weath·er·cock 
(wĕthər-kŏk′)
(wĕthər-kŏk′)n.
1. A weathervane, especially one in the form of a rooster.
2. One that is very changeable or fickle.
intr.v. weath·er·cocked, weath·er·cock·ing, weath·er·cocks
To have a tendency to veer in the direction of the wind. Used of an aircraft or a missile.