Why two mainsprings???

[DeweyC]

OK, I have done A/C clocks for over 30 years and never thought about this. Now a customer asked.

Why do Hamilton/Elgin 37500 and CDIA use TWO mainsprings?

Remember, the LeCoultre A-10 (equivalent to the 37500) does just fine on one mainspring.

The only speculation I can come up with is that it is like having two engines; if one breaks you likely can still get home.

The clocks are 8 day but were fully wound prior to takeoff. At most the pilot was in the air 12 hours or so. So I can only think this was a USN requirement to ensure the clock could still be used if one of the two blue steel mainsprings broke.

Has anyone ever seen an official explanation?

 

[gmorse]

Hi Dewey,

I'm afraid I have no idea on the aircraft clocks, but I have just received an 8-day Swiss strut clock with twin barrels:



The extended duration is provided by the extra wheel driven by both barrels.

Regards,

Graham

 

[Chris Radek]

With a train in the configuration of Graham's, the force on the extra wheel's pivots will be fairly small because the extra wheel is nearly centered between the barrels. If it had just one spring providing twice the force, the force on the extra wheel's pivots would be very high, and the diameter of the whole movement would need to increase to support the much larger barrel.