[1] The smallest working steam engine that the writer has ever heard of has a net weight of 4 grains. One hundred such engines would be required to weigh one ounce. The bore being 0·03 in., and stroke¹/₃₂ of an inch, r.p.m. 6000 per min., h.p. developed¹/₄₈₉₀₀₀ ("Model Engineer," July 7, 1910). When working it hums like a bee.

[2] "Aero," May 3, 1910.

[3] Part of this retardation was, of course, "increased resistance."

[4] Personally I do not recommend aluminium.—V.E.J.

[5] "Aeronautical Journal," January 1897, p. 7.

[6] Vide "Invention," Feb. 15, 22, and 29, 1896.

[7] Really aerofoils, since we are considering only the supporting surface.

[8] I.e., to express it as a decimal fraction of the resistance, encountered by the same plane when moving "face" instead of "edge" on.

[9] If the width be not uniform the mean width should be taken.

[10] This refers, of course, to transverse stability.

[11] See ch. vi.

[12] Also there is no necessity for gearing.

[13] In his latest models the writer uses strands even three times and not twice as long, viz. fourteen strands 43 in. long.

[14] This refers to¹/₁₆ in. square sectioned rubber.

[15] Of uniform breadth and thickness.

[16] In practice I find not quite so high a proportion as this is always necessary.

[17] Steel pinion wire is very suitable.

[18] See Appendix.

[19] As high a pressure as 250 atmospheres has been used.

[20] There was a special pump keeping the water circulating rapidly through the boiler, the intense heat converting some of it into steam as it flowed. The making of this boiler alone consumed months of work; the entire machine taking a year to construct, with the best mechanical help available.

[21] Model Steam Turbines. "Model Engineer" Series, No. 13, price 6d.

[22] See Introduction, note to §1.

[23] The voltage, etc., is not stated.

[24] Note.—Since the above was written some really remarkable flights have been obtained with a 1 oz. model having two screws, one in front and the other behind. Equally good flights have also been obtained with the two propellers behind, one revolving in the immediate rear of the other. Flying, of course, with the wind, weight is of paramount importance in these little models, and in both these cases the "single stick" can be made use of. See also ch. iv., §28.

[25] See also ch. viii., §5.

[26] Save in case of some models with fabric-covered propellers. Some dirigibles are now being fitted with four-bladed wooden screws.

[27] Vide Appendix.

[28] Vide Equivalent Inclinations—Table of.

[29] One in 3 or 0·333 is the sine of the angle; similarly if the angle were 30° the sine would be 0·5 or ½, and the theoretical distance travelled one-half.

[30] Flat-Faced Blades.—If the blade be not hollow-faced—and we consider the screw as an inclined plane and apply the Duchemin formula to it—the velocity remaining the same, the angle of maximum thrust is 35¼°. Experiments made with such screws confirm this.

[31] Cavitation is when the high speed of the screw causes it to carry round a certain amount of the medium with it, so that the blades strike no undisturbed, or "solid," air at all, with a proportionate decrease in thrust.

[32] In the Wright machine r.p.m. = 450; in BlÉriot XI. r.p.m. = 1350.

[33] Such propellers, however, require a considerable amount of rubber.

[34] But see also §22.

[35] "Flight," March 10, 1910. (Illustration reproduced by permission.)

[36] According to the author's views on the subject.

[37] Nevertheless some models with a very low aspect ratio make good flyers, owing to their extreme lightness.

[38] The chief advantage of cane—its want of stiffness, or facility in bending—is for some parts of the machine its chief disadvantage, where stiffness with resilience is most required.

[39] This is a good plan—not a rule. Good flying models can, of course, be made in which this does not hold.

[40] This is in theory only: in practice the monoplane holds both records.

[41] The best position for the propellers appears to be one in front and one behind, when extreme lightness is the chief thing desired.

[42] Because the number of strands of rubber in each bunch will be much less.

[43] Mr. Burge Webb claims a record of 500 yards for one of his.

[44] Flying, of course, with the wind.

Note.—In the "Model Engineer" of July 7, 1910, will be found an interesting account (with illustrations) of Mr. W.G. Aston's 1 oz. model, which has remained in the air for over a minute.

[45] These remarks apply to rubber driven motors. In the case of two-power driven propellers in which the power was automatically adjusted, say, by a gyroscope as in the case of a torpedo—and the speed of each propeller varied accordingly—the machine could, of course, be easily steered by such means; but the model to carry such power and appliances would certainly weigh from 40 lb. to 60 lb.

[46] Another and better way—supposing the model constructed with a central rod, or some suitable holdfast (this should be situated at the centre of gravity of the machine) by which it can be held in one hand—is to hold the machine with both hands above the head, the right hand grasping it ready to launch it, and the left holding the two propellers. Release the propellers and allow them a brief interval (about half a second) to start. Then launch boldly into the air. The writer has easily launched 1½ lb. models by this means, even in a high wind. Never launch a model by one hand only.

[47] Report on First Exhibition of Aeronautical Society of Great Britain, held at Crystal Palace, June 1868.

[48] The better way, undoubtedly, is to allow the competitor to choose his direction, the starting "circle" only to be fixed.

[49] Or 10 per cent. for duration of flight.

[50] In another competition, held under the rules and regulations of the Kite and Model Aeroplane Association for the best all-round model, open to the world, for machines not under 2 sq. ft. of surface, the tests (50 marks for each) were:—A. Longest flight in a straight line. B. Circular flight to the right. C. Circular flight to the left. D. Stability and landing after a flight. E. Excellence in building of the model.

[51] On the assumption that the model will fly straight.

[52] If permitted to enter; if not see Fig. 53.

[53] The design is patented.