The pilot can then fly just above the runway while the aircraft accelerates in ground effect until a safe climb speed is reached.
[8] The deflected or "turned" flow of air creates a resultant force on the wing in the opposite direction (Newton's 3rd law).
In wind tunnel tests, in which the angle of attack and airspeed remain constant, an increase in the lift coefficient ensues,[9] which accounts for the "floating" effect.
A third, hot gas ingestion, may also apply to fixed-wing aircraft on the ground in windy conditions or during thrust reverser operation.
How well, in terms of weight lifted, a VTOL aircraft hovers IGE depends on suckdown on the air frame, fountain impingement on the underside of the fuselage and HGI into the engine causing inlet temperature rise (ITR).
The severity of the HGI problem becomes clear when the level of ITR is converted into engine thrust loss, three to four percent per 12.222 °c inlet temperature rise.
It also occurs in free air (OGE) causing loss of lift by reducing pressures on the underside of the fuselage and wings.
Early VTOL experimental aircraft operated from open grids to channel away the engine exhaust and prevent thrust loss from HGI.
The Bell X-14, built to research early VTOL technology, was unable to hover until suckdown effects were reduced by raising the aircraft with longer landing gear legs.
[21] Ventral strakes retroactively fitted to the P.1127 improved flow and increased pressure under the belly in low altitude hovering.
[22] Lockheed Martin F-35 Lightning II weapons-bay inboard doors on the F-35B open to capture fountain flow created by the engine and fan lift jets and counter suckdown IGE.
The over-rotation caused one wing-tip to stall and an uncommanded roll, which overpowered the lateral controls, leading to loss of the aircraft.