"abripl" wrote in message
ups.com...
Does anybody have the Koch Chart formula (equation)? Or know where to
find it?

I don't think there is an actual equation that works generally. As an
obvious counter-proof to the idea that there is one, consider that density
altitude affects airplanes with normally aspirated engines differently from
those with turbocharged engines. The same Koch chart would not work for
both types of airplanes.

I haven't done a lot of research on the origin of the Koch chart, but I
believe that it's to be used as a general guideline, not as a precise
determination of how airplane performance is affected by density altitude.

If you do want to implement the Koch chart mathematically somehow, I'd
suggest that your best bet (in terms of ease of implementation) would be to
manually read off a range of pressure altitude and temperature combinations
to create tables giving the performance adjustment, and then interpolate
between the values for specific input of pressure altitude and temperature.

You could more accurately describe a Koch chart mathematically by actually
reverse engineering it (the scales on the middle portion of the chart appear
to be logarithmic and exponential for the takeoff distance and climb rate
reduction, respectively, so you simply need to measure the scales and
determine the base and power for those functions, and the pressure altitude
and temperature graphs appear to be linear), but that may be more trouble
than it's worth. Given that the chart isn't a precise way to determine the
performance change anyway, you may find it's overkill to analyze the chart
that way.

Pete