FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1914
1914 - 1239.PDF
DECEMBER 25, 1914 Edited b» V, E. Models Driven by Compressed Air. A lo-oz Model. (Continuedfrom page 1220.) FIGURE I is an illustration of a model biplane fitted with the reservoir described in last week's issue, and an ordinary double acting cylindrical-shaped slide-valve loco, engine, the complete weight of the entire model being slightly over 10 ozs. The span of the upper plane is 3$ ins. and the lower 31 ins. The planes are staggered to rather more than one-third their chord, which is S ins. The elevator is small, only 9 ins. by 2'S ins. j both planes and elevator have rounded ends and upturned tips. The centre of gravity is slightly behind the leading edge of the top main plane, but I must add that the model has not yet been tested in free flight, so some readjustment may be necessary in this respect. The main planes have a very slight negative angle when the fuselage or reservoir is horizontal. The propeller on the machine in the photo graph is a 10-in. diam. Normale, and is the only one so far tested ; sufficient thrust (from 2\ to 3 ozs.) is given by it to fly the model. As the photograph shows, there are eight struts to the main planes. Four of these • are arranged two and two in pairs in the centre between which the container passes, gripping it slightly. The container is not, however, held fast by this gripping, as was the case in the Bragg-Smith model, but "slung" in the following manner, by four pieces of very thin steel wire ; since both leading and trailing edges are similarly dealt with, we need only consider the former. One piece of wire is fastened to the top main plane, where the left-hand front strut joins it; this passes down underneath the container and up again to the place where the right-hand front Strut joins the upper main plane, where it is fixed. Another similar piece passes over the container and is joined to the bottom of the same struts, where they are fixed to the lower plane. The rear edge is similarly dealt with. The planes and their chassis are prevented from "rotating" by two steel wire stays carried from the rear edge of the top plane to the bottom of the engine fixing. The planes, &c, are prevented from shifting longitudinally on the con tainer by means of the fastening of a couple of the "sling " wires to the wire with which the container is bound. By the above means, we obtain a quite rigid fixture without nipping our "tender" reservoir. One fact worthy of notice is that the very light container, elevator and front chassis, combined with the biplane, engine, &c, and propeller in the rear have the effect of bringing the e.g. well back ; the rear edge of the lower plane is only about an inch from the bottom of the engine cylinder. The distance between the leading edge of the top main plane and the rear edge of the elevator is 155 ins. The main planes are of the smallest diameter—mag - nahum tubing with steel ribs. The struts are magnalium tubing. The elevator is of thin steel wire. The planes and elevator are all covered with Bragg-Smith proofed silk. The chassis is of steel JOHNSON. M.A. wire. The two rear wheels are two of Messrs. Bonn's aluminium disc wheels, I -5 in. in diameter. The front wheel is one of Messrs. Evans' 3-ply wood wheels, 1J in. in diameter. The machine is not yet quite finished, as both the elevator and front chassis are only fixed on temporarily. The weakest and most inefficient part of the machine it un doubtedly the engine. As already stated, it was originally a loco. motor ; it weighed 3 os. 4 grms. ; by judicious filing and cutting oil of superfluous parts, together with the substitution of a much lighter connecting roa (made from a piece of umbrella ribbing) for the heavy one shown in Fig, 2, the weight was finally reduced to 175 oz., or just about one-half. At high pressure, however, it un doubtedly wastes at least 56 per cent, of the air ; in spite of this, so near as I can calculate without actual trial, a hand-launched flight should give about a 20 sees, duration, with an initial reservoir pressure of not more than 1 to lbs. A more efficient motor would easily raise this to half a minute. The loading works out at about 4'5 ozs. per sq. ft., a very light loading ; but the idea was to make use of the same planes on a heavier model fitted with a larger container. For instance, if the total weight were a pound, the loading would be about 7 ozs., a very good and useful loading. What we want for better results if a larger container and more efficient engine. There should be no difficulty in jnaking a similar container of three times the capacity to weigh not more than 8 ozs. Since our planes and rear chassis weigh only slightly over 3 ozs., we have still nearly 5 o«s. left for the motor, propeller, elevator, and front chassis, which should be ample. Of course, three times the capacity would not give us three times the duration, because our motor must be more powerful, i.e., it must use more air per any specified time, but it is, I think, a fair inference to assume that it should double our duration, and that with such a machine, charged to some no to 120 lbs., certainly not more than 150, a duration of a minute could be obtained. We could either have a container about 3 ft. lung by 2*5 ins. in diam. or keep the length the same and make the diameter 3 ins. Considerable interest appears to have been aroused by what we have written on compressed-air motors, and quite a number of letters have reached me, some of which are printed below. Now the writer wishes to make it quite clear what he has in his mind. Readers of FLIGHT must not draw the erroneous conclusion thai he considers such motors as the best for model aeroplanes. They certainly take a back scat when either petrol or flash boiler steam plants are concerned, but they are much easier of construction, and they are much better suited for the ordinary juvenile amateur than the other two types, which require not only to be made by an expert but worker! by one as well j moreover, they are much cheaper (a very important item), and they are (as opposed to rubber) an engiiud model. The only part outside the scope of an ordinary amateur is the Fig. 1.—A 10 02. compressed-air driven biplane, and on the right (Fig. 2) the engine used shown fitted with simple speedometer for experimental purposes. 1239
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
