ground effect


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ground effect

[′grau̇nd i‚fekt]
(aerospace engineering)
Increase in the lift of an aircraft operating close to the ground caused by reaction between high-velocity downwash from its wing or rotor and the ground.
(communications)
The effect of ground conditions on radio communications.

ground effect

ground effect
In-ground effect.
ground effect
Out-of-ground effect hover.
ground effectclick for a larger image
ground effectclick for a larger image
The ground effect on a half-wave, horizontal dipole antenna, viewed from the axis of the wire. At A, the radiation pattern in the absence of ground; at B the radiation pattern for an antenna height of ¼ wavelength over perfectly conducting ground; at C, a typical radiation pattern for antenna height of ¼ wavelength over normal ground.
i. The change in the aerodynamic reaction on an aircraft caused by the proximity of the ground. An aircraft, helicopter, or any other flying machine flying very near to the ground experiences an increase in lift. This additional lift or cushioning is caused by an effective increase in the angle of attack by the deflection of the downwash and without an increment in the induced drag. The ground effect diminishes rapidly when the aircraft is higher than about half a wingspan or three-quarters of a diameter of rotor disc above the ground. Other factors that influence the ground effect are the nature of the ground, its slope, and the prevalent wind. In the case of rotorcraft operating near the ground, induced drag is reduced, and the lift vector becomes more vertical as a result of the reduced inflow velocity. The vortex ring becomes smaller, and hovering can be sustained with less power.
ii. All unwanted effects caused by ground interference on radars, radio NAVAIDS (navigational aids), and other electromagnetic systems. See ground clutter.
iii. The modification of the directional pattern of an antenna system, especially at the very low, low, medium, and high frequencies, by the presence of the surface of the earth underneath the antenna. The effect is more pronounced in the vertical, or elevation, plane than in the horizontal plane. Ground effects have a large influence on the optimum distance at which the communication is realized.
References in periodicals archive ?
Soso, M; Wilson, P, "Aerodynamics of a wing in ground effect in generic racing car wake flows" Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 220(1):1-13, 2006.
Ground effect definitely exists when flying a fixed-wing aircraft close to water.
A final thing to keep in mind is that what goes up must come down: The ways an airplane experiences ground effect when taking off and climbing away from the landing surface are inverted when descending to and landing on it.
The force of impact is a squared function--it is far, far better to hit obstructions off the end of the runway at 20 knots than while staggering along in ground effect at 60.
Too often, short-field accidents involve gutless planes that seem to be able to accelerate in ground effect, but once they climb beyond this free energy source, they falter and settle back to the ground.
Ground effect is caused almost exclusively by the reduction of induced drag, which the author does correctly point out.
High-wing aircraft suffer less from ground effect than their low-wing brethren; similarly, low-wing airplanes with particularly short gear legs--I'm talking in particular to Comanche and Mooney drivers--suffer even more than, say, a Bonanza.
The vehicle features a matt black paint job, along with a light blue ground effect kit, 20-inch 'Gianna Crown' alloys with mild blue accents, and a chrome finish for the front grille, window surrounds and side steps.
It seems the last time many pilots thought about ground effect was when watching their first flight training video.
Once you're a couple of feet above the landing area, you'll likely still have some excess speed, since you'll be in ground effect.
If your glidepath is very steep, you may blast right through ground effect, so when making steep approaches at low airspeeds, be extra vigilant that you maintain enough energy for the roundout and flare.

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