A loadmaster loads an aircraft so that the center of gravity is positioned near the aft limit of the CG envelope rather than at a mid-range position. Which of the following is a characteristic effect of this aft CG loading?
- AIncreased longitudinal static stability and heavier elevator control forces
- BReduced longitudinal static stability and lighter elevator control forces, with reduced trim drag
- CNo measurable effect on stability or handling characteristics
- DA significant increase in stall speed due to reduced tail download
Show answer & explanationAnswer & explanation
Correct answer: B. Reduced longitudinal static stability and lighter elevator control forces, with reduced trim drag
As CG moves aft, the moment arm between the CG and the horizontal tail shortens, reducing the tail's stabilizing download requirement. This reduces trim drag (improving efficiency) but also reduces the airplane's longitudinal static stability, making elevator control forces lighter and the airplane more sensitive in pitch, which can increase the risk of over-controlling or difficulty recovering from an upset.
Why the other options are wrong
- A. Aft CG reduces stability and lightens control forces; it does not increase stability.
- C. CG position measurably affects stability, control forces, and trim drag; it is not negligible.
- D. Aft CG typically slightly reduces stall speed (less tail download needed), not increases it.
Aft CG Effects
Moving the CG aft reduces the horizontal tail's download requirement, decreasing longitudinal static stability and elevator control forces while reducing trim drag and slightly lowering stall speed.
- Aft CG reduces required tail download
- Reduces longitudinal static stability
- Lightens elevator control forces
- Reduces trim drag, improving cruise efficiency, but reduces stall/upset margin
Memory trick: Aft CG: less tail push, less push-back on the stick — light but less stable