Hatz Biplane Association

Just reread your post and see that the C/S is already built. I'm not sure if you might still be able to modify it, but it's not too late in the game to build a new C/S if the differences are major to you and you want the Classic style C/S. If it's built for the 18 gal. tank, you might use an engine with less fuel burn or plan on a header tank behind the firewall.

JMHO

I built from the CB1 plans but used a lot of Classic ideas. I thought of calling mine an SC1 (sorta classic). Mostly, I rounded the fuselage more with extra stringers, used an 0-320, and built a Classic style tank (mine is riveted together as per RV tanks instead of welding). Actually, the CB1 does use compression tubes in the C/S (one per side) located just inside the C/S end ribs. There is an inner rib on each side of the C/S that the tank sits in between. These ribs are about 6" in from each end of the C/S making the tank smaller at 18 gal. I eliminated the inner ribs on mine and used a double compression strut (with a diagonal tube connecting the upper and lower tubes to stabilize the spars) on each side located just inside of the end rib. My tank is similar to the Classic tank with around 25 gal. The extra fuel is needed to feed the larger 0-320. I like the Classic tank as it is a piece of cake to remove if needed. The CB1 tank removal would include cutting fabric.
As far as hand holds, the location choices are many and open for interpretation.

Good luck, have fun!

I don't have a set of CB-1 plans to refer to so perhaps other can chime in here, but what I do know is:
1. The CB-1 uses compression ribs and the Classic uses compression tubes
2. The CB-1 tank sits a little more inside the CS and is fabric covered and the Classic tank serves as the actual top skin in that location
3. The Classic has additional bracing to support and provide fore & aft locations to anchor the tank
4. The Classic has a larger tank due to #1 & 2 above
5. The CB-1 trailing edge is fabric covered and the Classic trailing edge is sheeted in plywood
6. Location of the handholds is different between the two

Also, the gap between the CS and the top wing panels is rather large on the CB-1 and is covered by an aluminum strip vs. approximately 1/4" gap and no covering on the Classic. This has to do with the location of the brackets at the root of the wings or CS or both... not sure as I don't have plans to compare.

What is the difference between a CB-1 center section and a Classic? I purchased a CB-1 project that includes a completed center section and finished ribs. The project came with a set of CB-1 plans and I have a set of Classic plans coming next week to compare the two, but could someone fill me in on the differences?