Further to the above:
3.3 TAIL DOWN-FORCE
As previously mentioned, the tailplane generates the tail down-force. To understand how this force is generated, it is merely necessary to visualise the airflow past the aircraft (Figure 105).
Notice that the downwash strikes the tailplane at an angle. If the diagram is now turned upside-down, it will be appreciated that the tailplane will generate a force in the same manner as do the wings. Figure 105 shows the force resolved into a downward-acting component, which is the tail down-force, and a backward-acting component, which is obviously drag.