✈️ #23: How ground effect planes bend the rules of the air

It’s been a few months since the last issue of this newsletter came out. There are even new subscribers (welcome!) that have never received a new issue in their mailbox. So, it’s time to pick up the pace again!

This issue is about a topic that has fascinated me ever since I learned about the Ekranoplan. Better known by it’s infamous nickname “the Caspian Sea Monster”. This vessel was a warship operated by the Soviet / Russian Navy on the Caspian Sea during the 80s and 90s. What made this warship so special was its ability to fly just above water by using ground effect. It is this same ground effect that modern companies are using to build highly energy efficient aircraft to revolutionize zero emission transportation.

What is ground effect?

As most of you know, aircraft can fly because a low pressure area is created on top of the wing, lifting the aircraft. At the same time, the relative high pressure area below the wing tries to compensate, or fill up, the low pressure area. In flight this creates an airflow perpendicular to the direction of the aircraft around the tip of the wing.

Because this airflow is perpendicular to the airflow over the wings it is causing drag: induced drag. This type of drag is higher at lower speeds (during take off and landing for example) than at higher speeds.

When the aircraft is flying close to the ground (as shown in the image below) this disturbing airflow has less change to reach the top of the wing. Thereby reducing the amount of induced drag and creating a sort air cushion on which the aircraft floats. This makes it possible to fly significantly more energy efficient, making it possible to use less energy for the same speed. Ground effect works whether you fly above land or water. However, when looking at safety, operating above water is by far the preferred option.

Is it a plane? Is it a boat?

Several companies worldwide are developing aircraft that will hopefully make this highly efficient mode of transportation available in the coming years. The one that has probably gained the most traction in the media and amongst investors is Regent. This U.S. based company is building, what they call, the Viceroy seaglider. A battery electric “wing-in-ground-effect” vehicle.

The seaglider, competing with both ferries and aircraft, is six times faster than ferries while at the same time generating less noise and emissions than aircraft because of the electric drivetrain. The vehicle they are developing at the moment will be able to carry 12 passengers over a distance of 290 kilometers with a top speed of 290 kilometers per hour. The second seaglider will have a capacity of 50 passengers with the same range and speed (all based on current battery technology).

Because Regent’s craft (that’s the word they use) is able to float and will be certified as a boat, it doesn’t have to comply with the extensive fuel requirements that apply to aircraft. These requirements are limiting the maximum trip distance of the already limited range of Regent’s electric aircraft competitors, while not affecting the range of the Viceroy.

Related: Issue #10: Fuel planning for electric aircraft ⚡️⚡️

The fact that companies like Japan Airlines and Hawaiian Airlines are some of the investors makes it clear what kind of market Regent is aiming for: densely populated coastal area’s. The 290 kilometer range is enough for some high speed island hopping in Hawaii or to quickly travel from one Japanese city to another. On the U.S. mainland, connecting cities across the Great Lakes or along the long coastlines could be commercially interesting routes.

Since these type of aircraft can only operate on and above water, their operational capacity is limited, making the number of profitable routes limited as well. Nevertheless, they can be an unbeatable solution for specific situations. Especially when using electric motors that pollute a lot less, they can be ideal for connecting inner cities near large bodies of water.

It will take some time before we’ll be able to see these planes soaring above the water. However, if you want a real life demonstration of this natural phenomenon, and you missed out on seeing the Ekranoplan, just go to the park and see birds fly above water. They know about ground effect too.

Thank you for getting all the way down to the end of this issue of Second Century! If you have any questions or suggestions you can contact me via [email protected] or send me a message via LinkedIn.

For more about me, visit giel.io