Patent GB-684315-A (GB)
Title: Means for indicating the angle of orientation of a dirigible craft with respect to a desired path relative to ground
IPC: G01S1/54
Filed: 1949-02-18
Abstract: 684,315. Radio - navigation. OFFICE NATIONAL D'ETUDES ET DE RECHERCHES AERONAUTIQUES. Feb. 18, 1949 [Feb. 19, 1948], No. 4466/49. Class 40 (vii). A system for detecting angular displacement of the longitudinal axis of a moving body, such as an aeroplane or ship, with respect to a predetermined line of travel or away from a given point comprises a radio transmitter at the point radiating a beam of energy performing periodic angular sweeps and two longitudinally spaced aerials on the moving body associated with a receiver and an indicator showing the time-spacing of the signals received by the aerials. The transmitter will preferably have a beam rotating at constant angular velocity (w) and in such a case the time spacing t is given by:- where e, α, l and D are as shown in Fig. 1. Thus, for given values of l and w As D is normally large and not changing rapidly over short time periods sin α may be regarded as proportional to t for such periods. Alternatively, if D is determined by other apparatus, a quantitative determination of a can be made. To measure t the pulses of energy received when the beam sweeps through the two aerials may be amplified, detected, differentiated and applied to brighten the trace of the time-base scan of an oscilloscope. The time-base may be triggered by a separate receiver receiving signals radiated omnidirectionally when the rotating beam passes through a predetermined direction. The system may be combined with the distance and lateral displacement indicating equipment of Specification 684,313, the value for distance obtained by such equipment being practically unaffected by the drift angles α met in normal practice. A development of this combination involves the use of three aerials, the two lateral aerials (e.g. on an aircraft's wing tips) functioning as described in Specification 684,314, whilst the third aerial in co-operation with the first two gives an angular displacement indication according to the present invention. In one form of cathode-ray tube indication for this, in which the horizontal time-base is triggered by an omnidirectional signal as before, two spots 21 are produced by the laterallyspaced aerials, their separation being dependent on the distance to the transmitter and the lateral displacement of the mid-point of the line joining them from the centre vertical of the tube being dependent on lateral displacement off course. A third spot 22 produced by the signal received by the third (tail) aerial lies mid-way between the spots 21 for zero drift angle and to one side or the other in dependence on the magnitude and sense of the drift angle. As described in the last-mentioned Specification, the spots may be deflected vertically by signals from an altimeter so that spots 21 define a glide path in conjunction with curves 23 marked on the tube. The drift angle indicating point may be suppressed when the distance points 21 are close together, i.e. at large distances from the landing place. Instead of a rotating beacon two spaced transmitters defining hyperbolic equiphase lines, e.g. by synchronized frequency modulation, may be used. In this case the drift angle indication may be combined with the distanceindicating system of Specification 684,089. Specification 691,294 also is referred to.