Originally Posted by
Pilot DAR
If there were no tail downforce, the airplane would not behave as expected (and required for certification) in stall recovery. This is a prime element of determining the aft C of G limit - there still must be enough tail downforce, that the nose wants to drop when down elevator is applied . . . Certification requires that a pull always be required when airspeed is slowing toward the stall.
This was the problem Boeing faced with the 737 Max. The geometry of the new (further forward) engine nacelles generated an extra pitch up moment which reduced the control wheel pull as the stall was approached. The solution was to arrange that the stabilizer (= tailplane) reduced the TDF by adjusting its angle of incidence. If they had designed a fail-safe system (using both angle of attack sensors rather than just one and a comparator to prevent false readings triggering the stab input) the Max debacle would have been avoided.