FAA Airline Transport Pilot (ATM)Transport Aerodynamics and High-Altitude OperationsMedium
A transport aircraft is loaded so that the center of gravity (CG) is near the aft limit rather than near the forward limit, with all other factors held constant. How does this aft CG loading primarily affect the airplane's stall speed?
- AStall speed is unaffected by CG position; it depends only on weight and configuration
- BStall speed decreases because less tail download is required, reducing effective wing loading
- CStall speed increases because the aft CG reduces elevator authority at high AOA
- DStall speed increases because the tail must produce more download
Show answer & explanationAnswer & explanation
Correct answer: B. Stall speed decreases because less tail download is required, reducing effective wing loading
With an aft CG, the horizontal stabilizer/elevator needs to produce less nose-down download (or may even produce upward lift) to balance the aircraft, reducing the effective total lift the wing must generate to support the same gross weight. This lowers the required wing angle of attack for a given speed, resulting in a lower stall speed compared to a forward CG condition.
Why the other options are wrong
- A. CG position does affect stall speed through the tail download effect, so this is incorrect.
- C. Aft CG can reduce stall recovery margin due to reduced pitch authority, but it does not increase stall speed itself.
- D. This describes the forward CG case, which requires more tail download and increases effective weight/stall speed.
CG Effect on Stall Speed
An aft CG reduces the tail-down force needed for trim, lowering the effective wing loading and resulting in a lower stall speed compared to a forward CG, though aft CG reduces stall recovery margin.
- Forward CG requires more tail download, increasing effective weight and stall speed
- Aft CG reduces tail download, decreasing stall speed
- Aft CG reduces static longitudinal stability and stall recovery margin
Memory trick: Aft CG: lighter tail load, lower stall speed