102 RESULTS OF MODEL TANK EXPERIMENTS TO 



Runs 6 and 7 — brakes, 12 feet by 14 feet at 90°, 



Run 8 — brakes, 12 feet by 14 feet at frame 76, and another pair 8 feet by 18 

 feet at frame 95, set at 90°. 



Run 9 — brakes, 10 feet by 14 feet at 90°. 



Run 10 — brakes, 8 feet by 14 feet at 90°. 



Run II — brakes, 8 feet by 14 feet at 70°. 



Run 12 — brakes, 12 feet by 13 feet with the top edge placed one foot below 

 the water line. All other runs were made with the top edge at the water line. 



Run 13 — brake, 8 feet by 21 feet at 80°. 



Plate 52 shows the pressures per square foot on the brakes as indicated on the 

 plate by the runs numbered. 



The following deductions are made: — 



The stopping power varies directly as the projected area opposed at 90° to the 

 fore-and-aft line. 



One pair of brakes is more efficient than two, as shown by run No. 8, where 

 the combined area is 624 square feet for the two brakes, the stopping power or re- 

 sistance opposed is not in the same proportion as the pair of 12 feet by 14 feet, 

 giving 168 square feet. 



The pressure per square foot practically decreases as the width of the brake is 

 reduced and, by plotting curves of pressures at various speeds for different widths 

 of brake, it is found that after a certain width is passed the pressure per square foot 

 is not increased. 



After these curves were determined, the model was fitted with a pair of brakes 

 II feet 8^ inches (projected area) by 14 feet deep, fitted so as to be tripped and 

 thrown out from the traveling carriage of the model tank. A set of guides was 

 fitted so as to keep the model in position under the carriage, yet allow it to advance 

 freely when the carriage was stopped. 



The foot-way along the tank was marked off in equal distances from a cer- 

 tain point far enough from the starting point to allow the carriage to reach the 

 proper speeds. The model was then brought up to speed, the carriage stopped at 

 the determined point, the model released with the brakes thrown out, and the times 

 marked by stop-watches at each marked distance until the model was brought to 

 rest or the limit of the tank reached. 



For each speed the model was released with the brakes closed, so a comparison 

 was obtained and shown on Plate 53 of speed reduction per foot traveled and on 

 Plate 54 the speed reduction per second traveled. 



As a matter of interesting data, the following table showing the instantaneous 

 stopping effect of a pair of brakes of different sizes has been compiled from the 

 curves shown on Plate 51 : — 



