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. 



