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Aviation History
1931
1931 - 0866.PDF
FLIGHT, AUGUST 14, 1931 THE BARROS STALL WARNING DEVICE An Interesting Device which Warns the Pilot, in an Audible Manner when the Aircraft is Approaching the Stalling Point •* Hr^HE solution of the problem of the inadvertent^J) III stall rests with an instrument which can, without II' fail, automatically detect a loss of flying speedand transmit to the pilot a warning which he cannot fail to understand, allowing him sufficient time toease the stick forward and stabilise the machine. The Barros Stall Warning Device provides an efficientmeans of detecting the approach of a stall and conveying a definite warning at a predetermined angle of incidencebefore the stalling point of the machine is reached. The Warning Unit is let into the inter-cockpit com-munication tube. It comprises a casing containing a small bell movement, designed for the purpose, whichoperates on the diaphragm, mounted, as seen, on a drum, into which are fixed the tubular members, they in turnholding the speaking tube. The object of having the small drum is that, being directly connected to the speak-ing tube, inter-cockpit communication between pilot and passenger is in no way impaired. It will be seen that all that is required of the pilot onentering his machine is to connect his head-phones to the in a trice out of harm's way, without altering its adjust-ment. When the machine is on the ground, the normal ten-dency of the spring rod will be to be making contact, so an automatic cut-off is provided in the form of a smallcompression lever, controlled by two small vanes, as seen in the photograph, which, when the machine lands, forcesthe contacts apart. Now, assume that the detector is adjusted to the re-quired angle, and the machine accelerated over the ground. At a speed of about 35 m.p.h. the air pressure on thevane is sufficient to deflect it and hold it down at its lower limit. A slight increase in speed, and the auto-matic cut-off lifts, freeing the way for contact to be made at any time. While the machine is flying normally, nothing happens.Directly the flying speed drops to a certain point, the angle of incidence of the supporting surfaces commence toincrease in relation to the air flow, and it therefore follows that the surface resistance of the detector vane decreasesfor the same reason. Naturally, as the resistance de- The warning device is illustrated on the left, at- tached to a typical interplane strut. At its foot is the buzzer which is connected in the cockpit tele- phone pipe. On the right is one of the buzzer drums open showing the belt-type mechanism, and on the extreme rig"ht is the small battery-box with plug-in terminals on the top. (FLIGHT Photos.) speaking tube in the ordinary way, so that, when thedetector completes an electric circuit, the warning will easily be heard by the pilot through his telephones. The Detector It is common knowledge to those acquainted with aero-dynamics that the stalling speed of any given type of aircraft alters with the load, whereas the angle of inci-dence at which a machine stalls is always constant. The detector of this device can be said to operate on incidence,though it is actually an effective combination of that and speed. The photograph illustrates the detector fitted toan inter-wing strut. It consists of a small vane fixed to a spring-steel rod, which is mounted in a tube andadjusted to have an upward tension. The fore part of the tube is insulated, and has a wedge-shaped contactstud. This shape is the means by which the contacts are kept clean, owing to the rubbing movement it induces In order to obviate damage to the detector vane whenhousing the machine in a confined space, a quick release is provided, which enables the pilot to fold the detector creases on the vane, the rod rises, gradually or swiftly,according to the rate the aircraft is losing way, until the two contacts touch ; the electrical circuit is completed,and the warning is heard by the pilot, whose wandering attention is drawn back to the machine in ample time totake the necessary precautions. Any source of electric current of low voltage may beused, but provided with the set is a container to take a battery known as the Ever Ready No. 1215, which, withnormal use, lasts about 12 months. The following features of the Barros Stall WarningDevice should be carefully noted: —It operates before the stalling point is reached. It does not interfere with thepilot's controls. It does not require observation. No structural alteration to the machine is necessary whenfitting. It is designed to fit any type of machine. It is simple to fit and adjust. Mr. J. Barros, Room 17, 8, Princes Street, London,E.C.2, is the designer, and all inquiries should be addressed to him, mentioning FLIGHT. 812
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