The primary advantage of a variable incidence tailplane at high speed is

• A. Reduced trim drag
• B. Increased drag at high speed
• C. Lower stability
• D. More lift at low speeds

Answer: (A)

The main idea is that trimming forces and associated drag can be made more efficient by letting the tailplane’s angle be adjustable at high speed. A variable incidence tailplane lets you set the tail’s angle so that only a small trimming moment is needed to keep the aircraft level. At high speed, the wing and fuselage interactions create a nose-down or nose-up tendency that the tail must counteract. If the tailplane has to produce a large downforce to trim, it generates more drag (trim drag), which hurts cruise efficiency. By adjusting the tailplane incidence, you reduce the required downforce while maintaining stability, so the tail’s drag contribution drops and overall drag decreases. That’s the primary advantage.

This isn’t about increasing drag at high speed, lowering stability, or producing more lift at low speeds. Those effects aren’t the goal of a variable incidence tailplane; the point is to minimize trim drag while preserving control and stability.