October 1937 Radio-Craft
[Table of Contents]
People old and young enjoy waxing nostalgic about and learning some of the history of early electronics.
Radio-Craft was published from 1929 through 1953. All copyrights are hereby acknowledged. See all articles
This paper originated from the
National Archives of the United States of America. Its contents are
in the public domain. All text and images are the property of U.S. legal citizens. An article written
by Charles E. Planck, of WIT, appeared in the October 1937 issue of Radio-Craft magazine titled
"'Air-Track' System of Blind Landing."
It uses a lot of the material in this report.
"Air-Track" System of Blind Landing
THE HISTORY AND DEVELOPMENT OF THE WASHINGTON INSTITUTE OF TECHNOLOGY.
JOSEPH M. MAHZOLF, Jr.
NOVEMBER 18, 1938
THE HISTORY AMD DEVELOPMENT OF THE WASHINGTON INSTITUTE OF TECHNOLOGY
I. Summary. II. Introduction. III. Formation and Organization of the Institute. IV. The Work of the
A. Development and Performance of Air-Track.
B. The Work of the Broadcasting Division,
C. Other Developments of the Institute. V. Conclusion. VI . Bibliography.
The Washington Institute of Technology wa3 formed in 1933 to develop an instrument landing system,
already well begun at the Bureau of Standards. It has its offices located in Washington, D. C. and its
experimental laboratory at College Park, Maryland. Closely associated with it and also located at College
Park, Maryland is its two "manufacturing associates" Air-Track and Scientific Concrete Service Corporation.
The Institute's chief objective is to test and develop more fully the present Air-Track equipment.
The Air-Track instrument landing system employs three elements, the runway localizer for guidance in
the horizontal plane, the glide path for guidance in the vertical plane, and the marker beacon to serve
as a warning to the pilot of the proximity of the airport. All the ground equipment except the marker
beacon is located in an automobile trailer which may be moved to other runways as weather conditions
dictate. Also located in the trailer is an automatic monitoring device which insures the operation of
the transmitters within closely prescribed limits. In the plane the pilot has a visual cross-pointer
instrument on the instrument panel, which enables him to follow a curved path down to the runway and
a safe landing in any kind of weather. The Broadcasting Division of the Institute renders valuable service
to radio stations and radio engineers. This service includes allocation engineering, site surveys, coverage
surveys, directional antennae design, construction of antennae tuning and phasing equipment, and a frequency
In addition to these major interests, the Washington Institute of Technology holds the patent rights
on many other devices which have been
developed in connection with their regular work.
Since its inception in 1933, the Institute has steadily grown in size, and with the probable adoption
of an instrument landing system at all airports, it is safe to assume that it will enjoy a continued
growth and expansion.
The Washington Institute of Technology is a corporation which was formed for the purpose of experimentation
and further development of an instrument landing system previously conceived by certain scientists at
the Bureau of Standards. The progress accomplished at the Bureau of Standards ha3 teen adequately covered
"by a previous thesis entitled "History and Development of the Bureau of Standards' Radio Beacon Experiment
Station at College park, Maryland", written by Robert W. Beckham and dated December 18, 1936. It is
the purpose of this thesis to set forth the history and development of the Washington Institute of Technology
which is, in effect, an account of the subsequent developments along this line. It is for the instrument
landing system, known as Air-Track, that the Institute has achieved an international renown.
The offices of the Institute are located at present on the eighth floor of the McLachlen Building,
10th and G Streets, N.W. , Washington, D. C. The laboratory, where all the research and testing is done,
is located at College Park, Maryland and is Just south of the College Park Airport in a convenient position
for experimentation in airplane instrument landing systems. Associated with the laboratory is a factory
for the manufacture of Air-Track equipment and also a laboratory for the purpose of research in the
scientific control of concrete ingredients and strength. The last named establishments, however, do
not belong to the Washington Institute of Technology proper, but are closely associated with it.
Aside from the above permanent locations, there are field parties which are established in various
localities as situations warrant. For example, at the present time a party is located in Pittsburgh
because of the installation of Air-Track equipment at the Pittsburgh Airport. The Washington Institute
of Technology is centered at College Park, Maryland with offices in Washington, D. C.
III. FORMATION AND ORGANIZATION OF THE INSTITUTE.
As mentioned briefly above, the earlier developments of an airplane instrument landing system were
first developed at the Bureau of Standards in Washington, D. C. However, the Economy Act, passed by
Congress in 1933, made it necessary either to discharge the scientists connected with this work or to
give them work in which they were not interested. It was at this time that Col. Sidney F. Mashbir organized
the Washington Institute of Technology and invited the Bureau of Standards' scientists to join his organization
and continue their research where it had been so abruptly terminated at the Bureau,
Thus, the chief objective in forming such a company was for the purpose of research and further development
of an instrument landing system. Since that time, the Institute has gained other aims, but still its
predominant work is in the testing and further development of Air-Track.
The Washington Institute of Technology is incorporated in the State of Delaware and the controlling
interest of stock is held by Col. Sidney F» Mashbir, who is the president of the company. At present
the Institute is financially self-supporting due to its income for services rendered to radio stations
and radio engineers which will be explained in more detail later. The Institute is subdivided into two
main divisions, the Aircraft Radio Division and the Broadcasting Division, each of which has its distinct
work to do, although they are very closely connected.
The personnel of the Institute has steadily grown since its inception in 1933. As mentioned above,
the president is Col, Sidney F. Mashbir, while the nucleus of the company still comprises the scientists
who have left the Bureau of Standards - The following men were all originally connected
with the Bureau. Gomer L. Davies is the Chief of the Aircraft Radio Division and Dr. Frank G. Kearia
the Chief of the Broadcasting Division. They were accompanied by engineers Gerald H. Ifintermute, now
the senior engineer of the Aircraft Eadio Division, and the late William Or ton and also by the mechanicians
Hi chard Greene, senior mechanician, who is at present employed at Pittsburgh, Harold Horsman, and Daniel
%brand, Both of whom are employed at College Park, Maryland. From this small group in 1933 the Institute
has grown until its staff now numbers over 20 engineers and technicians.
Several Views of Air-Track Factory at College Park, Maryland
17. THE WORK OF THE INSTITUTE.
A. DEVELOPMENT AND PERFORMANCE OF AIR-TRACK.
The Air-Track instrument landing system is a proposed solution of the problem of landing a plane
safely when the visibility is very poor. It consists essentially of three distinct transmitters — the
runway localizer, the glide path, and the marker "beacons — each of which has its own function to perform.
The runway localizer transmitter employs two loop directional antennae placed at an angle to each other.
It depends for its success on the fact that a loop antennae sends out its maximum power in the plane
of the loop and none at right angles to the loop. If points of equal field intensity be plotted, it
is found that the radiation pattern is in the form of a figure eight. When two loop antennae are used
in conjunction at an angle to each other, the points of similar field intensity from each loop overlap,
giving four paths at right angles to each other along which the radiations from both loops are of equal
intensity. One of these paths is directed down the runway and by his instruments the pilot can determine
whether he is to the right or left of the runway, since the field intensity from one loop will be greater
than that from the other loop if the pilot is off his course. Naturally, it will be necessary that the
radiations from the two loops be different in form in order that it will be possible to distinguish
between the two and thus determine in which direction the pilot is off the course. Formerly this was
accomplished by use of the "interlocking A and K, signals." This merely means that the A ( • — ) is
sent out on one loop, while the N ( — •) is sent out on the other. However the signals alternate. In
other words, the dash
Note Cross-Pointer Instrument above Instrument Panel
Schematic Diagram Showing:
(1) Boundary Marker Beacon
(2) Control Room
(3) Trailer in Position
of the N would "be sent out on the first loop; followed by the dot of the A on the second loop; followed
by the dot of the N on the first loop, and that in turn followed "by the dash of the A on the second
loop, and then repeat the cycle. If the pilot was on his course, the signal he received in his phones
was a steady Team, which would change to a condition where one signal predominated if he strayed from
his course. However, this system proved undesirable and has been replaced in Air-Track equipment by
a modulation system, wherein the carrier wave has a frequency of 110 megacycles which is modulated to
a frequency of 90 cycles in one loop and 150 cycles in the other loop.
These impulses are separated in the plane by means of a reed-converter. This merely consists of two
vibrating reeds, each of them having a natural vibrating frequency coinciding with the modulated frequency
from one of the loops. The output from these reeds "buck" each other and actuate a vertical pointer
which swings to the right or left as the field intensity changes. Thus, when it is exactly vertical,
the pilot is on his course.
This runway localizer beam gives the pilot guidance in the horizontal plane so that he can head directly
down the runway. However, he also needs guidance in the vertical plane so that he will land at the right
point. This is the function of the glide path transmitter. The points of equal field intensity lie on
a curve similar to the one shown in the accompanying figure* Of course an infinite number of such curves
exist. This is utilized by tuning the receiver in the plane to the particular curve best adapted to
the natural gliding angle of that plane. Also by varying the output of the transmitter these curves
can be raised or lowered in order to clear obstacles or flying hazards.
General Shape of Curve Joining Points of Equal Field Intensity Emitted by the Slide Path Transmitter
The Pilot Follows the Lower Portion of the Curve
Ordinarily there would tie similar curves emitted to the rear of the transmitter and away from the
runway. However these are removed "by the use of reflectors thus leaving only the desired curves down
The output from the receivers actuate a horizontal pointer which goes above or below its neutral
position to correspond with the position of the plane above or below its predetermined path. This instrument
is so constructed that, if perchance the receiver or transmitter should cease to operate, the pointer
will fall below the horizontal, indicating to the pilot that he is below his path and he will climb,
thus placing himself out of danger*
By combining the runway localizer and the glide path, the pilot has guidance in both the horizontal
and vertical planes. However, it is highly desirable that the pilot should know his approximate position,
relative to the field* This is accomplished by placing a marker beacon at the approach end of the runway
and also another at a known distance beyond the end of the runway. As the pilot flies through the vertical
"curtain" sent up by the marker beacons, be hears a tone in his phones and a light flashes on his instrument
panel. This enables him to tell them he is over the field. The marker beacon aerial is permanent in
position and is strung close to the ground. Thu3 it interferes in no way with the landing of the plane
and is not a flying hazard.
The frequency used on the runway localizer transmitter is 110 megacycles; that of the glide path
transmitter is 91 megacycles, and the marker beacons operate on 75 megacycles. There was considerable
difficulty encountered in developing the present ultra-high frequency transmitter used for the localizer,
however it is much superior to the original type, since it is not as readily affected by weather conditions.
Also this system is unique in that all the ground equipment, except the marker beacon, is located in
Pictorial Diagram of Air-Track Equipment in Operation at Pittsburgh Airport
The first installation for instrument landing of aircraft under regular airline operating conditions,
has been completed at Pittsburgh for use by Pennsylvania Central Airlines. Photo shows Air -Track portable
transmitting equipment stationed on west end of 5700 ft. runway of Pittsburgh's famous all -paved airport;
also alternate positions at ends of other runways — the action of glide path, localizer and marker beacons
— and of cross-pointer instrument by which pilot lands.
Marker beacon at edge of field informs pilot when he crosses boundary, by sound in earphones and
light flashing on instrument panel
Four course localizer, range 20 miles, actuates vertical needle. One beam projected along center
of runway. Pilot knows when right or left of course; obtains position anywhere within 40-mile boundary
of field; actuates horizontal needle.
Trailer can easily be disconnected, towed to another position, connected and transmitters placed
in operation in a few minutes.
automobile trailer which may lie moved from one runway to another to correspond with the prevailing
weather conditions. This makes a single installation serve any number of runways. An added safety device
is the automatic monitoring system which is located in the trailer and consists essentially of a receiver
which insures that the transmitters shall operate within closely prescribed limits. If not within these
limits, the transmitters are shut off and a warning signal is sent to the control tower at the airport,
from which the proper adjustments are made.
The equipment in the plane is very simple, consisting merely of a receiver employing a detector circuit
and two stages of audio amplification. It is very compact in form and all of the equipment, with the
exception of the control box» can be located at any convenient place in the plane. Thus the only part
of the equipment which must be in the pilot's cockpit is the control box and the visual cross-pointer
instrument on the instrument panel. This use of the visual indicator instead of the older aural method
marks a long step forward, inasmuch as it allows the pilot to maintain voice communication with the
airport throughout the entire time interval of landing.
The introduction and general use of such an instrument landing system should have a tremendous effect
on airline development in the future. First and most important of all, it will promote safety especially
in bad weather and decrease materially the number of accidents which occur at airports during the approach
and landing operations. In addition, it will facilitate traffic control at airports and make it possible
to land more planes in the same amount of time, thus relieving congestion at the more crowded airports.
Also it will make possible the establishment and maintenance of regular airline schedules in spite of
the weather. This will result in a tremendous increase in the number of passengers to travel by airplane,
if they can depend on the printed schedule.
Airplane Recently Acquired "by Air-Track for Experimental Purposes
With so many obvious advantages in the use of such a system, it is logical to ask, "Why has it not
been adopted and in general use?" There are many reasons for the delay. It is the general belief that
its installation will have to come as a Federal aid to airports because of the cost. At pre- sent, the
Bureau of Air Commerce has no authority to use its funds for airport improvements but only for airway
aids (between airports). Such authorization must come from Congress which introduces considerable question
as to its probable time of. adoption. Furthermore, it will be necessary to first agree on a system which
is acceptable to all concerned and then to train pilots in its use. All these details require time and
must be further developed before adoption.
B. THE WORK OF THE BROADCASTING DIVISION.
In addition to the work done by the Washington Institute of Technology in the testing and development
of Air-Track equipment, it also renders valuable service to radio stations and radio engineers. These
services cover many fields and, while some are routine duties, others require much technical knowledge
and foresight. All, however, are very necessary to commercial radio stations.
Under the head of allocation engineering are included all the details and considerations which enter
into the allotting of frequency bands to radio stations. This work is concerned mostly with the opening
of new stations and the insurance of their proper operation. Also in connection with this work, the
Institute conducts site surveys. These surveys are made to determine the effect of buildings, ore deposits,
etc. on transmitters, and to determine the most advantageous place at which to locate a permanent radio
The Radio Laboratory of the Washington Institute of Technology at College Park, Maryland
station. In order to do this, portable transmitters are set up at the place in question and the location
tested. Such surveys eliminate the guess-work in the location of a station and prevent the construction
of an expensive broadcasting station only to find that it is in a poor location.
The Institute also conducts coverage surveys for radio stations already in existence in order to
determine the strength of the emanations from the station and the amount of territory which a radio
station serves. This has an important commercial aspect since the station can base its charges to commercial
advertisers on the number of people which it reaches. This is especially important in metropolitan areas.
In addition, the Institute also is doing important research work in the development of proper designs
for directional antennae in order to prevent interference between radio stations. Furthermore, it develops
and constructs all manner of antennae tuning and phasing equipment. This construction is done at College
Park, Maryland and the equipment is sold to radio stations and radio engineers.
In addition to these services, the Institute conducts a frequency monitoring service consisting of
routine tests on operating stations to determine their frequency accurately. The frequency of the station
is calibrated against the signal received from the Bureau of Standards by telephone which is accurate
to one cycle in ten million cycles over a period of one minute. By comparing the two signals and counting
the number of beats, the number of cycles that the frequency being tested is in error may readily be
determined. This is done periodically to insure that the station is within the limits prescribed by
the Federal Communications Commission and is conducted for the benefit of the radio station. This work
is all done on a contract basis and helps materially to make the Institute financially self-supporting.
C. OTHER DEVELOPMENTS OF THE INSTITUTE
Although the development of Air-Track and the services rendered to radio stations, as described above,
constitute the major part of the work done "by the Washington Institute of Technology, there are several
additional developments which are worthy of note. The Washington Institute of Technology holds patent
rights on many important developments, largely in the realm of radio* These include several important
innovations in the design of directional antennae. Also an improved radio direction finder has been
developed largely in connection with its aeronautical experimentation. Another device known as the gun
compass has also been perfected. This is a variation of the earth inductor compass and finds its chief
application in small boats, since it is not so readily affected by the rocking motion. Another development
consists of a low capacitance cable for use in ignition systems of airplanes or automobiles, giving
a hotter and larger spark. It has been used for several years in Naval aircraft. These developments
are merely a few of the many patents held by the Washington Institute of Technology.
There is one other organization which is closely allied with the Washington Institute of Technology
and should be mentioned. It Is known as the Scientific Concrete Service Corporation. Its organization
is entirely separate from the Washington Institute of Technology. However, actually, it is closely allied.
It holds a position similar to Air-Track. Scientific Concrete Service Corporation has developed a means
of accurately controlling the ingredients of a mixture of concrete. By insuring a precision control
of these ingredients, especially water, it is possible to effect a saving in cement and also insure
more uniform strength in the final concrete. The Corporation also has an establishment at College Park,
Maryland. Thus at College
Park, Maryland is located the Washington Institute of Technology laboratory and its two "manufacturing
associates", Air-Track and Scientific Concrete Service Corporation.
Until the present time, the Washington Institute of Technology has "been very successful in its developments
and has steadily grown in size. It renders valuable aid to radio stations, and if instrument landing
systems are installed in all airports, as they probably will be in the future, their services will be
in demand because of their previous experience. If the system adopted is Air-Track, the Institute will
grow much faster. In the light of the above observations, it is the opinion of the writer that the Washington
Institute of Technology will continue to grow in the future, barring unforeseen difficulties of a financial
or technical nature.
Before concluding, the writer would like to express his sincere thanks for the courteous aid which
was extended to him by members of the Washington Institute of Technology staff, and especially to Dr.
Frank G. Kear, Chief of the Broadcasting Division, and Mr. Charles 1. Planck, who have been most obliging
in extending the information needed for a thesis of this nature.
"Report on the Status of Instrument Landing Systems"
V f . 3. Jackson, Chief of Radio Development Section, Bureau of Air Commerce, Safety and Planning
"The Washington Institute of Technology Air-Track System of Instrument Landing"
"by Hemy W, Roberts in "Aero Digest", April, 1937.
"Under The Weather "
"Fortune Magazine", June, 1938 Air Commerce Bulletins
#23, Volume I, Pages 5-6 # 8, Volume I, Pages 15 - 16 #20, Volume II, Page 526
Bureau of Standards Research Papers No. 435 and Ho. 581
Dr. Frank 5. Kear, Chief of the Broadcasting Division of the
Washington Institute of Technology Mr. Charles S. Planck, Publicity Manager of the Washington
Institute of Technology
Posted October 7, 2016