送交者: HunHunSheng 于 2006-1-07, 20:43:25:
They can be upgraded by using latest electronics.
Aerodynamics potential has been pretty much maxed
out and left not much for further improvement so
that there is no need to uograde basic structure
B-52 came out in 1950s and it is planned to
be used maybe up to 2050s as many predicted.
But internally it can be a very new plane.
The same thing for Chinese F-7. It is based
upon Mig-21 but it is very much improved
from original one