Spark length vs watts

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "S & J Young by way of Terry Fritz <twftesla-at-qwest-dot-net>" <youngs-at-konnections-dot-net>

List,
 
I took a few somewhat crude measurements of DC power into my twin TC vs spark
length.  I held the voltage constant at 12 KV and varied the BPS and measured
the milliamps and spark length as best I could.  It appears spark length is
proportional to DC watts raised to the 0.45 power.  This plots as a straight
line approximately.  (Plotting spark length vs sqrt power gives a curved plot.)
 
Data is as follows:
 
BPS    watts    spark inches
 25     60        10
 50    108        12
100    228        18
150    384        24
200    600        28
250    720        31
300    864        34
350   1056        37
400   1188        39
450   1308        41
500   1440        42
 
Spark lengths are difficult to determine.  My TC is a twin, and I used two
sharp breakpoints extending past the toroids aimed at each other.  When the two
coronas start to connect, the center inch or two brightens considerably
(interesting effect).  That is the condition I measure the spark length.
 
So I wonder if John Freau's "efficiency" formula would be a bit more accurate
if it was 1.7 x wall power raised to the 0.45 power?
 
Someday I will try to get some data where power is held constant and measure
spark length vs BPS.  I may have to wait until I get my triggered SPDT spark
gap going as my RSG seems to crud up rapidly, degrading performance and
affecting measurements.  Electrodes are #10 brass bolts.  (I know - use
tungsten ...)  
 
--Steve