FAA Airline Transport Pilot (ATM)Aircraft Performance and Weight and BalanceMedium
A heavy transport rotates near its balanced field length limit and lifts off while still within one wingspan of the runway surface. The pilot notices the airplane accelerates and climbs sluggishly as it climbs out of this region. Which characteristic of flight within ground effect explains why the airplane may have become airborne before reaching its normal climb speed?
- AParasite drag increases sharply due to surface friction, forcing an earlier rotation
- BInduced drag is reduced near the surface, allowing the wing to generate sufficient lift at a lower airspeed
- CA higher angle of attack is required near the ground to produce the same lift
- DThe stall speed increases due to reduced downwash near the ground
Show answer & explanationAnswer & explanation
Correct answer: B. Induced drag is reduced near the surface, allowing the wing to generate sufficient lift at a lower airspeed
Ground effect reduces the wingtip vortices and downwash, which lowers induced drag and effectively increases the wing's lift-to-drag ratio near the surface. This can allow the airplane to become airborne at a lower-than-normal airspeed, but it may then settle back or struggle to climb once it leaves ground effect.
Why the other options are wrong
- A. Parasite drag is largely unaffected by proximity to the ground.
- C. Ground effect reduces the required angle of attack for a given lift, not increases it.
- D. Ground effect actually reduces stall speed slightly, not increases it.
Ground Effect
A reduction in induced drag and downwash experienced when an aircraft flies within approximately one wingspan of the surface, effectively increasing wing efficiency.
- Reduces induced drag and required AOA for a given lift.
- Can cause premature liftoff at lower-than-normal speed.
- Can cause 'floating' during landing flare.
- Effect diminishes rapidly as altitude exceeds one wingspan.
Memory trick: Close to the ground, the wing 'cheats' — less drag, easier lift.