I've read that you should balance a low wing plane upside down and a high wing plane right side up. How does one balance a bi-plane?

Usually the balance point is too far forward to balance on the lower wing, so in most cases the upper wing.

Yup upper wing.

Well, it depends, my hostetler skybolt has the CG on the leading edge of the lower wing, it would almost be off the trailing edge of the upper wing, usually most bipes are balance upright, but this skybolt I have plans for and the kit needs to be balanced upside down. Where is the mark on the plans or in the instructions?

The easiest (and safest way) is to use a sling. See my messages at http://www.rcuniverse.com/forum/m_17...tm.htm#1715012

There is no mark on the instructions. It is a CMP biplane, and the Chinglish instructions contain no information on the CG at all.

I have had three biplanes and I have no idea how I balance them (that is, I have no plan on how to do it). One is my own design so I had to decide on the CG location. I just balance it. Top wing, bottom wing, fuselage. If the CG is in mid-space, it will give you an opportunity to solve the problem and you will learn a lot from that. That point is always only a starting point. Slight CG adjustment is usually needed for optimum performance.

It doesn't happen to be the christen eagle, because I have one, I could go look at mine.

When I flew rubber powered freeflight, a good starting point for bipes was 1/3 the average cord of both wings. Witch is not as simple as it sounds. I have a diagram in a book called 'Rubber Powered Flying Models'-By Don Ross but I can't reproduce it.(copyright)-sorry -BW