EXPLORATION BY AIRPLANE 399 



might give a greater factor of safety because it can fly with a Hght 

 load on a small part of its total power or it can fly with its maximum 

 wing load on less than the available power; on the other hand, if 

 the machine is loaded to the capacity of its engines, the certainty of 

 carrying out the full flight is not as great as with a single-power unit. 

 Failure of any one of the several engines would, with a maximum load, 

 mean either a forced landing or the dumping of some of the load, 

 thereby curtailing the flight. Where, as in the Arctic, safe forced 

 landings are possible and where there is a possibility of finding sus- 

 tenance on the ice during a forced return march, a single-power unit 

 offers several advantages if the maximum wing load is to be carried 

 at the start of the flight. With a single-power unit there is a great 

 economy in initial expense and in upkeep and personnel required. 

 Because of its lighter weight it has greater maneuverability on the 

 ground. However, if economy in initial expense need not be considered 

 and sufficient personnel is available, multiple-engine machines with 

 normal loads are more suitable for the work. 



Airplanes constructed almost entirely of wood afford fewer chances 

 for petty annoyances and inconvenience in extremely low temperatures 

 than all-metal craft, which could not be handled or even accidentally 

 touched with bare fingers without injury. Wooden planes also over- 

 come some of the difficulty experienced with compass deviation in 

 steel-frame machines. All hinges and moving parts of a plane for use 

 in the Polar Regions should be free and lubricated with some form of 

 dry lubrication. 



For exploration limited to reconnaissance or for detailed surveying 

 by means of aerial photography the airplane has many advantages 

 over the airship. These advantages are high speed, maneuverability 

 in the air and on the ground, economy in material and expense, and 

 flexibility in arrangement of plans. Airplanes are more suitable for 

 mapping than airships, since the essentials for that work are high 

 speed, constant speed, and constant height and direction. Airships 

 may be used successfully in the Arctic if expense need not be con- 

 sidered, but they would not be serviceable in the Antarctic, where 

 offshore winds of great velocity are frequent. 



AiR-CooLED Versus Water-Cooled Engines 



The power units in a machine for polar work may be either air 

 cooled or water cooled. Air-cooled engines have an advantage in 

 inherent lightness per H. P., ease of maintenance, and freedom from 

 trouble due to failure of the cooling system. Light, convenient and 

 controllable heaters for warming the air before it enters the car- 

 burettors can be attached, without reducing the power of the engine. 

 Available water-cooled engines have in the past been more reliable 



