Extending flaps increases drag more than lift. With an increase in drag, the climb performance is degraded – both climb angle and climb rate are reduced.
We have seen how the 4 forces are balanced in a steady climb, but if the aircraft is banked the lift vector is tilted and the component of lift that opposes weight reduces.
Any attempt to increase lift while banked will also lead to an increase in drag. As most training aircraft use full power to climb, there is no extra thrust to overcome this extra drag and therefore climb performance has to be reduced.
Climb performance is best in a straight climb with the wings level and commencing a turn will decrease both climb rate and climb angle. For this reason, bank angle in a climb is often limited to about 15° in training aircraft.
The weight of a climbing aircraft acts down towards the centre of the Earth, opposing the climb.
Any increase in weight will reduce climb performance and any decrease in weight will improve climb performance.