I needed some 2.5" bore flexible air hose to go from the bulkhead to the intake of the heater unit in my Domino Pimlico kit-car that I am totally rebuilding. The hose needed to turn through 90 degrees with a tight bend.
This works superbly, and is easy to fix with long cable ties. I made up the flange to bond to the bulkhead using some 2.5" glassfibre tube and some 3mm thick epoxy-glass FR4 board. My large stock of hole saws came in handy!
Hint: I wrapped a few turns of self-amalgamating tape on the outside of the glass-fibre tube. This creates a high friction surface so that the air hose doesn't slip off.