Re: Medhurst Table

To: tesla-at-pupman-dot-com
Subject: Re: Medhurst Table
From: Hollmike-at-aol-dot-com (by way of Terry Fritz <twf-at-verinet-dot-com>)
Date: Sat, 09 Jan 1999 10:29:15 -0700
Approved: twf-at-verinet-dot-com

In a message dated 1/9/99 2:56:59 AM Mountain Standard Time, tesla-at-pupman-dot-com
writes:

> Original Poster: "Barton B. Anderson" <mopar-at-uswest-dot-net> 
>  
>  Has anyone hacked at the Medhurst table to derive k via
>  h/d? I'm simply looking for a quick way to calc k in a
>  spreadsheet rather than using vlookups, etc... hoping
>  someone has already done the hacking.
>  
>  Thanks,
>  Bart
>  
>  
Bart,
    I wanted to know the same thing, so I used Ed Sonderman's awesome excel
spreadsheet(the VLOOKUP table) and did this.  I found the K to vary linearly
if H/D was greater than or equal to 2.  Since most coilers don't design coils
with a ratio lower than that, this equation works and is very convenient.

K = 0.100976*(H/D) + 0.309630

If you want K for the entire series including (H/D) less that two, it becomes
a forth order equation.

K = 0.0005x^4 - 0.0097x^3 + 0.0648x^2 - 0.0757x + 0.4723

I did both of these by plotting the table onto a chart and inserting a
trendline.  Both equation had good correlation coefficients (0.999 or so).  I
doubt it is worth the trouble to use the second one, but showed it anyway.
Hope this helps.
Mike