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Cruise Economy And Climb Performance  
User currently offlineGlom From United Kingdom, joined Apr 2005, 2823 posts, RR: 9
Posted (10 years 11 months 3 weeks 1 day 16 hours ago) and read 4239 times:

Obviously the wing has to be different to deliver both, as most obviously demonstrated in the two different wings for the 783 and 788. But it is already possible to make an adjustable wing through the use of flaps and slats. Flaps and slats give better takeoff performance but they're retracted fairly soon after takeoff and most of the climb is down with a clean wing. Isn't it possible to device a flap and slat mechanism that can be used throughout the climb to give good climb performance on a wing, which when clean gets good cruise economy?

3 replies: All unread, jump to last
User currently offlineProk From Netherlands, joined May 2005, 36 posts, RR: 0
Reply 1, posted (10 years 11 months 3 weeks 1 day 13 hours ago) and read 4214 times:

Flaps and slats will reduce the rwy length for take off. Disadvantage of flaps at climbout is the increased drag. Clean config will give you BETTER climb performance, so no need for a different flap and slat system.

User currently offline727EMflyer From United States of America, joined Mar 2005, 547 posts, RR: 0
Reply 2, posted (10 years 11 months 3 weeks 1 day 12 hours ago) and read 4196 times:

Really the flaps are like the low gears in an automobile. As they are deployed, lift increases but so does drag, the result is the airplane can fly at slower speeds. Flaps can actually hinder climb performance. Unfortunately I don't know about airliners, but if I fly a C172 with full flaps I simply can not climb unless I have a good headwind.

The secret to improving climb performance lies in a blend of higher power and wings that produce less drag (other ways of reducing drag are good too). If you can get the same airspeed with a higher angle of attack and a similar amount of releative drag you should get better performance.

User currently offlinePihero From France, joined Jan 2005, 5174 posts, RR: 78
Reply 3, posted (10 years 11 months 3 weeks 1 day 7 hours ago) and read 4174 times:
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As 727EMflyer has stated, flaps are for low speed maneuvers only and they are not used above a ball park speed figure of 230 kts.
That's the way they are designed.

As we are speaking of take-off performance, the crew has to chose between reducing the runway length necessary for a given weight and in this case,they will use high flaps settings, or if runway length is not the limiting factor, use the lowest setting to improve climb performance.

In order to climb, one has to consider two factors :
1-The engine thrust (the more thrust, the better)
2-The wing characteristics.The best angle of climb will be achieved at the best lift-to-drag ratio (aka Cl/Cd).
If one considers this ratio, a clean wing will always have a better one than with flaps extended as the high lift devices generate an absolute hell of drag rise when extended.

Taking Glom's initial question a bit further, probably all aerodynamicists and all manufacturers dream of a perfect "mission adaptative wing" which could change its aerodynamic characteristics, like thickness and curvature during each phase of flight, thus adapting to weight or maneuvering requirements as need arises. Some of this concept is already apparent on modern combat airplanes through the use of the leading edge flaps.


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