250 SYMPOSIUM ON AERONAUTICS. 



still larger wings, beams of aluminum alloy or steel. In the great 

 aeroplanes of the future, we may have an op])ortunity to use a lattice 

 construction combining a great moment of inertia with a minimum 

 of material. The smaller the structure the less favorably can we 

 employ the material. In many cases to give sufficient security against 

 local injury and deterioration we make parts several times stronger 

 than would be indicated by a strength calculation alone. For ex- 

 ample, no matter how small the aeroplane, we would use no less than 

 a certain minimum rib thickness and cover with a fabric of sufficient 

 weight and strength to stand exposure. Consequently, in the small 

 aeroplanes, we build relatively heavier than necessary. 



4. The exploration of the upper air has now become of pressing 

 concern to those who expect to navigate in it and, in a gene^'al way, 

 to designers of aircraft. Dr. Blair's soundings are most illuminating 

 and it is especially gratifying to note the progress which our own 

 Weather Bureau is making in this work. For the airship and 

 balloon, especially, a knowledge of the pressure, temperature, and 

 wind at different altitudes is of first importance and it is to be hoped 

 that forecasts can be supplied the aeronaut before his ascent, which 

 will acquaint him with the probable conditions he will encounter 

 aloft. Dr. Blair's data, I assume, show typical conditions or rather 

 average conditions. It would be valuable if his explorations of the 

 upper air could be extended to show in addition the possible and 

 typical deviations from average values. The aviator is less con- 

 cerned with the average velocity of the wind than with its internal 

 structure ; the frequency and intensity of its gusts and their nature. 



5. The importance of a study of gusts is clearly brought out by 

 Professor Wilson's analysis of the effect of lateral gusts on an 

 aeroplane in flight. Professor Wilson has assumed gusts of given 

 intensity and direction and computed the effect upon a typical aero- 

 plane. There is abundant testimony of a qualitative nature as to the 

 violence of these effects in practice. Aviators speak of " air holes " 

 in explanation of uncontrolled diving and turning experienced. It 

 is of course evident that there are no holes in the air, and Professor 

 Wilson shows that gusts produce effects of the sort observed. Now 

 it is possible in the design of aeroplanes to so arrange surfaces that 

 the eifect of particular kinds of gusts is minimized. What we need 



