12 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, /I 



PART II. EXPERIMENTS 

 EFFICIENCY OF ORDINARY ROCKET 



The average velocity of ejection of the gases expelled from two 

 sizes of ordinary rocket were determined by a ballistic pendulum. 

 The smaller rockets, C, plate i, figure i, averaged 120 grams, with a 

 powder charge of 23 grams ; and the larger, S, the well-known Coston 

 ship rocket, weighed 640 grams, with a powder charge of 130 grams. 

 Plate I, figure 2, shows the rockets as compared with a yard- 

 stick, Y. 



The ballistic pendulum, plate 2, figures i and 2, was a massive 

 compound pendulum weighing 70.64 Kg. (155 lbs.) with a half 

 period of 4.4 seconds ; large compared with the duration of discharge 

 of the rockets. The efficiencies were obtained from the average 

 velocity of ejection of the gases, found by the usual ballistic pendulum 

 method, together with the heat value of the powder of the rockets, 

 obtained by a bomb calorimeter for the writer by a Worcester chemist. 



The results of these experiments are given in the following table : 



Table I 



Type of rocket 



Common. 



Coston ship. 



Efficiency 



2.54% 

 1.45 

 1.49 

 1.95 



1.75% 



2.27 



2.62 



Mean efficiency 



1.86% 



2.21% 



Velocity correspond- 

 ing to mean efficiency 



957.6 ft./sec. 



1029.25 ft./sec. 



It will be seen from the above table that the efficiency of the 

 ordinary rocket is close to 2 per cent " ; slightly less for the smaller, 

 and slightly more for the larger, rockets ; and also that the average 

 velocity of the ejected gases is of the order of 1,000 ft./sec. It was 

 found by experiment that a Coston ship rocket, lightened to 510 

 grams by the removal of the red fire, had a range of a quarter of a 

 mile, the highest point of the trajectory being slightly under 490 feet. 

 A range as large as this is rather remarkable in view of the surpris- 

 ingly small efficiency of this rocket. 



