AIR TRANSPORT — DURAND 519 



plant. Some sensible part of the total lift must be allotted to fuel 

 and to pay or fighting load and this means reduced power-plant 

 capacity as compared with the plane where a short burst of speed is 

 the sole object. 



Let us now turn to another item of airplane performance — range, 

 by which is meant the distance flown without grounding or refueling. 

 Here again the answer depends on the special conditions imposed; 

 and in particular on the division of the useful load between fuel and 

 pay load. If we go to the limit, with no pay load whatever, with all 

 of the margin between the total lift and the weight of the plane 

 devoted to fuel, consumable supplies, and minimum crew, it again 

 becomes possible to give an approximate answer to the maximum dis- 

 tance which can be flown. This distance works out to be from 8,000 

 to 9,000 miles ; and this again, we must note, is a performance worked 

 out within the framework of our present-day science, engineering, 

 and technology. It does imply, however, everything made subservient 

 to long-range flight — the maximum possible load of fuel, no head 

 winds or adverse weather conditions, every element contributing to 

 the desired result combined in the optimum manner and degree, and 

 everything operating with the highest attainable efficiency throughout 

 the entire flight. It also implies flying constantly with a speed such 

 that there will always obtain a certain fixed optimum ratio between 

 two characteristic coefficients of airplane performance — the so-called 

 lift and drag coefficients. The first of these relates the lift of the 

 plane to the speed, to the wing area, and to the density of the air in 

 which the plane is moving. The second relates the drag, or resist- 

 ance to motion, to the same conditions of the flight. Now it works 

 out that for maximum range, or otherwise for maximum distance 

 per pound of fuel, the ratio of these two coefficients — lift divided by 

 drag — should be a maximum; and this implies a speed continuously 

 changing with fuel consumption and with the consequent lightening 

 of the plane — high speed at first when the plane is heavy and decreas- 

 ing as the plane becomes lighter with the consumption of fuel, but 

 always so adjusted as to meet this condition between these two 

 coefficients. 



When we ask how near has present achievement approached such 

 a range as 8,000 or 9,000 miles, we find a somewhat wider gap. The 

 present record is about 7,000 miles. When we realize, however, the 

 remote chance, for a period of 60 to 80 hours, of a complete absence 

 of all adverse weather conditions and a continuous perfect function- 

 ing, during this period, of all factors contributing to the desired end, 

 the larger margin between actual and ideal performance is not sur- 

 prising. It should also be noted that it is too much to expect prac- 

 tically a continuous exact regulation of the speed of the plane in 



