I have had very good results using HiTec 85 servos and BlueBird brand of servo
http://www.balsapr.com/
Both generate 42 - 50 oz torque on 4.8 volts. The HiTec are about 1/2 the size of a standard servo and the BlueBirds are about 1/3 the size. Depends on how thin the wing is and whether or not you want them completely concealed