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Aviation History
1940
1940 - 1464.PDF
458 MAY 16, 1940 CORRESPONDENCE The Editgy does not hold himself responsible for the views expressed by correspondents. The names and addresses of the writers, not necessarily for publication, must in all cases accompany letters. ARMY CO-OPERATION IN NORWAY ' Using the Roads I HAVE read with interest the article by Capt. Macmillanconcerning the difficulties of army co-operation work in Norway. He concludes that it is not possible to base air- craft of the Lysander type in Norway itself. Now, for a great many years it has been stressed that the Lysander could land on, or take off from, a football pitch. That statement has appeared in Flight, as well as other aero- nautical publications, time after time. If it is true, then I state most emphatically that Lysanders could be operated from local bases in any patt of Norway, from within a dozen miles of any spot that Capt. Macmillan might care to pin- pont on a map. His article, had it been written about fighters or heavy bombers, would have been far more convincing. There is, of course, a partial solution even to the use of fighters in local bases, other than frozen lakes. That is, fly them on and off the roads, which would, in effect, be somewhat narrow runways, f am fully aware of the obvious objections, such as disorganisation of traffic, but as I have followed the campaign in Norway, I gather that the whole success, or failure, of the Allied forces has hinged upon the need for first-line fighter aircraft to have been in action from the word "Go." Norwegian roads between main towns are good, and except where they pass through forests are free from side obstructions like hedges and brick walls. Aircraft operating in such a man- ner would run the usual hazards of war, but I contend that it would have been practical. Ground transport would have had to wait, and night flying would have been washed out, but it would have helped. As things have panned out, there seems to have been no very serious effort made either to use Lysanders, which have been designed specifically for use in difficult tight fields (and Norway does not consist of nothing else but mountains), or to improvise with such facilities as were available in the shape of roads. If the R.A.F. had to develop types of aircraft for every possible terrain, there would be no end to the new types that would appear in droves. As it is, types exist that can be adapted to every probable scene of operations, such as Nor- way, and if they are not used there, I would say that it was because of the Higher Command showing a lack of initiative rather than of any geographical obstacle. When the enemy forces the war into a new theatre it is up to us, the Allies, to overcome difficulties, not just to sit back and say that nothing could be done. JOHN V. HEWES. Ashtead. FUTURE AERO ENGINES WHat is tne Maximum Pouier ? TN your issue of April 25, T noted with much interest the de- -*- tails and illustrations of the Douglas B 19 bomber. The military value of this machine may be very small, but its technical value and interest is of overwhelming importance. The engines specified for this plane are Wright " Duplex" Cyclones of 2,000 b.h.p., driving 16ft. Hamilton airscrews. It would appear that six of these engines are included, not four. Total power output is 12,000 b.h.p. for take-off, and the power loading 131b./b.h.p.; even this figure is higher than that of the Ensign. However, it is by no means un- reasonable to suppose that the power of the " Duplex " will increase from 2,000 b.h.p. to 2,200 b.h.p., just as the Cyclone 14 has been rerated at 1,700 b.h.p. for the new CW-20 trans- port. One of the Sunday papers recently informed its unfortunate readers that the Douglas B 19 could carry a 30-ton load of bombs from America to Japan and return without stopping to refuel. A technical expert has stated, on the. other hand, that a machine of this size could not carry any bomb load for a range of only 1,600 miles. The latter statement is based on the assumption that the wing structure weight varies directly as the cube of the span if the wing loading remains constant. The weight of the wing can, of course, be reduced by increasing the loading, but the wing loading of the B 19 is obviously low, about 3olb./sq. ft. If we compare a span of 210ft. with one of 70ft., it will be clear for all to see that the bigger one must weigh more per unit area. In the figures that I give below, it is interesting to note how the wing loadings of Short flying-boats have increased, ^e wi"« °* U'e projected 163,000 1b. being much smallerthan that of the lighter B 19. C-class boat G-class boat Projected boat. Wing area .. 1.500 sq. ft. 2,160 sq. ft. 3.380 sq. ft. Wing span .. 114 ft. 134 ft. 169 ft. approx. Wing loading 27 lb./ sq. ft. 34 lb./sq. ft. 48 lb./sq. ft. Power plant 920x4 1,380x4 2,100x6. 3,680 b.h.p. 5,520 b.h.p. 12,600 b.h.p. Power 11 lb./b.h.p. 13.3 1b./b.h.p. 12.9 lb./b.h.p. loading Take-off time 24 sec. 30 sec. — Cruising 164 m.p.h. 180 m.p.h. 237 m.p.h. speed Using six 2,100 b.h.p. engines produces certain disadvant- ages that are bound to affect performance adversely by com- parison with four engines of 3,150 b.h.p. Presuming that the former engines drive 16ft. 3m. airscrews, 63! per cent, of the wing length will be immediately behind the airscrew discs, re- suiting in a turbulent flow over almost the entire surface; to this, we must also add the greater installation drag. olX or Four ? Although most of the very large aircraft that have been projected specify six or more engines, I am of the opinion that this is purely a passing phase. The Queen Elizabeth is powered by four engines of a combined output of something ijke -| million s.h.p., the giant flying-boat of the future may well mount four engines totalling 25,000 b.h.p.Progress in the direction of very high power in individual engines seems to be governed almost entirely by the limitations imposed on the designer by the airscrew manufacturer. It does seem now however, that the airscrew designer will largely overcome the weight problem in the near future with hollow blades of magnesium allloy and by using four blades in- stead of three. What is the largest possible individual aero-engine ? By individual, I mean a single crankshaft engine, as opposed to those having two or more crankshafts. The largest prac- ticable unit is almost certainly the 42-cylinder, liquid-cooled multi-bank with seven banks of six cylinders. The 54-cylinder multi-bank is not a practical proposition, mainly because of the Very restricted space between each bankBoth the Pratt and Whitney Co and the Wright Aeronauti- cai Corporation have been engaged in the design and evolution of new engines in the 4,000 b.h.p. class for some time pastBoth are liquid-cooled jobs. The former being of H type, prob- abiy wjtn four banks of eight cylinders, the latter is a 42-cylinder multi-bank, also liquid-cooled. ^ Cylinders G-200. Operating on fuel of 90 octane number, this engine has a take-off output of 1,200 b.h.p., 133^ b.h.p. per cylinder. Presuming that this engine were rated for operation on fuel of 100 octane number, the power per cylinder would almost certainly rise above the 150 mark, more than enough for the engine that I have in mind. Below are a few figures for this unit:— Engine type 42-cyl. multi-bank liquid-cooled. Angles between banks 510 25.7". Bore and stroke .... 6Jin. and 6fin. Bore/stroke ratio .. 1/1.1224. Volume 139.4214 litres (8,508 cu. in.) Take-off power 6,250 b.h.p. @ 2,600 r.p.m. Power per litre 4483 b.h.p. @ 2,600 r.p.m. Piston area power . . 5.05 b.h.p. @ 2,600 r.p.m. per sq. in. Maximum M.P.S. . . 2,979 f.p.m. Weight 3 tons. Weight per b.h.p. .. 1.075 1°. Diameter 57>n., 17.72 sq. ft. fr. area. Crankshaft length .. 54Jin. Airscrew 4-blade .... 26ft. diam. Airscrew disc area . . 551 sq. ft. Max. tip speed 912,521 f.p.s. @ 670.3 r.p.m. Reduction gear ratio 0.2578. Mounting two of the above engines, the Douglas bomber would have an immeasurably enhanced performance. As it is, this design is ahead of its time. The point to bear in mind is that it will result in the accumulation of data of in- calculable value for the future. JOHN W. MORRISON. London, N.W.3.
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