After reviewing the drawings of many possible projects, I have taken ideas from several and ended up with
a design I've not seen yet.

The rear rider would sit between or behind the rear wheels, and have the main steering/shifting controls,
With a semi-recumbent sitting position.
The front rider would be fully recumbent, and have the pedals out in front of the front wheel.
The sketch calls for a 20" front, with suspension fork. 26" rear wheels, with the seat suspended in
stead of the frame.

The design goal is two riders, but a smaller turning radius than a normal tandem, and a clear view ahead for both riders.
The first build would be a "test bed" using recycled parts and caliper brakes for lower cost.

Any thoughts or comments???