 69 and 70 of relay 31 are wired in series with a pair of capacitors 76, 77, and a relay coil 72. Relay contacts 69b and 70a are connected to a D.C. voltage source, and contacts 69a and 70b are earthed. Change over of switch 62 reverses the polarity of the voltage across the capacitors, and the relay 72 is temporarily energized while the capacitors are charging. This makes contact 73b and line 74 which leads to the hÀIND system is connected to a line 81. This is connected to a + Vi<SP>2</SP> signal on line 80<SP>1</SP> or a -Vi<SP>2</SP> signal on line 80 derived from the transformer secondary 54 according as contact 71a or 71b is made depending on whether switch 62 was changed over to select the pilot or internal static source. The rate of climb indication thus transiently rises or drops. The effect of changes of static source on the A.S.I. is simulated by energizing the answer potentiometer 42 of the A.S.I. system over line 48 by contact 49a or 49b of relay 31, a potential dropping resistor 51 being included between potentiometer 42 and its energizing source +E in the latter case. The effect of static leak on the indicated height is simulated as follows. Closure of contact 83b of switch 82 energizes relay 34, and makes contact 87b. Line 89 is thus energized from potential divider 88, and a modifying signal is led to the hIND system 1. A transient fluctuation in the rate of climb indication is also effected. One end of a relay coil 90 is connected to a potential source E (D.C.). The other end is connected through capacitors 91, 92 over line 84 to contact maker 83. Contact 83b is earthed, and contact 83a is connected to a potential source E (D.C.). Thus on changing over switch 82, the capacitors 91, 92 either charge or discharge. In either case, relay 90 is transiently operated, and connects line 95 leading to the hÀIND system, to line 94. The,latter is energized from a positive or negative reference phase source through contact 86b or 86a, according as relay 34 has been energized or de-energized by changing over switch 82 to the leak or no leak position. The effect of a static leak on the A.S.I. is also simulated. A line 96 connected to the A.S.I. system 39 is normally earthed through contact 85a of relay 34. When switch 82 is in the leak position, however, line 96 is connected through contact 85b to line 97, which is energised through contact 98b, unless the simulated true air speed is zero, when a motor 100 positions a cam 99 so that the cam follower 98 opens contact 98b and closes contact 98a, in which case a simulated static leak does not affect the (zero) reading of indicator 43. The effect of the angle of side slip # is simulated. A potentiometer 127 is earthed at its centre, and energized at each end by a VT signal from line 131<SP>1</SP>. The slider 127<SP>1</SP> is driven by the side slip system 125, and the signal on line 136 is fed through contact 138a of relay 28, line 139, and contact 140a of relay 31 to line 141. This line therefore carries a side slip corrector signal if the pitot head static source is selected, and icing conditions are not simulated. Line 141 is connected to the hIND, hÀIND, and A.S.I. systems over lines 143 and 145, 143 and 144, and 142 respectively. The effect of turbulent air is also simulated. A potentiometer 144<SP>1</SP> is energized by opposite reference phase voltages at its end, and is earthed at its centre. The slider 143<SP>1</SP> is moved bv the turbulent air control 141<SP>1</SP> and is connected to the A.S.I. system over lines 145<SP>1</SP> and 146. It is also connected over lines 145<SP>1</SP> and 147 through contact 148a of relay 28, over line 149, and contact 150a of relay 31 to line 151. This line therefore bears a turbulent air correcting signal if the pitot head static source is selected, and icing thereof is not simulated. The slider 143<SP>1</SP> is also connected over lines 145<SP>1</SP>, 147, and 155 and resistor 154 to contact 150b of relay 31, whereby line 151 bears a turbulent air signal if the interior static source is selected, irrespective of icing, the signal being modified by resistor 154. Line 151 is connected to the h IND  system over line 152, and to the hÀIND system over line 153. Further effects due to simulated icing conditions are as follows. When the icing conditions switch 101 closes contact 103b, and the static source icing switch 115 closes contact 116b, relay 28 is energized and closes contact 120b. This contact is in series with contact 123a of relay 31 across the energizing coil 9 of the motor of the hIND system 1 over lines 121, 122, and 124. As a result, when the external static source is selected and icing is simulated, the coil 9 is short circuited and the indicator 13 stays fixed. With switches 109 and 114 in the position shown, closure of contact 102b by the icing switch 101 de-energizes a relay 104 normally earthed at one end through contact 102a. This makes contact 106a, short circuiting the energizing coil 46 of the motor of the A.S.I. system, so that the indicator 43 stays fixed. On operating the pitot heater switch 109 to close contact 110b, however, the relay 104 is again energized, to simulate de-icing of the pitot tube. The relay can be de-energized again by closure of contact 112b of switch 114, to simulate failure of the pitot head heater.