Using the Chrono to measure take off acceleration
Hi All,
While some manufacturers are offering undoubtably expensive technical solutions to measuring one’s take off acceleration I have heard from two sources that many pilots hit the stop watch at the start of the take off roll. The suggestion is any performance A aeroplane should reach 80kts in 20 seconds or 100kts in 30 seconds. I have experimented with this on the 320 and a little bit on the 380 and it seems to work however it can depend on exactly when the stopwatch is started. A stationary start is easy, release brakes, set 30%, start the chrono then set thrust. A rolling take off though will potentially have the jet doing a fair few knots when the stopwatch is started.
One source I heard the idea from suggested he rejected a take off because the jet had not reached 80kts by 20s, chief pilot went mad, Commander insisted the jet was weighed and it was found to be ten tonnes over the loadsheet weight.
The performance margins of the new twins (like 787) are so slim, I wonder whether this would also work on them. Presumably they still have to meet the perf A requirements but seem to use up far more runway than other comparable types.
Anyhow long story short, does anyone routinely use this, precisely how do you use it and is there any online guidance?
kind regards,
Leslie