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Aviation History
1929
1929 - 0201.PDF
January 31, 1929 Supplement to FLIGHT I ENGINEERING-S^ SECTION . Edited by C. M. POULSEN January 31, 1929 The'Static Longitudinal StabilityLower, A.F.R.Ae.S Metallic Anti-Detonants. By H.A.M.I.P.T Detail Stressing. By H. Parkinson, A.R.Ae.S.I. CONTENTS of Seaplane Floats. By J. H.'.. ... S. Tegner, B.A., A.M.I.A.E., EDITORIAL VIEWS. Our subjects this month cover a fairly wide range, a fact which is to be welcomed as an indication of the increasing popularity of THE AIRCRAFT ENGINEER as a medium for the exchange of views and experiences. Mr. Lower, who is a member of the Technical Staff of Short Brothers at Rochester, contributes an interesting article on the static stability of seaplane floats, explaining how tests can be conveniently carried out with model floats by those who, like Mr. Lower, are fortunate to work with a firm possessing a water tank. Most people, unfortunately, lack these facilities, and are thrown back on the Froude tank for their results. For all that, Mr. Lower's article is, we think, of considerable utility. •' Ethyl " is by now a fairly familiar young lady, but it is to be feared that the great majority have not bothered overmuch to enquire into her pedigree and antecedents. Consequently it will doubtless be of interest to many of our readers to study the article contributed by Mr. Tegner, of the Anglo-American Oil Company, dealing with metallic anti-detonants. Mr. Tegner discusses not only " Ethyl " but also several of her relatives, and he may be excused for being partial to the famous young lady, who has already done good work for aviation and may be expected to do still more. In aviation we now have two ideals to strive for—-Professor Junkers' " all-wing " machine, in which all parasitic bodies such as fuselage and undercarriage have been suppressed, and Professor Melvill Jones's ideally streamline aeroplane. At first glance it might be thought that the Cambridge ideal would be more easily attained than the Dessau one, but this is open to doubt. Dr. Junkers may, by going to very large sizes, succeed in producing an " all-wing " machine, or something very near it, before we learn how to avoid the eddy-making resulting from placing two separately and individually perfect streamline bodies in combination. For all that, Professor Melvill Jones has done aviation a great service by pointing out exactly how much power we are wasting by designing machines producing non-streamline flow, and our sins in this direction are brought home to us in a rather startling manner in the paper of which we publish extracts this month. THE STATIC LONGITUDINAL STABILITY OF SEAPLANE FLOATS By J. H. LOWER, A.F.R.Ae.S. The longitudinal stability of seaplane floats, when at rest on the water, is of utmost importance ; with high-speed racing craft, where the reserve buoyancy of the floats is reduced to a minimum, the question has to be given due consideration, but one is of the opinion that in the case of seaplanes used for commercial purposes the statical stability about a transverse axis through the centre of gravity of the machine is of even greater importance, especially if the machines are of only small or medium size, since moments are easily applied, perhaps without thought, by personnel standing on the stern of the floats. Statical stability tests can be conveniently carried out with model floats, and in the following it is intended to describe a suitable apparatus and method of testing, and also to discuss some actual results which have been obtained. Description of Apparatus and Method of Testing Referring to Figs. 1 and 2, it is seen that the model floats are erected the requisite distance apart, to represent to scale the requirements of the full-size machine under consideration. A framework A is erected above the floats in such a manner as to permit a rod at B, representing a transverse axis through the C.G. position of the complete machine. The model is balanced about this representative C,G. posi- tion by means of lead weights on the framework A, and then attached to a vertical sliding frame C, through the connecting arms D, having ball bearings at the points of attachment to the rod B. The frame C is free to slide vertically, by means of ball bearings, in the guides E, and with the model attached is supported over pulley wheels F by weights W. The pulley wheels have ball-bearing centres and are attached to the rigid structure supporting the guides E. If A is the total weight of the complete machine under consideration, and S the linear ratio of the model floats to full size, then the model displacement when at rest is :—A'" = I and if <», = weight of model + framework A + balance weights &).2 = weight of vertical sliding frame C then2W = o>1 + «, - A,,,. Moments to cause the floats to trim fore and aft about the transverse axis through the C.G. position can now be applied by moving a known weight a measured distance along the top 82a D2
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