Seb sent me a PM about unconventional twin configurations. Since I think it's a good idea that everybody can participate, let's reply on the forum. I don't copy his PM, since it was a private one and it's up to him to make it public.
I'll kick off with my push-pull design. Tandem-seat, DO-335-like aircraft with a Rotax in the front and the back. CofG is a major issue. You can get away with that with 2 light engines and a relatively heavy payload (a Rotax weights the same as a single passenger), to keep the tail length acceptable. For heavier engines though (Lyc/Conti) that doesn't work so well anymore since the tail gets really long, draggy and heavy.
To avoid that problem, I can image a push-pull aircraft with an off-axis tailboom. Something like this design by TopAz:
Let's make it a big fuselage with a push and pullprop and a single tailboom, instead of the double tailboom of the Adam A500. I think that's an interesting design, considerably simpler than the double boom of a C-337/A500.
I'll kick off with my push-pull design. Tandem-seat, DO-335-like aircraft with a Rotax in the front and the back. CofG is a major issue. You can get away with that with 2 light engines and a relatively heavy payload (a Rotax weights the same as a single passenger), to keep the tail length acceptable. For heavier engines though (Lyc/Conti) that doesn't work so well anymore since the tail gets really long, draggy and heavy.
To avoid that problem, I can image a push-pull aircraft with an off-axis tailboom. Something like this design by TopAz:
Let's make it a big fuselage with a push and pullprop and a single tailboom, instead of the double tailboom of the Adam A500. I think that's an interesting design, considerably simpler than the double boom of a C-337/A500.