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Cruise Flap permits the addition of drag (lift) aftward of the CL, effectively displacing the cg aft, allowing the Tailplane to load, with attendant reduction in angle of attack, which reduces overall drag.
Hoot' Gibson tried this with a TWA 727 years ago, didn't work out so well when the FE stuck his oar in the water, and the result was a wild ride down....way down.
