270 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 



ing this has been further increased to 160 miles per hour, yet with 

 the same horsepower. We expect the Autogiro we have just finished 

 to do about 120 miles per hour with the 225 horsepower, only 5 miles 

 less than the first Mailwing, and if we compare this machine with 

 the first Mailwing it will be readily apparent that there is much 

 more opportunity for reducing drag in the Autogiro than in the case 

 of the early Mailwing. 



The Autogiro is much more susceptible and sensitive to improve- 

 ment than is the airplane, and responds in greater degree. For in- 

 stance, when we recently completed one of the first American ma- 

 chines, its initial flight test showed a high speed of 87 miles per hour. 

 When the pilot landed and reported the disappointing 87 miles-per- 

 hour speed, there were long faces to be seen everywhere. 



Senor Cierva held his peace, but when he went to work on his 

 figures that day he checked up everything and told me that 87 miles 

 per hour was correct because of the detail arrangements; and that 

 we would make a few changes in the machine and it would do 105. 

 After these changes were made the next day, the machine did 105, 

 much, I believe, to the surprise of the pilots and aeronautical experts 

 who were present. Later, with other modifications, it definitely is 

 expected to show around 120. 



The Autogiro has many more parameters than the airplane. In 

 their sum total and in their relationships to each other and to other 

 combinations, they present an almost infinite variety of viewpoints, 

 by means of which, through evolution and selection, engineers can 

 improve the Autogiro. For instance, in the airplane we have wing 

 area. In the Autogiro we have blade area, disk area, fixed wing 

 area, and the relation of the various areas. In the airplane we have 

 aspect ratio, or the relation of wing span to chord. In the Auto- 

 giro we have solidity, or the relation of blade area to disk area. In 

 the airplane we have the wing curve, while in the Autogiro we 

 have the curve of the fixed wing, curve of the rotor blades, and its 

 constantly changing effective curve, caused by its differing attack 

 as it rotates. In the airplane, we have angle of incidence. In the 

 Autogiro, we have the speed with which the air strikes the rotor 

 blades, which is constantly changing on account of the relation 

 between forward and rotational speed. Then, of course, there is 

 the all-important matter of good proportion of the above items. 

 Small improvements to parasitic drag, power loading, and disk 

 loading result in relatively large advances in performances. 



If an airplane, by streamlining or refining some of its parts, 

 increases it speed, say, 10 miles per hour, the same degree of 

 refining will increase the Autogiro's speed about 15 miles per hour. 



Finally, we are very fortunate in that, unlike the airplane, im- 

 provement to one phase of the Autogiro's performance helps the 



