This recumbent weighed in at 25 pounds. The main boom was made using 2″ aluminum tubing.
To eliminate stress on the aluminum frame I placed the seat mounds directly over the steering tube and rear wheel stays. The crank length was adjustable, but often the
hose clamps used to secure the crank tube would fail during hard pedaling. The frame still flexed a bit, but for the most part it was a good ride.