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Aerobeacons

Forum to discuss all areas of lighthouse technology such as optics, fuels, fog signals, radiobeacons, daymarks, construction, etc.

Postby Zachary » Mon May 30, 2005 9:09 am


What's the difference between a DCB224, 24, and 36 (if I missed any, let me know) aerobeacon?
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Postby Terry_Pepper » Mon May 30, 2005 9:00 pm


Zachary,

From what I have recently read, I believe the DCB-24 was so named as a result of its being approximately 24" in diameter, and the DCB-36 as a result of its being 36" in diameter.

I further believe that the DCB-224 was used to denote tandem mounted 24's.

I have a page on these oft overlooked optics at the following URL:
http://www.terrypepper.com/lights/close ... dcb224.htm

I would appreciate any additional insight anyone may be able to shed on the subject.
Terry Pepper
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Postby Lampist » Tue Jun 07, 2005 3:44 pm


Zachary & Terry:

Just a bit to add to what Terry has already said about DCB's. The DCB or Directional Coded Beacon was developed by the Lighthouse Service in response to the need to light airports or aerodromes when trans-continental flights were coming into vogue in the 1930's. Its hard to find an airport at night when it isn't lit. It was designed under a request from the Civil Aeronautics Board (today's FAA). Once it was developed the LHS realized what a useful thing they had built and started replacing many of the, difficult and expensive to maintain, Classical Fresnel lenses with them.

There were two standard sizes, the DCB-24 and the DCB-36 and as Terry pointed out they were 24 and 36 inches in face diameter. They could be placed back to back so that their beams would go out at 180 degrees to each other and they could be stacked, 2 above 2 and staggered 90 degrees and then you would have a beam every 90 degrees. You can also stagger them in other ways to produce even more unusual characteristics.

Their rotation speed is adjustable and they can be set to rotate at 1, 2, 3, 4 1/2, 6 or 12 revolutions per minute. So, if you had a single DCB rotating at 12 rpm you would see a flash every 5 seconds, with a double you'd see a flash every 2.5 seconds and with a stacked double you would see a flash every 1.25 seconds. So it was just about as fast as a mercury float lense with none of the hastle or expense. Their candle power was regulated by both the bulb used and the beam spread that was accomplished by using different lenses called spread rondels. A DCB using a 1000 watt bulb and a 6 degree beam spread would exhibit 1,100,00 candlepower, with an 18 degree beam spread 240,000 cp and with a 36 degree beam spread it would produce 140,000 cp. With a red shade it would produce 22% and with green 20% of the above cp. With a parabolic mirror and a clear lens with no rondels the cp was increased by 60%. So you can see that it is a very versatile little critter. ANd to top it all off it was weatherproof so it could stay outside and not even know it. The only problem with that was that they do have a pretty large "sail area" and a high wind will slow them down or even stop the rotation if they ar not covered with a lantern room.

I hope this information is helpful.
Jim Woodward
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Postby Zachary » Tue Jun 07, 2005 3:52 pm


Yes, it was, you seem to know quite a bit about Lighthouse Optics
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Postby Lampist » Tue Jun 07, 2005 3:58 pm


Zachary:

I hope I do. I've been working with them for 40 years.

Please take a look at my website at www.lighthouseconsultant.com and you find out more.
Jim Woodward
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Postby Terry_Pepper » Tue Jun 07, 2005 4:32 pm


Woody - Thanks for the additional information.
Terry Pepper
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