>This thread will help you out.>>http://www.airliners.net/discussions/tech_...ad.main/107310/Lot's of info there, thanks! I liked the statement regarding American Airlines, and the use of eight degrees minimum of flap, even though the Fokker 100 doesn't require it. They used at least eight, because some passengers were thinking something was wrong if no flaps were used.L.Adamson

Why take-off with zero-flap and only the leading edge slat? Simple, save wear and tear and reduce noise. Flaps (leading and trailing) add lots of drag. Also, even though the take-off roll is less, the rate of climb is also less. A clean wing is the most efficient state. Slats however, accelerate air over the top of the wing for much less of a drag increase and so permit higher angles of attack and reduced stalling speeds. Less drag means either a higher rate of climb or a lower thrust requirement (or somewhere inbetween). Meaning that take-offs noise sensitive areas argue for the use of less flap. Also, if you don't need the additional rate of climb the clean wing offers, then throttling back, as well as reducing noice, save engine wear and tear.

>Why take-off with zero-flap and only the leading edge slat?>Simple, save wear and tear and reduce noise. Flaps (leading>and trailing) add lots of drag. Also, even though the take-off>roll is less, the rate of climb is also less. A clean wing is>the most efficient state. snippedHowever, with many aircraft designs, the flaps do in fact, greatly increase wing area. Variants of this type of design were also used for the B-29 bomber back in WWII. Lift increases as a multiplyer of airspeed, and you must either have the airspeed, or wing area to support the weight. Therefor, with many aircraft, flaps MUST be deployed to a takeoff setting which adds wing area, and less drag than full flaps for landing. It's all tradeoffs for efficiency & load.L.Adamson

Hello All,The answer to the No Flap being used for takeoff for Mulit-engine aircraft is due to second segment climb requirements. It's used if the takeoff gross weight is high and the runway length is long enough. It means you will have a longer takeoff roll and rotation speed but you will have Less drag and higher rate of climb if you lose an engine after V1. As an example with the DC-9's we flew out of Denver, we could carry more fuel and passengers on a warm day (high density altitude)if we made the takeoff with slats extended and flaps retracted than we could if we used 5 degrees of flaps.We had performance data that provided us with higher V1,Vr and V2 speeds for a given takeoff gross weight/outside air temp/runway length for No Flaps. It meant you were rotating at the far end of the looooong runway but you were assured of being able to climb if you lost an engine. For non-believers I used to demonstrate this in the simulator by failing an engine in each configuration. With No Flaps they could maintain a minimum rate of climb but with 5 degrees of flaps and the same weight and outside air temp, they always crashed.One operator of the DC-9 requested performance data from Douglas while I worked there to be able to takeoff with NO FLAPS on the DC-9-10 (which did not have Slats)at high altitude airports in Mexico. As I remember the rotation speed was somewhere around 180Kts. (Oh my poor tires) :-)Ed Weber a.k.a tallpilot