View Full Version : 747 flap retraction
The Rage
18th Aug 2001, 21:53
Would anyone know why does the 747-400 buffets when flaps are being retracted between flaps 5 and 1, this i noticed is very evident on a heavy weight take off. I reckon it has something to do with the laminar flow over the wing as the leading edges are being retracted. I don't know if the other series have the same problem. Well its not a problem but i'm just curious!
OneDotLow
19th Aug 2001, 13:41
It is to do with lateral airflow I think...
The other day while doing a walk around, I asked the instructor why we cannot jettison fuel whilst flaps are in transit between 1-5.
He said it was due to the fact the airflow carried the fuel to the fuselage, which can cause fumes in the air conditioning system.
Methinks the two are related.
ODL
Cornish Jack
20th Aug 2001, 11:46
Rage and ODL
The 744 flaps 5 to 1 selection would almost certainly generate significant aerodynamic changes since it combines the largest area change with a removal of approx one third of the leading edge devices.
The 'no jettison with flaps between 1 and 5' rule is due to the juxtaposition of the jettison nozzles and the outboard L E devices. The vortex generation pattern will change markedly during that particular range of flap deployment/retraction.