wileydog3
we used a minimum acceleration check when I was in the USAF. Don't know if they still do but it was based on reach x velocity by the 1000ft or 2000ft marker. Very useful in the old KC-135 'water wagon'. We also computed a time.
Based on that previous practice, I began timing my takeoffs. I can't remember the exact numbers (now retired) but I think it was something like :30 seconds from application of takeoff thrust to rotation. IF it took more than :30 seconds you were heavy and if it took :45 seconds, you were very heavy.
As SLF I like to time T/O from application of T/O power. In a 747 if it's much over 45 secs you know you're really heavy.
On one occasion on a Saturday, a Lufthansa flight about 9:30 from Heathrow to Frankfurt, mainly business pax with little luggage (just carry-ons) I swear it was *12* seconds. And I'd always though A320s weren't fitted with the most powerful engines.