Horological Meandering

It took several months of negotiating, but I now own the rarest of Soviet military chronometers. It is a completely new and unused 13-20YM Air Force Chronometer with ALL the installation components. Made in 1973, it is so pristine that it came to me still packaged in its original 1/8-inch steel box, just as it left the factory more than 35 years ago.

The papers that accompany the kit indicate that it was originally sent by the factory to military unit No 13815 in Balashikha town near Moscow.

This chronometer was designed exclusively for the cockpits of long-range Tupolev strategic bombers. It was used to generate precision time signals for navigation and targeting systems. Fold-down flanges on the sides of the oak box were bolted to the navigator's cockpit panel. The mechanical time signal it produced was converted to 1-second electric impulses that were transferred via the 3-dial 'calculator box' to the plane's navigation & targeting systems. The small silver-colored metal box is a signal filter.

The movement in this chronometer is a modified version of the one that is found in the more common 6MX marine chronometer. Specifically, a lever escapement mechanism has been added that makes the movement less sensitive to the high-frequency vibrations produced by the aircraft in flight. The movement is also suspended from a brass ring by 4 sturdy springs that further reduce the effects of vibration.

The chronometer is accurate to a 1/4 second a day and has a 50-hour reserve. There is also an automatic thermostatically controlled heater, an electrical fuse, and a light that comes on when the lid is lifted.

If you would like to see additional information and photos, send me a PM.

Eat your heart out Dr. Strangelove...

-- Mark

nt

Wow Congrats you've got yourself a very important piece here

Any way I can get a similar piece?

Congrats on the fantastic addition to a fantastic collection.

- SJX

if your chronometer had been "used" in real life......er......death ! 

That is an absolutely marvelous find and historical record.

Thanks for sharing, Mark.

 

Regards,

MTF

No message body

a great piece of soviet military history Mark.

best

Graham

If that is correct, it puts a lot of big  brands to shame.

Congratulations Mark for sharing the historical timepiece with us.

Regards

Ling

Puts my AP Survivor to shame.

That's way cool. Great workmanship as well.

Thanks for showing us. Any possibility of seeing the movement?

Andrew

NT

Because the seals on the 'new' chronometer are intact, I cannot open it to photograph the movement. However, I have 2 other examples of the same exact model, so I have shot the movement of one of these (collection No. 0256). Please be cautioned that this one is in really used condition. It obviously served a long and productive life before it was removed from the cockpit when the plane was decommissioned.

-- Mark

In the last shot, there is a small wheel perpendicular to the plates.  What does it do?
A

The movement causes the small arm to beat against the wheel very precisely, once every second. Each time it touches the wheel it completes an electrical circuit which sends an electrical pulse via the 3-dial 'calculator' box and signal filter to the plane's navigation and targeting systems.

Although it looks like a gear, the small wheel doesn't turn. It is stationary. It is, however, manually rotated every once in a while to allow the arm to beat against a 'clean' area. If you look closely, you can see 2 blackened spots on the wheel in the photo where the steel has carbonized a bit. These are areas where the beater arm previously made contact to close the circuit.

- Mark

I will be looking at it all evening.

Awesome!

amerix

Great Mark,

 

Fusee and chain, conical hairspring, lovely functional finish but still aesthetically beautiful.

 

Thanks again for sharing this piece and the winding procedure below.

 

A whole other area of horology I know little about and I am getting that ‘tingle’ again. The thirst for knowledge is a great human trait.

 

Andrew

I should add that the jewels that encase the balance spindle are specially cut natural diamonds. The Soviets reasoned that if ruby jewels (Mohs hardness #9) reduce friction significantly, then diamond (Mohs hardness #10), which is the hardest substance in nature, would be even more efficient.

-Mark This message has been edited by asiaassoc on 2009-02-24 16:28:51

To wind this clock, the navigator unlocked the brass retaining ring and pivoted the bowl so the bottom faced up. He then took the winding key, which is stored in a slot in the upper right hand corner of the box, and inserted it in the hole in the bottom of the bowl to wind it. A spring-loaded revolving plate slides over the hole to protect the movement from dust when the key is removed.

These photos were not made from the new piece. They are shots of another chronometer of the same model in my collection (#0256). As can be seen in the photos, this one is in very used condition. It obviously lived a long and productive life in the skies before retirement.

-- Mark

Thanks for the pics!