Homero,

You may need to explain a little more about what you are asking. "Offset hinges", like the one in the first picture below are typically used for doors and not flaps. You may be asking how to offset the center of the flap pivot point. If so, you can imbed Robart type hinges, sort of like in the second photo. Or, you can use a standoff flap pivot point, such as in the third photo. There are other methods as well.

It might help if you mention the jet you are building.

Craig