747fan From United States of America, joined Jun 2007, 1165 posts, RR: 1 Posted (5 years 8 months 1 week 6 days 19 hours ago) and read 4668 times:
As a regular spotter at SDF, I see UPS A300's depart all the time and have noticed that they often takeoff with their flaps up (although their leading-edge slats appear to be down, and a section of inboard flaps right behind the engines are down). I've also noticed the same thing in photos/videos with the Fokker 100. Does anyone know why they can takeoff with the flaps up? Is it due to the efficient A300 wing? Also, I've noticed that A300's also takeoff with their flaps down sometimes; for example, FX seems to always use flaps on takeoff, sometimes AA. But why do they only put the flaps down for takeoff occasionally?
Depends on take-off weight and runway length. Higher weights require more flap. However a longer runway allows higher take-off speed, allowing less flap. In the latter case, climb speed is also higher.
"There are no stupid questions, but there are a lot of inquisitive idiots." - from Citadel by John Ringo
747fan From United States of America, joined Jun 2007, 1165 posts, RR: 1 Reply 3, posted (5 years 8 months 1 week 6 days 8 hours ago) and read 4598 times:
Quoting Starlionblue (Reply 2): However a longer runway allows higher take-off speed, allowing less flap. In the latter case, climb speed is also higher.
I've noticed that A300's with the flaps down during takeoff tend to have a more sluggish climbout than when they use only the "flaperons" and slats. Those things really appear to climb like rockets when they takeoff "flapless." I wonder if this has to do with the higher takeoff speed?
Flaps increase lift, but also increase drag. So, while flaps give you more lift at a lower speed letting you get off the runway faster, a flapless T/O has you flying at both a higher speed and a lower-drag configuration, so you climb faster after you manage to get off.