FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1911
1911 - 0943.PDF
OCTOBER 28, 1911. Ip££ INTERESTING EXPERIMENT* WITH PROPELLERS AND SPINNING MODELS. AN ACCOUNT OF SOME CURIOUS AERO DYNAMIC PUZZLES AND AN EXPLANATION OF THE SWERVING CRICKET-BALL. ONE of the most interesting lectures on the subject of aerodynamics which has been delivered in this country was that which Mr. Patrick Alexander gave before the ELECTRIC -, MOTOR If Eza zv Fi«l it? Fig. 3 Aero Club at King's College towards the end of 1906, and as the occasion antedates the appearance of FLIGHT, we do not doubt the reference to the subject will be fresh to many of our readers; in any case, we have taken the present opportunity of adding to the very interesting subject which Mr. Alexander then introduced. Mr. Alex- a n d e r ' s great forte is the making of e x p e r i - •*- ments, and his lecture gained its charm from the practical demon strations which he was enabled to give by the aid of a very simple apparatus, consisting of a small electric motor mounted on a balanced beam which in turn was pivoted upon a vertical spindle. The motor was thus so arranged as to be sensitive to any forces brought to bear upon it, and would tilt or sway according as the pressures might be longitudinal or transverse. Experiment I* On the end of the motor spindle a small two-bladed propeller was fitted, and, picking up another propeller, the lecturer mounted it upon a spindle which he held in his hand, and placed it opposite to that which was motor- driven (Fig. 1). The propeller which Mr. Alexander held in his hand was fitted with adjustable blades, and on placing them so that they lay parallel with the axis of the spindle, the screw (or paddle wheel as it had thus become) revolved rapidly in the same direction as the motor-driven propeller, thus proving that the column of air in which the blades were situated was following a spiral path. This fact was confirmed by altering the pitch until a position was found in which the blades lay parallel with the air-current, when the propeller remained stationary. Experiment II. Taking another propeller having solid blades, and mounting it on the spindle in the place of that having adjustable blades, Mr. Alexander again carried out a somewhat similar experiment. The free propeller was maintained in motion by the moving column of air, and not only did it revolve, but it immediately became evident that the whole propeller was advancing slowly but surely along its spindle in the teeth of the wind, thus showing that its own rotation, considered as an independent screw, was producing propulsive effort capable of _• __ overcoming the resistance of the air from X "** which it derived its own power of rotation. Each propeller-blade was, in fact, soaring. Experiment III. Still keeping the motor driven propeller in operation, Mr. Alexander took a sheet of tin, and held it vertically at the side of the propeller as close as possible to the tips of the revolving blades (Fig. 2). Then he slowly moved the plane away from the periphery, and the propeller was seen to follow it by attraction, the entire motor swinging round upon its pivot. This experiment was COUNTER KvVElQHT Fig. 5. direct evidence that the presence of the plane enabled the revolving propeller to form a partial vacuum on that side, thus upsetting the equilibrium of the apparatus as a S •=; \ V fifeS whole. Supposing, therefore, that the motor had been fixed instead of pivoted, some portion of its energy would still have been wasted in maintaining this difference of pressure. 945
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
