At the start of the summer I was looking for an interesting aircraft design project, to build my skills and project portfolio. After failing pretty hard at doing an electric aircraft project earlier in the year, I was bummed out and looking outside that domain. One interesting project idea that a floormate suggested was an ekranoplan, or wing in ground effect vehicle (WIG).
An ekranoplan is an air vehicle that flies very close to a smooth surface such as ice, water or tarmac in order to generate extra lift and fly more efficiently. When an aircraft comes into land it is effectively an ekranoplan, as it floats along the runway for a few seconds before settling. You can see the same thing in nature, with a goose or pelican cruising low across body of water.
Ground effect can dramatically increase the aerodynamic efficiency of a vehicle if the vehicle is sufficiently close enough to the surface. The rule used by pilots is related to wing span, though experiments show that the effect is more closely related to wing chord or length. To really start to get ground effect benefits, you need to be flying at a height above the surface less than the wing chord. This immediately leads towards an interesting design tradeoff, as a wing with a long chord is normally detrimental due to higher induced drag from decreased aspect ratio, though in an ekranoplan scenario you actually get efficiency benefits.
I thought it would be interesting to see what would be possible with a homebuilt ekranoplan, as few have been made. I got started by making some remote controlled models with flew reasonably well, and then went into a full componentry, Solidworks and spreadsheeting (ugh) effort over the first month or two of summer. I gathered a kayak, 35 hp two stroke (from a snowmobile), composite homebuilt materials and tools, avionics and even a propeller. Though towards the end of the summer my efforts on the project slowed down. I realised that I hadn’t done nearly enough structural analysis before purchasing components, and that my design would be severely overweight with what I had. Most of this realization came after I wrote up the design problem as a geometric program, which let me see the whole problem at once.
During the semester I didn’t make much further progress on solving the weight problem, and generally got discouraged by the whole thing. But now it’s winter break and I have enough time that I think I can have another more disciplined crack at the problem, with the hope of getting a formal design with reviews done by the end of the break to start building during the semester for a flight in the summer.
Before I get into the work I’ve been doing, I guess I should provide a short introduction to the mission and the vehicle.
I figured out the mission I wanted pretty much by accident. My initial mission for the vehicle was a commuter role for linking up coastal cities such as Boston and New York. The idea was that you could fly down the coast at airplane speeds without airplane regulations . You would also have a lot more options for little destinations such as islands and beaches. Additionally, such a vehicle would be much lower cost to operate than a full aircraft. Though as I was working on the Boston-NY range case (my home case), I realised that the relatively long range requirement was forcing the cruise speed down to be quite slow, almost to the point of a car. If that was the case, what’s the point of building the thing?
The cool thing is that if you can get from Boston to New York with an ekranoplan, you can get pretty much anywhere. The gap between the two cities by the closest ocean/river route is ~400 km.
If you look at a map of Earth and work out what the range you need to link from any one major land mass to another, then the largest gap is ~490 km, between Iceland and the Faroe Islands, just a little more than Boston-NYC. If you can make it that far, you can make it anywhere, provided each location has fuel and a suitable dock or landing beach.
This makes for the exciting possibility of a new (and quite weird) circumnavigation record. If you can hit that critical ~490 km range number (or a realistic number over), then all you have to do is link up from town to town around the world longer than 40,000 km and you’re in business for a record. So that’s what I’m trying to do, designing and building something that can hit that critical number reliably in realistic weather conditions.
I used to think that hitting the critical range of 500-550 km was super possible, though now the design is overweight so I’m not so sure. In the upcoming posts I’m going to try and tease out the correct solution.
1. If designed right with boating codes, and flown below 50ft, ekranoplans are technically boats even though they can often operate at an order of magnitude higher speed. The key is to keep the takeoff speed below “dangerous” boating speeds, but the flimsiness of anything flight-worthy generally makes that happen by default.