Where are the locations of the elevators or horizontal stabilizers in a Concorde?
There is no "horizontal stabilizer" on the Concorde like other commercial aircraft, the wing performs that duty because it is a delta-wing. The elevators for the Concorde are combined with the ailerons into something called "elevons" which perform both functions (Think stereotype paper airplane).

Note: Elevators and Horizontal stabilizers are not the same thing. Most aircraft have their elevators located on their horizontal stabilizers, only a few have the whole stabilizer as an elevator.

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