Category Archives: Aviation history

The LFR: 1920’s-1960’s Air Navigation

From the late 1920’s until the 1960’s, an important tool for air navigation was the Low Frequency Radio Range (LFR).

At its peak, there were about 400 LFR beacons in the United States, and many more worldwide. Each station consisted of a transmitter being fed into two directional antennas. One antenna was sending the Morse letter “A”, dot dash. The other antenna was sending the letter “N”, dash dot. The two signals were synchronized so that the two signals alternated. At four directions from the station, the two signals blended to produce a constant tone. If a plane was off this course in one direction, the pilot would hear the “A” start to get stronger. Off course in the other direction, the “N” would get stronger.

Aeronautical charts such as the one shown here would show the letter that would be heard in each of the four quadrants. Here, in the quadrants south and north of the station, the pilot would hear the letter “N”. In the east and west quadrants, he would hear the letter “A”. On the shaded lines, the pilot would hear the continuous signal. These “beams” would be about a half block wide near the station, and as much as several miles wide far from the station. Most air navigation followed routes along these beams. The course a pilot followed would be along airways connecting the stations, and flying cross country would be a game of “connect the dots” as the pilot flew from one station to the other.

Every thirty seconds, the “A-N” signal would be replaced with the call letters of the station, in this case, RL, which would also be transmitted in Morse.

Despite the simplicity of the system, the accuracy was enough to use for instrument landings, and instrument approaches using the LFR beacons were published for many airports.

For the pilot, only a normal radio receiver was required. In later years, more sophisticated receivers were employed, which would show the pilot visually whether he was on the “A” side or the “N” side of the beam. But in most cases, the pilot navigated by listening to the signal in his headphones.

LFR station using Adcock antenna (Wikipedia photo).

LFR station using Adcock antenna (Wikipedia photo).

Most of the stations operated between 190 and 535 kHz, with powers of up to 1500 watts. Early stations used crossed loop antennas, but Adcock antennas (phased verticals) were used in most later stations.

Directly above the station, there was an inverted “cone of silence” where the directional signal disappeared. Even in times of no visibility, the pilot would know that he had passed over the beacon when the signal disappeared.

Starting in the late 1940’s, the LFR began to be replaced by the VHF Omni Range (VOR). While the VOR required a special receiver in the aircraft, it was superior in that it could be used to “fly a beam” in any direction from the VOR station, rather than just the four possible with the LFR.

bc1206

Photo courtesy of Ian O’Toole, VK2ZIO, Kurrajong Radio Museum. Used by permission.

Shown here is a BC-1206C Range Receiver, which would have been installed in the aircraft for the purpose of receiving the beacons. This radio, manufactured by Setchell Carlson, Inc., of St. Paul, Minnesota, is a five-tube superheterodyne.  As you can see from the schematic, it’s not much different from a standard broadcast receiver.

REFERENCES

Click Here For Today’s Ripley’s Believe It Or Not Cartoon



Americans Enlist in Canadian Air Force, 1939

Seventy-five years ago today, December 4, 1939, the Canadian Government announced that U.S. Citizens would be permitted to enlist in the Royal Canadian Air Force. Recruits were required to be of “European descent and resident in Canada.” However, the Canadian government, eager to recruit American aviators, was quite lax on the “residency” requirement. Residency meant only that the applicant must be in Canada at the time he filed his papers.

This, of course, would have been a violation of American law and American neutrality. But even though 9000 Americans eventually enlisted, I’m not aware of a single case of an American being prosecuted for service with the Allies.

The Canadians had even been quietly recruiting in the United States, even though this was clearly a violation of U.S. law. Americans were initially required to pledge his allegiance to the British monarch, which could potentially lead to loss of U.S. citizenship. At some point, however, this was relaxed, and American recruits were required to merely obey RCAF rules and discipline for the duration of the war.

Some Americans had already enlisted. For example, De Peyster Brown, an American pilot who served in the Battle of Britain, had enlisted in the RCAF on September 9, by claiming to be Canadian.

 

References

The Americans in the RCAF



German Bird’s Eye View of Paris, 1914

ArizonaRepublican101014

A hundred years ago today, October 10, 1914, the Arizona Republican carried this aerial photo of Paris, taken from a German aeroplane. The paper notes that the pilot and photographer, one Lieutenant Thin, had received the Iron Cross. Undoubtedly the intended audience for this photo was the French: If the Germans can take a photograph from the air, then they can drop a bomb from the air, which is exactly what they had been doing.

In other war news, the papers were reporting that Antwerp had fallen, and that the Belgian government had reconstituted itself inside France.


Bombing of Paris, 1914

ParisBombs

A hundred years ago today, German zeppelins bombed Paris, Warsaw, and other cities.  The map above, from the September 28, 1914 issue of the New York Sun, shows the locations of the Paris bombs, near the Eiffel Tower.  In Paris, three were killed by bombs, one of which landed at a spot the American ambassador had passed only minutes earlier.

In Calais, bombs were dropped but failed to explode.  And the Poles managed to shoot down the zeppelin bombing Warsaw, taking the crew prisoners.

See also:  Fall of Paris, 1940

 


French WW1 Airship

FrenchBlimpThis photo, from the August 30, 1914 issue of the New York Sun, shows a French airship and British warships guarding shipping in the English channel. The paper also reports that German troops are now only 87 miles from Paris.

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