WILSON— AEROPLANE ENCOUNTERING GUSTS. 247 



Summary. 



In continuation of my previous work in gvists as affecting the 

 Curtiss Tractor JN2, I have discussed : 



1. Periodic Longitudinal Gusts. — It was found that, even in the 

 case of best resonance with the slow natural oscillation, the motion 

 was not much different from that produced by a simple head-on 

 gust until after a considerable time (over 14 sec.) had elapsed. The 

 amplitude of the forced oscillation (in up and down motion) which 

 ultimately became effective was about 5 times the amplitude of the 

 gust. This was not regarded as serious because true periodicity can 

 rarely be maintained in a head gust and because no pilot would 

 wait to let its effect reach such a magnitude. Periodic up gusts and 

 rotary gusts were considered as not likely to arise. 



2. General Theory of Resonance. — It was shown that for aero- 

 plane problems resonance meant different things for dift'erent prob- 

 lems. It was inferred that resonance was unlikely to be particularly 

 serious because in all probability its effect would either be small 

 or would take so long to become established that the pilot would 

 check it. 



3. Infinitely Sharp Gusts. — It was seen that the shock to a ma- 

 chine was mXuJ and mZ,J for a head gust, and mX^J and mZ^J 

 for an up gust. The serious case is mZiJ, the vertical shock in an 

 up gust which was about /^J/g times the weight, more than twice that 

 found for the sharpest gust previously treated. It would be still 

 more serious in a machine where Z„, was greater than in the JN2. 

 The Moral: Keep Z^ small, clashes with Hunsaker's conclusion^ 

 that lateral stability is incompatible with high wing loading — but 

 such an antithesis is common.'* Reference was made to impulsive 

 gusts. 



4. The Effect of the Propeller. — The assumption that a constant 

 power instead of a constant thrust was delivered did not very ma- 

 terially alter conditions of flight. 



5. Lateral Gusts. — The general equations were set up and 

 integrated. 



3 " Dynamical Stability of Aeroplanes," Washington, Smithsonian Misc. 

 Collect, 62, 1916, p. 77. 



* " The production of a laterally stable aeroplane is attentant with many 

 compromises," Hunsaker, p. 74. 



