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Aviation History
1943
1943 - 0378.PDF
T5O FLIGHT FEBRUARY IITH, 1943" AIRCRAFT CUN CONTROL SYSTEMS 1 4 Fig. 1—Diagrammatic representationof pneumatic gun control system. 1 is an air bottle, charged to 450 lb.per sq. in., 2 a reducing valve which reduces the pressure from 450 to150 lb. per sq. in., 3 is the trigger button, 4 relay, and 5 the gun. cools sufficiently to deposit moisture on the inside walls of the pipe and mechanism, a relay system has been proposed and tried, but not found necessary in practice. This system and the operation of the relay are shown diagrammatically in Figs. 1 and 2. Close to the jack on the gun, and in a relatively warm spot, is the relay. When the pilot presses his button he admits low-pressure air from the bottle, via a reducing valve, to the relay. This then admits high-pres- sure air direct from the bottle to the gun jack. The amount of moisture evolved by the expansion of high- pressure air between relay and gun is small and not likely to freeze. As there is only low-pressure expansion down the pipe between trigger button and relay and no expansion down the other high-pressure pipe, there is little likelihood of freezing troubles in them. Electro-pneumatic controls have also been proposed similar to the above with electric control means in TO GUN TRIGGER BUTTON Fig. 2—Operation of the relay. Normally the gun jack is open to the atmosphere as the valve, 1, is open. Any air in the jack escapes through the hole in the piston, 2, and out of the port, 3. When low-pressure air from the trigger button arrives at the relay, the piston, 2, moves to the left, first of all closing the valve, 1, and opening the valve, 4, thus admitting high pressure from the air bottle to the gun jack. When the trigger is released, a spring moves the piston in the other direction, shutting off the high pressure and releasing the gun pressure to atmosphere once again place of low-pressure air, and regulat- ing the admission of high-pressure air to the guns on or near them through small solenoid-operated pneumatic valves. These at first sight offer the advantage of simplicity of electric control and switch-selection without the disadvantage of the excessive weight of a pure electric system. Selection Applied to Pneumatic Systems The French, may be said to have developed the first pneumatic gun systems incorporating selectors. This may have been brought about by their early use of the Hispano cannon with or without attendant machine guns, leading to a logical desire to select. The armament of the French fighter of ten years ago—two machine guns and one cannon—may appear poor by present standards, but the same prob- lems were present in their control as on a modern machine. g CAMERA SELECTOR TO CAMERA GUN RELOADING CONTROLS SAFETY COCK Fig. 3 shows the gun system on the Potez 63 (1934) ; Fig. 4 that on the Bloch 151 (1937). The selectors on the first system consist of two separ- ate banks of triple valves, lever- operated. One has three spring-loaded levers which, when pressed down, re- load the two cannon or effect general safety by admission of air to the corre- sponding jacks on the cannon. The other has three levers with two posi- tions. With a lever .up- right that gun is isolated ; when down, it is in action. The firing relay is oper- ated by a Bowden cable from the pilot's trigger, this taking the place of the low-pressure system of Fig. 1. The Bloch 151 system is a later type with an im- proved selector unit. The actual selector is shown in Fig. 3—(Left) The pneumatic gunsystem, with selectors, on the French Potez 63 of 1934. Fig. 4—(Above)The 151 system of 1937 is a later type, with improved selector unit. Fig. 5, and combines the functions performed by the two triple valve bodies in the Potez 63. The unit is deliberately made large enough for a pilot with gloved hands to operate even in the dark, and the buttons are luminously engraved. The four fiat keys on the front of the unit, when pushed down, permit fir- ing of the respective guns or operation of the camera. In this particular system the left key controls the port cannon, the second from the left the*" star- board cannon, the third both machine guns, and the right-hand one the camera. The three left-hand buttons Fig. 5 — Theselector unit of the Bloch 151 com-bines the functions per- formed by the triple-valve bodies of the Potez 63.
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