Patent GB-568568-A (GB)
Title: Improvements relating to towing devices for aircraft
IPC: B64D3/00
Filed: 1941-06-25
Abstract: 568,568. Towed and coupled aircraft. KRONFELD, R. June 25, 1941, Nos. 7963/41, 8528/41 and 7072/42. [Class 4] For controlling the disposition of an aircraft relative to another aircraft, land vehicle, or watercraft to which it is connected by a cable or other member, the variations in relative disposition are communicated to a control element on or adjacent to one craft by a connection from the other craft, which element may either operate the controls of the one craft directly or enable the pilot to make the appropriate corrections even when the other craft is invisible as a result of darkness or cloud. Fig. 1 shows a glider 5 towed by an aeroplane 1 which also tows a pair of stable bodies 10, 11 connected together by a bar 17. These bodies, by following the movements of the towing aircraft enable the pilot of the glider to manoeuvre his machine in accordance with their indications. The bar 17 may form part of a rectangular frame connected to the tow lines by additional connections 19. Alternatively a drogue connected by a cable to the main towing cable may be used as an indicator. Where several gliders are towed by one aeroplane, stable bodies similar to 10, 11 are towed within sight of the several gliders. Fig. 4 shows a modification in which a lever 38 is universally mounted in the nose of the glider, its rearward end 34 carrying a small aeroplane or other pointer 33 movable by the lever within a sighting ring 44. The forward end of the lever is forked to engage the towing cable against which it is retained by a ball 41. Alternatively, the lever may be telescopic, its forward end being connected by a releasable pin to a fitting on the cable, the pin being withdrawn by limit cables when the towing cable is cast off. Automatic control of the glider may be effected by causing the end of the lever 34 to work in two slotted sliders connected to the pistons of hydraulic cylinders connected to slave cylinders for actuating the elevator and rudder. A yieldable joint may be provided in the telescopic lever to prevent damage due to excessive movements of the control vable. Variations in the towing cable tension may effect movements of a drag flap to correct the variations automatically for which purpose the cable has a spring telescopic coupling connected to the control. To prevent sag of the towing cable from affecting the indicator, the latter may be operated by a separate wire maintained under tension by a spring or a drogue, the indicator arm engaging this wire instead of the towing cable. Fig. 16 shows an alternative form of indicator compensated for variations in towing cable tension. A wire 71 connected to the main cable at 73 is maintained under tension by a spring 76 and moves a ball 78 within a ring 74 which may be adjustable. A cable-85 connects the ball to the telescopic element 87 of the main cable and any sag due to the slackening of the cable is compensated by a spring 84 connecting the ball to the ring. A similar connection may be used with a lever directly engaging the cable. Fig. 14 shows the construction of sighting ring which includes a transparent ring 80 illuminated by internal reflection from a lamp 81 which also illuminates the ball 78. A spirit level 82 may be incorporated in the upper part of the ring to indicate side slip &c. Machines flying abreast may be controlled in accordance with the variations of tension in lateral connecting cables.