Aircraft Recognition No. 2, Vol. 1

position in a fight. The fire controller withstands his head in the dome and calls directions to the gunners and pilot concerning the movements of the enemy fighters which are attacking. Tabs on the elevators or ailerons are another frequent occurrence in silhouettes. They are not a point of recog­nition but their use is interesting. These tabs are intended for the trimming of the machine indifferent conditions of load so that there is not too much pressure on the control stick—liable to be very tiring to a pilot on along flight. Trimming tabs are especially useful when flying with one engine out of action or when coming into land with flaps down. Lowering the flaps tends to make an aeroplane nose heavy because of the backwards move­ment of the centre of pressure along the wings. This nose heaviness can be counteracted by winding the trim- O cto b er, 1942 white and blue stripes, so that it would shine in pristine glory, until he had added nearly 40 lb. of each colour on the two sides. All these odds and ends which have to be toadded make an aeroplane of value in War naturally detract greatly from the performance. The Junkers Ju 88 is a good example. In March, 1939, the first Ju 88, cleaned up and with all external paraphernalia removed, setup a record speed of 321 m.p.h. for 621 miles carrying an internal load of 4,410 lb. The latest version—the Ju 88a 6—with all its military gear such as dive brakes, guns, aerial, and so forth, but without bombs or external bomb racks, does 281 m.p.h. —40 m.p.h. slower than when cleaned up. When the external bomb racks are added the top Aircraft Recognition LOOP AERIAL— A rotatable Direc­tion Finding radio loop aerial enclosed in a transparent streamlined fairing. This fairing is a familiar sight on most modern bombers. ELEVATOR BALANCE— Two methods of balancing elevators are shown in this sketch. The U-tube is loaded with lead in its leading edge and provides amass balance for the elevator. Another method shown on the same drawing is that of the horn balance at the tip which gives both aerodynamic and mass balance when loaded with lead. The servo trimming tab can also be seen. TAIL TRIM—The method of operation of the rudder trimming tab is shown in this drawing. The port motor is stopped and feath­ered. To counteract the pull of the live engine the trimming tab is wound on. It swings over the rudder and relieves the pilot of strain. ming tabs on the elevator down a little to raise the elevator and bring the nose up. Other things often seen on the control surfaces are mass balances which counteract the weight of the sur­faces. These take the form of lead-filled U-tubes on the rudder of the Heinkel He 111 and on the rudders of the Dorniers. In the Lancaster, for instance, they are in the form of lead bob-weights at the end of a metal arm. Before the introduction of these balance weights the flutter of control surfaces occasionally occurred at high speeds, in which case the aeroplane immediately became uncontrollable and often crashed. The same reason led to the abandonment of the red, white and blue stripes on the rudders of British military aircraft and their replacement on the fin instead. On one occasion after an R.A.F. Display the rudder of one of the aeroplanes taking part was found to have increased its weight by 230 lb. No wonder the machine was a little heavy in the hand. It turned out that an enthu­siastic Flight Sergeant had titivated the paint on the red, speed goes down to 276 m.p.h. And when the external bombs themselves are on it is reduced still further to 248 m.p.h. So that the addition of all the military gubbins reduces the speed by 73 m.p.h., or 23 percent. The same thing has happened with the Blenheim. The civil prototype—the “Britain F irst”—did 310 m.p.h. To-day the Blenheim IV with full load does 265 m.p.h. Of course, by careful polishing up the reverse can happen. For instance, look at the record of the little 200 h.p. Percival Mew Gull single-seat racers. They were entered for the King’s Cup Air Race for five years. In 1934 the Mew Gull did 191 m.p.h., in 1935 it did 209 m.p.h., in 1937 it did 233 m.p.h., in 1938 it did 236 m.p.h., and by 1939 it had reached 256 m.p.h.—all as a result of attention to detail. So, after the War, in anew King’s Cup Air Race pilots will have the joy of seeing by how much the speed of Stirlings, Halifaxes, Lancasters and Beauforts can be increased by whittling off the astro-domes, gun turrets, aerial masts, and so forth, one by one. 5
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