| Enough to stop the exhaust bubbling the paintwork around the flightdeck and being ingested into the engines! Longer if you are going into a headwind behind the other jet. You can see the effect on the TAT probe readings which can go up alarmingly. Longer for a big widebody, and enough to stop the jet in front buffeting you. Short enough to allow the airport to have more than about 2 jets taxiing at the same time! There is no set figure. |