WW1 "Radar"

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

Aerowerx

Well-Known Member
Joined
Dec 1, 2011
Messages
5,452
Location
Marion, Ohio
Well, not exactly radar. Acoustic actually, but quite clever I thought.

You can see a picture of one here.

And here is a transcript of the article:
Scattered across the U.K. today are huge concrete blocks with concave divots cut out of them. Most people who see them don't know their true purpose: A hundred years ago, the British government built these monumental structures as a way to pick up the sounds of approaching airships and know the Germans were coming.
If you think of sustained air raids against London, you probably think of the Nazi blitz of World War II. But that wasn't the first. Instead, the distinction rests with Germany’s zeppelin force of World War I.
Loaded with bombs, these airships crossed the Baltic and North Seas to attack Great Britain, attempting to lower morale and drive Britain out of the war. The German P-class airshipscould carry nearly three tons of bombs. Powered by four Maybach 3M C-X 6-cylinder inline piston engines, they could reach speeds of up to 57 miles an hour.
Germany began bombing targets in the U.K. in 1915, a time before the invention of radar. British engineers dreamed up a network of concrete blocks, each with a concave surface, deployed in the direction of approaching German aircraft. The concave surface would pick up the drone of airship engines before the human ear could, giving time for air and civil defense forces to prepare for the zeppelin's arrival.
The BBC has a gallery of these unusual devices as they stand today, more than 100 years after construction. They vary widely in size and shape, from 30 to 200 feet high. As the BBC explains, the eventual rise of faster-flying aircraft, coupled with the invention of radar, eventually made the concrete solution obsolete. Now abandoned, they litter the English countryside—and at least one was converted into part of a house after the war.



 

lr27

Well-Known Member
Joined
Nov 3, 2007
Messages
3,822
At Haystack, a radio telescope facility in Massachusetts, they used to have two old, quite large TV satellite dishes pointing at each other, 100 or more feet apart. You could stand in front of one and have a conversation at normal volume with someone standing in front of the other. That makes me wonder is they really had to make those sound mirrors out of concrete. Maybe there were some wood ones that have now rotted? Or maybe they were for detecting sound at lower than audible frequencies??

Anyway, thanks for the interesting diversion.
 

Aerowerx

Well-Known Member
Joined
Dec 1, 2011
Messages
5,452
Location
Marion, Ohio
I would guess that you answered your own question---two different ways.

Considering the weather in England, particularly the channel coast, wood would probably not last too long. Remember this was WW1 and they didn't have the wood protection techniques we have now.

Also, with the low drone of the zeppelin engines, the lower pitches would probably carry farther.

It was also probably easier to smooth the concrete into the right shape than bend a bunch of wood to a precise curve. Just cut a single piece of wood to the right curve and use it as a template on the concrete.

What I wonder is...Did they have someone sitting there 24/7, or did they have a vacuum tube amplifier and a microphone. This was at the very early days of the vacuum tube and I don't know if they were available yet.

If I was doing it I would use a telephone microphone at the focus of the parabola and someone sitting inside with headphones (which were available at the time time).
 

lr27

Well-Known Member
Joined
Nov 3, 2007
Messages
3,822
Somehow I think that if the English could keep some wooden buildings alive for centuries, they could keep a wooden dish thing alive for several years. I would also guess that they could make several wood dishes for the amount of labor, wood, and expense required to make the concrete forms for these things. Maybe they expected the dishes to be bombed? I guess it would take quite a few bombs to completely destroy a concrete one.
------------------

Maybe they could call these things on the phone? I suspect, however, that your idea of having someone right there would be more robust.
 

12notes

Well-Known Member
Lifetime Supporter
Log Member
Joined
Aug 27, 2014
Messages
1,018
Location
Louisville, KY
What I wonder is...Did they have someone sitting there 24/7, or did they have a vacuum tube amplifier and a microphone. This was at the very early days of the vacuum tube and I don't know if they were available yet.

If I was doing it I would use a telephone microphone at the focus of the parabola and someone sitting inside with headphones (which were available at the time time).
From the BBC article with the pictures: "Interestingly the Kilnsea mirror is one of the only structures to still have the remnants of the metal microphone pole that would have originally been used."
 

Aerowerx

Well-Known Member
Joined
Dec 1, 2011
Messages
5,452
Location
Marion, Ohio
Somehow I think that if the English could keep some wooden buildings alive for centuries, they could keep a wooden dish thing alive for several years. I would also guess that they could make several wood dishes for the amount of labor, wood, and expense required to make the concrete forms for these things. Maybe they expected the dishes to be bombed? I guess it would take quite a few bombs to completely destroy a concrete one.
------------------

Maybe they could call these things on the phone? I suspect, however, that your idea of having someone right there would be more robust.
Remember the Brits don't exactly think the same way we do!;)
 

Pops

Well-Known Member
Log Member
Joined
Jan 1, 2013
Messages
7,863
Location
USA.
Thanks , learn something new every day. I love history.
 

Jerry Lytle

Well-Known Member
Joined
Jan 3, 2014
Messages
356
Location
Newport, Oregon
There are couple of possible reasons to construct these out of concrete. First they needed to be very resistant to outside vibration either from wind or other local disturbing factors. A second could be the precision of reflector. Possibly a reusable form wood or metal for the reflecting surface. The tolerances could be easily controled by hand placement of the concrete mixture against reflector form.
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
7,376
Location
North Carolina
Concrete is a much better reflector of sound than wood. A good reflector only needs to be accurate to 1/10 of a wavelength. I don't know the frequency on the Zeppelins, but 100Hz as a total guess would only need a reflector accurate to 13".
 

Aesquire

Well-Known Member
Joined
Jul 28, 2014
Messages
2,402
Location
Rochester, NY, USA
Acoustic dishes were used in both sides in Europe in WW2. For early warning & to track raids.

It's a passive system, you have no way to know if you've been detected.

The Soviets also had an extensive network of acoustic listening posts in their air defense network.

The science center in Toronto has reflectors at both ends of it's big "cool science toys" hall, with stairs up to a plastic ring at the focus. Total cacophony of screaming children and equally noisy adults, but you can carry out a quiet conversation with a person at the far end of the hall. Neat!
 

BJC

Well-Known Member
HBA Supporter
Joined
Oct 7, 2013
Messages
10,797
Location
97FL, Florida, USA
Acoustic dishes were used in both sides in Europe in WW2. For early warning & to track raids.

It's a passive system, you have no way to know if you've been detected.

The Soviets also had an extensive network of acoustic listening posts in their air defense network.
The AVG used an acoustic system too; they relied on reports from people hearing approaching Japanese flights.


BJC

Edit: Also SOSUS
 
Last edited:

Aerowerx

Well-Known Member
Joined
Dec 1, 2011
Messages
5,452
Location
Marion, Ohio
IIRC, the Soviets had a bunch of microphones scattered around Siberia.

Listening for low flying B-58's I guess.
 

lr27

Well-Known Member
Joined
Nov 3, 2007
Messages
3,822
Such a system could be quite sophisticated now. I understand that some urban areas have a microphone system which is good enough to locate gunshots. This might be useful against stealthed aircraft as well. In that case, some of the techniques developed for sonar would probably be helpful. Hmm... I could see information derived this way being added to ADSB. Eventually. Maybe tracking flocks of birds, too, keeping airplanes out of the Hudson. I suppose you can find those with radar anyway.
 
Top