Next, to plot the expected track, one simply needs to determine 

 how much the airplane will have drifted at the end of each leg and to 

 find successive points along the expected track. 



The single-heading tracks with respect to the great circles can be 

 converted into another set of tracks, the single-magnetic-heading tracks. 

 The significance of these tracks is that a plane could be flown auto- 

 matically, or without the attention of a pilot. At the same time this 

 single-magnetic-heading flight offers the same advantages as general 

 single-heading flight, especiall}^ by lessening flying time. By plotting 

 all the tracks one can see that the single-magnetic-heading tracks lie 

 reasonably close to the great circles for several of the routes. It is the 

 recommendation of this paper that such long-range flights be made by 

 use of single magnetic heading, except for extreme routes like the route 

 between Auckland and New Year's Island, Tokj^o, and San Francisco, 

 For these last-mentioned routes the minimal flight paths are now 

 considered. 



Auckland to New Year's Island : The trip from Auckland to New 

 Year's Island is best shown on oblique Mercator projection. The time- 

 saving by single grid heading is about one hour. If the wind field were 

 accurately known, it would be possible to determine wind shear and 

 obtain the minimal flight path by which a still greater saving in time 

 could be realized. 



Tokyo to San Francisco : Using the pressure field we plot two single- 

 grid-heading flights on an oblique Mercator projection between San 

 Francisco and Tokyo. The route is sufficiently far north to permit 

 the use of geostrophic wind. Wind shear can be easily computed. 

 Thus, the minimal flight paths can be plotted. By flying this path, 

 an airplane which would normaUy take about seventeen hours to fly 

 from San Francisco to Tokyo would cut about thirty-five minutes from 

 its time. 



Discussion 



Dr. Spilhaus remarked that the vertical wind shear was more im- 

 portant than the horizontal wind shear, and should be taken into account 

 in estirtiating the paths of shortest time. Dr. Gringorten in reply said 

 that that was so, yet navigators preferred the flight at a constant level 

 and much more work was necessary if flight paths with varying alti- 

 tudes were to-be introduced. Dr. Spilhaus further remarked that the 

 chart used by Dr. Gringorten, an oblique Mercator projection, had to 

 be specially constructed for each pair of points used as arrival and 

 departure terminals for the aircraft. Dr. Gringorten agreed, but 

 claimed that the extra time spent on constructing the charts was w^eU 

 worth while. 



. Colonel Moorman pointed out that fhght paths are now fixed by the 

 location of airfields and navigational aids. Thus only in special cases 

 when time was of greatest importance would it be justifiable to deviate 

 from these prescribed paths. 



39 



