Radio Builds Railroads in the Sky
March 1948 Popular Science

March 1948 Popular Science [Table of Contents] Wax nostalgic about and learn from the history of early electronics. See articles from Popular Science, published 1872-2021. All copyrights hereby acknowledged.

For about a year before the end of World War II, with the surrender of Germany in May 1945 and Japan in September 1945, companies that had either voluntarily or forcibly converted their efforts and facilities to the design and production of weapons and support equipment, were running advertisements in magazines promising grand new products and services for the civil sector based on knowledge gained from "mother," that is the entity metaphorically credited for spurning invention. In many ways the promise was kept through advances in radio, medicine, automation, materials science, recovering and refining of raw materials, mass production, physics and chemistry, firearms, mathematics, land, water, and air-based transportation, etc. Lots of war surplus hardware was made available at huge discounts as a means of thanking the public for sacrifices made during the war. This "Radio Builds Railroads in the Sky" article from a 1948 issue of Popular Science magazine reports on a system of aerial navigation using a triangulation system, which derives from wartime methods.

Radio Builds Railroads in the Sky

By Devon Francis

Borrowing a barrelful of war-refined knowledge about radio and radar, U. S. scientists have come up with a brace of systems for making transport flying as safe and systematic as railroad operation.

One system is called TRICON (for TRIple COincidence Navigation). The other is known as the B-D Computer Aerial Navigation System.

Both are designed to take the nightmare out of navigating an airplane from one city to another when the weather closes down and even the birds start walking. The B-D Computer system also has another feature: it can be adapted for actually landing an airplane automatically with the aid of the federal government's experimental Instrument Landing System (PS, March '46, p. 74).

The present inter-city navigation system, in use for a score of years, has worked pretty well up to now. But the trouble with radio beams, or ranges as they are called, is that in thick weather airplane schedules have to be slowed for safety's sake. A beam provides only two lanes for traffic on any given airway.

The General Electric Co., for which Tricon was evolved, and the Minneapolis-Honeywell Regulator Co., which developed the B-D Computer system, say this is nonsense, and they present some answers.

Under either system, in the air space where only one airplane now flies in soupy weather hundreds could fly in complete safety. Let's look at Tricon first. Ever lose a favorite fishing rod over the side of the boat? After you got control of your temper, you took a line of sight on a tree on shore, and then on another one some distance from it, and calculated the angle between them.  

You did this so you could locate the spot where the rod had disappeared when you returned with a grapple. You oriented your-self. You "triangulated." Tricon proposes to create a whole scad of superhighways for transport planes on every airway in the United States with wholly automatic triangulation by radio.

Navigation by triangulation is nothing new. Transoceanic planes have used it for years. War's Loran system (PS, Feb. '46, p. 78) was, in essence, a means of locating an ocean vessel or plane by measuring angles and computing distances. What makes Tricon interesting is the way its originator, Dr. Luis W. Alvarez, of the University of California, proposes to do his triangulating.

As in Loran, he would use a "master" and a couple of "slave" radio sending stations. Each leg of the triangle separating them would be many miles long. They would "scan" a total distance of about 50 miles.

Families of these stations would be built at intervals along each heavily traveled airway. For every half mile of travel, a pilot would be advised by an indicator on his instrument panel whether he was where he was supposed to be. And this is the way Dr. Alvarez says it would work:

Radio pulses travel at a fixed speed. That's about 1,000 feet each millionth of a second. Now, supposing the "master" sending station and the co-ordinated "slaves" emit signals at the same split second. Any receiving set equidistant from all three stations would experience a simultaneous reception - the signals would come in by TRIple COincidence.

Secret Is in Timing of Signals

But if timing of the signals was slightly off - if the slaves lagged behind the master, for instance, by a millionth of a second - the point where their reception coincided would be 1,000 feet away. The master's signal would have traveled 1,000 feet while the slaves were making up their minds to send.

That's how Tricon sets up superhighways in the sky. By giving the sending stations a progressive change of pace, 500 times each second, 500 successive points at which their signals are received in triple coincidence are established. By juggling the order in which the three stations pulse in each one of those 500 separate cycles, just that many triply coincident signal locations can be spotted along a given airway. At none of them is the sending sequence of the three stations exactly the same.

So far, so good. Why 500 different sending combinations? Dr. Alvarez says the figure is arbitrary. Each traffic highway would need 100 triply coincident signal locations - one for each half mile of the 50-mile stretch being scanned. If there were two outgoing and two incoming highways, that would mean 400 locations. That extra hundred is a "barrier lane" separating opposing traffic, like the white line on the motorist's highway.

That's only the start of Tricon, Now for the gimmick: the system has separate command and control channels. In addition, each airplane using a Tricon airway would be equipped with an automatic "annunciator" radio transmitter. After all, the folks at selected intermediate stations on the ground want to keep track of the planes in the air. They also want to give them orders. So the annunciators would keep sending signals to the ground, and receiving equipment there would keep tab on every plane aloft.

Identification, position, course, altitude, and speed would be automatically recorded. This, in effect, would provide the counterpart of railroading's automatic block signals. Every aircraft would get a flasher signal from traffic control on the ground if it was getting too close to the tail of the plane in front of it, another signal if the plane behind was getting too close to its tail.

It may sound like a third piece of pie after a turkey dinner, but the sponsors of Tricon add that the whole system can be fed into the cockpit autopilot.

Tricon's shortcoming is not one of technical obstacles. Dr. Alvarez says it can be done. What may hold up inauguration of the system or cause outright abandonment of the idea is the expense of its installation.

The heavily traveled New York-Chicago direct airway is a case in point. Today it is served by 17 radio-beam stations. Tricon would replace them with no less than 42 master-and-slave stations, plus a number of stand-by transmitters for use if anything got out of kilter.

As yet, Tricon is only on the drafting board.

The other system for more accurate navigation, using Minneapolis-Honeywell's B-D Computer, not only is far simpler, but it has a running start on Tricon. The computer is in experimental use and has been recommended for adoption by the international airline trade association, ICAO.

It is a combination of an electric brain and a bird dog. The brain figures out the answers from all the variables - winds, distance, route, and aircraft speed - and the dog points where to go. The B-D will not do everything Tricon proposes to do. It won't keep ground stations posted as to the positions, courses, and altitudes of planes in the air. It won't flash red lights if there is danger of collision.

But the company originating it says it will raise today's "one-lane country roads" aloft to the status of 10-lane superhighways. Like Tricon, it will provide aircraft with a large number of flight paths on any given airway. That means added safety. Moreover it can be adapted to automatic landings.

B-D Computer operation requires three elements - the computer itself, a series of omnidirectional radio beacon stations (ODR), and distance-measuring radio transmitters (DME). ODR stations are now being set up by the government.

Can Set Up Hundreds of Airways

ODR differs from the conventional radio beam, emitting "A" and "N" Morse signals to keep a plane on course, in that it sprays a direction-indicating signal out to every point of the compass. Ordinary radio beams provide four airways, no more. ODR could provide hundreds, if necessary. Its freely scattered signal could be only confusing if it were not combined with a cockpit dial and needle pointing unerringly at the transmitting station. A pilot needs only to tune in the proper frequency. The needle says, "There's where you're going."

The needle gives him a line of position. He knows he is on the right road. What he doesn't know is how far along the road he may have come since taking off. So DME, issuing from a ground station too, is introduced. DME is only a variation of war-time's Shoran (PS, Aug. '46, p. 128). DME tells a pilot how far he is from a radio transmitting station. If he already knows he is on the right road, he has all the information he needs.

The beauty of the B-D Computer is that a dispatcher at an airport can send large numbers of airplanes separately down parallel lanes to the same destination. Planes can fly "off course" and remain on course.

A pilot figures his winds, altitude, and the course he has been told to follow before he enters his cockpit. These facts he feeds into the computer. If he is to fly 15 miles off to one side of a straight line between take-off and destination, he turns some knobs and loads the responsibility on the computer.

Then he feeds juice into the device. Instantly it begins digesting two signals - one from ODR and the other from DME. One signal gives him the compass bearing, the other the distance. A pilot can fly by watching the needle on his dial, manipulating his controls to keep it centered, or if he likes he can feed the computer's answers into the autopilot and sit back with the funny papers.

The plane will hold its track right up to its destination, turning from "off course" to on course at the proper moment. The computer takes head winds, cross winds, and tail winds in stride, and will switch from one ODR station to the next automatically.

It can be made to do other tricks. It will work a dial giving a pilot his estimated time of arrival at an airport. If he is advised in flight to slow down and come in for a landing 25 minutes later to avoid "stacking," he can consult the computer for the airspeed he should maintain to meet the new schedule. And, ODR, unlike the radio-beam system now in use, isn't affected by static.

The B-D Computer system, too, supplies a third piece of pie on top of the turkey. Just throw a switch. That feeds ILS (Instrument Landing System) signals into the autopilot in place of the ODR signals, and the plane proceeds to land itself.

Posted April 4, 2024