6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 62 



unstable, took his machine up to a good altitude and allowed it 

 to get into a spiral dive. The machine made five turns of a rapidly 

 winding and contracting helix before he could bring it out on a 

 horizontal path. If the controls had been only a little less powerful 

 the machine would surely have crashed to the ground. That the 

 controls were adequate was purely a matter of good fortune. The 

 experiment was a success in that spiral instability was demonstrated. 

 Only a few minutes of time was required. However, no information 

 was obtained as to the degree of instability present nor as to what par- 

 ticular changes would remedy matters. To complete the experiment, 

 it would be necessary to repeat the dangerous feat for every change 

 which suggested itself. Naturally, a designer will be very economical 

 in his suggestions under such conditions. 



§2. TYPE DESIGN 

 The type aeroplane selected for the first investigation is a two-place 

 biplane tractor designed by Captain V. E. Clark, U. S. A., while a 

 student in the graduate course in aeronautical engineering at the 

 Massachusetts Institute of Technology. This aeroplane is considered 

 to be representative of modern practice in aeroplane design. Its 

 principal dimensions are as follows : 



Wing area, including ailerons 464 sq. ft. 



Span, feet 41 max., 40.2 mean. 



Aspect ratio 7 



Gap 6.37 ft. 



Dihedral of wings, degrees 176-75 



Area, stabilizer 16.1 sq. ft. 



Area, elevators 16.0 sq. ft. 



Area, rudder 9.35 sq. ft. 



Length, body 24.5 ft. 



Depth, body, maximum 3.2 ft. 



Width, body, maximum 3.3 ft. 



Weight, bare 1,070 lbs. 



Weight, personnel 320 lbs. 



Weight, fuel and oil 415 lbs. 



Weight, full load 1,805 lbs. 



r 5.2 ft., in roll. 



Radii of gyration J 4-65 ft., in pitch. 



I 6.975 ^t-' ^^ yaw. 



Brake horse-power no 



Fuel and oil per B. H. P., hour 0.73 lb. 



