wrxpilot wrote:

Agreed... This "30 secs" rule is pretty impractical. I like to use
Sparky Imeson's rule of 71% rotation speed by 50% of the runway.
Having done a lot of my flying out of Colorado during the summer
months, it was a comforting rule of thumb.

interesting. That implies that your horizontal G somewhat increases with
speed during the second half. Based on a flat horizontal G throughout the
takeoff run, whatever speed you have 71% of at halfway point, you would just
about reach when you run out of runway.

(71% is roughly sqare root of 2)

regards,
Friedrich