Flight, April 1924

THE "ANNULAR" TYPE OF AEROPLANE

   THE process of flying the modern aeroplane has been described as “forcing a petrified ornithopter through the air." Whether or not the expression does adequately define flying as we know it today, it is not ДальшеMore>>> altogether inept, and, after all is said and done, that is practically what we are doing. That great progress has been made in this way cannot be denied, and recent light 'planes have demonstrated that extraordinarily good efficiencies are obtainable with the "petrified ornithopter." For all that, it is by now fairly well agreed that as regards efficiency we cannot hope to progress very much farther. Improvement there will be, certainly, but there is no reason to expect other than relatively small progress. That being so, the question not unnaturally arises whether we can be quite certain we are on the right track: whether it may not be just possible that other avenues should be explored, and whether it is really safe to assume that no other form of heavier-than-air craft gives any promise than the aeroplane of today and, possibly, the helicopter of tomorrow.
   It is by no means always unprofitable to look back, and as an opportunity has been afforded us of describing some early experiments that have hitherto been surrounded by a considerable amount of secrecy, we have thought it of interest to do so in the following notes. Quite apart from the question of future application of the experience gained during these experiments, the tests and experiments themselves, being considerably out of the common, are of interest, the more so as they have never really been thoroughly dealt with, at least not in modern times.
   The experiments to which we refer date back to 1911, and were continued over a period of some three or four years, i.e., up to the outbreak of war. The subject of the experiments was a most unorthodox wing-form in which the lifting surfaces were circular in plan, with a circular piece cut out of the centre so as to leave a wing of annular shape. This wing-form was originated by Mr. G. J. A. Kitchen, who has since won fame with his rudder for power-driven ships, about 1910 or so, and the patents were purchased, in 1911, by the late Mr. Cedric Lee, who engaged Mr. Tilghman Richards to put the ideas into practical workable shape. A biplane, which had already been constructed by Mr. Kitchen and was fitted with a 50 h.p. Gnome engine, was experimented with in 1911, but was wrecked by a gale blowing down the hangar. Attention was then turned to model gliders and full-size man-carrying gliders, with which latter many flights were made during 1911-12. The scene of the gliding tests was laid among the Westmoreland hills, and glides were made in very strong winds. In 1912 the work was transferred to London, and early in the following year to Shoreham. In the meantime Mr. Tilghman Richards had constructed at the East London College a 2-ft. wind tunnel, and in this a series of very thorough experiments were carried out on scale models of various sections, but all of circular, or annular, plan form. Reference to the results obtained will be made later.
   At Shoreham designs were carried out and a machine constructed to Mr. Tilghman Richards' design, and a Gnome engine of 80 h.p. was fitted. This machine was flown by Mr. Gordon England, who flew it round a large circuit without previous taxying. While the engine was running all went well, the machine behaving normally. In coming in to land, however, the engine stopped, and the machine got out of control and crashed. It was found that the cause was faulty weight distribution, the machine being tail heavy. By a coincidence this was not discovered while the machine was flying with engine on, as the thrust-resistance couple exactly cancelled the weight-lift couple. The machine was reconstructed and the trim altered. During 1913 a number of flights were made by Gordon England, Percival and Gordon Bell. The second machine came to grief owing to the temporary elevator breaking away and jamming "hard down" at about 800 ft. When about 40 ft. from the ground the air pressure broke off the jammed elevator and the machine righted itself and pancaked to the ground, Gordon Bell escaping with a severe shaking.
   A third machine was then built, using the same 80 h.p. Gnome and the same long extension shaft to the propeller. In No. 3, shown in two of the accompanying photographs, the undesirable features of Nos. 1 and 2 were eliminated, and the chief fault of these, excessive lateral stability due to dihedral angle, was avoided by having no dihedral. Gordon Bell flew this machine frequently from the beginning of 1914 to the outbreak of war. He demonstrated it before Mr. Winston Churchill and Lord French, who were much interested. Later on Mr. Cedric Lee, who was not a pilot, took the machine up, but landed it in the River Adur. Further experimental work was then abandoned, as the War called for concentration of effort in other directions. It is of interest to record, however, that during the experiments with the three power-driven machines some 11,000 miles were flown, totalling something like 128 hours in the air. The Shoreham machines, apart from their unusual shape, were interesting in that the only lateral control provided was the differential movement of the elevator flaps. It seems probable that the actual effect was to reassure the pilots rather than any real lateral controllability, as the flaps could not have been very effective in their dual role of elevators and ailerons. The high degree of natural lateral stability of the machines, however, gave rise to little trouble on this score. We understand that if Mr. Tilghman Richards were to design one of his annular 'planes nowadays he would so design the wings that the sides, or apteroid section, could be warped for lateral control.
   The Shoreham machines were of very difficult and expensive construction, as the plan view of No. 1 will show, and Mr. Richards has evolved a much simpler form of construction, in which all ribs lie in the direction of flight, while the spars form a polygon, as seen in plan. This form of construction should not be very much more difficult than that of the ordinary type of wing.
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