Patent GB-576037-A (GB)
Title: Improvements relating to apparatus for teaching celestial navigation
IPC: G09B9/52
Filed: 1943-12-28
Abstract: 576,037. Celestial globes for teaching navigation. LINK, E. A. Dec. 28, 1943, No. 21767. Convention date, Dec. 28,1942. [Class 146 (ii)] [Also in Groups XXXIII and XXXVII] Apparatus for teaching navigation involving a hollow hemispherical dome representing a portion of the real celestial sphere and having means for rotating it about its polar axis to simulate changes in longitude and the passage of time, as well as means for moving the dome along an arcuate track to simulate changes of latitude, has a constant speed motor for rotating the dome to simulate the apparent rotation of the celestial sphere about the earth, and a variable-speed, reversible motor under control of the instructor for modifying the speed of rotation in accordance with the assumed changes of longitude of the observer, the two motors driving the dome through a differential gear. The globe is fitted with lamps to simulate stars, those used for navigation having collimators as described in Specification 556,180, [Group XX], so that readings can only be taken on them when the sextant is within the narrow parallel beam extending therefrom. The apparatus is associated with a Link trainer for air pilots as described in Specifications 572,295, 572,379 and 572,569. A dummy fuselage 38 is mounted for tilting about a universal joint on a frame 36 by bellows devices, controlled by the pupil as described in Specifications 370,128 and 481,375, [Group XXXIII], the frame being rotatable also about a vertical axis 39 passing through an observer's cockpit 41. Mounted upon an arcuate rail 70 carried by a fixed framework 60 is a carriage 74 on which a dome-like structure 95 is rotatable about an axis which always passes through the cockpit 41. The carriage 74 is movable along the rail 70 by a cable 234 and electromotor 238, controlled by the instructor, against the pull of a cable 222 connected to a counterweighted quadrant 230 pivoted on a spindle 240. The various driving and indicating means are shown diagrammatically in Fig. 5. A synchronous constantspeed motor 94 drives a shaft 98 at two revolutions per minute, which by means of gearwheels 100, 102, 106, 108 and the worm gear 112, 116 drives the input shaft 118 of a differential gear 120. The output shaft 122 normally rotates at the same rate as the shaft 118 and drives through worm gear 124, 126 and a clutch, not shown, to turn the hub 170 of the dome through 360 degrees 59 minutes in 24 hours solar time to account for the difference between the solar and sidereal day. The clutch and setting mechanism are described in Specification 576,043. The frame of the differential gear 120 carries a worm-wheel 144 in mesh with a worm 134 on a shaft driven by series motor 128 which is reversible and variable in speed by the instructor who controls it in accordance with the changes of longitude indicated by a recorder 462 moving over a map on the instructor's desk 458 so that the apparent rotation of the celestial sphere is modified in accordance with the changes of longitude during a supposed flight. The motor 238 for effecting movements of the carriage 74 along the rail 70 is controlled in speed and direction by the instructor in accordance with changes of latitude indicated by the recorder 462. The recorder is described in Specification 484,243, [Group XXXIII]. The dome hub 170 has a gear-wheel 402 which drives through the gearing shown, a transmitter 414 connected to a receiver 416 by which the rotational movement of the dome may be indicated on a dial 422 at the instructor's desk. By correctly setting the dome at the commencement of a supposed flight, this dial will indicate the " Local hour angle of Aries " of the Navigation Tables. The shaft 110 of the worm 112 drives a similar transmitter 434 through gearing 114, 430, and its receiver 436 is geared to indicate solar time on a dial 440, a similar dial being provided in the observer's cockpit. The shaft 132 of the motor 128 drives a transmitter 142, the receiver 424 of which indicates the assumed longitude of the observer on a dial 426, and a gear 446 engaging the rail 70 drives a transmitter 442 to cause the assumed latitude of the observer to be indicated on a dial 456. The lamps for simulating the navigational stars, constellations and miscellaneous stars are selectively switched on by the instructor and controlled in intensity in accordance with the assumed visibility. A switch in the observer's cockpit enables the collimated stars to be switched out in order that their position may be indicated by recognition stars in the constellations. For this purpose the projector lens 372, Fig. 11, of the collimator 300 has a convex glass reflector 374 on its surface which reflects a ray from the lamp 376 of a recognition star, the reflection being visible from any point in the cockpit. The series-wound motors 128, 238 are each varied in speed by two independent controls which are supplementary to one another. One control varies the available voltage by selecting a tapping on an autotransformer, and the other varies the length of time that an interrupter switch in the circuit remains closed. This latter control comprises four cams, driven by a constant speed motor, for opening and closing four switches, any number of which can be 'placed in series in a circuit controlling a relay for operating the main interrupter switch by adjusting a ganged selector switch.