Aircraft R e cog nit ion Bits and Pieces O c to b er, 1942 AIRCRAFT RECOGNITION is entirely a matter of “knowing your aircraft,” not only in general but in detail too, until the whole machine identifies itself almost automatically in the mind from nearly any viewpoint. In training, although the general outline is the first and most important thing to absorb, the surprising thing is how helpful the detail can be, not merely in passing tests from silhouettes projected on a screen, but also in the snap spotting of low-flying aircraft which may flash for an instant over a hedge and begone. That is not to say that any aeroplane ever ought to be recognised by a single feature but that absolute familiarity with them does help towards the ideal. In these days of low attacks and low reconnaissance rod. This is because the two tubes—which measure the difference between the normal air pressure and the pressure caused by the speed of the aeroplane—are now mounted concentrically instead of one below the other. The idea is that when they are placed close together they can be electrically heated more easily to prevent icing up. Should that happen the pilot has no means of knowing his speed and consequently may lose control. The reason for putting the pitot on along stalk is to eliminate “position error,” which is caused by the effect of the airflow overawing upsetting the pressure round the “head.” The pitot head is avery important part of an aero plane’s equipment and so should not be used as a place 5 PRESSURE a HEED |T§ D 0 STATIC SEED DI-POLE EERBSL (LORENZ BEJM v BUND EPPRORCK) PITOT HEAD— The old and the new methods of measuring airspeed. Both are on the same principle but the drawing on the left shows the old two-pronged type which was very liable to icing. The drawing on the right shows the more modern type which can be electrically heated. The pitot head measures the difference between the pressure of the forward speed of the aeroplane and the normal air pressure. The difference between the two determines the airspeed. at “zero feet ”snap recognition is important on the ground just as snap recognition is important in the air in the melee of a dogfight. Furthermore, these “bits ancl pieces ”which are often criticized on a silhouette add a great deal to the interest of the subject when they are known and understood. Too much importance cannot be given to this interest angle, because without it the whole subject becomes flat and boring—and with it the enthusiast redoubles his knowledge unconsciously. What are all the bumps and knobs and loops and bulges which stick out from the average silhouette or show in the formidable “white line ”?Perhaps the most common is the rod which extends forward from the wingtip of most aeroplanes and is often invisible the plan view silhouette. This is the pitot head, the external evidence of the pilot’s airspeed indicator. It is named after a Monsieur Pitot (pronounced Peatow in the best circles) who invented the thing. In the old days it was in the form of a two- pronged fork but to-day it is usually seen as a single FOR BLIND A PROP A CH- The di-pole aerial for blind approach landings along a radio beam. This aerial is set under the fuselage on many Allied and hostile bombers. THE ASTRO DOME— Astro-navigation is an important feature of the operation of long range aircraft today. This drawing -shows the transparent astro dome in the roof of the fuselage of a bomber. From it sights can betaken of heavenly bodies— and for fire control the rather different bodies of enemy fighters. for hanging one’s hat or a useful lever for man-handling the machine on the ground. Another puzzling feature on many aircraft is the short rail supported in three places which often runs underneath the fuselage. This is the aerial for the Lorenz blind approach system used for guiding a machine into land by radio when visibility is bad. The same feature appears on German as well as British machines because the Lorenz system originated in Germany and is used by both countries in slightly different form. Another familiar feature is the“ astro dome ”—the bubble-shaped transparent bump which is often seen on the top of the fuselage of bombers. The“ astro dome ”is used for “shooting the sun ”or stars with a sextant to get navigational bearings when flying above clouds on along flight. Air Navigation by the stars has become very widely used since the War began and an expert navigator can locate his position to within a few miles by this means alone. The astro dome also incomes useful as afire control
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