Real calculators have trig and log functions. But a slide rule could do the job to three significant figures.
NMRA Standard S-8 Track Centers lists the scale radius and track spacing for various classes of equipment for clearance for curves from 0 deg (tangent) to 45 deg in 5 degree increments. A very useful document when determining required clearances for curved track. http://www.nmra.org/standards/sandrp/s-8.html Dave Heine (Who’s old enough to have used a slide rule and was in college when using a calculator in an exam was not allowed. My K&E log-log-decitrig slide rule was Christmas present from my parents in high school and much used for a few years.) From: [email protected] [mailto:[email protected]] On Behalf Of scale S only Sent: Saturday, July 07, 2012 9:55 PM To: [email protected] Subject: Re: {S-Scale List} Re: Basic Geometry Hi -- While it is not as accurate, there is a way to almost figure out these things in your head. For example, a 12 degree curve indicates that there would be 30 (360 divided by 12) 100 foot segments or 3000 feet circumference (close, not perfect) in a complete circle. Divide that by pi (3.14159) or for rough and dirty, 3 to get the diameter – roughly 1000 feet. Therefore, the radius is roughly 500 feet (less because of the rounding of pi). 500 divided by 64 will give you the REAL feet in S, or again rounding considerably, a bit less than 8 feet or a bit less than 96 real inches. In actuality, the real answer is a shade under 89 inches, or an error of about 10%. Still, this method will give you an approximation for planning purposes – if you are into that sort of thing. FYI, a 96” radius in S is close to a 10 degree curve, considered to be a minimum radius for standard gauge mainlines. I think there is also a table of these values in one of the NMRA data sheets. Have fun! Bill Winans
