A variable incidence tail plane with stabilizer trim as an alternative to a conventional elevator with trim can produce which of the following effects?

• A. Can produce excessively high
• B. Reduces residual control forces
• C. Control forces if out of trim
• D. Increases trim range

Answer: (A)

With a variable incidence tail plane, trim is achieved by changing the angle of the horizontal stabilizer itself rather than moving a separate elevator surface. This means the tail’s lift and the pitching moment it produces can change more dramatically with trim setting than with a conventional elevator arrangement.

If the aircraft isn’t properly trimmed, or when it flies in conditions where the tail’s aerodynamics respond strongly (such as rapid changes in speed or angle of attack), small control inputs can require large counteracting moments from the tail. Because the tailplane is large and its effect on pitch is substantial, these trim-induced changes can lead to very large stick forces—excessively high control forces—to maintain or adjust pitch.

So the key idea is that a variable incidence tail plane with stabilizer trim can produce excessively high control forces, especially when the aircraft is out of trim or in envelopes where tailplane lift changes rapidly. The other options describe outcomes that are not the primary concern or are more about benefits (like an increased trim range) rather than the potential for heavy control forces.