39

Forward flight is much more efficient than hovering. As airspeed builds, lift increases from "translational" lift as the air moves more horizontally over the disc. Since the relative airflow is more horizontal, the angle of attack for a given pitch angle is increased. The vortices and turbulence move behind and down from the helicopter so undisturbed air ...


38

It actually has exactly the same outcome! Well, in reverse. Wings generate lift by forcing air down (one way or another, let's not go into details). When the wings are close to the ground, the air that is forced down can't get out of the way, resulting in a higher pressure. Cars generate downforce by forcing air up. When air close to the ground is forced ...


27

There is no height at which ground effect is switched off. It just becomes less and less effective. There are two factors which determine how strong ground effect is.: Height relative to wingspan: The downwash cannot move into the ground so the induced flow field around the wing is distorted. In a first order approximation, the wing affects mostly the air ...


25

It's impossible to give a correct AND simple explanation I think. I would explain it like this if I was asked: The downwash from the wings and the downward component of the wingtip vortices create a higher than normal pressure area below the wings because the air hits the ground and can't "escape", increasing lift. Induced drag is reduced because wingtip ...


22

As speed increases, most helicopters pitch up. This is because the lift generated on the side of the retreating blade gets progressively less than the lift generated on the advancing blade side. Due to precession, the effect of this is felt 90 degrees later so instead of rolling to the left (or right, depending on which way the blades rotate) because of ...


22

For a simple and correct answer you need first to understand induced drag. Please read this answer if you feel unsure. Short version: The wing creates lift by deflecting air downwards. Induced drag is the consequence of this deflecting, because the resulting force of this deflection process is tilted backwards by half the deflection angle. Due to the ...


22

You're correct that the low wings produce more ground effect compared to their high winged counterparts. However, during takeoff and landing, it can result in undesirable handling qualities- the aircraft can 'float' the runway; on contrary, the high wing design is more stable. There are other reasons for STOL aircrafts to have high wing designs, most of ...


18

Because they are designed differently. As you've yourself pointed out, while an aircraft produces lift, the racecars produces downforce i.e. lift directed downwards. The following figure shows the design of the wing of an aircraft and the front wing of a racing car. Image from Ground Effect Aerodynamics by Erjie Cui and Xin Zhang Basically, the downforce ...


16

The visual effect in the picture you found seems to suck water out of the sea, in this real footage the f-18 air shockwave tends to push water down, and makes a trail.


16

I remember studying that ground effect happens within one wingspan. Although it reduces when you gain altitude. As mentioned in FAA’s Pilot’s Handbook of Aeronautical Knowledge: When the wing is at a height equal to its span, the reduction in induced drag is only 1.4 percent. However, when the wing is at a height equal to one-fourth its span, the ...


16

It turns like an airplane by tilting the lift vector. Watch carefully in this video, especially about 50 seconds in, and you can see the craft is turning by banking. It just can't bank very hard unless it climbs a little higher. This is one of the problems of GE aircraft; they aren't very maneuverable because they can only make gentle turns at the normal ...


14

The reduced pressure on the car not only exerts a downward force on the car, but an equal upward force on the ground. Mythbusters did an episode where they drove an Indy car over a manhole to show that it does lift the manhole cover slightly. The force on the ground is irrelevant because it doesn't move and is not attached to the car. But in your drawing ...


13

The ability of a ground effect (air)craft to able to fly with (small) perturbations in height from the ground is called height stability. In general, height stability is achieved if the derivative of the lift coefficient with increasing height is negative. In this case, a decrease in height (due to waves etc.) causes an increase in lift. As a result, the ...


13

And this video gives quite the explanation on how this happens... The way it works: condensation effects: the air speed increases as the air flows around the aircraft this can mean, that the air may travel faster than the speed of sound air pressure and temperature drop, when the airspeed increases this leads to condensation, because the cold air cannot ...


13

Ground effect height is primarily a function of the airfoil, and the "ground" surface. Smooth desert lakebeds have "better" ground effect than forest tree tops. Calm water is better than open water for smoothness. As I recall, there have been several times where planes have operated in ground effect for substantial distances, such as military aircraft ...


13

Best answer: the United States had no need for one. These kinds of large wing-in-ground-effect craft, while impressive, really serve no military purpose and provide no major military advantage for the US Armed Forces to possess. Aside from the internal Great Lakes, there are no major bodies of water within the United States of America where such a craft ...


10

At the high speed of the F-15s in the video ground effect is almost negligible. Ground effect is about the restriction of downwash by the ground, and at high speed and air density downwash is rather small. Also, the duration of close proximity to the ground is too short for ground effect to fully develop. The biggest effect will be air turbulence. Since air ...


9

The issue here is that ground effect requires there to be another body in which the airfoil is in close reference to (i.e. the ground). The wiki article sums it up nicely A substantial amount of downforce is available by understanding the ground to be part of the aerodynamic system in question You cant have ground effect occur inside an airfoil and ...


9

I suspect part of it is due to historical design: High-wing STOL worked in the past so why change it now? That said, there are numerous reasons why high-wings are good for STOL: Better visibility, no wings blocking the view below. Helps the pilot see/avoid obstacles on the ground. As you say, high wings also improve clearance over rough ground. This is ...


9

Here's my simplification, it's not the full story, but it covers the essentials. Lift: When you are in free space, the high pressure below your wing dissipates into the surrounding air. When you're in ground effect, the high pressure below the wing encounters an incompressible solid, and therefore cannot dissipate as quick, causing higher pressure below the ...


9

In the early 1920s ground effect was not as well studied as today, so it was not considered during development. These stub wings, mostly called sponsons, were meant for roll stabilization on the water, so they were aerodynamically shaped buoyancy aides. Dornier had studied the optimum hull shape in the early 1920s with water tunnel tests, and the result was ...


8

The ground acts as an aerodynamic mirror. When the wing approaches the surface it is as if an inverted wing comes from below. Their high pressure areas amplify each other, increasing the efficiency and thereby reducing the drag.


7

The amount of time a plane in a dive spends close enough to the ground to ingest foreign objects and thereby damage its engines is of order ~fractions of a second. For a plane that is about to strike a building on the ground, the idea of FOD damage to its engines is not even relevant.


6

Simple explanation: When out of ground effect, air on the bottom of the wing has plenty of room to move around. When in ground effect, the air on the bottom of the wing can't move around nearly as well and therefore pushes the plane upward to try and make more room.


6

Ground-effect analysis is generally completed using the method of images, where we imagine an opposite geometry providing a flow that interacts with the original geometry. The 2D case Katz and Plotkin have a good explanation; here is their diagram for the 2D case: For a flat-plate airfoil, the math works out to \begin{equation} C_\mathrm{l} =\frac{\pi \...


6

It's most definitely not urban legend. However, it also does not scale 1-1 with wingspan. Rather, it scales nonlinearly with above ground height to span ratio ($h/b$). The simplest analytical prediction for ground effect can be derived from potential theory and the circulation theory of lift. We know that the wing can be modeled as lifting line consisting ...


5

Remember that lift means the downward acceleration of an air mass. This bends the aerodynamic force vector backwards, so a small part of the pressure force acts against the direction of motion. If the ground blocks this bending, less of the aerodynamic force will be felt as drag. This is true regardless of the direction of this force - it can be up or down. ...


5

Koyovis' explanation is correct and deserves to be the accepted answer. However, as always, much depends on the details of the specific configuration - generalizations like those in your answer deserve to be treated with some caution. Ground effect does not always result in a pitch-down change. The Handley-Page Victor was famous for its ability to flare all ...


5

The aerodynamic centre of a wing shifts when it is in ground effect. Out of ground effect, the wing produces lift by accelerating air downwards. In ground effect the ground prevents the air from being deflected downwards, and more lift is produced due to increased pressure underneath the wing. This pressure has a different distribution than out-of-ground ...


5

One reason the US never pursued this design is that it can't operate effectively in rough seas. It needs a relatively calm surface, which limits where and when it can be employed. A potential opponent can plan for this shortcoming. In the early 1980's, there was a US Navy plan to conduct flight tests using the Hughes Hercules aircraft, to study ground ...


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