PDR1
In your second diagram the aircraft is climbing at constant speed and constant roc, so the forces must be in equilibrium. You show the thrust and drag as being in equilibrium, but we need to look a bit more closely at lift and weight
Let us start by sliding the lift arrow down and to the left until it's point touches the tail of the weight arrow. We now have two sides of a triangle of forces. For these forces to be in equilibrium, there must be a third force arrow joining the point of the weight arrow to the tail of the lift arrow.
You have shown lift being greater than weight, which means that lift is the hypotenuse and the third force must be at right angles to the weight. This means that we must have a horizontal force pointing to the left. What is this force?
If you are wrong and lift is less than weight, then the weight is the hypotenuse. In this case the third force arrow is acting up the flight path and meets the lift arrow at right angles. In conventional texts this is the excess thrust.
Now let's see where your arguments lead us if we have a very high-powered aircraft such as a modern fighter jet. If your diagram is correct it means that as we gradually increase the climb angle, the lift force must increase. When the climb angle is 90 degrees in a vertical climb, the lift force must be infinite. But no wing can produce infinite lift, so logically if your diagram is correct, no aircraft could ever achieve a vertical climb.
So, is it impossible to achieve a vertical climb, or are you mistaken in your arguments?
Last edited by keith williams; 6th Nov 2018 at 06:29.