View of the interior wall of the nozzle extension.
The F-1 engine nozzle extension features a double-walled construction. The
interior wall is comprised of 23 rows of overlapping shingles. Turbine exhaust
gasses, fed from the turbine exhaust
manifold and routed
between the walls of the nozzle extension, enter the main engine exhaust
flow through gaps between the shingles.
Since the turbine exhaust gasses are substantially cooler than the main exhaust
gasses, this provides film cooling for the nozzle extension.