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Aviation History
1941
1941 - 2179.PDF
SEPTEMBER I8TH, 1941. FLIGHT THE SPERRY FLICHTRAY Certain flight instruments on the aeroplane ore each pro- vided with a signal pick-up located between two stationary elements so that, when equi-distant between them, no deflection voltage is applied to the cathode-tube beam, bat when the instrument deviates from the normal set position a differential alternating voltage is produced and, when rectified and amplified, deflects the spot and makes a pattern on the screen of the tube. The pick-up used is a simple electro-magnetic type utilising the principle of the miniature Telegon alternating- current selsyn recently developed by the Kollsman Instru- ment Co., but only the transmitter element is employed for supplying deflection voltages for the Flightray. The necessary direct current is delivered to the commutated vertical or horizontal amplifiers by a balanced diode rec- tifier. As the pick-up is small, light and exerts negligible coercive force, it is readily applied to existing flight in- struments. And, since it operates at low audio frequen- cies, the leads to the Flightray can be of considerable length, hence the signal instruments may be located any- where on the aeroplane. By locating them on the flight panel, duplication of flighi instrument equipment aboard the craft can be avoided, and as the pick-up does not affect them they then become stand-by instruments. Dials with which they are provided may be set for any desired alti- tude, direction and speed, and flying then done by obser- vation of the Flightray without reference to -the primary instruments or any thought of numerals in feet, degrees or miles per hour. What the Pilot Sees Four pattern figures have been adopted for indication on the face of the cathode tube. These are (1) for altitude of the aeroplane, a long horizontal straight line, or arti- ficial horizon, that moves upward in a dive and downward in a climb and tilts at an angle when banking; (2) for direction, a short vertical straight line that moves to right or left of top centre to indicate amount of change of azimuth, or attitude of the vertical axis ; (3) for position relative to flight path, a small circle of light movable any- where on the screen from normal central position, deflected to right or left as the aeroplane flies to one side or the other of a guiding radio beam and up or down as the air- cralt departs vertically from the path of an approach glide beam ; and (4), for air speed, a short, straight, horizontal line that moves above or below centre as speed is in- creased or decreased from normal cruising speed. Intersection of the axis oi the vertical line with the horizon line at right angles through the centre ot the dial shows that the aeroplane is in straight and level flight, while with the light circle in the centre ot the face it is known to be directly on the radio-beam flight path, hence the utility of the instrument for blind flying and instru- ment landing. indicating Direction Directional indication by the vertical line takes the place of a rate-of-turn indicator, which experienced pilots found they did not need when Hying with the earlier ex perimental instrument. Movement ot the vertical line is limited to a segment of 20 deg. to right and left of azimuth, as marked in numerals above the face of the tube. This is done to avoid confusion of the pilot bv marking the periphery of the face in 360 deg and employing a radial line which moves oppositely from the o and the 180 deg. marks. This limitation of displacement ol tlit: vertical line to a segment ol 40 deg necessitates setting larger changes of course by hand to centralise the azimuth indication, but this has been found to be justified by the avoidance of confusion of indication. A method of azimuth indication which extensive tests have proved to have particular merit when making an instrument landing is the use of a radio compass for indi- cating direction. It is planned to make further tests of this, as it is believed to have value as a homing device for route flying as well as for instrument approaches and landings. A modification of the Flightray recommended by pilots who tested the instrument in hundreds of flights was that attitude and position of the plane be indicated in a pic- torial way, as by substituting a miniature silhouette of an aeroplane for the black-painted " bullseye " at the centre of the cathode-tube face, and that this silhouette be " flown " toward any of the luminous indicating patterns to bring the actual aeroplane back to correct heading, posi- tion or attitude. Movement of the circle of light about the face ot the instrument has been rrranged to be consistent with this idea, so that the miniature aircraft may be directed toward the circle wherever it may be. ^or example, in cruising OUTER MARKER BEACON LIGHT (purple) A.S.!. HIGH- SPEED MARK A.SX RAY LANDING PATH RAY A.S.I. LOW- SPEED MARK NNER MARKER BEACON LIGHT (amber) DIRECTIONAL GYRO SCALE DIRECTIONAL GYRO RAY GYRO HORIZON RAY MARK REPRESENT- ING AEROPLANE FACE OF THE SPERRY FLIGHTRAY. The gyro horizon tay moves up and down and tilts with changes in attitudtof the aeroplane ; the short horizontal line moves up and down with changes in air speed. The short vertical line moves right or left with variation from true course. The circle forming a corona around the black centre wanders ovet the faceto indicate position of the aeroplane relative to the flight path. Marker lights are in the upper corners and a bail bank indicator is below the face.
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