Thursday, August 13, 2015

The long forgotten beam (reprint)

On the Beam



DakotaNorwayThe old-timer sat in the pilot's lounge with his coffee, listening to the student pilots discussing their navigation assignment. Like dolphins bounding to the water's surface, keywords occasionally reached his ears: "Waypoints," "VORs," "GPS," "Radials" "OBS," "Compass locators," "DME," "Victor-Airways."

He shook his head smiling wistfully and stared at his coffee. So much has changed, he thought. Student pilots don't even get sent to the hangar for a bucket of prop wash anymore.
The old-timer's mind drifted back to the '40s, when he was a young airline pilot. Radio navigation was so different then. "A" and "N," which side on this leg?
While early flashing beacons were economical and a great aid for night-time navigation in clear weather, they were of no value in overcast conditions, or during the day when they weren’t even turned on. And they were sometimes difficult to locate in the distracting light of urban sprawl. These handicaps hastened the development of the LF navigation system.
Radio beacons in the 190 to 535 kHz radio band had formed the earliest LF navigation system. These powerful, 1500-watt beacons were spaced about 200 miles apart and defined electronic airways. A pilot flew for 100 miles guided by the beacon behind him and then tuned in the beacon ahead for the next 100 miles. The beam width was about 3° so it was important that the pilot promptly tune in the station in front. At 100 miles and a 3° beam width, the aircraft was "on course" if it were within ±2.6 miles of the airway centerline.
The beacons transmitted two Morse-code signals: the letter "A,"  •   , and its opposite, the letter "N,"   •  . When the aircraft was centered on the airway, or electrical beam, these two opposite Morse-code signals merged into a steady, monotonous, hypnotizing tone. Broadcast of the beacon's Morse-code identification interrupted these tones twice a minute.
If the aircraft drifted off course to one side, the Morse code for the letter "A" could be faintly heard. The greater the drift, the stronger the "A" Morse code signal. Straying to the opposite side produced the "N" Morse code signal.

Four-course radio range 
The four-course radio range. One antenna's figure-eight pattern transmits Morse-code "A," and the other antenna's figure-eight pattern transmits Morse-code "N." The "On-Course" signal develops where the two figure eight-patterns overlap (shaded) and the two Morse-code signals interleave to provide a constant tone.
The illustration shows the beacon's two figure-eight transmission patterns. Where they overlapped was "the beam." One can see that technically, beams weren't actually transmitted. But the term "on the beam" was so entrenched with pilots that it became common usage.
Because of the dual loop-antenna system used, each beacon defined four airways, and hence this system was named the four-course radio range. With the letter "A" to the aircraft's left heading towards the beacon on two of the courses, and to its right on the other two courses complicated navigation. Worse, the letters didn't stay put. When the aircraft passed over the beacon, from inbound to outbound, the letters switched from one side of the airway to the other.
Station passage was marked by a "cone of silence," where the aural tone briefly disappeared as the aircraft flew directly overhead.
When possible, radio-range stations were located near an airport, and situated so that one of the four beams lined up with the principal runway, "thus facilitating radio approach landings under conditions of low visibility."
While not pin-point accurate, the radio-range system was a great leap forward over simple dead-reckoning navigation or flashing beacons.
Pilots became very skilled at flying the four-course radio range. As mentioned, a station identified itself every half-minute. It first broadcast its call letters in the "N" quadrant and then in the "A" quadrant. Pilots could hear both broadcasts. If the two signals were equal volume, a pilot knew that he was "on course." But, for example, if the call sign from the "N" side was louder, he knew that his aircraft was off center and he should adjust his heading towards the other side of the airway. Many pilots found it easier to stay on course by monitoring the call-sign transmissions than by listening to the steady tone.
In fact, a pilot was encouraged to fly off-center from a radio-range beam, to fly the right-hand edge of the beam. This reduced the possibility of encountering an aircraft coming from the opposite direction, particularly when flying IFR in the days before ATC assigned altitudes.
Eighteen months after the four-course radio range system was launched it was deemed essential to aviation. This navigation system revolutionized airline transportation as much as the introduction of the DC-3. For the first time, scheduled air service meant just that. Only infrequently did poor weather or low ceilings or limited visibilities cancel a flight.
When flying through mountain passes in IFR weather or on a dark night, the pilots paid close attention to the tones in their headphones. Palms became moist in the cockpit when static from electrical storms interfered with the reception of those crucial signals—or when beacon signals bounced off the canyon walls and gave false information.

Radio Direction Finding

Lear Radio CompassThere are several types of equipment under this general head. In each case, however, use is made of the directional characteristics of a loop antenna. The loop may be either fixed or rotatable.
The LF radio-range system had two principal drawbacks: it provided no information on the aircraft's position nor whether it was flying to or from a beacon. If a pilot were flying along aknown airway he could extrapolate the to/from situation with a drift off course slightly to pickup the "A" or "N," then deduce from the charts whether the beacon was in front or behind him.
A number of maneuvers were available to a pilot to eliminate the ambiguity of which direction the beacon was relative to his heading, or to determine which quadrant of the radio range he was within, or identify which beam of the range he was intercepting. These maneuvers had names such as the 90° turn method and the parallel method. Useful as they were, they each required a significant deviation from the aircraft's intended course, sometimes even a 180° turn away from the station.
The installation of marker-beacons every 20 to 30 miles along the airway partially informed the pilot of his position. Each beacon transmitted a distinct identification signal and so on passage a pilot could mark his progress to the next four-course station.
The old-timer shook his head again, his thoughts deep into the past.
The Radio Compass was the first glimmer of hope in determining bearings to a radio station, of filling the information void of the four course radio range. It added a fixed loop antenna and visual indicator to the receiver system. With this system, as long as the aircraft was headed directly toward a radio station the needle of the indicator remained centered; headings to the right or left of the station resulted in a corresponding deflection of the needle.
The radio compass was chiefly used as a "homing" device, and bearings of radio stations off the line of flight could be obtained only by turning the aircraft toward the station and noting the magnetic compass heading when the needle was centered.
Replacing the fixed loop antenna with a rotatable loop eliminated this cumbersome maneuver. This system was called a Radio Direction Finder. With the rotatable loop, bearings could now be obtained without turning the airplane itself. The pilot or navigator would rotate the loop, usually mounted on the fuselage below the cockpit, to the position of minimum signal strength, or "null." The bearing to the radio station was then read from a graduated, mechanical dial.
By repeating this procedure with a second beacon an aircraft's position could be determined by triangulation after locating the two stations on the flight chart.
DC-3 showing ADF antennaThe Automatic Direction Finder, a marvelous invention, followed the RDF. Finally, a self-contained apparatus for aircraft navigation was available. Gone were rotatable loop antennas and guess-work readings from mechanical azimuth dials. The ADF indicator needle alwayspoints directly towards the beacon, which now could be a Non Directional Beacon—NDB. Rick Covington's photograph of a Piedmont DC-3 shows the ADF antenna mounted below the cockpit.
The NDB provides good, basic navigation capabilities. An aircraft can follow the ADF needle to home to the station, although this is poor navigation practice—see later. The aircraft can track a specific NDB radio radial—electronic highway—to fly a specific course to or from the NDB station. The pilot can use two crossing radials to triangulate a position for a navigational fix. With a timer, it’s even possible to determine time and/or distance to and/or from an NDB station.
In addition, and probably the most prominent use of the NDB, it can provide an instrument approach procedure for landing. A pilot could now locate a runway without actually seeing it, to descend through overcast and/or low visibility conditions and land the aircraft by reference to the ADF indicator, the compass and the clock or a timer.
Yep, mused the old-timer, as he refilled his coffee, the ADF sure simplified navigation.

Credits


thank-youAlthough I did the keyboarding for this site it contains the fine contributions of many people.
With no prior experience in building a website I was overwhelmed at the generosity of those that I asked for permission to either reproduce their work, or for their technical help, or to use their designs, artwork and descriptions.
Many thanks to those listed below in alphabetical order, who so willingly shared their talent so that I could assemble these webpages:
Bob Austin, of Mission Viejo, California. A scenerio in the VOR Approaches section required an over-kill list of mountaineering equipment for Mr. Benjamin Counter. Counter intends to "scale" southwest New Hampshire's 3165 ft. Mt. Monadnock, the second-most climbed mountain in the world, behind only Mt. Fuji in Japan. Since Florida's highest "mountain" just reaches 345 ft. I had to look elsewhere for an expert. Bob Austin jumped right in, providing an awesome equipment list, which I had to shorten. Any omissions are my work, not his. Bob has the credentials to provide an accurate and complete list, too. In his climbing he's completed six big-walls including two El Capitan routes—The Nose and Triple Direct. Thanks, Bob. Just reading your equipment list I could imagine the wind fiercely blowing off the face of the mountain, daring any climber to move higher.
Wagner Beskow, for his Handy Sheet 3.0. Wagner, a Brazilian in New Zealand taking his Ph.D., assembled this one-page compendium of useful facts for the flight-simmer. "It takes a while for a beginner to find all that information and when he does it's all scattered and difficult to refer to. The idea was to produce something useful that could stay around without cluttering the 'cockpit' too much." Thanks, Wagner. I wish I could say my cockpit was uncluttered now.
Boeing Company, photo of 40-A mailplane. The 40-A, a fabric-covered mail plane, was Boeing's first commercial success. Built in 1927 (the year Charles Lindbergh crossed the Atlantic), it carried mailbags and—load permitting—two passengers. http://www.boeing.com/companyoffices/gallery/boeinghistcom.html
Tom Christine, Electrical Engineer, Federal Aviation Administration. Tom was very helpful on specifics about present-day Non Directional Beacons, including their power levels, uses, their friendly coexistence with GPS, and frequency limits of the LF band. Thanks Tom.
Mario Corral, Sydney, Australia, who sent me the sketch of the homing pigeon. Mario patiently explained to me some similarities and differences between homing pigeons, racing pigeons, and carrier pigeons. Thanks Mario for keeping me on the right track.
Rick Covington, photos of the Piedmont DC-3 in the "On the Beam" section. Thanks Rick ... an excellent photo. You can find more of his photographic expertise at www.airliners.net. He photographed the Piedmont shown here in Durham, N.C.
Mike Genovese for the finest interior shot I've seen of any aircraft. "The shot was taken in Nassau in the early 90's... the plane was just sitting there unattended as we (crew of a major airline) walked by on the ramp... I could not resist the opportunity for the 'Kodak Moment!' ... " Great pic Mike and keep your camera handy as you jet to all those tough destinations. See www.airliners.net for more of Mike's work.
Jesse Kempa for his virtual E6-B calculator program. This program does it all, and best of all, it's freeware. Input True Course, TAS, wind speed and direction and on the click of a button it returns the Wind Correction Angle and Ground Speed. It will calculate distances between points with known lat. and long. coordinates, and on and on. Thanks Jesse for a great utility.internet.oit.edu/~kempaj/e6b.htm
Brian Kostick, the gauge programmer of the very-useful digital Elevator Trim indicator. With it the pilot has repeatability in elevator trim settings. Thanks to Brian, Br5an@aol.com, for an instrument that I rely on and for his quick willingness to let me use it in this panel.
Paul Lutus ... who wrote the freeware HTML editor "Arachnophilia" which I used in assembling these webpages. Arachnophilia is a full-featured, nearly perfect editor—and now v4.0 is even better with a 120,000 word spell-checker. Paul has an outstanding philosophy on life, too. Thanks, although we've never "met." www.arachnoid.com
Alice Marks ... for the extraordinary sketch of McGirr field. That picture is the essence of the intermediate fields that Air Mail pilots aimed for when facing an emergency. Her artistry instantly backed me onto McGirr field—into the new era of Air Mail, with the wind sweeping across the plains, striking me in the face. But then, it should have because Alice Marks's father was McGirr field's caretaker and Alice grew up there. She has a wonderful first-person account of the activities at the field that beats anything you'll read in stuffy history books. Take five and go to her site and relive the experience. http://www.halcyon.com/cliffsan/airmail/air_mail.html. Thanks Alice, twice ... for sketching McGirr field to keep that kernel of history alive and for letting me share it with others.
Ned Preston, Agency Historian, Federal Aviation Administration. Ned provided the chronology on when VORs were introduced, a whole wealth of information on the four-course radio range and on the light-beacon system used to identify the airways at night before radio navigation facilities were in place. Never met a more helpful person. Thanks Ned.
Bill Rambow for his many e-mails answering so many questions. Bill designed the incomparable dual panel for the Douglas DC-3 / R4D / C-47. A restored, flyable U.S. Navy R4D at the Mid Atlantic Air Museum in Reading, Pa. was the model for his work. A finer piece of work I've never seen. Thanks for the encouragement, Bill.
Tom H., "Rumple," a gentleman who always sets his work aside to answer the other fellow's questions. I reaped the benefits of his very-methodical air-file testing. He also designed the manifold pressure gauge for the training panel in my Virtual Airline. Tom is very visible on newsgroups and forums patiently answering questions that are asked over and over. Thanks for being there, Tom.
Sarah at Airline History Website for the photo of the KLM Douglas DC-5 which opens the VOR Navigation section. I only recently learned that a DC-5 had ever existed and wanted to include a picture of it. Since Sarah's site has 350 Airline Histories, 1700 Airline Pictures, and 150 Airliners from 1920 to 1999, I knew it would be there. Why is Sarah interested in all this stuff? ... because she's a pilot—and more. She writes software for and sells IFR flight Simulator programs for real IFR training. Thanks Sarah for the great work that you put into your site.airlines.freeuk.com/airlines
Chris Sheldon, fwog@mindless.com, from the U.K. He photographed G-AMPZ at Manchester Airport, and it appears here in the IFR Charts section. The aircraft belongs to Atlantic Airways (previously called Air Atlantique) who are based at Coventry Airport. The first letter in the registration number, "G," denotes a U.K. aircraft. Chris exhibits his work at www.airliners.net. Thanks Chris.
Russ Strine, Mid Atlantic Air Museum in Reading, Pa. Here's another fountain of information. A very busy man at the museum, he pushed his papers aside and spoke with me for an hour on the telephone about aviation in the old days and VORs and NDBs and answered questions that I just wasn't savvy enough to ask. He gave me some anecdotal stuff, too, that you can't find in books. Thanks for your time, Russ, and all the information. www.maam.org
Barry Thomas, Silversmith, who created the magnificent chalice pictured in the section on tracking ADF's inbound. That section's lead-in story centers around Mr. Benjamin Counter's desire to fly to Meriden, Connecticut, 'The Silver Capital of the World' to buy some silverwork. The chalice pictured was not created in Meriden, nor even in the U.S. Barry Thomas is a silversmith in rural Derbyshire, England. Meriden earned the Silver-Capital title in the late 19th century and it is doubtful that it still retains the rights to that sobriquet. Thanks Barry for the great picture, too. More of his masterpieces can be found athttp://easyweb.easynet.co.uk/bthomas.
Rod Watson, for his stunning photograph of the Gay Head Lighthouse on Martha's Vineyard, Massachusetts. Rod has visited over 170 lighthouses in the US. and the Lighthouse Gallery section of his website, Rod's Photo Gallery, includes photographs of most of those lights, organized by geographic locations. He photographs more than lighthouses, too. Thanks, Rod, for a great picture.Rod's Photo Gallery
Roland Zuiderveld, from Sweden, for his totally awesome picture of a DC-3 descending out of the clouds at dusk to land. Roland also displays his work onwww.airliners.net. Thanks Roland, and if you take any more pictures like this one I want to hear about them.
Many others contributed to my virtual airline webpages and were just as generous. They are identified on that site. Assembling a webpage is so much easier with the assistance of people like these.
With thanks,

Charles Wood 

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