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Aviation History
1945
1945 - 0813.PDF
APRIL 26TH, 1945 FLIGHT 453 Fig. 4. Simple gyroscope represented by a spinning bicycle wheel. DANGERS IN TURNING screw. Many pilots do not understand that effect very clearly, and a simple explana- tion given below may be of use. A balanced rotating body tends to maintain its axis of rotation. If a force is applied tending to turn the axis in a certain plane, the axis does not follow the force applied but begins a new rotation at right angles to the plane of acting forces. This can be easily verified and demonstrated by a simple ex- periment. Take a bicycle with its axle suitably, ex- tended from one end. I/Vxxt this end (A) of the axle </n the :op of a pillar support as >wn in Fig. 4. If the wheel Is stationary it is necessary to support the other end (B^of the axle, since otherwise the wheel will topple over, following the action of gravity. But spin the wheel rapidly in the position as shown in Fig. 4. On releasing the free end of the axle the wheel retains its vertical position so long as it continues to spin at high speed, but it acquires a new rotational motion round the vertical axis A-A. In other words, the axle A-B begins to rotate in a horizontal plane, perpendicular to the direction of acting gravity forces. This new motion of the wheel is called the '' precession.'' Why it arises instead of the expected toppling over of the wheel may be simply explained by the device shown in Fig. 5. Two plates A and B forming two walls are fixed to a rota table support C on the base Tr. Between the walls the ball E is circling, being attached to the spindle F by a^Jirfn elastic thread. Let us imagine now that the base is being banked as shown by the arrows. The ball E attached only loosely to the spindle will preserve its original motion —climbing upwards, as shown in Fig. 5 But in that motion it encounters now the banked wall B, pressing against it and causing thus the rotation of the support C around the vertical axis. The .effect will b<; the same if the two walls are removed and instead of them the ball E is attached to the spindle by a firm non-elastic blade. In this way such a device clearly shows the effect which in a flying plane is produced by the airscrew during turns. The airscrew tends then to lift or to press down the nose of the Fig. 5. Gyroscopic effect demonstrated by two plates on a rotatable support,a spindle and a ball attached to it by a thin thread. Axis of rotation Fig. 6. The principle of precession. aircraft thus in creasing o r diminishing the angle of inci dence. This tendency is not the same for all aircraft, as it depends on relative senses of rotation of the airscrew (gyro- scope) and of the turn. Fig. 5 shows clearly that if the ball E is flying upwards and the contrap- tion is banked to the left, it will rotate anticlock- wise looking from above. But if the ball flies down- wards in the same conditions it will turn the contraption clockwise. A simple rule for the gyroscopic deviation may be deduced in the following way: — Let us represent rotational motions or moments tending to produce them by lines with arrowheads pointing in the direction perpendicular to the plane of rotation. The arrowheads are located at the side looking from which the rotation appears to be clockwise. Then, as may be seen from Figs. 5 and 6, the precession has always the sense from the vector representing the rotation of the gyroscope jjself to the vector representing the moment tending to turn the axis of the gyroscope. Let us examine the case of an aircraft with the airscrew rotating clockwise as seen from the pilot's seat. Here the vector of the airscrew rotation points to the tail of the aircraft. In left turns the vector of the turning moment points downwards. The precession according to the rule of Fig. 6 is directed from the tail downwards, depressing the tail and rising the nose. In right turns Lucb an aircraft has tendency to dip the nose. An aircraft with an anticlock wise airscrew is, of course, subjected to the opposite gyro- scopic effects. The gyroscopic effect adds to the difficulties of a turn by producing'the necessity of different steering while turn ing in different senses and therefore may increase an erroi caused by other factors* Of course blind flying or flying following instrument indications avoids all above-mentioned deceptive impressions. It is advisable, in making turns, to rely more on instruments than on visual observation. A.I.D DINES AND DANCES TDEFORE the war it was the custom for the Aeronautical-LJ Inspection to give an annual dinner to "contractors," in other words, to representatives of the aircraft industry. Thispleasant custom has suffered some interruption during the war, but recently the Southern Area of the A.I.D. gave a dinnerand dance at Southampton to representatives of firms in the area: Vickers - Armstrongs (Supermarine), Saunders - Roe,Folland Aircraft, Airspeed, A.ST., Fairey Aviation, Cunliffe Owen, Jesseman Rubber Co., Wad ha in Bros., Autometal Craft,and Longfleet Motor and Engineering Mr. A. H. Mitchell, of the A.I.D., was in the chair, andproposed the toast of the guests. Capt. E. D. Clarke. M.C., responded. Commander James Bird (Vickers-Armstrong) pro-posed the toast of the A.I.D., the response to which was given by Mr. G. Manning, Director-General of the A.I.D. since thedeath of Col. Outram. Mr. R. G. Green (Principal Inspection Officer of the Southern Area) proposed the toast of the ladies,to which Mrs Mitchell replied. Commander James Bird paid tribute to the sound founda-tions laid by the late Col. Outram, and referred to the A.I.D. stamp as the hall mark of British aircraft. This, he felt, wouldbe of the greatest possible value to future British civil aviation. The good relations between the A.I.D. and the industry wereemphasised, and the menu card carried a very appropriate cartoon by Cumberworth, showing the lion taking coffee withthe lambs. The wording was " It Really Happened." A most enjoyable evening. The A.I.D. has ever been a good host, andon this occasion it certainly lived up to its reputation. THE INDUSTRY AND THE A.I.D. A T a recent gathering of the A.I.D. Technical Staff Association in London Sir Stafford Cripps, in paying a tribute to the aircraft industry, stressed the importance of this countrypaying due attention to the power of being able to expand rapidly in case of need. The development of civil aviation wasone way of ensuring this, and he expressed the hope that the A.I.D. would play their part in'this field as well as in aircraftconstruction for the defence services. Sir Wilfrid Freeman, unable to attend, sent a message to theA.I.D. Technical Staff Association, in which he thanked the A.I.D. "for the help and loyalty which they have given meas A.M.D.P. and Chief Executive. It would be difficult l<> exaggerate the debt which the aircraft industry and the countryowe to inspection. You had it in your power to make or break the country's air programme. You Made It!"
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