Casey Akin Wrote:
========================================
> Looking from the other side of the spectrum,
> why 15 years or 1472 days...
>
> Why not 10 years and 920 days, or 20 years and
> 1840 days? Was the 15 years a good threshold
> that engines would last? Or is this just a number
> that was placed and hasn't failed?
Regarding the 1492 days, Rich Muth Wrote (above):
========================================
> "1472 is four FRA "calendar years." And the old
> steam rules allowed for four year tube jobs (and
> perhaps some extensions).
>
> The reason a calendar year is 368 days long, is
> that is 4 x 92, or an FRA quarter. And
...
>
> The reason an FRA quarter is 92 days is that no
> matter what date (lets say, July 15) an inspection
> is performed, if you schedule the next quarterly
> on the same day (say, October 15) you will never
> be late (over 92 days) for the next inspection,
> regardless of which months, leap years, etc. are
> involved. You do not need a Julian day calendar
> (or taking off socks and gloves) to count actual
> days."
>
> Clear as mud, isn't it?
Yep. From December 15 to the Ides of March = 31 - 15 + 31 + 28 (or 29) + 15 = 90 (or 91). The date chosen is subtracted from the first month and added to the last, so it cancels out and you get the following combinations
; you might do your next quarterly a day or two (or three) early, but you'll never do it late
:
Jan-Feb-Mar = 31 + 28 + 31 = 90 (or 31 + 29 + 31 = 91)
Feb-Mar-Apr = 28 + 31 + 30 = 89 (or 29 + 31 + 30 = 90)
Mar-Apr-May = 31 + 30 + 31 = 92
Apr-May-Jun = 30 + 31 + 30 = 91
Jun-Jul-Aug = 30 + 31 + 31 = 92
Jul-Aug-Sept = 31 + 31 + 30 = 92
Aug-Sept-Oct = 31 + 30 + 31 = 92
Sept-Oct-Nov = 30 + 31 + 30 = 91
Oct-Nov-Dec = 31 + 30 + 31 = 92
Nov-Dec-Jan = 30 + 31 + 31 = 92
Dec-Jan-Feb = 31 + 31 + 28 = 90 (or 31 + 31 + 29 = 91)
So, as Rich pointed out, 92 days per quarter X four quarters per year X four years (the old standard) gives
92 X 4 X 4 = 368 X 4 = 1472.
Presuming that most small tourist railroads operate about four months per year, - June, July, August & September - that would be 122 days. 1492 / 122 = 12¼ years. Others might operate only weekends, firing up on Friday to be ready for Saturday, or 12 days in a typical month; 1472 / 12 = 122⅔ months = 10¼ years. So where did the 15 Year rule come from?
- El Abuelo Histœrico, Greengo y Curmudgeoño de los Locomoturas Viejos y Verdes,
aka Der Grossväterlich DünkelOlivGrünDampfKesselMantelLiebHabender
Edited 1 time(s). Last edit at 10/28/2014 03:41PM by Russo Loco.
