Portion of an illustration from a WWII British manual.
Click to enlarge image.
An early BSA airborne bicycle folded for been parachuted by itself. [From a
WWII British manual] The early model BSA airborne bicycle is characterized by the double thin
tubes between the seat and pedals. The seat fits into a separate tube attached
to the back of the pair of tubes.
There are variations. The earliest examples seem to have flat hinges where the
bike folds. These were soon changed to cast hinges however.
The braces for the pedal crank also appear to consist of 4 braces - two
forward and two rearward.
On a specimen that I examined, one of the two large wing-nuts that enable the
bicycle to fold, has raised letters "BSA" inside a depression.
Leather seat may have metal name plate on back saying B.S.A. as well as an
oval marking stamping on the sides.