James, it's all about acceleration. If the vertical component of lift is not equal to the weight of the aircraft (assuming drag and thrust balance each other) then the aircraft is continuously increasing its rate of descent (or climb). That's normally not what you want to achieve. So even in a descending turn you have to load up the wings, so that the vertical component of lift and drag balance the weight of the aircraft plus the vertical component of thrust.
The factor that slightly complicates this is that the increased g-loading increases drag. And the drag has a vertical component as well since we're slightly nose-down and descending.
All in all, I think that in a descending turn you don't have to load up the wings as much as in a level turn. But the exact amount is beyond me, right now. I've never been good at 3D-trigonometry.
Last edited by BackPacker; 9th Feb 2009 at 13:48.