For the CLto (take off lift coefficient), is there some way to estimate this?
I was thinking of using CLmax but wouldn’t this be too big? I was thinking maybe CL cruise?
Aviation Stack Exchange is a question and answer site for aircraft pilots, mechanics, and enthusiasts. It only takes a minute to sign up.Sign up to join this community
For many airplanes the lift-off lift coefficient is determined by the maximum pitch angle before a tail strike occurs (minus some safety margin, of course). Before take-off, the speed which allows flight at this pitch angle is computed so rotation is not initiated too early.
If your configuration allows to be stalled with the achievable pitch angle during ground roll, taking off at this maximum lift coefficient is unsafe and most likely counter-productive. Normally, drag near stall is growing disproportionally with angle of attack, so rotating too early will create high drag which leaves less thrust for further acceleration. Also, any flow asymmetry between the left and right wing near stall might cause an unstable rolling motion which can ruin your day and the airplane with it.
For fast-accelerating airplanes a safety factor of 1.1 for lift-off speed can be considered (which means lift-off occurs at 82.6% of the maximum lift coefficient) and for more conventional types this could be increased to 1.2 (so the lift coefficient is only 70% of its maximum). Details depend on the shape of the drag polar and the stall behavior the particular design.
The lift coefficient for cruise will most likely be too low to allow for a reasonably short take-off distance, unless we speak of a motor glider.