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Aviation History
1945
1945 - 0242.PDF
130 FLIGHT FEBRUARY IST, 1945 CORRESPONDENCE The Ediiuv docs not hold himself responsible for the views expressed by correspondents. Hie names and addresses of the writers, 110I necessarily for publication, must in all cases accompany letters. ABOUT AMPHIBIANS A Question of Efficiency I SHOULD like to suggest to your correspondent, Mr. Han-cock (Flight, January 18th) that, although the sacrifice in weight and efficiency in making a seaplane amphibious wouldbe less than the sacrifice for a flying boat, the overall efficiency of the former would still be well below that of the boat. In any case, if the system of mounting the wheel in the floatwere considered, how is Mr. Hancock going to get adequate wheel travel, allowing for the fact that the all-up weight of amodern machine is considerably greater than that of the old Flycatcher. P. R. PAYNE. ASYMMETRY AGAIN Less Manoeuvrable than Conventional Types I READ with considerable interest Roger Teimant's article(Flight, January nth) on the subject of ultra-long-range fighters, for I think the subject requires clarification. To-daywe have two distinct types of long-range fighter—the ordinary single-seat fighter overloaded with jettisonable long-rangetanks, and the two-seat fighter which carries its own navigator; the latter type can also carry an overload of fuel. The first type, more manoeuvrable than the second, appearsto have reached the limit of its range because the length of take-off and the structural strength of the aircraft sef a limit tothe fuel load, and the strain on the pilot to the duration of flight. This limit is about 2,500 miles. The conventionaltwo-seat twin-engine aircraft, with a total of 3,000 h.p., has a range of 1,600 miles and a consumption of three m.p.g.; onetype of aircraft in this class has taken a load of 2,000 lb. of borpbs in addition with ease. It could, instead, take 750 gal-lons of fuel in external tanks if suitably modified. This would weigh 3,300 lb. and give a total range of just over 3,000 miles.This would provide a useful stop-gap for the Pacific war. For a more permanent solution I would suggest one of thetypes which Roger Tennant rejects, with engines in the fuselage and right-angle shaft drive to the airscrews in front of thewings. This would entail distributing weights far from the vertical and lateral axes, but very near the longitudinal axis,which is much more important. The disadvantage is an increase in one of the minor limitations of rate of turn, theadvantages the ability to cruise on one motor without yaw, and more rapid roll. The machine suggested by Mr..Tennant, on the other hand,appears to be dependent on an unreliable glider, to be less streamlined and manoeuvrable than the conventional typewould be, and to be unable to achieve the performance figures laid down J. G. HENRY. AIRBORNE OUNCES Rivals to Heath Robinson THE undejsigned, working under the theory upheld by Mr.C. 1... Brokenshaw (Flight, January 4th), have devised equipment for shooting ducks at night or in English fog. Ourdevice consists of a metal plate six feet by six feet, set hori- zontally on springs about a foot from the ground. Through anelectrical system a gun, aimed over the area of the plate, is fired when the plate i^ forced downward from the weight of thebird flying over it. We have not been able to test it under actual conditionsbut if it fails we shall suppose it is because Mr. Brokenshaw has neglected to regard the fact that he is dealing with dynamicforces and that hydrostatic pressure is equal in all directions. We are not ornithologists, but we believe that a bird remainsaloft by exerting a force on the air by the downward sweep oi its wings, the air in turn exerting (according to Newton's thirdlaw) an upward force on the bird. In moving its wings down- ward the bird displaces a certain quantity of air. Since airhas mass and has been set in motion it possesses momentum. (Momentum = Mass x Velocity). Now, if this air is allowedto impinge upon an object (in the case of this problem, the floor of the cage), a force is exerted on that object, since therate ol change of momentum is foice. (Force = Mass X Acceleration.) This argument then would tend to uphold Mr.Brokenshaw's conclusions and no doubt does as long as the bird remains very close to the floor of the cage, but as soon as the bird is at any appreciable height from the floor compres-sion of the air takes place due to the air already in motion tending to set successive layers of air in motion. This hydro-static pressure is equal in all directions and is dissipated in all directions to the surrounding atmosphere. Therefore, the forceexerted on the floor of the cage and, ultimately the reading of the scale, is dependent upon the height of the bird from the floor. CAPT. W. G. GOEBERT. IST LT. J. W. READ. ORGANISING FOR EFFICIENCY Operating Costs and Speed IN Flight of January nth Mr. Colin C. Richardson makes thesomewhat sweeping statement that it is useless to design an aircraft with a cruising speed of-130 m.p.h. as it simplycannot cope against strong headwinds. Whilst one need not dwell thereon, it nevertheless is a factthat for many years prior to this war aircraft with cruising speeds of less than 130 m.p.h. were maintaining the majori/^of our Empire Air Services. Be that as it may, the Bristol Aeroplane Company have notlet the grass grow under their feet, and if a cruising speed of 130 m.p.h. is quoted this should not be read out of the text.What your correspondent has obviously overlooked is that, in designing the Bristol Freighter, we have concentrated onproviding a specialised machine for the specific purpose of air freighting, where operating cost takes pride of place overblock to block speed. In point of fact, the still-air speed of the Bristol Freighter on 60 per cent, of take-off power is 170m.p.h., and the all-out level speed obviously well in excess of this. It is, however, our contention that the thinking freightoperator of post-war years will appreciate that if he is to estab- lish his business on a profit-making basis, he will require amachine which combines high payload with low operating cost and 100 per cent, reliability with minimal maintenance cost.Such a combination cannot be achieved at high speeds—hence the logical evolution of the Bristol Freighter. K BARTLETT, Sales Director,Bristol Aeroplane Co., Ltd. AIR CARGO TRANSPORT Time on Ground a Vital Factor THE question raised in the correspondence in your columns(Flight, December 7th and January nth) as to whether aJ fortune can be made by transporting cargo in a specialised^machine such as the Bristol Freighter will doubtless depend upon the exigencies of the Chancellor of the Exchequer. We must, therefore, confine our attentions to the questionas to whether such a machine is likely to provide the means of earning rich reward regardless of what will become of ourill-gotten gains I suggest that a machine such as the one referred to, will be one of the first machines to do so if correctlyoperated. It is not surprising thai your correspondents are somewhatat variance on the subject of the annual number of hours to be flown in order to attain the low costs per ton-mile which havebeen quoted for the machine in question, for it would seem that insufficient attention has been paid in the past to the vitalnecessit ' of achieving 3,000 flying hours per annum as a mini- mum if air-freight is to come into its own. Given the most economical, reliable machine, which we aregiven to understand the Bristol Freighter will be, and sufficient freight to ensure, say, a 75 per cent, load factor, which againwe are told will ceitainly be available if the freight rates are right, then the main factor would seem to be the necessity ofreducing the forced time on the ground for an air cargo liner, which at present would seem, even under the most favourableconditions, to be one hour's loading for one hour's flying. A somewhat frightening figure, but one which can be reduced bya half or more if ground organisation is given the attention it undoubtedly calls for, and, what is still more important, ifsome form of pre-loading is introduced. The figures of annual operating hours quoted from Americacan become a snare and a delusion for the would-be air-freight operator unless it is realised that it is one thing to embark or
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