Editing Ground effect (aerodynamics) (section)

===Rotorcraft===
When a hovering rotor is near the ground the downward flow of air through the rotor is reduced to zero at the ground. This condition is transferred up to the disc through pressure changes in the wake which decreases the inflow to the rotor for a given disc loading, which is rotor thrust for each square foot of its area. This gives a thrust increase for a particular blade pitch angle, or, alternatively, the power required for a thrust is reduced. For an overloaded helicopter that can only hover IGE it may be possible to climb away from the ground by translating to forward flight first while in ground effect.<ref>[https://archive.org/details/DTIC_ADA002007 HANDBOOKS, OPERATIONAL READINESS, MISSION PROFILES, PERFORMANCE (ENGINEERING), PROPULSION SYSTEMS, AERODYNAMICS, STRUCTURAL ENGINEERING], Defense Technical Information Center (1974)</ref> The ground-effect benefit disappears rapidly with speed but the induced power decreases rapidly as well to allow a safe climb.<ref>{{cite web |url=https://www.abbottaerospace.com/downloads/agard-r-781/ |title=Aerodynamics of ROTOR CRAFT |website=ABBOTTAEROSPACE.COM |date=April 12, 2016 |pages=2–6}}</ref> Some early underpowered helicopters could only hover close to the ground.<ref>Basic Helicopter Aerodynamics, J. Seddon 1990, {{ISBN|0 632 02032 6}}, p.21</ref> Ground effect is at its maximum over a firm, smooth surface.<ref>{{cite book |url=https://rotorcraft.arc.nasa.gov/FAA-H-8083-21.pdf |title=Rotor raft Flying Handbook |year=2000 |publisher=Federal Aviation Administration |pages=3–4 |access-date=2021-11-03 |archive-date=2016-12-27 |archive-url=https://web.archive.org/web/20161227042500/https://rotorcraft.arc.nasa.gov/faa-h-8083-21.pdf |url-status=dead }}</ref>