Page:Popular Science Monthly Volume 89.djvu/66

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52

��Popular Science Monthly

��much in demaiul by naval organizations. Since last September he has been professor at the United States Naval Academy at Annapolis.

The underlying reason for the experi- ments was that the Institute has within three or four years established courses in aerodynamics, for the purpose of familiarizing young men with the design and construction of aeroplanes and airships. For the laboratory work in connection with these courses the Institute has hatl installed a wind - tunnel and accom- panying equip- ment.

The timnel is one of the important ones of the world and is equip- ped with an "aerodynamic- al balance" unique in this country. There is only one like it in the world. The Institute is therefore prepared to work on the scientific features of wind -currents. Hitherto such tunnels have been t'mployed for the

���I'huto by LpvicJl

Here the distinction between real wind apparent wind is very close

lacings, and the

��testing of propelk'rs and determining the pressures on bodies of different shapes. The knf)wledge thus gained is of great assistance in making airships of the least resistant form.

Professor Everett hit on the idea of using this tunnel to discover what is the effect on a sail when subjected to <Iifferent winds. He lias been able to tell whcTc the center of pressure is located in a sail, the amount of pressure for a gi\en wind velocity and the angle which the boom should ni.dve with the longitudinal axis of a boat.

The experiments were in.uK' with .i single sail, a mainsail, coi)ii(| exacth on

��a scale of ^4, of an inch to the foot from a winning model of last season. The original was known to be a success- ful pattern and the miniature sail was carefully cut and made in precisely the same proportions as the large pattern. In the experiments no attempt was made to repnxluce the deck above which the sail would hang. Nor was a jib used. Either of these would ha\e introduced disturbances in the nature

of deflections of the a i r- current, which would have injured the chance of get- ting accurate results.

Another variation from natural condi- tions in sailing was that the boom was fast- ened to the mast, but the gaff or upper boom was free to swing off into any angle to which the wind dro\e it. The sail was set b \- I w o halyards as on a yacht. It was attached and to the boom

and gaff by inni r etlge or luff was hekl in place against the mast by small brass rings.

In the wind-tunnel of the laboratory the construction is such that uniformly moving currents of air without swirls in them blow against the object testoil. The mast with its sail was set up within the tunnel, and the effect of the wind on the sail was measured. The sail w.is set at tlifferent angles to the direction of the currents of air, and measuri'nu-nts were made at each angle.

It was shown that the angle l)etween the boom ,nu\ center line should be .ibout half the angle between the fly and center line.

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