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Aviation History
1914
1914 - 0989.PDF
SEPTEMBER 25, 1914, [fDOHf] Edited by V. E. The Building of My First Power-Driven Machine. By LEONARD H. SLATTER. (Continued from page 970). THE floats were next proceeded with, and although their very large sixe worried me at first, I soon got used to them. You will excuse me if I digress slightly here, but I should like to try and explain that feeling of «' bigness " that attacks the novice when he starts to launch out into a larger machine. It struck me very forcibly nearly all the way through, and it was through reducing the some what large, as it appeared to me at first, fuselage that caused the fire disaster. As I had it at first, it would have been almost entirely immune from this danger, but letting my taste for "daintiness" swamp my common sense, I paid for it in full. If it had not been for this lesson, I should probably have underfloated the machine, and it is to this point I am coming. Having calculated the size of floats necessary, working on a factor of flotation of two, I proceeded to make one. Of course, it appeared simply huge, but I had learnt my lesson ! I knew the calculations were correct, and decided to let things stand. How they first appeared to me is very cleverly illustrated by the next photograph. The floats being closest to the camera, they are out of proportion to the rest of the machine and it really illustrates the point very well (Fig. 4). The floats themselves have a single step, and have slightly upturned prows. The centre of flotation of these floats was arranged to come as far back as possible, i.e., as close to the e.g. as possible, in order to relieve the tail float of any unneces sary weight. This in turn allows a small float being placed under Sw f§N X \^ x^, ^ A Fig. 4.—Mr. Slatter's power-driven underneath. Plwto by Air. Conolly. model, as seen fr.-m the tail, and thus the weight of this float does not have any great effect on the position of the e.g. It might be of interest to note that the weight of the two main floats is not quite 5 ozs-> arjd this for floats capable of floating 12 lbs. is a very satisfactory result. The strength of them can be gauged from the fact that on several occasions the machine has on her taxying trials charged up the banks without the slightest damage to the floats. A hint about the tail float: in the setting of the size of this float no flotation factor neei be used. Make the float to carry the estimated load, and no more. Immediately the thrust comes on the tail float comes off the water, and if the centre of flotation of the main floats is not too far in advance of the e.g. it never touches again. The suspension of the floats on this machine is absolutely rigid, as I had no time to spare to design a spring connection. This will form one of the many refinements I intend incorporating in my second attempt. The main surfaces were the next things to be settled. The weight of the machine was in the neighbourhood of Sf lbs., and of Course it was desirable to keep the unit loading down as low as possible without using excessively large planes. The length of the fuselage proper was 4 ft. 6 ins., the total length of the machine was in the neighbourhood of 5 ft. 3 ins., and this restricted the span to about 6 ft. In order to have a correct mini mum gap between the tail and main plane the chord could not exceed 12 ins. on the fuselage ; that is to ensure the tail unit being totally unaffected by the air passing over the main planes. In order to get as big a chord as possible it led me to make the planes of the same plan form as a bat's wing. That is the chord increases from the root to the centre, where it has its maximum value, and again diminishes towards the tip. This shape not only relieves the general appearance from that atmosphere of rigidity expressed 989 JOHNSON, M.A. by the two edges being parallel, but also enabled me to get a suitable area without making the machine look unduly squat. The chord at the root is 10 ins., rising to a maximum of 13^ ins., and the nett area is just over 6 sq. ft., thus giving a loading of just under a pound per sq. ft. The making of these wings repre sented my first attempt at making a double surfaced plane. How ever, acting on Mr. Grove's advice, I made all the ribs on a couple of jigs, with the result that the camber, &c, of either wing was identical. However, I fell into the trap of not inserting a sufficient number of ribs to prevent the silk sagging and giving an undulating camber. I should give as a maximum pitch of ribs no more than 3$ ins. In order to lighten the wing structure all the ribs need not be of the full section. Alternate ones can be in the nature of dummies, and are only needed at the hump of the camber. The wings are attached to the body by steel pins inserted in the ends of the main wing spars, and were originally braced top and bottom by two stays of 26 gauge steel wire. However, as the lower wires are taken forward to the chassis, which gave them a considerable forward rake, it necessitated the addition of a third upper wire taken to some point near the tail in order to prevent the planes jumping out of their sockets at the slightest provocation. The attachments of the bracing wire to the cabane are in the form of self-straining hooks, and form a quick erecting and tightening device at the same time. The machine has taken just over three months to build in both spare time and time I have made spare, and altogether I can look back on the building of the machine with the greatest interest. The set of conditions met with in the building of a model such as this are altogether different from those met with in the making of the rubber-driven model. In conclusion, I should just like to add a few words as to the behaviour of the machine on the two occasions I have had the model out. The first time was just prior to my leaving for my holdidays. This formed the only trial that the machine was likely to get before taking it to the Welsh Harp for the hydro competition, initially, this trial was made in order to test her taxying capabilities, the water and surrounding trees not allowing any attempt at a free flight. It was essential to know to what extent the torque affected the run in order to see if the flotational base was large enough. Now as to what actually happened. Mr. Conolly and myself took the machine to Wimbledon very early in the morning in order to take advantage of the calm generally prevailing at this portion of the day. The machine was safely transported between us, and it did not take long to get the plant going. This, combined with the attitude of the machine on the water, augured well for a successful start. Having got the engine going strong, the machine was placed on the water, but before releasing it we took the precaution of throttling down the engine. Finally being released, the model took a semi circular path and struck the shore about 20 yds. further down. On Mr. Conolly's suggestion, I slightly set the fin against the torque and attempted a second run. This time I pointed the head more directly across the pond, still anticipating a circular path. Whilst waiting for the engine to speed up I inadvertently got hold of something hot, with the consequence that I released her somewhat prematurely. To our astonishment she made straight for the opposite shore. At first her speed was somewhat reduced, and I sauntered round to meet her on the far side, nursing a burnt thumb. About half-way round I noticed her speed beginning to accelerate, and I also did likewise, and just managed to reach the point she was making lor in time to stop her. The last quarter of the way across the machine was travelling all out, and I am not likely to readily forget the task of stopping a machine travelling at 25 m.p.h. The propeller seemed to stretch from wing-tip to wing-tip, and I do not seem to remember much till the propeller smashed itself across my arm. It seems that when I caught hold of the one wing and swung it ashore the machine whipped round, with the result mentioned above. Mr. Conolly and myself have each got a piece of that pro peller to remind us of a " very gallant action." The stopping of the machine was absolutely compulsory, as it was going straight for a stone buttress. Mr. Conolly vouches that the machine was clean off the water for the last yard or two. For myself I cannot say, as I hardly had time to steady myself, preparatory to stopping her, when she was on me like a "ton of bricks."
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