Ground Effects


How does a wing in ground craft work? What is ground effects?
Could this be used for safe public transportation?

In: 1

Wings push air downward. The downward moving air can create a pocket of higher pressure when just above the surface, increasing lift available. Alternatively, it allows an equal amount of lift to be generated at lower speeds compared to when at higher altitudes, without changing wing configurations.

It can be used a couple different ways. I wouldn’t say “safer” necessarily, but DARPA for one is funding high capacity transport “aircraft” that travel by ground effect over oceans.

Wing pushes air down. Air moves down. If the air did not move down as easily, the wing could push harder. Having the ground right there makes a huge difference in how easily the air can move.

Ground effect vehicles take advantage of this to get more lift from the same wing/amount of air.

Airplanes are already a super safe means of public transport, in large part because they are far away from anything that they might collide with. Their biggest hazard is the high speeds involved. A ground effect vehicle can take advantage of lower speeds, but still has to go quite fast, can’t steer well, and is seriously limited by weight.

So, they’re not really competitive with anything. Cars maneuver better and can carry more, planes are faster and can carry almost as well, and trains can carry *way* more.

Car wings aren’t normally what we think as ground effects. They are like airplanes, but inverted to push the car down. Ground effects are about the shape of the car interacting with the ground below it through the air boundary layer between the two. Done right, it can in effect suck the car to the ground, thus more downforce without wings.

However, this really only matters for cornering, and the effect is only significant at higher speeds. So unless you have a city bus cornering hard at 100 mph, it really has no application there.

But ground effects in another implementation can be used for public transportation. Say you have two cities over 100 miles apart on a sea or lake, and you want transportation between them. You can make an airplane with short, stubby wings that wouldn’t normally be able to fly, but it can fly low over the water due to the ground effect interaction between the wings and the water. This configuration has much lower drag than a regular airplane, and thus saves fuel. The Soviet Union made some of these.

BTW, Howard Hughes’ “Spruce Goose” flew only once, but it didn’t really “fly” as in fly like a normal airplane. The entire test flight never exceeded 70 feet, so it was still flying on ground effect the whole time.

Downforce is exactly the same thing as lift on planes its just that the wings are upside-down so they generate an overall force that pushes the car down.

As with planes lift is a combined effect including air moving faster abow the wing to create a low pressure zone above it so there is a force pushing the wing up. The other effect is air resistance, if the wing (any surface actually) hits the oncoming air in an angle it directs a the air down, the opposite force (from Newton’s third law) can be broken up into a component that is pushing the plane back and one that pushes it up. This adds drag but also lift. Now flip everything upside-down and thats wings on cars.

Addig downforce from the wings help to keep the car close to the track to make sure the car can be controlled. If to much air gets under the car and the front lifts a bit that can send the car flying because of the aforementioned drag effect. So pushing the car to the track helps to avoid this and now it can make turns at great speeds as faster airspeed more downforce more grip.

Another thing that is wildly used is the underbody of the car. Making air move faster below than above the car creates low pressure below which pushes the car to the ground. So effectively this turns the whole car into an upside-down wing.

Wings are great for better control at high speeds and keeping the car on the track at really high speeds. And can even allow the car to be lighter, a car that is too light will have less grip but with a constant high speed in mind aerodynamic grip is enough for making the car control well. But race cars cant really be too light because of rules regarding minimum weights. But still a lot of race cars rely heavily on aero grip F1 cars generate about as much downforce as their weight.

Of course more wing do mean more drag, so this effects top speed. And if wings directly air up to push the car down that creates a low pressure zone behind the car pulling it back, an effect known as pressure drag. There are many solutions but its mostly about getting air behind the car. Plane wings slove this with vortex generators little spikes on the wings that create turbulence so the air “rolls” behind the wing. A golf ball has a rough surface for the same reason.

As an everyday application wings are pretty much unnecessary. Cars on the roads dont go at fast enough speeds for them to go flying and are usually way heavier than race cares. So even at the fastest speeds these 1-2 tonne cars remain fully controllable. But of course they accelerate slower and have slower top speeds. Adding wings isn’t necessary and adds drag to the car. Now drag is very important for cars travelling long distances as it directly effects fuel efficiency. So its really important to keep air resistance as low as possible because if you are maintaining a constant velocity on level ground that is what consumes your fuel. (And of course the friction between the road and the tyres and all the gears and moving parts also create losses but those are rather minimal.) So for fuel efficiency we want to keep drag minimal so dont add thing that aren’t required and cause drag.

Pressure drag is something that can be lowered by adding vortex generators for example. Or winglets on the tips of wings for planes that also reduce drag.