FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1910
1910 - 0810.PDF
CORRESPONDENCE;. * The name and address of the writer (not necessarily for publication) MUST in all cases accompany letters intended for insertion, or containing queries. to the necessity of obtaining as soon as possible the experimental Correspondents communicating with regard to letters which they have read in FLIGHT, would much facilitate ready reference by quoting the number of each such letter. NOTE.—Owing to the great mass of valuable and interesting corre spondence which we receive, immediate publication is impossible, but each letter will appear practically in sequence and at the earliest possible moment. ROYAL AERO CLUB AND FLIGHTS OVER TOWNS. [7731 In the present state of the science of aviation, the practice ot flying unnecessarily over towns or thickly populated areas is considered by the Royal Aero Club to be not only fraught with considerable risk to the public, but also useless in furthering the progress of aviation. The Club is therefore forming a special committee to deal with such cases as may come to its notice, and to inflict such penalties as it may think necessary upon any of its members or certified aviators who make such undesirable flights. September 28th, 1910. HAROLD E. PERRIN, Secretary. HIGH SPEED AND POWER. [774] The articles entitled '' Can We Fly Faster for Less Power ? " are of great interest to me, also the curves and formulae of great utility. There is one point, however, I would like some opinion on. The curves have evidently been calculated on the assumption that the "aerofoil" is of no thickness. Now will these graphs apply to curves of which the angle of incidence of entry of top surface is much greater than that of lower surface (such as the Bleriot plane) ? At any rate can we neglect the top surface of " dip " ? If so the graphs will apply, I suppose. The article seems to lead to an aeroplane whose planes have variable angles of flight as well as variable curvature. As this is hardly feasible in practice, is not the former faculty a good compromise ? Even if the angle of incidence were varied from the angle of the top edge to angle of bottom, a good range of resistance would result. The great point is—is the dipping angle so negligible ? Some opinion on the points raised would be most interesting to me, and perhaps to others. Barrow-in-Furness. CLAUD W. RIDCOCK. [Possibly the reduced scale on which the diagrams were neces sarily reproduced, led our correspondent to overlook the fact, which he will notice on closer investigation, that the angles of deflection shown on page 532 are measured between the mean tangents. The mean tangents have been taken as lines bisecting the angle formed by the upper and lower surfaces at the leading and trailing edges of the planes. We do not know if this measurement will subsequently be justified by experiment, for like the rest of the points brought forward in these articles, it is merely a suggestion. On the other hand, it appears to us to be a plausible way of making a beginning, and as we pointed out, the deductions themselves, which have been presented in the form of charts and data, are not neutralised by the method of measurement, because if subsequent practical investiga tion shows that the effective angle is greater or less than the amount obtained by the method stated, the charts will still apply to the revised process for they are essentially based on effective values. Our correspondent suggests that our article leads to the con clusion that planes with variable camber or variable attitude should be adopted ; but the point that seems to be of such great interest in the deductions is the fact which theory shows a certain fixed angle to represent a minimum resistance irrespective of all other conditions of flight. In other words, the camber of the plane, in so far as the camber is determined by the angle, is a fixed quantity in advance for any machine designed to possess the quality of least resistance to flight. If Zahm's coefficient of skin-friction is correct, and if our other assumptions, on which we based our calculation for the power expended on aerodynamic resistance, are also accurate, then theory defines the camber in question as one that is represented by an effective angle of 50. It is obvious that the efficiency of the angle is based on the assumption that the aeroplane flies with a fixed attitude relatively to the real wind, for any change in the angle of incidence causes a virtual change in the angle of deflection, and thus destroys the premises of the argument. On these and other practical grounds planes of variable camber or variable angle 01 incidence might possess advantages if they could be introduced in a practical form. One of our chief objects in writing this series of articles was to suggest a logical and comprehensive way of regarding the general problem mathematically. Incidentally we hope to draw attention data that is needed to place the theory of the aeroplane upon a decently accurate theoretical basis. Even the comparatively narrow field covered by the articles in question shows quite a number of points that are unsettled. The skin friction coefficient is one of them ; the effective value of the angle of deflection and the proper relationship of the angles of entry and trail is another, as also is the value of the effective sweep. It may, for instance, conceivably be found that the best relationship between the angles of entry and trail is a function of speed, in which case the theoretically ideal plane would have a variable position of maximum camber, but a constant angle of deflection. It will be remembered that our specimen cambered sections on page 532 showed alternative designs for cambered sections having the maximum camber one-third and one-quarter of the chord from the leading edge respectively. In the absence of such data it is obviously impossible to do any reliable quantitative work, but we can at least try to review the general situation and construct plausible theories with a view to better appreciating what it is we require to know. Experimental work is proverbially slow, and it is for that reason worth a great deal to feel that any particular series of tests are being carried out for the definite purpose of filling a certain hiatus in an established line of thought. — Er>. ] AUTOMATIC TAILS. [775] I read your correspondent's letter (688) in the current number, and your Editorial note thereto, dealing with the effect of the slip-stream from the propeller and the difficulty of inducing models to take a gliding position at the stage of their flight at which propeller action ceases. It has occurred to me that the main or the tail planes of elastic- driven models could be so mounted and connected with the elastic that as the tension of the latter slackens during flight the angle of incidence of the planes would be automatically varied to give a compensating effect. If any of your readers has time to experiment on the lines suggested, his results would possibly be of interest. In this connection it is interesting to note that during the vol plane, of which we have heard so much of late, it seems to be a frequent practice to re-start the engine when approaching the ground. Am I correct in supposing that (in the case of machines with tractor mounted in front) a righting effect is produced by an increased lift of the main-planes due to the slip-stream of the propeller ? Manchester. A. W. LAMBOURNE. [This suggestion for using automatic tails on models is well worth trying, and we hope some of the numerous readers of FLIGHT who devote their spare time to the art will see how it works out in practice. We shall be pleased to have descriptive letters accompanied by sketches of any systems that are tried. The restarting of the engine at the termination of the vol plane is a practice adopted by pilots of biplanes as well as those of mono planes, and its purpose is to compensate for the slowing up effect produced when the aeroplane is turned on to a horizontal path. The principle of landing at high speeds consists in abolishing the angle of descent at the last moment so that the final flight takes place parallel to the ground. It is impossible to maintain this parallel flight for any considerable distance without driving the machine by the propeller, and it is for this reason that the engine is accelerated, generally spasmodically, while landing.—ED.] GLIDING IN NEW ZEALAND. [776] I have been a reader of your valuable paper for three months only, but I can see that it is a journal anyone interested in aviation should not be without. I see that subscribers give their experiences in gliding flights with models and full size machines, so I will give you mine for publication if you think it worth that publicity. I started to build a monoplane last November of the Bleriot and Antoinette design, with a few new features. The chief dimensions were 26 ft. span, 25 ft. length over all, weight 196 lbs. I built the machine intending to fit an engine, but when it came to the time I found I could not get one suitable for the work. I then wondered if I could get the machine to glide, so I took it to the top of a hill with a grade of about I in 3^, and started the machine by running alongside and then leaping into the seat. I let the machine coast down the hill .till it attained a pace of about 21 miles an hour and then tilted the main planes so that the machine made a leap of 25 ft., and I assure you I got the surprise of my life, for the machine only had 170 ft. of sustaining surface and lifted 350 lbs., which is equal to about 2 lbs. I oz. to the sq. ft. I kept experi- 808
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
