266 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1912. 



AERIAL BREAKERS. 



The term "aerial breakers" is used here in analogy with water 

 breakers as a general name for the rolling, dashing and choppy winds 

 that accompany thimderetorm conditions. They often are of such 

 violence, up, down, and sideways in any and every direction that an 

 aeroplane in their grasp is likely to have as uncontrolled and disas- 

 trous a landing as would be the case in an actual hole of the worst kind. 



Fortunately aerial breakers usually give abundant and noisy 

 warnings, and hence the cautious aeronaut need seldom be, and, as a 

 matter of fact seldom is caught in so dangerous a situation. How- 

 ever, more than one disaster is attributable to just such winds as 

 these — to aerial breakers. 



CLASSIFICATION. 



The above nine types of atmospheric conditions may conveniently 

 be divided into two groups with respect to the method by which they 

 force an aeroplane to drop. 



1. The vertical group. — All those conditions of the atmosphere, 

 such as aerial fountains, cataracts, cascades, breakers, and eddies 

 (forward side), that, in spite of full speed ahead with reference to the 

 air, make it diihcult or impossible for an aeronaut to maintain his 

 level, belong to a connnon class and depend for their effect upon a 

 vertical component, up or down, m the motion of the atmosphere 

 itself. Whenever the aeronaut, without change of the angle of attack 

 and with a full wind in his face, finds his machine rapidly sinkmg, he 

 may be sure that he has run into some sort of a down current. Ordi- 

 narily, however, assuming that he is not in the grasp of storm break- 

 ere, this condition, bad as it may seem, is of but little danger. The 

 wind can not blow into the ground and therefore any down current, 

 however vigorous, must somewhere become a horizontal current, in 

 which the aeronaut may sail away or land as he chooses. 



2. The horizontal group. — This group includes all those atmos- 

 pheric conditions — wind layers, billows, eddies (central portion), 

 torrents and the like — that, in spite of full speed ahead with refer- 

 ence to the ground, abruptly deprive an aeroplane of a portion at 

 least of its dynamical support. When this loss of support, due to 

 a running of the wind more or less with the machine, is small and the 

 elevation sufficient there is but little danger, but, on the other hand, 

 when the loss is relatively large, especially if near the ground, the 

 chance of a fall is correspondingly great. 



CONCLUSIONS. 



1. Holes in the air, in the sense of vacuous regions, do not exist. 



2. Conditions in the atmosphere favorable to precipitous falls, 

 such as would happen in holes, do exist, as fallows: 



