It's a Boat! It's a Plane! No, It's an Ekranoplan!

In a previous blog entry [See "This Is Not a Lizard!" ], I told you about the Tuatara, a lizard-like reptile that is not a lizard. In the world of transportation, there is a Tuatara-like vehicle -- an airplane-like, hovercraft-like aircraft that is not an airplane or a hovercraft. First, some background about flight:

Why does an aircraft lift off the ground? Why does the forward motion created by a propeller or a jet engine result in an upward lift? It's all in the wing design. A wing generates lift because it creates a difference in air pressure: The bottom wing surface has a higher air pressure than the top surface, so the aircraft goes up. However, this difference in air pressure creates wingtip vortices -- swirling air where the high and low air pressures circulate at the tips of each wing (see the photo, which shows colored smoke revealing the vortices). These vortices are the reasons migratory birds fly in a v-formation -- each bird, except for the leader, is using the upward spiral of the wing vortex of the bird in front. They therefore need less energy to stay aloft. How do they know to do that? That's a rhetorical question; I'm not answering that here.

However, these vortices create drag on an aircraft -- increasing fuel consumption and turbulence. If only there is a way to disrupt these vortices to increase the efficiency of flying. Of course, there is a way to do so, or you wouldn't be reading this blog entry with the catchy title.

Wing In Ground Effect

The Wing In Ground Effect (WIGE) is the reduction in drag experienced by an aircraft when its altitude is equal to the aircraft's wingspan above any level surface (land, sea, or ice). The most significant effects occur at an altitude about one-half the wingspan. In other words, if the aircraft's wingspan is 30 feet across, the WIGE is most prominent when it is traveling at an altitude of 15 feet. This occurs because the ground breaks up the wingtip vortices. In addition, the proximity of the ground increases the air pressure on the bottom of the wings, which in turn increases the lifting power. The effects of wingtip vortices and WIGE can be observed when racing cars or speed boats appear to go airborne at high speeds. If they could sustain their speed without having to touch the racetrack or the water, they would become ekranoplans.

Ekranoplans -- Ground Effect Vehicles (GEVs)

Ekranoplans are aircraft that employ the WIGE to use less energy to travel faster and carry more weight than conventional vehicles. Ekranoplans do not meet the legal criteria to be referred to as airplanes, and their operators generally do not need to possess a pilot's license. In fact, ekranoplans usually cannot even fly much higher than the length of their wingspan. When they travel over water, they often resemble a hovercraft, but they are also not considered boats or hovercrafts. They can travel over 450 mph. There are GEV versions that travel over land in place of automobiles and trains.

The technology actually has been around for quite awhile. The Soviet Union experimented with various GEV designs, since they could transport a significant amount of materiel and troops at a high speed below radar detection. In fact, the name "ekranoplan" is derived from Russian. Have a look at one such Soviet vehicle in action:

The "Caspian Sea Monster" Ekranoplan