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SMITHS Floor Type Drift Sight - Type Av 917
This instrument has been designed to meet the demand for a Drift Sight which can
be easily operated by the pilot.
THE DIRECTION AND SPEED OF THE WIND CAN BE FOUND BY THIS SIGHT.
It consists of:
(A). A casting approximately 6.5 In by 6.5 In.
(B). A special negative lens, 6In. diameter, giving a wide, clear field of view.
(C). A rotatable grid ring, carrying seven parallel drift wires, and engraved at
its forward end with a drift scale of 300 to Port and Starboard, In two-degree
divisions. This scale Is read against an Index mark engraved in the casting "A"
Three wind speed .scales are also engraved on the grid ring for air speeds of
80, 100 and 120 miles per hour.
(D). A remote control which can be fitted In any convenient position In the
cockpit, giving powerful but sensitive control of the grid ring. Weight: 21 ozs.
METHOD OF USE
(1). TO FIND DRIFT. The angle of drift on any course Is obtained by flying a
straight course and operating the Remote Control until objects on the ground
appear to run along, or parallel to, the drift wires on the grid ring.
(2). TO FIND THE WIND SPEED AND DIRECTION. (a). Obtain the direction of the wind
by flying into the wind until no drift is discernible, and noting the reading of
(b). Turn through 90°, fly at either 80,100 or 120 miles per hour airspeed, and
obtain the drift as in(1) above. The speed of the wind can then he read against
the index mark of the appropriate scale on the grid ring.
USED BY THE HOUSTON-EVEREST EXPEDITION
SMITH'S AIRCRAFT INSTRUMENTS
Branch of: S. Smith & Sons (Motor Accessories). Ltd. AVIATION INSTRUMENT
185, GT. PORTLAND STREET, LONDON, W1
Telephone : " Welbeck 7916 (4 lines) 'Telegrams: Airspeed, Wesdo, London."