FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1909
1909 - 0290.PDF
MAY 22, 1909. FLIGHT ACCORDING TO LANCHESTER. MR. F. W. LANCHESTER, WHOSE NAME IS SO WELL KNOWN IN CONNECTION WITH MOTOR CARS, HAS BEEN INVESTIGATING THE PROBLEM OF FLIGHT FOR THE PAST FIFTEEN YEARS. AT AN EARLY PERIOD HE SUCCESSFULLY CHECKED HIS THEORETICAL DEDUCTIONS BY MODEL EXPERIMENTS, AND MIGHT WELL HAVE BEEN THE FIRST TO HAVE MADE A SUCCESSFUL MAN- CARRYING FLYER, BUT THAT MR. DUGALD CLERK, ANOTHER LEADING AUTOMOBILE AUTHORITY, PERSUADED HIM NOT TO TURN HIS ATTENTION FROM HIS IMMEDIATE ENGINEERING PURSUITS. SELDOM, perhaps never in its history, has the magnificent lecture hall of the Institution of Civil Engineers held an audience which so frequently demonstrated an intensely appreciative interest as when* Mr. F. W. Lanchester discussed the aerodynamics of flight before the members of the Institution of Automobile Engineers. Speaking with inimitable lucidity and precision on problems which were often abstruse, Mr. Lanchester succeeded in an hour and a half in conveying to his hearers a concrete grasp of a subject for the full treatment of which he has found two large volumes no more than sufficient space in print. In our own treatment of the subject, therefore, it has been necessary to adopt a certain latitude of scope in order to make up somewhat for the obvious deficiencies of a printed account of a lecture which was frequently punctuated with special references to lantern slides, diagrams, and model experiments. It is a common occurrence that the most lucid addresses are the least convincing in type, and indeed any literal report of a lecture, as distinct from a " Paper," is often apt through this very cause to be well-nigh unintelligible. In the following article we have endeavoured by every means in our power to do justice to the most able disquisition which has yet been delivered on the theory of flight. The Resistance of a Flyer. In approaching the problem of flight, even from a general and comparatively superficial point of view, a most obvious query which might well be asked at once by anyone taking an intelligent interest in such matters, is as to how a flying machine might be expected to The resistance that has to be overcome in moving a loadfrom one place to another can be expressed as a percentage of^the load Itself. It is least in a cargo boat and most in aflying machine, as the above figures show. compare with other forms of locomotion in the matter of resistance to transit. On land it is common to express the value of this resistance as a percentage of the total weight of the vehicle itself, and the co-efficient thus obtained depends, as all engineers know, on the nature of the tyres and road. With pneumatics it is about 2 per * On April 28th. cent., with solid rubber tyres 3 per cent., with iron tyres on wood pavement, say zf2 per cent., and on macadam roads, say 3'3 per cent. Railways under ordinary con- ditions offer a resistance which is only 1 per cent, of the load, while ships like the " Lucania " have a co-efficient traction of 07 per cent., which in an 8-knot cargo boat may be reduced to o'i per cent. Here, there- fore, at the outset are some well-known values, which have been established by numerous experiments, and must necessarily serve as a basis for comparison in the case of new methods; hence the reasonableness of an immediate inquiry into the resistance of an aeroplane. If an investigation is made of the Voisin and Wright flyers (Table I), which are pre-eminently the only two really successful types at the present day, it will be found that the values for the co-efficient of traction are not less than 13-5 per cent, and 12-5 per cent, respectively, figures which are both in the nature of four times the value obtained from quite indifferent systems of traction on land. Arising out of this possibly unexpected result is the question as to whether such high resistance is essential to dynamic flight, which leads, of course, to a close investigation of the factors of which the resistance in question is a function. A model Wright Voisin TABLE 1. Velocity. Ft.-Sees. .. 17 ... 58 ... 66 —-Table of Power Expended. Lbs. Sustained per h.p. Indicated h.p. Thrust h.p. — ... 220 SO ... 76 34 ... 62 Resistance. Per cent. I4'712-5 •••«*•* -: Langley's Error. ^ ^ It would be only proper under such circumstances to turn in the first place to the records of such a prominent man in the annals of flight as Professor Langley, and here certain statements of obvious significance are at once apparent. Langley has stated, in so many words, that the horse-power required diminishes as the velocity of flight increases ; also that the skin-friction of a flying machine is negligible. In Professor Langley's opinion, therefore, it is very evident that high resistance in flight is not essential. It will be shown later that the first part of his conclusion, viz., that the horse-power diminishes as the velocity increases, has its basis in fact; but it may be mentioned at once that the assumption as to the negligibility of skin-friction in air is entirely invalid, and because of this fact Prof. Langley's view is fundamen- tally at fault. Proof of Skiri'Friction. That skin-friction is not negligible may be shown by a very simple experiment, in which a light hollow sphere, such as, for instance, a little celluloid ball, is caused to be The rotation ofa light sphere supported on aninclined jet of air demonstrates theexistence of skin- friction. 292
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
