Patent GB-423922-A (GB)
Title: Method of and apparatus for the acoustic determination of the direction of aircraft
IPC: G01S1/72
Filed: 1933-05-09
Abstract: 423,922. Calculating-apparatus. ELECTROACUSTIC GES., Werk Ravensberg, Kiel, Germany. May 9, 1933, No. 13512. Void [Abridged as open to inspection under Sect. 91 of the Acts, Nov. 13, 1933]. [Class 106 (i)] The bearings of an aircraft (assumed to be moving at constant speed and altitude along a path F) relative to a point K, Fig. 1, are determined electroacoustically at measured time intervals and from these data the bearings of the craft relative to a distant point S are stated to be calculated and transmitted thereto. Corrections are made for errors resulting from the velocity of sound, and the direction of the wind. Corrections are also made, it is stated, for the parallax between the points S, K, and for the time taken to make the calculation and train a searchlight &c. at the point S, but there is no detailed description of the latter correction. Two successive acoustically determined directions K12, K13 of the craft fix the " listening roof plane " containing the path of flight F and the point K. The inclination e and the parallels s, s1 are thus known. The perpendicular distance KW of the path of flight F from point K is then calculated by a Wheatstone's bridge method from which the inclination #1 of the " roof plane " of the point S (containing path F) is calculated. The acoustic directions K12, K13 correspond to true or optical directions K14, K15, respectively, and instead of transmitting to the point S the bearings of point 15, relative thereto, the bearings of a point 21 are stated to be transmitted, it being assumed that the craft will have reached this point by the time the calculations have been effected and the searchlight trained. The azimuth and altitude angles alpha, # may be transmitted for biaxial searchlights, and the roof plane inclination #1, side track angle #, and angle # in the roof plane, for triaxial searchlights. The electro-acoustic direction finder 402, Fig. 2, for example, as described in Specification 369,360, [Group XXXVIII], is manually adjusted by hand wheels 400, 401 and the azimuth and altitude angles of the direction K12, for example, found thereby, are transmitted through differential gears to an arm 42 rigid with a bevel gear 56 rotatable on a shaft 41, the bearings 40 of which are mounted on a gear wheel 39. The arm 42 carries a light projector 43 whereby a spot of light is projected on to a translucent hemispherical shell 44 in a position corresponding to the acoustic bearings of the aircraft. Successive positions of the light spot are marked with a crayon on the shell 44. As the aircraft is travelling horizontally these points lie on a great circle of the hemisphere 44 which determines the inclination e, Fig. 1. To transmit this setting to the calculating apparatus, the shell 44 and mechanism therein are rotated by a hand wheel 104 through gearing 102, 100, until the horizontal diameter of the marked great circle is coaxial with the fixed axis of a stirrup 46, Figs. 2, 5, which is then rotated until coincident with the markings. The angular displacement of the shell 44 (azimuth angle) is indicated on a fixed scale 47. Sound and wind velocity correction. Rotated synchronously with the gear wheel 103, Fig. 2, is a wheel 350, Fig. 7, bearing a scale 353. A plate 351 is rotatably adjusted about an axis 360 until its pointer 352 indicates the known wind direction on scale 353. The bearing block of a scale disc 354 is adjusted along a radial slot 355 in disc 351 until a pointer 357 on the block indicates the assumed wind velocity on a scale 356 on disc 351. A pointer 359, connected to a slotted bar 358 through a toothed wheel and rack, is adjusted to read the absolute speed of the aeroplane (assumed known) on scale 354. The distance between the axis 360 and a pin 362 carried by a slide rod 363 and engaging the slot in the bar 358 therefore corresponds to the relative speed v2 of the aircraft with respect to the ground. The rod 363, through a lever 367, displaces the stirrup 46 axially (in the direction of movement of the light spot) an amount v2/a Î r , where a is the velocity of sound, v2 the relative velocity of the aircraft obtained as above and r is the radius of the hemisphere 44, Fig. 2. If a rider 248 on the stirrup 46 be now moved manually to coincide with the light spot on the hemisphere 44 it gives relative to the stirrup the true optical bearing of the aircraft at point K, Fig. 1. Determining the roof plane inclination #1. The perpendicular distance KW, Fig. 1, is first determined by a Wheatstone's bridge method. Considering a tangent to the marked great circle on the shell 44 parallel to the path F, Fig. 1, then the ratio of the length of the tangent subtended by two consecutive optical directions K14, K15, to the distance d travelled by the aeroplane between these direction determinations is equal to the ratio between the radius r of shell 44 and the distance KW. Otherwise v2À#<t> / v1À#<t> = KW / r where v2 is the relative velocity obtained above, v1 the corresponding velocity reduced to the tangent, and #<t> the time interval between the direction determinations. The bridge comprises resistances 210, 211, 212, 213, and a galvanometer 214, Fig. 5. Resistance 210 corresponding to v2.#<t> is adjusted by a rider 215 driven by a running mechanism 202 during the interval #<t>. The resistance 211, corresponding to the tangential length v1.#<t>, is carried in the stirrup 46, wound according to a tangential law, and tapped off by contacts rigid with riders 248, 249, which are manually positioned as described above to indicate the optical directions at the beginning and end of interval #t. Resistance 213 represents r, and 212 corresponding to the distance KW is mounted along a bar 49, Fig. 6, which is so geared to the stirrup 46 that it indicates the angle of inclination e of the listening roof plane on a co-ordinate sheet 59. A slide contact 200 is adjusted along bar 49 by rotating a knob 58 until the bridge is balanced when the triangle KWW 1, Fig. 1, is indicated on the sheet 59. The equation above may be written #<t>/v1.#<t> = KW/v2.r .Consequently the running mechanism 202 may be run at constant speed and used as a chronometer to indicate #<t>, while the resistance 213 is made variable in accordance with v2.r and is tapped off by a rider 365, Fig. 7 rigid with the bar 363. A second rider 216 Fig. 5, driven continuously by the running mechanism after the first direction determination is provided and by switching it in to the bridge circuit to replace rider 215 (after the distance KW has been found), and continuously moving rider 248 to maintain the balance of the bridge, light spots on the shell 44 corresponding to further direction determinations should coincide with the point of this rider. If coincidence is not obtained the correction required for the distance KW is easily effected. The triangle KW1W, Fig. 1, being known, the distance KS1 must be found to obtain #1 Accordingly, a wheel 301, Fig. 8, is coupled to follow the movements of the wheel 103, Fig. 2, rigid with the shell 44. A concentric disc 308 is adjusted about its axis K2 to read on a scale 307 on disc 301 the relative bearing of the stations K, S, Fig. 1. A sliding block 303 on the disc 308 is radially adjusted to read the distance KS on a scale 306, and moves a slotted link 302 along a guide 600 such that the distance K, 304, is equal to KS1 and the angle #1 is given, Fig. 8, on the sheet 59. A linkage arrangement 314, 316, 310, Fig. 8, is described as being set by a bridge method to obtain the angles y &c. and cause through gearing 332, 343, wheels and axles 342, 348, 338, 346 to take up corresponding positions whereby the required angles may be transmitted to biaxial or triaxial searchlights.