large lucite windows for visual and hotographic observation. 

 C sras with synchronized flash lamps oJ the Edgerton high-speed 

 bype were a regular part of the equipment. 



Althougl the propeller pump and drive motor produced con- 

 siderable noise in the audible range, It was found that the 

 tunnel was comparatively quiet in the sound range above 6,000 

 cycles per second. Therefore, microphones mounted at the 

 focal points of spherical a.nd ellipsoidal reflectors were de- 

 veloped for investigating the sound produced by the flow 

 passing the projectiles both under cavitation and non-cavitating 

 conditions. These reflectors had double walls encli ir ?r air 

 space and were installed in a water-filled tank attached to 

 one of the lucite windows directly opposite the model under 

 test. Sound measurements with this equipment were made in the 

 range of from 10,000 to 100,000 cycles pen second. 



In order tc study the effect of the propeller drive on 

 projectiles, small electric motors were developed that could 

 be mounted within the models. These ic tors proved to be 

 capable of driving the propellers at correct model speeds and 

 thrusts. TV' actual operating speeds of the propellers v/ere 

 as high as 11 ,000 rpm. 



Polarized Light Flume . 



T >P polarized light flume developed tc make possible the 

 visual studies of the flow patterns around various types of 

 projectiles was similar tc the high-speed water tunnel in 

 pr±nciple but was or: a much smaller scale, It had a working 

 section si;; inches vide, 12 inches deep and four feet long, 

 end operated only at low velocities, the maximum being in the 

 neighborhood of five or six feet per second. A suspense on of 

 8 minute quantity cf very fine clay particles in the water of 

 the flume made the flow pattern visible when the water was 

 veined with transmitted polarized light. Although the results 

 from this flume were purely qualitative hey proved tc be very 

 useful net only in delineating the general flow pattern, but 

 alsc locetir: - rioi s sources of hi sturbance w] ich might 

 result ij an increase in resistance or s loss in stability. 



Controlled Atmosphere Launching Tank . 



The controlled atmosphere launching tank with its asso- 

 ciated apparatus was constructed for the pxxrpose cf studying 



7 - 



