Originally Posted by
Vidab
Not the case in the 747-400/-8. There is a distinct change in the force required around the 9-10 degree range. The tail moving into ground effect is the cause.
Proper technique is to rotate at 2.5deg/sec with no pause to target 12.5 deg. initial (which is tail strike territory). However, executed properly this ensure about 18 inches of tail clearance at max weights prior to liftoff. A two stage rotation is not required to protect the tail. Mostly, on the 747 at least, if you see it it's just poor technique.
40 (plus or minus one) inches tail clearance depending on the flap setting is the appropriate number for the -400, slightly different for the -8(at least according to the FTCM). As for the change in force, it seemed more like at 12.5 degrees to me but I will check it out again in a couple of days. As well, 15° is the initial target attitude according to the FCTM.
I had been wondering what the reason was for the force change. Quite a convenient aerodynamic feature to have if it is just the ground effect as the cause.