Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.
What was considered in 1937 to be a breakthrough feat for a
full-size airplane is today accomplished regularly in model
airplanes. What took hundreds of pounds of generators, radio
gear, sensors, and actuators to perform the first-ever fully
automatic landing is now done with a few ounces of microminiaturized
GPS receiver, processor, MEMS sensors, servos, and a LiPo battery.
HobbyZone Sportsman S+RTF(see video
at bottom) is an example. Most modern commercial aircraft
are capable of landing themselves in an emergency situation.
Just today there was a news report of
an American Airlines pilot that died in flight and the copilot
took over to land the airplane; however, that Airbus A320 could
have handled the job if necessary.
Short-Wave Radio Lands Army Plane Without Human Aid!
Radio-Craft brings you probably the first detailed story
in any radio magazine, of how Uncle Sam's robot plane made perhaps
the world's first entirely automatic landing, as told by Captains
C. J. Crone and G. V. Holloman of the United States Army Air
Fig. A - The flight and landing paths of
the U.S. Army plane C-14 Cargo as it made the world's first
completely automatic airplane landing without a pilot's aid.
Much has been written in recent months concerning the personal
equation during flight and the influence of this equation on
accident rates. The newer developments in modern-aircraft, to
insure high performance, have required an increasing number
of cockpit devices, all of which demand the attention of the
pilot at some time or other during any given flight.
Pilots have felt and .expressed the need for simplification
of the various controls that must be manipulated and have expressed
the need for this simplification in no uncertain terms. This
simplification means that many of the functions now performed
by the pilot in flight control and navigation must be done automatically.
The landing of aircraft is no exception to this general trend.
With this in mind, the personnel of the Materiel Division, U.S.
Army Air Corps, over 2 years ago began active prosecution of
development work to simplify the procedure of instrument landing
by making it automatic.
Fig. B - Views inside the cockpit of the
Army airplane showing the radio compass and relay; the automatic
landing equipment (inset 1), and the frequency selector control
box (inset 2).
For over a year Air Corps test airplanes have been flown
automatically over distances that have indicated the thorough
reliability of the devices employed. This was one step in the
perfection of automatic landing. The features therefore that
are built into the automatic landing system are not only useful
for the landing but are used throughout the entire flight of
the airplane across the radio navigational aids with which the
United States is provided. Test airplanes from Wright Field
have been flown automatically from Wright Field as far as Texas,
and return, under automatic control. Several flights have also
been made from Wright Field via Buffalo, New York, to Newark,
New Jersey, and from there via Langley Field, Virginia, to Wright
Field, Dayton, Ohio. Of course the automatic landing involves
other factors besides control of direction. These factors are:
(1) control of altitude, (2) engine control, (3) glide control,
and (4) further engine control after landing.
With the provision of the Air Corps automatic landing system
in an airplane and with the installation of the new "Z"-type
radio range beacons, the airplane may be flown automatically
from station to station, from East to West Coast. If we imagine
a group of the future "Z"-type radio ranges placed in a line
joining the runway of the landing field and extending to a point
5 miles therefrom, some idea will be gained of the essential
features of the Air Corps automatic landing system.
By reference to Fig. A, which represents the path of flight
and landing made by the Army C-14 Cargo airplane on Monday,
August 23, 1937, a generally clear idea will be obtained of
the path of the airplane in the horizontal plane. The insert
shows the airplane flight path and landing path which the Army
airplane followed in executing what is believed to be the world's
first entirely automatic airplane landing! This illustration
should be self-explanatory and in itself is evidence of the
continuation of development on the Air Corps system of instrument
Fig. C - One of 4 mobile "guiding" stations
for automatic landings; (1) 1,000-meter radio compass locator
antenna, (2) 4-meter marker beacon antenna. Both transmitters
operate continuously; the operators in the truck do nothing
after starting the L.F. compass guiding station and H.F. marker
On Monday, August 23, 1937, after over 2 years of intensive
research and design with respect to automatic control features
and automatic flight procedure, 2 entirely automatic landings
were made in the period of an hour under adverse air and wind
conditions by Capt. Carl J. Crone, Director of the Instrument
and Navigation Laboratory and Capt. George V. Holloman, Assistant
Director of the Laboratory and Mr. Raymond K. Stout, project
engineer in automatic landing. Since that time additional landings
have been made in which disinterested personnel have been carried
as observers on the flights in order to check robot landings.
In the execution of an automatic landing, using the U.S.
Air Corps system, it is necessary for the pilot of the airplane
bring the airplane to a definite altitude, determined by the
sensitive altimeter, and to place the airplane within the range
of radio reception of the ground radio facilities. It is, of
course, desirable to place the airplane generally in the direction
in which it is expected to land, but this is not necessary as
was determined in flight and can be understood by reference
to Fig. A in which the airplane was actually placed in a position
which headed it 180° away from the direction of final landing!
When the pilot has placed the airplane at a selected altitude
in the vicinity (20 miles or less) of the landing field, the
master landing switch is closed and the airplane proceeds through
the following routine in accomplishing the automatic landing:
(a) The selected altitude is automatically maintained and
the airplane's heading is changed so that it flies in the direction
of the radio guiding station most remotely located from the
(b) The new robot landing controls the "take over" as described
Sequence of Operations
The altitude control device, shown at A in insert 1, Fig.
B, maintains the proper altitude during the initial approach
as just noted. The directional relay, which interlocks the radio
compass and the gyro pilot and which therefore causes the change
in heading of the airplane, is shown at B in Fig. B. Adjacent
to this relay is shown the radio compass marked C, the frequency
of which is automatically set by the interaction of the marker
beacon receptor D working in conjunction with the frequency
selector E (insert 1, Fig. B). The pilot of the airplane is
informed as to the correctness of automatic settings by observing
the frequency selector indicator F (insert 2, Fig. B). (That
is, when the airplane passes over the marker beacon, the frequency
changer in the airplane is set automatically in order to select
on the radio compass receiver the frequency of the next succeeding
station. In other words, the impulse received in the airplane
from passing over the marker beacon is used to start in operation
the frequency selector and changer.)
Fig. D - The automatic throttle control used
for automatic landings. The inset (1) is a close-up of the control
Through the automatic and cooperative action of these devices,
the airplane heads to the compass guiding station (Fig. C) farthest
from the landing field as shown in Fig. A. Upon reaching that
station the frequency is automatically changed to Station No.3
where it is again automatically changed to the frequency of
Station No.2 where the frequency is again automatically changed
to that of Station No. 1 while at the same time the engine throttle
is automatically operated by the throttle engine shown at G
(insert 1, Fig. D); and again shown in H, Fig. D. (That is,
the ground radio equipment operates the same as lights burning
on the ground. They are placed in operation by ground operators
and nothing is done to them until their use is no longer required
and they are turned off. The effective range of the markers,
at low altitude, is throughout a circle 1/8-mile in diameter.)
The throttle engine is interconnected with the altitude control
in such a manner that should the airplane reach its minimum
altitude prior to reaching radio station No. 1 the throttle
engine will be so actuated to control the airplane in such a
manner that it will maintain accurately the minimum altitude
required for the operation of the automatic landing system.
Fig. E - Left, 1 - side view of the Army
test plane C-14B showing the various antennas used in connection
with the automatic landing system; right, 2 - a switch on this
landing strut of the plane automatically controls the engine-throttling
apparatus just as the plane makes contact with the ground.
After passing Station No.1 the throttle engine is so actuated
that the airplane maintains a selected glide angle and rate
of descent until "ground contact" is made. When ground contact
is made, the throttle engine is further actuated by the landing-gear
switches, one of which is shown at I in Fig. E2, which in turn
causes the engine to be idled and proper braking applied.
There are 4 mobile (truck) ground transmitting stations as
shown in Fig. A. Each truck, shown in Fig. C. carries 2 transmitters;
one (which has a transmitting range of about 35 miles) is for
guiding the airplane by means of the radio compass to the truck
position. These transmitters operate in the radio beacon band
of 200 to 400 kilocycles. The other, or marker beacon transmitter,
operates on the ultra-short wavelength of approximately 4 meters.
At the present writing, the automatic landing system has
been flown so that all of the landings made to date have been
made under cross-wind conditions varying in intensity as high
as 11 miles per hour.
Fig. F - The gyro pilot or "automatic pilot" shown at J permits
automatic flight control for an almost indefinite period. The
master landing switch (1) and the axillary reset switches (2,
3, 4 and 5) are additional items for use in automatic landing.
The Sperry gyro pilot has been used throughout as the automatic
flight control feature of the airplane. Certain additions to
the Sperry pilot have been required in order to provide for
the automatic control of direction. At J, Fig. F, is shown the
Sperry gyro pilot installation; left of this unit is shown the
master landing switch (1) and the auxiliary reset switches (2,
3, 4 and 5).
The series of tests conducted through the last 2 years have
brought many humorous incidents not the least of which have
been such terms as "nervous shoe laces" and jittery hands" which
have always been evident to the observer watching the pilot
keep "hands off" during the automatic landings.
Figures G and E1 are views of the airplane used in the conduct
of all of the experiments on the Air Corps automatic landing
system. In these photographs, the various antennas are identified
as: 11, the antenna for the communications transmitter and receiver;
12, the balanced antenna for the radio compass; 13, the radio
compass loop antenna; and 14, the marker beacon receptor and
Fig. G - At 11, the communications transmitter and receiver
antenna; Fig. E, shows others.
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB.
Its primary purpose was to provide me with ready access to commonly needed formulas and reference
material while performing my work as an RF system and circuit design engineer. The Internet
was still largely an unknown entity at the time and not much was available in the form of
All trademarks, copyrights, patents, and other rights of ownership to images and text used
on the RF Cafe website are hereby acknowledged.