586 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 8 



THE POWER OF MANEUVER 



In many forms of aircraft, power of maneuver is vital. Does the 

 increasing speed of flight have any effect on this vital requirement 

 whether because of a limit to the endurance of the human body or of 

 the airplane itself? It is also important to know whether we are 

 approaching some physiological limit to either the rate of climb or the 

 vertical speed of dive. We are all more or less familiar with what is 

 known as caisson disease. This trouble arises when a diver working 

 under several atmospheres of pressure, with much nitrogen absorbed 

 into his blood, comes to the surface and the surplus gas bubbles out as 

 the pressure is relieved. During the climb of an airplane, the atmos- 

 pheric pressure is also gradually relieved, but here the rate of change 

 of pressure is so slight, and the total change of pressure so small, that 

 the physiological effect is unimportant. Since, however, the rate of 

 dive is vastly greater than any possible rate of ascent, it is reasonable 

 to ask whether in this more rapid action physiological difficulties may 

 not occur. Here an arithmetical parallel is of service. Even if we 

 take a direct dive through 8,000 feet at as high a speed as 400 miles 

 per hour, the total change of pressure is no more than any swimmer 

 would encounter who dived 10 feet deep into water; moreover, the 

 total time taken by the air dive, some 7 or 8 seconds, does not represent 

 anything more sudden than would be encountered by such a swimmer. 

 We may, therefore, conclude that there is little to fear in this case also. 

 As Wing Commander G. S. Marshall, of the Eoyal Air Force Medical 

 Service, put it in his lecture 5 to the Society: "Power dives are done at 

 the almost unbelievable speed of 30,000 ft. per minute without ap- 

 parent harmful biophysical effect." As regards acceleration in taldng 

 off, or deceleration in landing, these are not anything to which the 

 human frame does not easily adapt itself. This applies also to the 

 catapulted take-off. The acceleration to which we are all subjected 

 in a motor car driven in normal London traffic is just as severe. 



There are, nevertheless, other accelerations which arise during flight 

 which are of a totally different character. These are the ones due to 

 centrifugal force. An airplane steadily banked on a turn at 45° will 

 impose a horizontal force on its occupants equal to their own weight 

 and this combines with the normal weight of the body so that the total 

 weight on the passenger's seat is increased by almost half as much 

 again. Banking at 60° would double this load. 



There are also large centrifugal forces introduced when an aircraft is 

 suddenly pulled out of a dive. In almost any aircraft the controls are 

 so powerful that it is mechanically possible for the pilot so to manipu- 

 late the elevator as to break a wing. Of course, for this to happen the 

 acceleration imposed has to be exceedingly great, equivalent, perhaps, 



» Royal Aeronautical Society, January 1933. 



