Hangar 9 SU-26MM Sukhoi Assembly Manual page 19

The picture below is of the tail end of the pipe tunnel.
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5. Temporarily mount the pipe mounts and install pipes
to center the mounts before they are glued. Use lubricant on
the pipes for easier passage through the mounts when they
are not glued yet. Pipe mounts will not touch the floor of
the fuselage and need to be glued to the sides and bottom
former.
Hangar 9 3.1m Sukhoi SU-26MM ARF Assembly Manual

6. Once mounts are centered mark the spot on the sides
and formers.

7. Remove the pipes and use an acid brush to apply
30-minute epoxy to the sides of the mount and fuselage.

8. Reinstall the mounts and allow time for epoxy to cure.
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