64 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27 



The total flying weight of Old No. 4, including fuel and water, was 4132 

 grammes (9.] Lbs.), a much larger weight Hum had been contemplated when 

 the original designs were made. A detailed statement of the weights of the 

 various parts of the aerodrome, together with some data as to its density, is 

 given on the preceding page. There were provided in the wings and tail ap- 

 proximately 2 sq. ft. of supporting surface to the pound of weight, which would 

 have been barely sufficient to sustain the aerodrome, even if it had been success- 

 fully launched and the wings had been built much stronger than the flimsy con- 

 st ruction in use at this time. 



An air chamber, which served the double purpose of floating the aerodrome 

 and of providing a moveable weight by which the center of gravity could be 

 shifted to the proper position relatively to the center of pressure*, was con- 

 structed of the thinnest sheet-iron and attached to the midrod. 



This aerodrome, the fifth in actual construction, and the first, after years of 

 experiment, to be carried into the field, was transported to Quantico, where the 

 first trial with it was made on November 20, under the conditions described in 

 Chapter IX. 



1894 



The aerodrome, No. 4, which has just been described, had not been put to the 

 test of an actual flight, for reasons connected with the difficulties of launching, 

 which are more fully described elsewhere; but. when the completed machine was 

 more fully studied in connection with the unfavorable conditions which it was 

 seen would be imposed on it in trials in the open air, many possibilities for im- 

 provement presented themselves. It was seen, for instance, that a better design 

 might be made, in which the engines, boiler and aeolipile might be placed so that 

 the center of gravity of each would lie in the same vertical plane as the central 

 line of the aerodrome. In order to do this the construction of a single midrod, 

 which was the distinguishing feature of < >ld No. 4, had to be essentially departed 

 from, the midrod of this new one, No. 5, being opened out into two rods, so to 

 speak, which were bent out so that the open space between them furnished a 

 sufficiently large hull space to hold the entire power generating apparatus. In 

 arranging the machinery within this hull, it was provided that, as the water and 

 fuel were expended, the center of gravity of the aerodrome would shift little, 

 and. if at all, backward relatively to the center of pressure. 



Instead of the two small engines, which it will be remembered were mounted 

 on the cross-frame in No. 4, a single engine with a larger cylinder, having a di- 

 ameter of 3.3 cm. (1.3 in.) and a stroke of 7 cm. (2.76 in.), capable of developing 

 about 1 H. P. was used. This engine was mounted within the hull near the for- 

 ward end and drove the propellers by suitable gearing. 



