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Aviation History
1945
1945 - 2002.PDF
OCTOBER IITH, 1945 FLIGHT 391 of high speed during aerobatics may be made. The accuracy of this instrument even for landing speeds is ± 2 m.p.h. The Kollsman G.i is another rather interesting instru- ment which is unusual in that it indicates true air speed, automatically computing three functions—pitot pressure, static pressure and air temperature—by means of three capsules. All three are exposed to static pressure exter- nally, but internally one has pitot pressure, another is evacuated and the third has vapour pressure. All are con- nected to the pointer mechanism by means of linked ful- crums; and a bimetallic link is introduced to correct temperature variations. With regard to this instrument there was, however, no exhibited indication of its degree of accuracy in registering true speed. Mach meters of three types were on view. Actuation in each case embodies a mechanical linkage by which the motion of a capsule subjected to pitot-static pressure is suitably modified by the motion of an aneroid capsule sub- jected to the same static pressure so as to read directly the * Mach number. Another interesting instrument was a multi-capsule man- ometer used for pressure-plotting in flight. This instrument consists of 32 capsules arranged around the inside of a • cylindrical body, with each capsule connected by a simple lever system to a bell-crank carrying a small mirror pivoted Pitot-comb for registering variation in flow from behind a wing. on the axis of the cylinder. A projector system consisting of lamp, lens and cross-wire projects a spot of light on •to the mirror whence it is reflected on to the film contained in an F.8 camera. Each of the capsules is connected to a union on the exterior of the cylinder so that tubes from, say, 32 different points along a wing can each be connected to a capsule, and thus a pressure diagram of the flow form over the wing for any particular flight condition may be recorded on the film. A trailing static instrument for the measurement of static pressure of the air without interference from disturbed air flow about the aircraft consists of a closed tube having a number of small lateral holes, fitted to the nose of a stream- lined b5dy with tail-vanes to keep it at zero yaw and pitch. The instrument is suspended from the aircraft and static pressure is conveyed to the static side of a A.S.I. This par- ticular instrument might well be used in conjunction with a special Venturi-pitot device which measures correct total bead of airstream up to 40 deg. angle of incidence relative to the moving air. It consists of a small pitot tube with its open end pointing downwind embodied in a Venturi tube, the pitot pressure being conveyed to the pitot side of a A.S.I. A rather ingenious instrument devised primarily for small aircraft carriers is a wind-direction and velocity indicator incorporating a wind vane carrying a slotted spring plate. Rotation of the vane and deflection of the slotted plate is registered through standard micro-Desynn transmitters, the accuracy of the instrument being approximately ± 2 deg. for wind direction and ± 0.5 knot over a range of 10-45 knots wind velocity. Pitot-comb (port) behind Spitfire airscrew to investigatebehaviour of flow at very high speeds. Gyroscopic instruments included a rate-of-roll metet embodying a spring-restrained Schwein electrically driven gyro in conjunction with a standard Smith's micro-Desynn transmitter and receiver to record rates of roll of fighter aircraft. On a range with a maximum of 0-250 deg. per second readings are obtainable to within ± 2 deg. per second. At the other end of the scale another rate of roll meter employing a three-phase A.C. squirrel-cage gyro actuating a micro-Desynn transmitter provides, due to the large moment of inertia and high speed of the gyro rotor, for the recording of very low rates of roll. For example, on a range of 0-15 deg. per second readings are obtained to within ±0.1 deg. per second Control Forces and Movements Considerable space in the exhibition was devoted to con- trol force and movement indicators of various types. Many of these were for specific applications only, that is to say elevator or aileron or rudder forces, but an interesting mock-up (a photograph of which we include) showed the installation for both control force and control movement indicators set up in an instrument panel so that the in- quisitive could test how it worked. The system embraces R.A.F. miniature Desynn transmitters and standard Smith's receivers, and records control force to within an accuracy of ± 0.5 lb. In actual fact the indicator panel would not, of course, be fitted before the pilot, but would be placed somewhere in the aircraft in conjunction with a camera to record the readings given. Another ingenious device, a mock-up of which was shown, is a flying control space/time recorder for measure- ment of control deflections and differential motion against a common time scale. The purpose of the instrument is, for example, to record the time lag, etc., between a pilot's input movement and the output movement of a servo unit to operate a control service. A very interesting system which does not truly come under the heading of instrumentation is concerned with Chemical coating on wing of Kingcobra for graphic indicationof breakdown from laminar to turbulent flow.
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