I can´t understand how the B747 climbs better with flap 20 than 10, it needs further explanation !!!!! Please 747 FOCAL try your best!!!!!
With a large flap setting the aircraft becomes airbone earlier but with shallower climb gradient. That means that if the obstacle (or noise monitor) is close to the liftoff point, a large flap setting is advantageous. A distant obstacle (or noise monitor) requires a small flap setting, the aircraft becomes airbone later but with steeper climb gradient.
Taking off with F20 allows a greater height over close in monitors, but this doesn´t mean at all that your angle nor your rate of climb are higher than with F 10. Am I right?
Flap setting for maximum TOW vs OBST depends on the position of the obstacle (same criteria for noise monitor).
Flap setting for maximum TOW vs RWY is between 25 to 50% of the full deflexion. The larger the flap setting (approved for take off) the higher TOW vs RWY.
Flap setting for maximum TOW vs CLIMB( 2º segment) is the smallest (even 0º if approved for take off).