Hi Charles,

I think that a spring with this configuration is what Chris was 
describing, and it would be a "zero-length" spring.

I sent this just before Jack's message came in.  It bounced back due 
to being too large with the image, so I've placed the sketch here:
http://www.jclahr.com/science/psn/as1/heli/spring.GIF

This isn't the same as the spring effect of a tape measure, where the 
metal tape is slightly crowned.

I've modified my page on zero-length springs to emphasize Jack's 
point that not every spring that has coils touching when relaxed will 
have "zero-length."

Cheers,
John


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