When, in 1891, it was decided to attempt to build this steam aerodrome, the only engine that had been made up to that time with any claim to the lightness and power I was seeking, was the Stringfellow engine, exhibited at the Crystal Palace in London, in 1868, which it was then announced developed 1 horse-power [p031] for a total weight (boiler and engines) of 13 pounds. The original engine came into the possession of the Institution in 1889 as an historical curiosity, but on examination, it was at once evident that it never had developed, and never could develop the power that had been attributed to it, and probably not one-tenth so much.
With the results obtained on the whirling-table at Allegheny as a basis, a theoretical computation of the weight which 1 horse-power would cause to soar showed that, with a plane whose efficiency should be equal to that of a 30 × 4.8 inch plane set at an angle of 5° and moving at a speed of 34 miles an hour, 1 horse-power would support 120 pounds.[19] With a smaller angle even better results could be obtained, but as the difficulties of guidance increase as the angle diminishes, I did not venture to aim at less than this. In this computation, no allowance was made for the fact that these results were obtained by a mechanism which forcibly maintained the supporting surface in the ideal condition of the best attainable angle of attack as if in perfect equilibrium, and above all in the equally ideal condition of perfectly horizontal flight.
Besides this, I had to consider in actual flight the air resistance due to the guy wires and hull, but after making an allowance of as much as three-quarters for these differences between the conditions of experiment and those of free flight, I hoped that 1 horse-power would serve to carry 30 pounds through the air if a supporting surface as large as 3 feet to the pound could be provided, and this was the basis of the construction which I will now describe.
The general form of this Aerodrome No. 0, without wings or propellers, is shown in the accompanying photograph in Plate [10]. Its dimensions and its weights, as first designed, and as finally found necessary, are as follows:
| COMPARISON OF ESTIMATED AND ACTUAL WEIGHTS OF PARTS OF AERODROME “0”—IN POUNDS AND OUNCES. | ||||
| Estimated | Actual | |||
| lbs. | oz. | lbs. | oz. | |
| Engines | 4 | 0 | 4 | 1 |
| Boilers and Burners | 8 | 11 | 13 | 14 |
| Pumps and Attachments | 0 | 0 | 1 | 10 |
| Steering Apparatus | 0 | 6 | 0 | 0 |
| Frame of Hull and Braces, including bowsprit and tail tube | 7 | 7 | 8 | 11 |
| Oil tank covering and pipes | 0 | 0 | 0 | 13 |
| Shafts, ball bearings (2:1) and wooden propellers (1:7) | 1 | 14 | 3 | 8 |
| Wings (5:4) and guys (0:9) | 4 | 0 | 5 | 13 |
| Tail | 1 | 5 | 2 | 2 |
| Jacket at prow | 0 | 0 | 4 | 0 |
| Total without oil or water | 27 | 11 | 44 | 8 |
(The weights attained in the actual making were, as is seen, nearly double those first estimated, and this constant increase of weight under the exigencies of construction was a feature which could never be wholly eliminated.) [p032]
After studying various forms for the hull or body of the prospective aerodrome, I was led to adopt the lines which Nature has used in the mackerel as most advantageous so far as the resistance of the air was concerned, but it proved to be difficult in construction to make the lines of the bow materially different from those of the stern, and in this first model the figure was symmetrical throughout.
As I wish that my experience may be of benefit to the reader, even in its failures, I will add that I made the not unnatural mistake of building on the plan on which the hull of an ordinary ship is constructed; that is, making the hull support the projecting bowsprit and other parts. In the aerodrome, what corresponds to the bowsprit must project far in advance of the hull to sustain the front wings, and a like piece must project behind it to sustain the rear wings and the tail, or the supporting surfaces of whatever kind. The mistake of the construction lay in disjoining these two and connecting them indirectly by the insufficiently strong hull which supported them. This hull was formed of longitudinal U-shaped ribs of thin steel, which rested on rings made of an alloy of aluminum, which possessed the lightness of the latter metal with very considerable toughness, but which was finally unsatisfactory. I may say parenthetically that in none of the subsequent constructions has the lightness of aluminum been found to compensate for its very many disadvantages. The two rods, which were each 1 metre in length, were with difficulty kept rigorously in line, owing to the yielding of the constructionally weak hull. It would have been better, in fact, to have carried the rod straight through at any inconvenience to the disposition of the boilers and the engine.
PL. 10. STEEL FRAMES OF AERODROMES NOS. 0, 1, 2, 3, 1891 AND 1892 [◊]