2 SMITHSONIAN MISCELLANEOUS COLLECTIONS \'OL. 62 



wind tunnel method ])erniits a leisurely study of the forces and 

 couples produced by the wind on a model; (2) that the stafif of the 

 Xational Physical Laboratory, Teddington, England, have developed 

 a wind tunnel of remarkable steadiness of flow and an aerodynamical 

 balance well adapted to measure with precision the forces and couples 

 on a model in any position; and (3) that the results of model tests 

 made at the above laboratory are applicable to full scale aircraft. 



Consequently it was decided to reproduce in Boston the four-foot 

 wind tunnel of the National Physical Laboratory, together with the 

 aerodynamical balance and instruments for velocity measurement. 

 Dr. R. T. Glazebrook, F. R. S., director of the National Physical 

 Laboratory, most generously presented us with detail plans of the 

 complete installation, including the patterns from which the aero- 

 dynamical balance was made. Due to this encouragement and assist- 

 ance we have been able to set up an aerodynamical laboratory with 

 confidence in obtaining a steady flow of air of known velocity. The 

 time saved us by Dr. Glazebrook, which must have been spent in 

 original development, is difficult to estimate. 



The staff of the National Physical Laboratory have developed 

 several forms of wind tunnel in the past few years. In 1912-13 Mr. 

 Bairstow and his assistants conducted an elaborate investigation into 

 the steadiness of wind channels as affected by the design both of the 

 channel and the building by which it is enclosed.' The conclusions 

 reached may be summarized as follows : 



(i) The suction side of a fan is fairly free from turbulence. 



(2) A fan made by a low pitch four-bladed propeller gives a 

 steadier flow than the ordinary propeller fan used in ventilation, and 

 a much steadier flow than fans of the Sirocco or centrifugal type." 



(3) A wind tunnel should be completely housed to avoid effect of 

 outside wand gusts. 



(4) Air from the propeller should be discharged into a large 

 perforated box or diffuser to damp out the turbulent wake and return 

 the air at low velocity to the room. 



(5) The room through which air is returned from the diffuser to 

 the suction end of the tunnel should be at least 20 times the sectional 

 area of the tunnel. 



(6) The room should be clear of large objects. 



' Technical Report of the Advisor}- Committee for .\eronautics, London, 

 1912-13. Report No. 67. 



^ It is of interest to note that ^tr. Eiffel lias used a helicoidal l)l(>\ver in his. 

 new wind tunnel. 



