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Aviation History
1937
1937 - 1024.PDF
382 FLIGHT. APRIL 22, 1937. of intensive development work give promise of reducing the weight by approximately one-third, but does not explain how the reduction is to be effected. Captain Barnwell refers to the use of hollow blades. Past ex perience with welded steel blades has not been altogether encouraging, owing to troubles with cracking. Perhaps the compressed wooden blades now being developed may be found to be one solution; synthetic resin blades may be another. But apart from the quite sufficiently disturbing question of airscrew weight, there is also that of airscrew diameter. As already mentioned, this cannot be greatly reduced without spoiling the efficiency, and closely linked with this problem of airscrew efficiency is that of noise. For instance, an airscrew to absorb 2,000 h.p. will, it is estimated, require a diameter of about 17ft. if it is to have good efficiency. If it is running at the speed now usual, i.e., about 1,200 r.p.m., the speed of the airscrew tips will be 1,068 feet per second, which is approaching quite closely to the speed of sound. That this may reduce efficiency is but one side of the question. It will certainly also increase airscrew noise, and in large commercial aircraft this may prove a serious objection, as Mr. Lipscomb pointed out during the discussion of Mr. Fedden's recent lecture on aero engines. In view of these considerations it would be well to ponder very carefully whether all the effort now being turned in the direction of larger and still larger aero engine units is likely to take us far along the right road. As the size of aircraft increases—and there is even, indication that, in flying boat work at least, this ten dency is insistent—the only alternative to really large power units seems to be a multiplicity of units. Mr. Fedden mentioned the possibility, evidently with a view- to obtaining the views of aircraft designers, of six or even eight engines in line on the leading edge of a large monoplane. Mr. Lipscomb alone of our aircraft de signers thought it worth while to give Mr. Fedden a pointer, and he expressed some disquiet at the idea oi so many engines across the wing. It may be that for the really large machine of the future we shall have to come to a combination of the tandem and in-line-abreast engine arrangements. Air screw shafting is likely to add a good deal of weight, but so will the two-speed airscrew gear which appears to be unavoidable if we attempt to convert 2,000 or 3_,ooo h.p. into thrust with a single airscrew; and as aircraft increase in size, the problem of housing the smaller engine sizes inside the wing becomes a little easier, whereas the stepping-up of engine size to keep pace with aircraft size must tend to keep us where we are at present in the matter of projecting engines. The Dornier Do. X was premature in its engine arrangement, but a modifica tion may succeed. TIME FLIES : Even the hustlers and bustlers of New York paused recently to goggle at Capt. Frank Hawks' new monoplane, with which, sponsored by an American watch company, he hopes to make his " come-back" in the record-breaking game. The engine is a Pratt and Whitney Twin Wasp of over 1,000 h.p. The undercarriage is retractable—and so are both pilot and windscreen : after reaching his altitude Hawks lowers his seat, and the screen automatically closes flush with the fuselage.
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