Shadow and Sirens

[Robert Gift]

We may get to see this siren, in Yantai, China, again in 2009!


I suggested my wife now visit her aging parents every year, not every two years.

July 22nd, 2009 a total solar eclipse will be seen in China.
We should try to combine visiting her parents with going to Shanghai to be in the path of totality.
This is likely the closest we will ever get to this rare phenomena in our lifetimes.
Her parents and sister and sister's husband laugh at me.
"Who care see moon shadow?"

(I have been in moon shadow once! - La Paz, Mexico, June 1991. Anyonelse here been in the moon's shadow?)

Then we should be present when Yantai performs their annual air raid siren test August 15th. Hopefully this siren won't fail to operate as in 2006.




We were in China during the horrible May, 2007 earthquake. Nothing was felt in Yantai.
We learned that a week later China would mourn her dead with sirens, ship and locomotive horns, etc.
We climbed to the top of the hill to see this siren.
Surprisingly, some other Chinese people made the climb to also see it!
This siren was not raised and operated.
But we heard the one pictured at the top.

[CABLEVision]

I've heard that, those sirens have a magnet on the chopper and one on the stator, so it always is shut when power is off. Is that right?
Seems like if there was a magnet it would make the chopper un-balanced.


PS: Are you going to be there for the Olympics?

[Robert Gift]

I've heard that, those sirens have a magnet on the chopper and one on the stator, so it always is shut when power is off. Is that right?
Seems like if there was a magnet it would make the chopper un-balanced.

You are correct.
The stator ports blocked by the red rotor vanes.
When I moved the rotor, as it stopped, it reversed direction as though pulled by a magnet and parked closed.
I never found the magnet, but had to get out of there.
I assume there is one magnet and each vane has magnetic metal.
Very clever design to keep out birds, insects and snow.

(After I test my 2t22, I move the rotor so that both 10-port and 12-port
stators are blocked.)

PS: Are you going to be there for the Olympics?

No. Far too expensive and my wife would not want to be even near Beijing with all the people, pollution and August heat.
Too bad they could not do this at a better time - like September.
Chinese have this superstition about the number eight.
This is eighth year, eighth month, eighth day.
Wonder if Opening Ceremonies start at 8 p.m.?

[Daniel]

Don't the Chinese also consider the number four unlucky, and often request that their license plates and addresses not have a 4 on them? I'd heard that the Mandarin word for "four" is a slightly different tone from the word for "death," or something like that.

With that siren, the magnet may be embedded in the rotor and stator, or perhaps inside the motor itself. Could there be an active electromagnet that activates when the motor is shut off? That would not only close the ports but also slow the rotor speed faster.

[Robert Gift]

Don't the Chinese also consider the number four unlucky, and often request that their license plates and addresses not have a 4 on them? I'd heard that the Mandarin word for "four" is a slightly different tone from the word for "death," or something like that.

You are exactly right - as usual.
The number four sounds just like the word "death". Same in Japanese.

With that siren, the magnet may be embedded in the rotor and stator, or perhaps inside the motor itself. Could there be an active electromagnet that activates when the motor is shut off? That would not only close the ports but also slow the rotor speed faster.

I assume there is one magnet which pulls on whatever rotor fin stops closest, centering the fins over the stator openings.
I failed to count the ports, but doubt the motor had the same number of poles so that this could be accomplished internally.
Also it would require less "torque" if it could act on the outside circumference of the rotor.
The siren coasted down normally.

I would hate to hear one artificially slowed, except that I have applied the brake to a Q as we neared scene.

Looking up into the rotor intake:


Looking though a port into the rotor chambers: