Fatal crash Arizona

At 23:50 07 May 2014, Bruce Hoult wrote:
However your height estimates are systematically biased 20% too large.
Well, about 8% for a pull-up, and 17% for a dive - at the high-speed end of
the scale.
(Better and worse, respectively, at the low-speed end.) Whereas your rule
is about 10%
low throughout.

By me: 28^2 - 12^2 = ~800 - ~150 = 650 ft (784-144 = 640 if you do it
exact)
By you: 130+120+110+100+90+80+70+60 = 760 ft
By you with my -20% correction: 760 - 152 = 608
And the truth (from v^2 = u^2 + 2gh ... whence we both started, I'm sure)
is 708.66 ft. (I
knew you'd like the ".66" ;o) )

Spreadsheet he http://tinyurl.com/mzokpyk for those amused by such
things.

But of course these are both rules of thumb, intended more to give better
understanding
than for exact calculation. I have more often referred to mine in
discussing recovery of
lost speed low on finals (or after a low winch-launch failure) than for the
120kt beat-up
case!

On Friday, May 9, 2014 4:44:38 AM UTC+12, James Metcalfe wrote:
At 23:50 07 May 2014, Bruce Hoult wrote:
(Better and worse, respectively, at the low-speed end.) Whereas your rule
is about 10% low throughout.

Yes, it's deliberately biased a little to the low side from the true (as you note) /4.7516 to make it more of a "guaranteed to pull up that far". Also useful for "I'd like to be down on that ridge line, but I don't want to overspeed". Of course in that case the height difference is going to be pure guess anyway.

I've contemplated using /4 for dives where you want to make sure you have some minimum speed, but I think that overdoes it. /4.5 would be better but not easy to calculate in your head.