IN AN AIR PILOT'S COCKPIT

Dominion, Volume 11, Issue 236, 24 June 1918, Page 6

IN AN AIR PILOT'S COCKPIT

AEROPLANE INSTRUMENTS L ; : iNEW FIELD FOR SCIENCE ■.'■' The pilot's cockpit in an aeroplane J eontains au intricato assortment of in- '■ :'. tstruinents necessary for proper control and navigation by day and night. The : niost important of these, viz., indicators ■ tor air speed/height, and engine, speed, : -. : .together with compass and watch, aro ■ '■■''. .mounted in such a position as to be plainly visible to the'pilot while steering; surrounding theso are the gauges and cocka for petrol and oil tanks, switches for engine magnetos, navigation - ;;and landing lights for night flying, etc. ', •;•'■"-"■■"' "•■'■Speed Indicator. ■".'■The' most interesting is tho indicator ■devised to ehow the aeroplane's ejpeed ; 'through the air. A 'pressure.head is hxed ;'6n some part of tho aeroplane facing the direction of travel, generally on an outer interplane strut wnere it will be free from the stream of air deflected by the airscrew. Tubes run to the indicator under the pilot's ey6, conveying tho airpressure, either causes a coloured liquid to rise in a transparent tube set vertically in a graduated scale, or presses ■ ■■■ "On a spring working against a diaphragm - which moves a pointer over a dial. ; The aeroplane moving through the air : must be.' considered exactly as a ship travelling through the water, either with .' or against tides and currents. If the aeroplane's normal speed is 100 miles per : hour in still air, its speed over the ground will bo the same, but against a -head wind of 80 miles per hour its ground speed would be only ( 70 miles per "' < hour—and 130 miles per hour, when flying down-wind. In all cases the instrua meht would still show 100 miles per hoiir as'the air speed. Ground speed can only be got by noting the time taken to pass ~. over certain places, the distance apart ,'• of which are known-to the airman by map or otherwise. In a balloon, which about in tho air, and is 'not propelled through it by any power,, this in- ' strument would be used to indicate- tl-.e force of wirid blowing, which would correspond with the balloon's Epeed over the ground.

S. The Height Indicator. 'The height indicator is an aneroid barometer, the dial of which , is graduated in hundreds of feet, and not in the equivalent height in inches of the mer- . ourial barometer. When an aeroplane climbs or descends rapidly the aneroid does not" immediately respond to the change in altitude. The pointer on the dial lags behind, and for this reason, as well as tho fact that barometers are : effected by temperature, it can only be a- general guide to an airman. The dial -can be screwed round to register zero", at the (jrouml level from which the , aeroplane sets out. ■ The development of anti-aircraft gun- . nery is evidont when past and preo'-nt height indicator dials are compared. The first machines sent out ■ for active serTice were equipped with instruments registering to 6000 and _ 10,000 feet as a maximum; it was considered that no aircraft would ever need to fly above 0000 feet. The range of anti-aircraft puns caused a change to 16.000, then 20,000 feet, until to-day machines aru fitted with instruments registering up to 30,000; Aeroplanes are frequently "wingtd" at 20,000 feet, 30,000 feet will be the limit until machines are designed that will climb beyond that height* and can be with appliances to 6upply the airman with oxygen. \ ' .. .

; Revolution Indicator. ...The engine revolution indicator, driven : off some revolving part of the engine, as a very necessary instrument.. A pilot, ■when Tunning his engine oh thn ground beforo a flight, gets an. idea of his en- ■ gine's condition by noting tho maximum number of revolutions per minute. When the speed falls below a fixed number for each different type of engine, flight is, ' of course, impossible; there would bo insufficient power to leave the ground much less allow a, margin for a quick climbing. The time-pieoe is usually an ordinary lever-watch (8-day) mounted in a frame padded with horse-hair to reduce the efiects'of vibration. Air Voyager's Compass. Unhampered by clouds or winds, tho airman, when hying over land, rarely looke at his compaes, especially if over country which he has seen from the air many times. However, when flying over the sea or clouds, or by night, steering has to be done by compass. The aeroplane magnetio compass is of the liquid type, i.e., the needle »nd card are connected, isnd move in a bowl filled .with alcohol, the spirit being -used to avoid freezing. The card is immersed in the liquid and kept from contact with the glass cover by the buoyancy of a flout contained in. the centre of the card, which also prevents the weight of the card being thrown on the needlo.pivot. It was found that the ordinary (nonfloating) compass was too "lively," the needle oscillations made it unreadable' in an aeroplane. The liquid in which the card is immersed acts as a drug, the time taken for the, needle and card to settle being about a eixth of that taken by the more sensitive ordinary compase. ■ The dial is marked with luminous paint for night flying, and, in common ,with all other instruments, a small electric lamp can be."switched on for -better illumination. ■;■.---■

The difficulty, is ■to design .a compass that will be steady under all conditions. When flying in clouds or fog, where the airman has no visible point ahead by ■which to' hold on his course, tho aeroplane begins to go-round in circles. This tendency is inherent in all machines, owing to the "torque" of the engine, i.e., the reactipn of the airscrew revolving in one direction results in screwing the aeroplane off a straight course. Due to this. continual circling and tho fact that the needle and card tend always to. hold to the north, a iotary motion is set up in the card which in turn is transferred to the liquid, so that the whole goes 6wirling around in the bowl. Recent developments in compasses have been along the lines of producing a non-spinning type. Where possible all metal within about, two feet of the compass mounting is nonmagnetic, but errors due to local attraction are unavoidable- and, like ships' compasses, aeio-cornpasaes have to be "swung." A part of tho aerodrome is marked out for "swinging," with the "cardinal points" of the compass, north, south, east and west, permanently lai<l out on the ground, over the centre ot' which the aeroplane* with compass to be tested, is placejl. The errors, when facing each direction, are rioted, and by the introduction of "correcting magnets," set in a magnet block directly underneath the compass bowl, local deviations are counteracted to a great extent. A table of corrections is then prepared and fixed in the pilot's cockpit, showing the reading for steering to true courses, ho that in flight tho pilot will either add or deduct a certain number of degrees to arrive at the compass course for his various headings. In tho Fokker monoplanes, and eoiiio other machines captured from the Germans, the compasses were usually mounted out on the wing near the body of the machine (with tho idea, probably, of avoiding the use of non-magnetic metal), an arrangement allowing the pilot only an approximate instrument in such machines, as they rarely crossed the linee in, search of ilight3 but remained aloft over certain areas near their-aerodromes to attack British machines on Teconnaissance bent, far into German territory.