THE OFFICIAL PUBLICATION FOR BONANZA, BARON & TRAVEl ...

Golden Age of Exploration
The navigators during the golden age of exploration, after
accurate timepieces were developed, did the calculations with
pen and paper, a process that required a great deal of computation
time. But that was all OK since the vessel was moving
very slowly. At 450-plus knots in the 707, the math was in tabular
form in the above-mentioned publications. Good thing,
too, since the first handheld calculators (Casio Personal M-l)
did not appear until about a year after I started navigating. And
although we all learned to use the sight reduction tables, there
would have been few or none who would have been able to
handle the manual method of the necessary computations.
By knowing the approximate position of the aircraft, we
would take an assumed position (AP) on the chart that was fairly
close (maybe 100 miles maximum) to our estimated position.
By using the sight reduction tables and air almanac, we
would be able to determine that IF we were at the assumed
position, we would see the selected body at a certain altitude
at the exact desired time of the fix. Since
we actually were not at the AP, we
would see the body either higher or
lower than the computed height.
Let's assume we determined that
we should see the body 40 degrees
above the horizon if we were actually at
the AP at the desired time of the fix.
(Refer to my previous article in the
August issue on page 10372 on how the
Kollsman Periscopic Sextant functioned.) However, with the
sextant we measure the altitude as 41 degrees. Now, the only
way we can see it higher is to be closer to the SP of the body.
Picture yourself in a room with a light fixture mounted on the
ceiling. As you enter the room, the light fixture appears at
some low angle of elevation. As you get closer, it gains altitude
until you are directly under it, at which time it is at your zeni th
or 90 degrees above the horizon.
Since in our example we see the body one degree higher
than we should have seen it at the AP, our actual position is 60
nm toward the body. Since we know the direction we took the
observation, we can plot a line out of the AP for 60 nm, draw
a line at right angles to that plotted line and we now know our
actual position is somewhere on that 90-degree line.
By doing the same procedure for one or two other bodies
and crossing the first line of position (LOP) with the second
LOP, we can get an actual position for the time of the fix. If
three stars or other bodies are used, and the three LOPs do not
form a pinpoint on the chart but rather a triangle of hopefully
small dimensions, the triangle is bisected so the center is located
and that is the fix position.
I have read accaunts of pilots
going to the rear lavatory of a DC-4
or other such airplane or window,
taking a celestial observation from
the porthole and claiming to get
an accurate LOP from such a
sighting location. I really doubt the
result would have much accuracy.
Techniques taught in navigation schools
Of course, there were many techniques taught in the very
fine Pan American World Airways (gone but not forgotten)
Navigation School and many others developed by the individual
navigators as they gained experience to make all the monkey
motion described in this article take a relatively short time.
There were also needed corrections to the observed altitude
that might need to be used in these computations. These
might include refraction caused by the bending of light as it
passes through the earth's atmosphere (you can see about 3
degrees over the horizon at low body elevations) when shooting
bodies at very low elevations; the semi-diameter of the
earth when shooting close Objects such as the sun, moon or
planets (stars are considered to be an infinite distance away,
and the fact we are not taking the observation from the center
of the earth is negligible for stars and only comes into play
with close-in bodies when they begin to get rather low in elevation);
and many other such corrections as necessary to make
the resultant computations as accurate as
possible within the capability of the navigator's
equipment to determine angles.
I have read accounts of pilots going
to the rear lavatory of a DC-4 or other
such airplane or window (Beech 18s,
Cessna 172s, etc.) and taking a celestial
observation from the porthole and claiming
to be able to get an accurate LOP
from such a sighting location. I really
doubt the result would have much accuracy. Although being able
to accomplish reliable fixing using celestial observations does
not take more than an average working brain, one needs proper
training and a suitable place to take the observations and equipment.
A three-star fix could be computed, shot and plotted in
about 15 minutes and would provide a definite position for the
navigator. Hopefully the position would be on the flightplanned
track drawn on the navigation chart, proving that the
heading slips being passed up to the pilots were good ones and
that the pilots were able to fly those headings.
That last concern was a real issue at times. I have had very
senior captains fly off the posted heading as much as 20
degrees for no other reason than that they misread the compass.
Well, we had to make allowances for those really old
guys. After all, some were pushing past 55 on their way to 60!
ABS Life Member l ewis C. Gage has AlP multiengine land with
Boeing 707/720/747 {Airbus-3tO rotings. Commerciol singleengine
land: flight instructor MEl/SEl airplanes and instruments;
ground instructor advanced and instrument: flight navigator:
flight engineer; mechanic-airplane and engine: and FAA parts
manufacturing authorization. Flight time: 15,QOO-plus hours. Lew
may be contacted at 2255 Sunrise Dr., Reno, NV 89509.
Phone/ Fax: 775-826-7184. E-mail: sunrisereno@gmail.com