FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1937
1937 - 2108.PDF
n8 FLIGHT. JULY 29, 1937. " Katzmayr "Effect." The note by W. L. Cowley (R. & M. No. 569, written in March, 1925) explains that Katzmayr made three distinct sets of experiments. In the first, the average values of lift and drag were measured when the angle of incidence of the model was varied in a steady horizontal wind; in the second, -the model wing was made to oscillate up and down bodily; and in the third, the model wing was fixed, but the direction of the wind was varied by means of vanes, changing from an upward to a downward slope alternately. Katzmayr found that in the first set of experiments the L/D ratio diminished as the oscillations increased in amplitude, but that alter ing the frequency had little or no effect. In the second set of tests it was found that the polar curves were not quite so favourable as when the model was at rest. In the third set of test Katzmayr found that there was consider able improvement with increasing amplitude, and negative values for the average drag were obtained, in some cases for relatively large values of the average lift. Three French experimenters, Toussaint, Kerneis and Girault, tried the effect of combining the motions of experiments one and three, but concluded that no improvement could be obtained in that way. Cowley does not, however, accept this conclusion as a general one, and points out that by having the two motions suitably out of phase, a very large improvement should be possible. From these considerations it is concluded that, from the point of view of getting the maximum energy out of a " bumpy " wind, the waves should be large in relation to the chord of the wing, but from the point of view of the wing itself, its oscillations should be smaller than those associated with bird flight.—Ed. THE "KATZMAYR EFFECT" I N Flight of July 15 a highly interesting article appeared about man-power flight, further commented on in "The Outlook." Attention is called to the "Katzmayr Effect." Now, there is some difference between the K.E. and a flapping wing, in so far as the latter must have the highest K.E. at the wing-tip and no effect in the middle of the wing. In my opinion, the whole thing must have something to do with the tip vortex. The ease with which birds " row " with their wing-tips must be explained by the way they make use of the tip vortex as they move the tips in an opposite direction to the air circulation. In this way they not only have a propeller of the highest efficiency, but at the same time partly neutralise the tip vortex, which has the same effect as if the wings were of extremely high aspect ratio. In this restiect I would like to draw your attention to the fact that birds that specialise on soaring flight, like the alba tross, have a very high aspect ratio, whereas " rowing " birds, even long-distance flyers, have a mucji smaller ratio (apparently because of their "rowing" a high ratio is not wanted). If the above is true, it would be very interesting to carry out experiments with models or even gliders with wing-tips capable of both torsional and flexural oscillation. In my opinion, only 40 per cent, of the wing needs to make this movement. However, the only question that remains is how to construct such a wing. H. C. VAN ODIJCK. Amsterdam. SAILPLANE FIGURES I - HAVE read Mr. Bradshaw's article on "Man-Power Flight" with much interest, and as he invites comment from readers with experience of modern gliders, I would like to criticise the figures he gives for a possible glider which he uses as a basis for his proposed man-power machine. Starting with his estimated weight of, 80 lb. for a glider: An intermediate-type glider which I designed about 1930, called Scud I, was, I believe, one of the lightest and smallest soaring gliders that has been made. It weighed 103 lb., was of 25 ft. span, and had a gliding angle of about 1 in 14 at 30 m.p.h., that is, a sinking speed of about 190 ft./min. Mr. Bradshaw's weight of 80 lb. looks, therefore, a possible figure, but he also supposes that such a glider would have a gliding angle of 1 in 30 at 8 m.p.h., which is, as he says, a sinking speed of about 24 ft./min.—-in other words, an efficiency eight times that of the Scud I, which means that a Scud I would require eight times the power for level flight. Also, if Mr. Bradshaw's machine has a flying speed of 8 m.p.h, only (which would certainly be necessary to give this pheno menally low sinking speed) the wing area would have to be nearly sixteen times as great as that of Scud I, i.e., 1,280 sq. ft. This would rather upset the 80 lb. weight estimate. Examples of more highly efficient sailplanes which I have designed and which more nearly approach Mr. Bradshaw's gliding angle (but not sinking speed) figures include the Scud II which holds the British height record of 8,323 ft. This was of 40 ft. span, had a gliding angle of about 1 in r8 at 30 m.p.h., sinking speed 150 ft./min. and weighed about 190 lb. It was lighter than other machines of its class. More recently there was Scud III, wdiich may be classed among the highly efficient modern sailplanes. It has a span of 45 ft., weighs 260 lb., has a gliding angle of 1 in 22, an^ sinking speed of about r2o ft./min. This value of sinking speed is just about as good as is being obtained with modern sailplanes, but is still about five times greater than that ol Mr. Bradshaw's machine. It will, therefore, require five times the power for level flight, assuming it weighs only 80 lb., but it weighs 260 lb. (which is lighter by at least 50 lb. than most machines in this class). So, if we add 180 lb. to Mr. Bradshaw's gross weight figure of 230 lb. we get 410 lb. Thus our figure of five times more power required becomes iX =8.9 times more power required, which compares with • 230 eight for a machine of Scud I's weight and sinking speed. It can be seen, therefore, that whichever end of the scale we take figures of known gliders, whether of large span and weight and low sinking speed, or small span and weight and higher sinking speed (sinking speed being proportional to span/weight ratio, and power required to sinking speed and actual weight), the power required for level flight is about eight times that supposed by Mr. Bradshaw. It may also be of interest to mention that Scud III was also fitted with a retractable auxiliary engine unit when it was known as the Carden-Baynes Auxiliary. The engine was a 250 c.c. Villiers, which gave 8-9 h.p. at best at 3,500 r.p.m. with an airscrew efficiency of not more than about 50 per cent. ; that is, we had perhaps 4 thrust h.p. I believe this is actually the lowest-powered machine which has been made to leave the ground under its own power and fly successfully. The purpose of the auxiliary engine was to enable the machine to take off without launching gear or hill-side up- current being necessary and climb to a sufficient height for thermal or cloud soaring to be possible. The engine was then stopped and the engine unit retracted into the neck of the fuselage. The engine unit with gear added about 50 lb. to the all-up weight, or about 10 per cent., which is about 5 per cent, increase in sinking speed or power required for level flight. The thrust h.p. available for climb was about 1.5 and the power required for level flight about 2.5 t.h.p. or 5 b.h.p., which is about eight times man-power (not Bradshaw power!). With regard to Mr. Bradshaw's assumptions on man-power, can it be assumed that if a man can deliver ^ h.p. with his arms and | h.p. with his legs, he can necessarily deliver a total of 1 h.p. if both arms and legs are working at the same time? For instance, could a man, pumping up a motor tyre with one hand, do this just as well if he was pumping up another tyre with another pump with the other hand, and two other tyres with two foot pumps with his two feet, all at the same time? L. E. BAYNES. Heston. THIS RECORDS BUSINESS I TRUST you will forgive me referring to a matter which is now somewhat out of date. Owing to my being away at the time I did not get my copy of Flight for June 10, and so did not see the letter from Mr. Ronald Walker, in which I was challenged to plead that I was misreported. There was no need for your correspondent to have issued his challenge, as I have not the slightest intention, either now or at any other time, of withdrawing any remarks I made about the Royal Aero Club, or any other club for that matter. If Mr. Walker had troubled to make further enquiries, instead of rushing into print and issuing challenges, he would have found it was so. What I was attempting to explain was that my remarks had nothing to do with the fantastic interpretation that was put on them, in which I was practically accused of casting asper sions on other record breakers, and bewailing the fact that I did not get my fair share • t publicity, both of which assertions are so absurd as to require no answer. Record breaking is, after all. such a small part of aviation that surely it can be spared spiteful and sarcastic remarks such as these, especially when they are not true. As to "falling back on the old defence of being mis- reported,'" I in turn will challenge Mr. Walker, or anybody else, to testify that I ever at any time said " We Yorkshiremen are a tough lot," or "Pioneer flights such as mine," etc., etc. Although such remarks are absurd, they nevertheless appeared in numerous newspapers as having been said by me, so appar ently there is just a chance of being misreported at times. All of which points to the same old story— do anything out of the ordinary and there is always somebody kind enough try to pull one down; this appears to be especially so in the case of record flyers. Harrogate. H. L. BROOK.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
