What is the primary advantage of a variable incidence tailplane on high speed aircraft?

• A. Reduced trim drag
• B. Increased stability
• C. Improved climb performance
• D. Higher maximum speed

Answer: (A)

The main idea is trimming efficiency. A variable incidence tailplane lets the tailplane angle be adjusted so the tail provides the required pitching moment for trim with little or no large elevator deflection. At high speeds, large elevator deflections create substantial drag, so by changing the tailplane’s incidence to balance the aircraft more directly, you can maintain the desired trim with much less deflection and thus much less trim drag. This improvement in trim efficiency is the primary advantage. The other effects—stability, climb performance, or maximum speed—aren’t the main benefit of this feature.