Originally Posted by
TrayflowInUK
By doing this they also serve to increase braking effectiveness because, at the point of touchdown, most of the aircraft's weight is still borne by the wings and this will only decrease incrementally as the aircraft slows.
Dumping the lift as soon as possible after touchdown puts the aircrafts full weight on the undercarriage quicker, which increases the braking effectiveness.
And even if you were to retract the flaps immediately upon landing, the aircraft would have probably covered 1000 ft or more of runway by the time the flaps could be retracted enough to make a significant difference. Not good enough; the acft needs to dump lift ASAP, hence the spoiler deployment upon touchdown.
with regard to braking.....mechanical braking with the tires....is minimal at touch down no matter how much weight you take off the wings. reversing the engines is much more effective at high speeds...until the plane slows into the effective range of the mechanical braking. engine braking with jet engines and tire braking have an inverse relationship with speed. using the tire brakes at the high speeds of touch down has small effect, until speeds are lowered. with no jet engine slowing first....you best have a VERY long runway!!!
leaving the flaps down would be much more helpful in slowing the plane than trying to get them up to improve braking...it would put more weight on the tires....but being down is the best option for slowing.
there are so many variables on landing, water, snow, ice, winds, how long the slab is,....sometimes its nice to be able to tell the folks in the back how much work we do up front in a few seconds.
thanks for all the inputs...nice to see experience stepping up to the plate !!