Patent GB-767776-A (GB)
Title: "improved radio direction finding chart recorder system"
IPC: G01C21/14
Filed: 1954-10-08
Abstract: 767,776. Flight training apparatus. CURTISS-WRIGHT CORPORATION. Oct. 8, 1954 [Nov. 13, 1953], No. 29110/1954. Class 4. Flight training apparatus for plotting the position of a simulated aircraft on a chart having a variable meridian tilt comprises means for deriving quantities responsive to the movement of said aircraft with respect to two mutually perpendicular axes; means for modifying said derived quantities in accordance with computed meridian tilt, motive means for moving a tracing element along two independent mutually perpendicular dimensions of said chart in response to said modified quantities to trace the path of said aircraft, and computing means responsive to the position of said craft for computing the instant meridian tilt. A simulated airspeed indicator 1 operates slider contacts 5, 6 of potentiometers 2, 3 which have resistances each with one terminal connected to the secondary winding of an AC transformer 7 and the other terminal grounded. The slider contacts 5, 6 take off voltages Œ E and Œ E of equal magnitude and opposite phase which are led to terminals 8 and 9 of a cosine resolver 10, the other terminals of which are grounded. The resolver has insulated sliding contacts 13 and 14 operated from a simulated compass 2<SP>1</SP> by a shaft 16 and connected respectively by conductors 17 and 18 to amplifiers 19 and 20 to supply voltages representative of instant velocity components of flight, without effects of wind drift, as projected on a pair of mutually perpendicular North-South and East- West axes defining a Cartesian co-ordinate system. To introduce the effects of wind drift alternating voltage from transformer 7 is applied to potentiometers 21 and 22 having wiper arms 23, 24 adjusted by a control 25 calibrated to represent wind velocity to supply voltages to a wind drift resolver 28. This has insulated sliding contacts 29, 30 adjusted by a control 31 calibrated to represent wind direction relating to the North-South axis, and connected by conductors 32 and 33 to the amplifiers 19 and 20. The output of the amplifiers is fed to a rotary transformer 34 to control the operation of plotting equipment to trace out a simulated flight on a chart C. The purpose of the transformer 34 is to take account of the fact that the angle of meridian tilt, i.e. the angle between a vertical line and the North-South lines on the chart varies across its length, and the outputs from amplifiers 19, 20 are fed through buffer amplifiers 37 and 38 to the primary windings 35 and 36. The secondary windings 39 and 40 are rotatable as a unit from a motor 111 by a link 114 in accordance with variation in the angle of meridian tilt over the flight path on the chart. The ouput voltages X and Y from windings 39 and 40 are fed through amplifiers 41 and 42 which provide " feed-back " to integrating motors 43 and 44. Motor 43 has two phase windings 45 and 46, winding 45 being energised by the output of amplifier 41 and winding 46 by a voltage e, the junction of the windings being grounded at 47. Motor 44 has windings 48 and 49 respectively energized by output of amplifier 42 and voltage e with the common junction grounded at 50. The motors 43 and 44 are respectively coupled to generators 51 and 52 which have two-phase windings, the windings 53 and 56 being connected to supply voltage e and windings 54 and 57 being supplied with feed-back voltages from the amplifiers 41 and 42 respectively, the windings of both generators being grounded at a common junction. Motor-generator sets 43, 51 and 44-52 drive lead screws 59, 60 respectively connected to slotted arms 62 and 64 which control the movements of a plotting pen 58. Resistors 67, 68 and 71 grounded at one end and energized at the other end by a voltage +E. Wiper arm 69, moved by arm 62 picks off a voltage fed to an amplifier 73 and wiper arms 70 and 72, both moved by arm 64, pick off voltages fed to amplifiers 74 and 106 respectively. The output from amplifiers 73 and 74 energize primary windings 75 and 76 of a resolver 77 which has secondary windings 78, 79 arranged for rotation according to the angle of meridian tilt over the simulated flight to give output voltages X<SP>1</SP>-Y<SP>1</SP> representative of distance components of the aircraft as projected on axes extending through the chart origin O. Potentiometers 80, 81 connected to ground and to a voltage -E, have wiper arms 82, 83 which pick off voltages representative of horizontal and vertical coordinates of a radio range station R relative to the chart origin O, the outputs of arms 82 and 83 being connected through amplifiers 84, 85 to primary windings 87 and 86 of a resolver 88 having secondary windings 89, 90 rotated in accordance with variation of angle of meridian tilt. To obtain control quantities determinative of the bearing angle at any instant during the simulated flight, the ouput voltages Y<SP>1</SP> and X<SP>1</SP> of windings 78 and 79 are subtracted from the output voltages y<SP>1</SP> and x<SP>1</SP> of windings 89 and 90 by means of summing amplifiers 91, 92 whose outputs energize primary windings 93, 94 of a resolver 95 having secondary windings 96 and 97 rotated through a link 103 and gearbox 99 by two-phase motor 98. The motor is energized by the induced voltage in winding 96 through an amplifier 100 which energizes winding 101. The other winding 102 is energized by a reference voltage e 1  and the motor rotates the secondary windings of resolver 95 in a direction tending to reduce to zero the voltage induced in winding 96. The winding 97 is connected through an amplifier to an indicator 105 which indicates the distance of the simulated aircraft from the reference radio station. In order to calculate the angle of meridian tilt and to operate the motor 111 the voltage picked off by wiper arm 72 is fed to an amplifier 106 to be summed with a negative voltage -E 1  in amplifier 107, the output of which is fed to one end of a potentiometer 108 which is wound so that a tan # function is derived at its wiper arm 109, where # is the angle of meridian tilt of the middle latitude of the chart. The arm 109 is set manually in accordance with the angle # of the particular chart used. Arm 109 is connected to an amplifier 110 which energizes a control winding 113 of a two phase motor 111, the other winding being energized by a reference AC voltage e 2 . The motor is connected through a gearbox 114 to the wiper arm 115 of a potentiometer 116 energized at opposite ends by supply voltages of opposite polarity +E2 and -E2 and grounded at its centre point whereby the arm 115 provides a " feed-back " voltage to the amplifier 110 to balance continuously the input voltage on arm 109.