The Indianapolis times. [volume] (Indianapolis [Ind.]) 1922-1965, 1928-07-27
Aviation
AVIATOR FACES
DIFFICULT TASK
FINDING COURSE
Pilot Must Be Accurate at
Figures, Calculations
in Fog, Night.
Rn Times Special

81 IfmeS SDectdG
NEW YORK, July 2A-A ship at
sea usually takes it bearing once a
day, at noon and following a COM
pass course it can pillow the seas for
tWenty-four hours with compare
lively small error, especially on large
liners which have automatically con-
trolled helms. But not so with an.
airplane.
The difference and the difficulty
is this, a ship at sea is influenced
by the wind to far less extent than
is an airplane; it's speed is prac-
tically constant, whereas that OF a
plane varies, if only slightly, from
one minute to another, depending
on the steadiness of the pilot and
the fluctuations in the strength of
the wind, easily determinable in a
ship, are extremely difficult to de-
tect in a plane, and the same can
be said of changes of direction.
Finding Air Position
To find an air position in the day.
time four things are necessary: a
bubble sextant, an aerochronometer
rated to Greenwich apparent time,
tables for solving the triangle and
chart with an aircraft plotter Com
bined protractor and ruler.
With these instruments the naviga
tor must first determine the exact
second of time. This is a fairly
simple matter, the exact sun or star
time being obtainable from two
aerochronometers, one set to Green
wich sidereal time and the other to
Greenwich apparent time.
Next lien of position is made by
observation through the bubble sex
tent, When the horizon is visible it
is used in preference to the bubble,
due allowance being made for alti-
tude; when it is not the bubble
forms an artificial horizon, and a
slight error in this respect may
throw the observation out by sew
eral degrees.
Use Sun in Daytime
The line of position having been
observed and plotted, which shows
the plane to be flying in a given
direction at some unknown point,
it is necessary to solve the triangle
formed by the observers zenith, the
Pole and the observed body. Special
tables and instruments are COM
piled and made for the solving of
this triangle, some of them very
complicated, others reasonably
simple.
Once truly solved, a second line
of position is formed and at the
intersection Of the two lines the
exact position of the plane is
found, and it is thus possible to
correct the compass course.
In the daytime the object OBJ
served is, of course, the sun; but
at night it is a star. A special type
of bubble sextant is preferred, an
aerochronometer and star altitude
curves.
Fog, Storms Hamper
The method of determining the
position is exactly the same, except
that almost invariably the bubble
has to be used for the horizon,
which is rarely plainly enough Wis
ible at night.
Naturally, when there are no
heavenly bodies to be seen and no
horizon, as when flying through fog
or storms, celestial navigation breaks
down and planes are dependent on
radio direction or the compass, bank
and turn indicator and the inclin-
ometer
Instrument flying was used by
most of the long-distance ocean
airmen. However, with the develop
ment of radio it seems a fair OBJ
servation to say that radio will play
ton and will for all practical pur-
poses displace celestial observation
n. L