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Aviation History
1943
1943 - 0655.PDF
MARCH IITH, 1943 FLIGHT 265 CORRESPONDENCE The Editor does not hold himselj responsible for the views expressed by correspondents. '1 he names and addresses of the writers, not necessarily for publication, must in all cases accompany letters. AS REQUESTED " Flight" Recognition Feature in Booklet Form I HAVE been collecting the recognition series "Aircraft Typesand th^ir Characteristics" since they first appeared andiiiid them invaluable as an aid to teaching aircraft recognition to A.T.C cadets. If republished in booklet form, many an instructor who is already doing more than a full day's work would be ever- lastingly grateful to you for taking ffQm his shoulders hours of preparation. A. R. LAMB. [Our correspondent's suggestion is one that has been made by many other readers. The series will now be reprinted in book form and issued from Flight offices.—ED.] EX R.A.F. PILOTS How They May Become Civil Pilots 'T'HE ex-K.A.F. pilot who enquires, in Flight' of February X 25th, how he may qualify as a civil pilot should consult the Statutory Rules and Orders and Air Navigation Directions. He will find all the information he requires in the latter and, ' if he can pass the medical examination, details of which are given in paragraph 94, he should make application to the Secretary of State for Air, 25, Julian Road, Bristol, for an application form. He will find that a Royal Air Force pilot may be exempted from the practical flying tests but must pass the technical examination. Particulars of this are given in the second part of paragraph 99. The issue of these licences is not a particular interest of the Board except that it carries out part of the technical examina- tion on behalf of the Secretary of State, but I would like to take this opportunity of.assuring your correspondent and other pilots and engineers in the Services that considerable thought is being given to ensuring that they will be able to use the knowTedge and expeiience gained in the Royal Air Force to help them to qualify for work in civil aviation after the war. T. R. THOMAS, Secretary, Air Registration Board. "A QUESTION OF STABILITY" Advantage of the Castering Nosewheel WE can fully endorse " Indicator's " timely remarks in yourissue of February 18th on "ground looping" and tail- wheel shimmy of conventional aircraft. It is astonishing that aircraft are still allowed to misbehave on the ground in a manner which would not be tolerated in a car, however cheap. The cause of the directional instability is clearly the use of a relatively freely-castering tailvvheel, because with this arrangement any small sideways force on the aircraft produces a curvatuie of its path in such a direction that the centrifugal iotcc set up acts in the same direction as the original force. This is a state of unstable equilibrium because the curvature will increase at an ever-increasing rate until a ground loop takes place, unless the pilot takes rapid action to rebalance the outfit. The original disturbing force may arise from winds, unequal engine pull, etc., or from an accidental devia- tion from course. A little consideration will show that a castering nosewheel acts in the reverse manner, i.e., alters the path so as to produce a centrifugal force neutralising any disturbing force, and this is why a tricycle machine is directionally stable even some- times to the point ol being difficult to turn off its straight- ahead course. In a conventional aircraft, the solution of the problem of instability is to prevent the tailwheel from castering during take-off or landing. Stability is achieved in this case pro- vided that the tyre characteristics are taken into account in design to ensure that tail tyre drift under sideways forces applied to the aircraft as a whole does not exceed main- wheel sideways drift. This is not a difficult matter. Several Allied and enemy aircraft incorporate such a tail- lock, with a manually or automatically operated control for un- locking the caster when free castering is required for parking, etc. • . • A tail-lock, it should be noted, also eliminates shimmy- Apart from the damaging effects on the structure, shimmy is also the chief cause of tail-tyre wear and is responsible for a serious annual wastage of high-quality rubber. It seems to us that the tail-lock is the only solution to these problems, and though controversy may be expected on the method of operation, it is surprising that it has not been adopted in British aircraft as elsewhoie. "TWO AUTOMOBILE ENGINEERS." FIGHTER SPEEDS Schneider Trophy and Record FiguresM AY 1 kindly call your attention to a slight error in facts and figures which appeared in the correspondence page ot the February 18th issue of Flight? The letter was signed J. H. Darlington, and he quotes an- other correspondent as saying that the Supermarine S.C.B. won the Schneider Trophy for Great Britain in 1931 with an aver age speed of 4071 m.p.h. The trophy was won at an average speed of 379.05 m.p.h., and 407.5 m.p.h. was the speed s«t up by the late George Stainforth during his successful attempt on the air speed record. A REGULAR READER. "AB INITIO PER DUMBO" The Cine Cartoon as a Flying Instructor I SHOULD like to put forward an idea which 1 have toyedwith for some time, and having recently seen it in opera- tion in a somewhat similar manner to that I had visualised. I am convinced of its possessing intriguing possibilities. The idea is that of utilising the otherwise unobtainable quali- ties of the cinema cartoon ior, particularly, instruction in the flying branch of the R.A.F. The cartoon I saw was an American one and consisted ol aircraft performing all the wonderful stunts which impress the public ! I think that if a few pilots and studio artists got together they could produce a film of great value. Probably the R.A.F. Training Command has many good instructional films already, but they could never obtain such "close-ups" as are possible with this blanch of cinemaphoto- graphy. Views of "cut-away" aircraft in flight (pilot, et«., in lull view !) could be shown, and one of the best methods of instruc- tion—that of showing the wrong way first—<:ould be used to the utmost advantage. Effect of controls, airflow, instruments, etc., could all be vividly poitrayed in a manner otherwise impossible. Perhaps my enthusiasm is unfounded, but 1 should like, at least, to have the idea considered by competent authorities. "MICKEY." W RANGE CALCULATION Variation in Weight of Fuel THEN calculating the amount of petrol required ior a proposed flight the method used, so far as I am aware, is to multiply the average petrol consumption in gallons per hour by the estimated number of hours' flight and add a suitable emergency reserve. If the power output of the engines under given conditions is proportional to the volume ot petrol consumed, this will give the right answer, but is this so. or does power output depend on the weight of petrol consumed.' If weight is the true factor, is it not possible that the above method may lead to dangerous conditions? Let us consider an example: Specification D.T.D. 230 lays down that the Sp. Gr. of 87 octane petrol shall "not exceed 0.79." In practice the actual value of the Sp. Gr. may vary by as much as 5 p*er cent. Therefore, taking things at theii worst, a machine provided with a certain number of gallons of petrol may have only 95 per cent, of the expected weight of petrol on board and consequently have its range reduced by 5 per cent.—150 miles on a range of 3,000 miles ! To pursue the matter further, what will be the effect ol a change in Sp. Gr. of the petrol on the engine? Let us sup- pose that while a machine fitted with c.s. airscrew, etc., is being flown level at constant air speed the fuel delivery is switched from a tank containing high Sp. Gr. petrol to one containing low Sp. Gr. petrol. Will it be necessary to alter the throttle opening, and what will be the effect on boost pressure and mixture strength? Perhaps one of your-readus could supply the answers. •• PINT POT."
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