I was going to append this to the Paketa thread because it had morphed into frame materials & construction but I thought it better to start a new one. This is not really tandem specific but a tandem could benefit more from advances because of the larger frame.
This goes back 30 years when I had just graduated from college and had interviews with 2 aerospace companies that supplied rockets to the government: MacDonnell-Douglas and General Dynamics. They made Atlas and Titan rockets (don't recall which was which). They showed me the process to make the rocket casings.
One took very large, curved aluminum panels (partial cylinders) about 3/4" thick (guess). Using a giant CNC mill they removed most of the material from the inside leaving a thin aluminum skin with a spiderweb of ribs. This was welded to other similar panels into a giant cylinder that would support its own weight. The smooth skin was on the outside.
The other process was to make a giant soda can - but out of thin stainless steel. The can was unable to support itself unless it was pressurized - just like standing on an unopened soda can -vs- an opened one.
Would it be possible to make a bike frame like the latter method? My understanding is that the reason they cannot make thinner wall tubing is because it would crush under light pressure. If it were possible to make some (maybe not all) of the frame members (e.g. top tubes, down tube, boom tube & part of the seat tubes) out of very thin wall metal (steel, titanium, aluminum, magnesium) and pressurize it so the skin was always under tension, could they not make the walls significantly thinner?
I realize that depressurization could result in a catastrophic frame collapse but if they can make it work for rockets, why not bikes? They could include a pressure gauge and possibly a valve to pump up the frame (just like tires).
If this is not practical for consumer bikes, how about a controlled fleet of racing bikes?
I doubt that I'm the first one to consider this. If this has been considered before and discarded, why?
Do great minds think alike (or not)?