Water tanks in fin
There are two water types of ballast trim tanks in the fin of the JS-3, an
expendable tank ahead of the shear web and non-expendable tank(s)
behind the shear web.
Figure 7.8-6 (SN003-079)
7.8.4.1 Expendable water ballast
The expendable water ballast in front of the fin shear web is used to offset
the CG change due to the water ballast in the main inboard wing tanks.
The tail tank must be filled according to the procedure provided in
Paragraph 4.5.7.1