522 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 9 



weather conditions to influence the result — with all these conditions 

 assumed, it again becomes possible to determine with a fair degree 

 of approximation the maximum duration of flight, regardless of dis- 

 tance flown. The answer works out to be from 90 to 100 hours. The 

 present record is in the neighborhood of 85 hours. 



In connection with range, note was made of a condition to be ful- 

 filled affecting the relation between the two coefficients of lift and 

 drag, and it will be recalled that for maximum range the speed must 

 always be such as to put the plane in an attitude of flight such that 

 the ratio of these two coefficients has its maximum value. For maxi- 

 mum duration there is a similar condition, but not the same. For the 

 latter the fraction which must have its maximum value has for its 

 numerator the coefficient of lift multiplied by its own square root 

 and for the denominator the coefficient of drag as before. It may 

 also be noted that the speed of the plane will be less for maximum 

 duration than for maximum range. 



The gap between present record performance and the figures given 

 above is again readily explained by the difficulty of insuring almost 

 perfect functioning of all the factors entering into the final result 

 during a period of say 60 to 100 hours, including the absence of un- 

 toward weather conditions, and further by the fact that, owing to its 

 small economic importance, there has been but little real attempt to 

 extend this particular performance to its ultimate limit. Range is 

 a much more important item of performance for all economic and 

 commercial purposes, and has, therefore, attracted the major effort 

 in this direction. 



Let us now turn to another item of airplane performance — altitude. 

 How high can a plane rise above the level of the sea? The extreme 

 achievement here can hardly be said to have any economic or 

 commercial significance. So-called stratosphere or substratosphere 

 flights, to which I shall recur in a moment, are in the immediate fore- 

 ground of present-day practice; but the extreme of possible and even 

 present achievement in this direction lies far beyond the possibilities 

 of immediate utilization commercially. 



As in the preceding case of extreme performance, we assume every- 

 thing about the plane and its loading made subservient to high alti- 

 tude climb ; and that these conditions are all combined in the optimum 

 manner and degree and that throughout the climb all of these factors 

 function together with the highest attainable efficiency. One more 

 condition must be noted. The engine must be supercharged — that is, 

 the air supplied to the engine for the combustion of the fuel must not 

 be the thin rarefied air of the higher altitudes, but air at sea-level 

 pressure or as near to that condition as may be found attainable. 

 The logic of the situation is clear. Power is developed through the 

 combustion of fuel, that is, its chemical union with oxygen. A fixed 



