The American Society of Mechanical Engineers

2 TRANSACTIONS OF T H E A.S.M.E. JANUARY, 1941
has also had its period of tremendbus expansion. B ut neither of
these had to overcome such a serious reluctance on the part of the
public to accept a mode of travel so new and different—one th at
took them out of their accustomed element and into the air.
Both of these other modes of transportation had heavy indirect
subsidies, such as land grants and highway construction. Aircraft
transportation has had similar assistance of federal and
municipal funds in airway and airport construction. Beaconlighted
routes have been built, forming a network over the entire
country for night flying, and radio-range routes now perm it the
radio navigation of any aircraft with a radio receiver.
The subsequent drop is definite evidence of the increase in size of
the aircraft unit, which factor in itself would cause a decrease in
the number of such units landing per day a t an air terminal.
T e c h n i c a l A d v a n c e o f T r a n s p o r t A i r p l a n e s
As in air traffic, so in the transport airplane itself, the progress
of fourteen years has been tremendous. D uring the period from
1925 to 1939, the transport plane has changed from a small
single-engined biplane, carrying 2 passengers in addition to the
pilot, weighing 1 ton gross, and costing less than $10,000, to a
large monoplane with either 2 or 4 engines, carrying 30 to 70
F i g . 2
A n n u a l A ir w a y M il e a g e a n d M i l e a g e F l o w n D a i l y o n
U n it e d S t a t e s D o m e s t ic A i r L i n e s
--- — ----- I 1 3 0 0 1 3 0 0
F i g . 4 G r o s s W e i g h t a n d U s e f u l L o a d , U n i t e d S t a t e s T r a n s ­
p o r t A i r p l a n e b
F i g . 3 N u m b e r o f A ir p o r t s i n U n i t e d S t a t e s a n d S c h e d u l e d
A i r - L in e L a n d in g s p e e D a y a t T y p ic a l A i r T e r m in a l
Airway mileage in the U nited States has grown from an annual
total of 2,000,000 miles flown by scheduled air transports in 1926
to 10,000,000 in 1928; 30,000,000 in 1930; 50,000,000 in 1933;
and 90,000,000 in 1939. The year 1934 shows a characteristic
depression dip in the curve. The curve for mean daily air-miles
flown closely parallels th a t for the gross annual mileage, as shown
in Fig. 2.
The increase in the number of airports has been an im portant
trend, perhaps not closely related to long-distance, scheduled, air
transport, but an indication of the growing interest in and use of
aircraft by private owners, which occurred principally between
1926 and 1932. The 500 airports of 1926 had increased to 2100
in 1932. I t would be expected th a t eventually there would occur
a leveling out in the increase of the number of airports. This
has definitely occurred during the last four years.
The number of landings per day of scheduled air-line transports
at a typical air term inal may also be used as an index of the trend.
A curve of landings, Fig. 3, based on studies made a t the Chicago
air terminal, rises sharply from ten in 1928 to 34 in 1931 and then
drops with the depression, rising again in 1936 to a peak of 44.
F ig . 5 U n it C o s t o f T y p ic a l A ir T r a n s p o r t an d I n v e s t m e n t in
T r a n s p o r t P l a n e s , U n it e d S t a t e s D o m e s t ic A ir L in e s
F i g . 6
P a s s e n g e r C a p a c i t y a n d L a n d i n g S p e e d , U n i t e d S t a t ic s
T r a n s p o r t A i r p l a n e s