b is the distance from CG to the end of the fixture.
Yes, object d can rotate around the pin. Lets say you had a motor directly on the pin that reacted to the G forces to keep object d in it's orientation.
Say you've got a fixture on a wing that undergoes a 10g vertical maneuver going through the CG of the fixture, and on the end of the fixture is an object "d" on a linkage distance "a" from the fixture. If you need to use torque to resist that loading scenario the torque required would just be T...
