FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1910
1910 - 0622.PDF
(TGGHI AUGUST 6, 191a. available to show, but there can be no doubt that all the successful flyers at the present time have the broadside-on aspect, and have, moreover, as high an aspect ratio as the constructors have found feasible. Constructional Limitations. It is not difficult to understand that constructive difficulties interfere with the realisation of what is theoretically desirable. A designer might wish to have an aspect ratio of say 10 or 12, because it is known to exist in some species of birds, but would be only too likely to find, when he came to try and build a practical flyer of those proportions, that the constructional difficulties of making it sufficiently strong and rigid without being too heavy, were so great as to make it necessary for him to finally be satisfied with an aspect ratio in the order of 5 or 6. It may perhaps here be mentioned, as it is a point on which there is occasionally some little confusion, that the question of monoplane,, biplane or triplane, does not affect the numerical value of the aspect ratio as obtained by dividing the chord into the span. The aspect ratio is obviously a function of each deck separately, and is the same for a monoplane as for a biplane of similar deck proportions. We draw attention to this fact because so many people are fond of talking about the length of cutting edge, and very often seem to imagine that a biplane is therefore twice as advantageous in this respect as a monoplane of the same span. Like many of these ideas of somewhat indefinite origin there is a funda mental strain of truth underlying the general conception, but as we have shown, the length of cutting edge by itself is unimportant, except so far as it indicates a high aspect ratio, that is to say unless it implies that the span is several times longer than the chord. The Yacht as a Glider. We now come to the Fig. 14. second part of Mr. Sherrin's query, which relates to the proportions of sails used in yachts. On this subject the views of a naval architect naturally constitute those of the proper authority, and in this connection Mr. Linton Hope has favoured us with a general resume of the situation. It is, of course, perfectly proper to consider the sail of a yacht as an aeroplane in principle, and as such it is regarded by those who have to do with the designing of sails. The yacht designer has for years been putting into practice principles which have, so to speak, had to be re-discovered in the art of flight. The Bulging Sail and the Cambered Deck. The bulging sail, for instance, is the analogy of the cambered deck of a flyer (Fig. 13—the sketch is purely diagrammatic), or perhaps, in deference to the older craft, we ought to have put the statement the other way about. The likeness between the two is, in fact, carried very far indeed, for sails are designed to have their maximum fulness situated well up towards the leading edge or luff of the sail. It is precisely the same in the cambered DECK OF A FLYER. Fig 13, deck of a flyer, although it would seem that the latter can? stand a much greater camber in proportion to its chord than the sail of a yacht. Sailing v. Soaring. Making up to windward is analogous to soaring with a glider, the wind strikes the sail obliquely, and the resultant Fig. 15. of the wind pressure is slightly inclined forward (Fig. 14), due to the sail's fulness or camber. This forwardly inclined resultant splits up into two components, one of which, the smaller of the two, is the propelling force in the direction of the keel. The other constitutes the heeling force which tends to make the boat capsize, but is resisted by the ballast. In the glider (Fig. 15), this other component is that which supports the machine in the air, so that here is the great and vital difference between the two cases which prevents the analogy holding good all along the line, and lies at the root of the answer to Mr. Sherrin's second query. Shape of Sails. The yacht designer has not half the love for this lateral component of wind pressure which exists in the heart of the flight enthusiast, but he has perhaps even more respect for it, and he cuts his sails accordingly. Adequate sail area the yacht is bound to have, just as in the case of a flyer, but the disposition of the surface is, as we have shown, governed by considerations which do- 620
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
