# The Naked Scientists Forum

### Author Topic: Flying in ground effect  (Read 2021 times)

#### kalayzor

• Jr. Member
• Posts: 24
##### Flying in ground effect
« on: 17/01/2008 22:01:27 »
Wings are equivalent to half a venturi (with rarefied air above the wing as the other half - if this isn't correct, please correct me), right?  Thus is how lift works.

However, why in the world does ground effect work?  For those who don't know what it is, ground effect is when the aircraft is flying within a wingspan of the ground and gets extra lift for doing so.  The explanation that I've heard is that air gets compressed under the wings, holding up the aircraft...but why doesn't the ground just act as the other half of a venturi for the bottom half of the wing, decreasing the pressure differential between the top and bottom of the wing and also lift thereby?

#### Eagle333

• First timers
• Posts: 5
##### Flying in ground effect
« Reply #1 on: 17/01/2008 22:43:54 »
Yes, when a wing moves through the air, the air moving over the top, goes faster than the air on the bottom. Hence a low pressure is created on the top & a high pressure on the bottom. That difference in air pressure causes the air to “lift” or push the wing up.

The air on the bottom moves towards the tip of the wing, then up & over producing wingtip vortices (turbulence). That is drag. When flying within the 1 to 1.5 distance of the wing span, above the ground, the vortices get disturbed and “straighten out” due to the venturi effect, hence less drag, and in increase of lift due to the “cushion” of air, which is an increase of air pressure, hence more lift. At half the wingspan, you really notice it. At low speeds, the angle of attack of the wing is greater, speeding up the air over the top.

#### kalayzor

• Jr. Member
• Posts: 24
##### Flying in ground effect
« Reply #2 on: 20/01/2008 14:43:06 »
So the venturi effect more or less nullifies wingtip vortices, but how does this cushion of air come in?  If the venturi effect applies, wouldn't the air not be compressed, and if it was, wouldn't that decrease the pressure differential and thus the lift (I'm assuming that this all applies to the air under the wing)?

#### The Naked Scientists Forum

##### Flying in ground effect
« Reply #2 on: 20/01/2008 14:43:06 »