I was on my way out to dinner earlier this evening, when a thought struck me. And, before you ask - yes, thanks, it
WAS a painful experience!
Anyway, it occurred to me that we need to be a bit careful when talking about lift increasing in the initiation of a climb, from S+L flight. The sum of all lift is considered to act thru the Centre of Pressure, at a right angle to the relative airflow. This gets awkward to describe without the aid of diagrams but, if worst comes to worst, I'll make some and post them.
Anyway, the simple act of applying some or all of the reserve thrust, increases the magnitude of the thrust force. In a diagram, this is represented by lengthening the thrust vector by a representative amount. The additional thrust creates the change in AofA, and the increased angle creates a movement of the CofP and, in our blackboard/whyteboard diagram, we see that the lift vector line is inclined toward the tail of the aircraft, in relation to the horizon. This is because it is still acting at a right angle to the relative airflow.
The actual physical length of the lift vector line is still the same but its inclination, relative to the horizon has effectively reduced it's magnitude in comparison with the assumed weight vector line, which is still acting vertically downward thru the CofG. This is why we've said, for years, that lift is less than weight in a climb and it matters not at all whether it's at climb initiation, or in the ideally envisaged steady-state climb.
The "total reaction" is now of greater interest to us as this is what determines our climb. To find the location and magnitude of the vector for total reaction, we resort back to our imaginary diagram and draw a line from the top of the lift line, parallel to the thrust line. This line obviously moves forward. Stop drawing this line when a tangential line will meet the forward end of the thrust vector line. Connect this point to the CofP by a straight line and you've found the vector for total reaction.
This is the vector line that we compare to the weight vector line, to find a new equilibrium that allows the aeroplane to stabilise in the climb. Thus, it really isn't true to say that lift is either equal to weight or greater than weight. This cannot be true because we have upset those forces in initiating the climb.
There are other factors that come into consideration, such as :
1. the effect of prop torque, which I think the Americans call P-factor; and
2. how to sustain the climb.
I'm ignoring those because the basic topic is already complex enough.
Who wants to go next?