chrisN, the situation being discussed is the analysis in two
dimensions of the forces operating on an aircraft. The
intent is to simplify as far as possible while still being
able to generate useful predictions of the actual system
behavior.
So yes, the reaction force T, is the result of the sum of
the set of reaction forces operating on each element of
the aircraft...however that is a complication that doesn't
help us understand what is happening in the system.
Its easy to make things more complicated, the trick is
simplifying while keeping the nub of the problem intact,
-- Andrew