The American Society of Mechanical Engineers

The T ren d of A ir T ran sp o rtatio n
By E D M U N D T. A LLEN , 1 SEA TTLE, WASH.
The year 1925 m arked th e b eginning o f air transportation
as an industry. Since th en it h as advanced th rou gh su c­
cessive stages o f grow th and developm ent u n til today as
the author believes air transport is in th e state o f tra n sition
betw een th e pioneering period and th a t o f m ature
growth. Airway m ileage by scheduled air transports in
the U nited S tates has increased from a to ta l o f 2,000,000
m iles flown in 1926 to 90,000,000 in 1939. Air passengerm
iles in 1938 aggregated 600,000,000. In th is paper th e
author reviews th e tech n ical develop m ents in aircraft and
im provem ents in airway operation w hich have m ade p ossible
th is phenom enal grow th. Every phase o f th is d e­
velopm ent w hich has played a part in th e su ccessfu l and
safe operation o f th e airw ay system s o f th e present day is
treated com prehensively in order th a t an understanding
may be gained o f th e futu re possib ilities o f air transport
and th e lin es along w hich it w ill advance.
AIR TRA N SPORTATIO N has arrived a t its present state of
commercial success in the space of a very few years. So
^sudden has been its development th a t the public has
hardly been able to keep pace w ith it, or to understand it, or to
accept it fully, although certainly patronage of this mode of
travel is steadily becoming more and more general.
To the outsider, who catches only the high lights and does not
see the effort and meticulous research th a t make possible the
spectacular developments, the advance of aviation and of air
transportation has been one series of sensations after another.
No sooner has the news of one innovation cooled than another
startling announcement supersedes it. In other words, it is an
industry which, because there has been so much to be accomplished,
has been moving ahead not a t a walk but at a forced run,
just as fast as engineers could make it move and as fast as air
traffic could pay for it.
Air transportation as an industry started scarcely fourteen
years ago, with a long, long way to go. Scarcely stopping to
consider what the ultim ate goal m ight be, those responsible for its
being proceeded on their course with the idea of finding out more
about th at goal along the way. Literally, they looked to the sky
as the limit.
How far has air transportation progressed along its course
What are its present status and its future prospects M ost new
industries, th a t are sound, first go through a period of growth and
then arrive a t a state of m aturity. The first stage is one of rapid
change and development, merging into the second, which is one of
refinement and the perfection of detail. In which stage does air
transportation find itself today Or is it at the merging point
between the two periods
The engineer likes to make graphs and study curves. When
they begin to flatten out, he feels th a t some sort of limit or goal is
being approached, be it tem porary or perm anent. He knows
1Director, Aerodynamics and Flight Research, Boeing Aircraft Co.
Prepared for presentation at the Transatlantic-Airplane Session at
the canceled Fall Meeting of T h e A m e r ic a n S o c ie t y o f M e c h a n i­
cal E n g in e e r s which was to have been held jointly with The Institution
of Mechanical Engineers of Great Britain, New York, N. Y.,
September 4-8, 1939. Presented at a Meeting of the A .S .M .E ., Los
Aneeles Section, July 11, 1940, Los Angeles, Calif.
N o t e : Statements and opinions advanced in papers are to be
understood as individual expressions of their authors, and not those of
the Society.
th a t the effort m ust be greater for further accomplishment and
gain. Is the curve of efficiency in airplane performance flattening
out How about the curve of airplane reliability
A study of the records of the last fifteen years and of the present
trends of the industry gives some enlightenm ent on those
questions. The author believes such a study will show that,
parallel to the developm ent of other forms of transportation, air
transport has reached the transition between the pioneering
period and the period of m ature growth. I t will also show th at
the optimum airplane is closer a t hand; th at, having reached a
certain leveling out in performance and size of aircraft, the
industry is concentrating now more definitely upon the finer
problems of perfection in safety, comfort, and reliability.
R e v i e w o f R e c e n t A i r - T r a n s p o r t D e v e l o p m e n t s
One of the best ways to judge the future trends of any industry
or to see the present direction of its developm ent is to look back a
short distance into the past of th a t industry. In such a review,
it is necessary to go back far enough to get beyond the seasonal or
short-swing tendencies. Fortunately, in the air-transportation
industry, it is possible, in the space of a few years (1925 to 1940),
to view the entire history of a m ajor development, its early faltering
steps, its seasonal ups and downs, even its decline in a major
economic depression and its partial recovery tow ard a normal
level.
1
Fio. 1
P a s s e n q e r - M il e s a n d T o n -M il e s F l o w n o n U n it e d
S t a t e s D o m e s t ic A i r L in e s
To look back over the record of the past through the eyes of the
traffic m an is most inspiring, especially when it is considered th a t
the figures are merely an indication of w hat m ay be expected of
the future. Air passenger-miles in the U nited States have risen
from 120,000,000 in 1932, fairly steadily except for regular seasonal
w inter declines, to a total of 600,000,000 in 1938. There
was a slight dip in the rising trend when in 1934 the num ber of
passengers carried actually decreased as compared with the num ­
ber in the preceding year, b u t this was due prim arily to the depression.
Cargo transportation by air, principally in the form of
air mail, has similarly increased in ton-miles flown. The rate of
this increase has been approximately 50 per cent per year, Fig. 1.
In some other transportation fields, it is true, the growth has
been equally rapid. Rail transportation grew more rapidly than
air transportation during its early boom, and bus transportation