Originally Posted by
megan
The 747 tanker likewise uses full flap when doing drops, perhaps to keep engines spooled up where throttle response is better, tactic also used by the Red Arrows who fly their formations at times with speedbrake deployed. Whatever the reason I'm sure the tankers have a good explanation.
Thanks,
I will note that the 747 max flap setting is 30 instead of 40. That being said, the overall drag profile is not necessarily determined by this(for example, a 777 at flaps 30 has inboard flaps at way more than 30 degrees).
Of note, I flew the old 737-200 for a short time period. As one was slowing down and configuring on final approach, you could set a pre-planned final approach power setting using a fuel flow setting and the aircraft speed would slowly decrease and stabilize close to Vref. Landing with flaps 30 - set a FF of 3000 lbs/hr, landing with flaps 40 - set a FF of 4000 lbs/hr(which is a 25% increase). We also memorized the pitch attitudes required for approach. I believe that it was +3 degrees for flaps 30 and 0 degrees for flaps 40, which also seemed to me to be a significant difference in pitch. I took all this to mean that the amount of drag for the last 10 degrees of flap was significant.
That being said, I think there is plenty of engine thrust above the idle(or slow spool up) range at flaps 30 for a go-around but significantly less drag. Maybe it is different for the more modern versions with different wings and engines.