wrote:
When the density altitude is
high you need to carefully plan this out... even allowing for some
extra margin of safety. That's part of flight planning.

I have a simpler trick.
The longest takeoff distance in my POH mentioned is 350mtr (1150ft).
I multiplied this by 2(grass, upslope, etc.) , so anything longer
than
700 mtr (2300 ft) is fine.
I know this number, only if I'm going to something shorter I
calculate
the whole thing again.


That may work well if you only fly out of lower elevations, but go
back and look at your first sentence. When density altitude is high,
you need to CAREFULLY plan this out. The simple trick that you
mentioned in your post has resulted in many flatland pilots getting
killed while operating out of high mountain airports in the summer.

To illustrate this, one of my primary instructors had me plan some
flights out of high mountain airports on a hot summer day. In several
cases, the density altitude was slightly higher than the plane's
service ceiling and the takeoff distance exceeded the (apparently) long
runway length.

It's possible that your particular plane could get out of any 2,300
ft. field at any density altitude, but that rule of thumb will not work
with many planes.

John Galban=====N4BQ (PA28-180)