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Aviation History
1940
1940 - 0856.PDF
2&4 MARCH 21, 1940 CORRESPONDENCE Editor does no' hold himselj responsible for the views expressed by correspondents. The names and addresses of the writers, not necessarily for publication, must in all cases accompany letters. SPOTTING FOR WARSHIPS Kcnigsberg Action Recalled 1 AM writing to correct a statement which you made onpage 188 of your issue of the 29th. You state on this page that the Sea Fox which took part in the Graf Spee action was the tirst machine in the history of warfare to spot for the guns ot a warship in action. I believe 1 am right in saying that this statement is incorrect. Lately I have been reading The Konigsberg Adventure, by E. Keble Chatterton. This book describes the tracking down and destruction of the German cruiser K6niq,sberg, and later the end of the 4.1 guns of the cruiser which her crew took with them after their ship had been destroyed in the Rufiji Delta. The monitors had got the range so well while the aircraft wasspotting that nearly all subsequent shots were hits. London, N. 11. I. MAILER. PROPELLER TIP VORTICES Phenomenon Repeated with Models IN a previous issue of Flight there was a touched-upphotograph of fog trailing from the tips of the propeller blades of a Hampden bomber. This phenomenon is, of course, due to the high velocity of the core of the tip vortices, and it struck me that it would be interesting to see if these could be rendered visible in a model airscrew with the aid of a smoke jet. MODEL AIRSCREWS MAKE VORTICES. On the left is a fine-pitch airscrew, while the middle and right-hand pictures show airscrews of coarser pitch and smaller diameter. The speed was 1,200 r.p.m. Because ot the mudbanks and shallowness ot the riversforming the- delta, up which the Konigsberg went on the spring £ides and failed to get out again, the Navy had to employthe monitors Severn and Mersey. On July 6, 1915, these monitors approached to an esti-mated distance of 10,800 yards, and opened fire over the trees which completely hid the cruiser. Their fire was controlledby a Henry Farman machine piloted by Flight-Commander J. T. Cull, with Flight Sub-Lieutenant Arnold as his observer.This attack failed because the enemy's fire was so accurate. The spotting machine had to return home before the end ofthe action. On July 11 the attack was repeated, and a Henry Farman machine, again piloted by Cull and with Arnoldas observer, spotted for the guns. This time the KSnigsberg was defeated, but with one of her very last shots she dis-abled the Henry Farman and the machine came down in the river and its occupants were rescued by the monitor I'ersey. By using a stroboscope I was able to follow the wholedevelopment and subsequent behaviour of the vortices in great detail, and it therefore struck me that some photographswould be of interest. I have enclosed the three best of sixty exposures. In eachcase the propeller was rotating at about 1,200 r.p.m., and the exposure was about 1/3,000 sec. In print No. 1 a fine-pitch propeller of 17m. diameter wasused, and it will be seen that three vortices are visible; these also render the jet contraction visible. In prints 2 and 3 a I4in. propeller of fairly coarse pitchwas used, and in both cases the blade has just passed and has left the vortex behind it. The flow downstream from thescrew is too turbulent for more than one vortex to show clearly. No. 2 shows clearly the structure of a vortex. The reduceddefinition towards the centre indicates the greater velocity. Hounslow. J. DUBBURY. . Club Flying in India '"PHE number of pilots in training at the seven subsidised J- flying clubs in India has trebled in the past year. The number of 30 at the beginning of December, 1938, had be- come 88 by December, 1939. During the financial year 193S- 39, 64 pilots were trained while for the year 1939-40 it is estimated that 92 will be the total. Provincial Governments are taking an increasing interest in the flying clubs. The United Provinces Government gives a grant to the United Provinces Flying Club as does the PunjabGovernment to the Northern India Flying Club. The Govern- ment of Bengal has a similar scheme under consideration. ^ Expanded Neutral Services '"THE airline companies of the "Oslo Powers" some timeJ- ago agreed between them to expand their activities as from March 1. There will be three daily services twrnScandinavia to Amsterdam, and four as from March 15 when the dinvt «:rvice from Oslo to Amsterdam is reopened.
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