If a high winged plane is balanced upright and a low wing plane is balanced inverted, how do you balance a mid wing plane?

Thanks,
doubledee

If the mid-wing has any dihedral at all, you'll want to balance upside down. Since most mid-wings have no dihedral, you can balance either right-side up, or inverted.

Sideways?

Dr.1

Support the wing on the side where the most mass is.

If you balance a high wing plane upside down, you'll be lucky to get it in that stable point, because the plane will want to swing to a stable position with the mass under the wing. The same will hold for your mid-wing plane. Most of the mass will be above or below the wing, and you will find a stable point with the mass oriented below the wing.

Most likely, that will be with the gear down.

Good luck,
Dave Olson

In accordance with the instructions.

Actually, lacking instructions follow Scars advice.

Tie a loop in the middle of a piece of string so you have two equal lengths of string on either side of the loop. Now tie a loop on one end to loop over the propellor. Secure the other end of the string to the rear of the plane (if the plane has flying wires, tie to them. Otherwise you'll have to customize the fastening technique.) Make sure the lengths are still close to equal (it doesn't have to exact). Now hang the plane from the ceiling, making sure the string is as far forward (behind the prop) as you can. It can be a bit un-nerving to hang your plane this way but it works.
Get a plumb-bob and hang it from the same hook the plane is hung from. Let everything come to rest and the plumb-bob will be pointing to the C.G. of the plane. I use an empty film canister and BB's to then balance the plane.

This method will allow you to find the C.G. and the lateral balance. I use it when balancing my Somethin' Extra.