TRANS-ARCTIC AVIATION—PLISCHKE 289 
temperatures experienced at altitudes of 30,000 and 40,000 feet or 
more, and our larger bombers repeatedly encounter temperatures of 
25° to 50° F. below zero without considering it a limitation upon their 
effectiveness. 
In the polar regions there is less diurnal change and less tempera- 
ture variation than elsewhere. Flying temperature is said to be 
hazardous neither at extreme heat nor at extreme cold, but at an 
intermediate range in the vicinity of, and especially just below, the 
freezing point of fresh water, for it is at this temperature that ice 
forms on the aircraft and weighs it down. Such freezing is not very 
troublesome in the Tropics except at high altitudes, and even in the 
polar regions icing is less of a problem than it is in the northern half 
of the Temperate Zone—where air lines function regularly according 
to well-integrated schedules. 
Various technological improvements were devised to prevent, or 
at least substantially reduce, the formation of an ice covering on 
the wings and fuselage of a plane. This is evidenced by the fact 
that fighter planes are constantly flying through the lower aerial 
zones saturated with the moisture which causes the icing, and perhaps 
especially by the fact that effective aerial warfare is being waged 
in the foggy and moist atmosphere surrounding the Aleutian Islands 
and the shipping lanes to Murmansk. Planes also are used for recon- 
naissance purposes at low altitudes by the Soviets along the Northern 
Sea Route between our northwestern coasts and the Arctic ports of 
the Soviets. 
A number of polar explorers, including Richard E. Byrd, who 
has flown in both polar regions, contend that polar flying is practi- 
cable only at certain times of the year. The spring months, from 
March to May,-are said to be best suited for aviation in the Arctic, 
because the snow is still hard and smooth and there is less fog than 
there is at other times of the year. But this objection seems to be 
concerned more with landing and taking off than with flying itself. 
and it certainly does not apply to long-range nonstop flying. 
At first glance it would seem that a genuine problem of polar avia- 
tion is the prevention of oil from freezing and the difficulty of start- 
ing the motors in severe temperatures. But oil will not freeze while 
the motor is operating and can be preheated before the motor is 
started. The problem of starting the motor in sub-zero temperatures 
was solved some 15 years ago, when it was learned that fireproof 
hoods or special coverings can be used to keep motors warm when 
a landing is made, as well as for starting a cold engine. A tube leads 
from this hood down to a heater which conducts heat up to the motor, 
or powerful warming lamps may be fitted to the motor. In this man- 
ner the motor can be preheated to. any temperature, and multi- 
