Traditional sea and air lift platforms have significant operational constraints that limit flexibility. Sea lift platforms provide highly efficient transportation of large payloads, but require long transit times (days to weeks), large highly developed ports, and large standoff distances in contested environments. Conventional strategic airlift platforms provide high speed, but require long prepared runways and have limited capability to support maritime operations. Vertical Takeoff and Landing (VTOL) and other maritime aircraft have limited range/payload capacities and are dependent on shipboard or shore based servicing and launch and recovery infrastructure.
Ground-effect vehicle (GEV), or wing-in-ground-effect (WIG)
A ground-effect vehicle (GEV), also called a wing-in-ground-effect (WIG), ground-effect craft, or ekranoplan (Russian: экранопла́н – “screenglider”), is a vehicle that is able to move over the surface by gaining support from the reactions of the air against the surface of the earth or water. This is also called wing-in-ground effect: when an aircraft is close to the ground, it operates significantly more efficiently than it does higher up. The additional air pressure underneath the aircraft at altitudes below half the wingspan adds extra lift, and you also get a corresponding reduction in lift-induced drag. Typically, it is designed to glide over a level surface (usually over the sea) by making use of ground effect, the aerodynamic interaction between the moving wing and the surface below. Some models can operate over any flat area such as frozen lakes or flat plains similar to a hovercraft.
A ground-effect vehicle needs some forward velocity to produce lift dynamically and the principal benefit of operating a wing in ground effect is to reduce its lift-dependent drag. The basic design principle is that the closer the wing operates to an external surface such as the ground, when it is said to be in ground effect, the more efficient it becomes. The ground effect increases the closer you get to the surface, peaking at an altitude around 5 percent of the wingspan, where you can get a craft operating some 2.3 times as efficiently as if does in free air.
Given similar hull size and power, and depending on its specific design, the lower lift-induced drag of a GEV, as compared to an aircraft of similar capacity, will improve its fuel efficiency and, up to a point, its speed. GEVs are also much faster than surface vessels of similar power, because they avoid drag from the water.
On the water the aircraft-like construction of GEVs increases the risk of damage, should they fail to avoid other vessels. Low altitude brings high speed craft into conflict with ships, buildings and rising land, which may not be sufficiently visible in poor conditions to avoid. Since most GEVs are designed to operate from water, accidents and engine failure typically are less hazardous than in a land-based aircraft, but the lack of altitude control leaves the pilot with fewer options for avoiding collision, and to some extent that discounts such benefits. GEVs may be unable to climb over or turn sharply enough to avoid collisions, while drastic, low level maneuvers risk contact with solid or water hazards beneath. Aircraft can climb over most obstacles, but GEVs are more limited. Furthermore, the limited number of egress points make it more difficult to evacuate the vehicle in an emergency.
While designs can vary greatly by manufacturer, the vehicles tend to closely resemble traditional planes, with the lower half of the chassis built to allow the craft to float on the water’s surface. While a WIG vehicle’s characteristics are comparable to an aircraft, they are still required to operate as a waterborne vessel and comply with conventional shipping rules, according to the International Maritime Organization.
Numerous attempts have been made to capitalize on this effect for quick, efficient transport over water.
Led by Alexeyev, the Soviet Central Hydrofoil Design Bureau (Russian: ЦКБ СПК) was the center of ground-effect craft development in the USSR.USSR built some manned and unmanned prototypes, ranging up to eight tonnes in displacement. This led to the development of a 550-tonne military ekranoplan of 92 m (302 ft) length. The craft was dubbed the Caspian Sea Monster by U.S. intelligence experts. Although it was designed to travel a maximum of 3 m (10 ft) above the sea, it was found to be most efficient at 20 m (66 ft), reaching a top speed of 300–400 knots (560–740 km/h) in research flights.
German engineer Günther Jörg, who had worked on Alexeyev’s first designs and was familiar with the challenges of GEV design, developed a GEV with two wings in a tandem arrangement, the Jörg-II. It was the third, manned, tandem-airfoil boat, named “Skimmerfoil”, which was developed during his consultancy period in South Africa. It was a simple and low-cost design of a first 4-seater tandem-airfoil flairboat completely constructed of aluminium. The prototype has been in the SAAF Port Elizabeth Museum since 4 July 2007, remained there till (2013) and is now in private use. Pictures of the museum show the boat after a period of some years outside the museum and without protection against the sun
In Korea, Wing Ship Technology Corporation has developed and tested a 50-seat passenger version of a GEV named the WSH-500. Iran deployed three squadrons of Bavar 2 two-seat GEVs in September, 2010. This GEV carries one machine gun and surveillance gear, and incorporates features which reduce its radar signature in a similar manner to stealth.
One of the current leading players appear to be Sea Wolf Express, which plans to begin a passenger ferry service between Helsinki, Finland and Tallinn, Estonia, using a Russian-built Ground Effect Vehicle (GEV) in 2019, and Wigetworks Private Limited, operating out of Singapore.
Airfish-8, thelatest incarnation of the Lippisch design is 56.4 ft (17.2 m) long, with a reverse delta wingspan of 49.2 ft (15 m) and a carbon fiber reinforced plastic body to help keep weight down. It uses a 500-hp (373-kW) V8 car engine, running on regular unleaded fuel, to drive two mid-mounted pusher props in front of a large T-tail. It seats six to eight passengers plus baggage and two crew, and it’s simple enough to fly that pilots can get certified for the Airfish in less time than for a regular pilot’s license. Range is around 345 mi (555 km) with a top speed just under 120 mph (200 km/h) and a cruising speed more like 92 mph (148 km/h).
Its biggest challenge is operating over choppy water or bad weather. In high winds it would need to take off directly into the wind, meaning the passengers would cop an absolute pounding as they hit the waves head-on before reaching liftoff speed. In fact, takeoff and landing will likely be the Airfish’s biggest weaknesses, because those are the times when it’s got to act like a boat.
As soon as it hits takeoff speed and rises out of the water, everyone’s in for a smooth, fast, and efficient ride. It can also dock anywhere with a pier and a bunch of floating pontoons, without taking up a massively unwieldy space at the marina. Safety-wise, these kinds of GEVs are pretty good. In regular operation, it’ll rarely go more than 10 ft (3 m) above sea level, so in the case of some sort of failure – unlikely in itself given the simple powertrain – you can just glide it to a more or less regular landing and float about waiting for emergency services. However, the turning radius isn’t terrific, though, so in low visibility conditions, there’s always the chance of running into a boat, which wouldn’t be very safe at all.
DARPA novel WIG Design
WIG vehicles achieve increased aerodynamic efficiencies and address many of the operational limitations of the traditional sea and airlift platforms in maritime theaters, but they are unable to operate in high sea states and have limited capability to avoid collisions in congested environments, says DARPA. DARPA posted a RFI in Sep 2021 to potentially support the development of new DARPA efforts
focused on novel seaplane and Wing In Ground effect (WIG) capable vehicles.
DARPA is interested in the design of a new class of vehicle that addresses the major operational limitations of traditional air and sea lift platforms. Although related to prior and current WIG vehicles, there are significant differences that DARPA believes enable a highly innovative and transformational concept. Specific features of this new concept are:
Takeoff and land in the water (up to Sea State 3) for runway independence.
Maximize flight time in ground effect for increased range, endurance, and survivability
Extended out of ground effect flight capability for obstacle avoidance, flight over land, weather avoidance, etc.
High sea state operation for in-ground effect flight as well as takeoff and landing and extended on water operations
Low cost manufacturing techniques and design choices (e.g. unpressurized fuselage)
Large operational payload (100+ tons) and capability of carrying multiple amphibious vehicles
DARPA is seeking platform that needs to takeoff and land at up to sea state three and be capable of operating outside the ground effect zone to dodge obstacles and inclement weather. (Sea states are a widely recognized measurement of the ocean’s surface conditions, with sea state zero representing calm waters and nine indicating massive waves up to 50 feet high. Sea state three would consist of lightwaves up to four feet high.) The problem with that requirement, is two-fold, said Mark Montgomery, a retired rear admiral and now a senior fellow for the Foundation for Defense of Democracies. There is the obvious kinetic problem associated with a wave hitting the craft, but the more difficult challenge is that even small waves can disrupt the WIG effect and turn the craft’s ride turbulent — and less than fuel-efficient.
DARPA seeks to identify additional novel concepts and configurations that meet these objectives. Ongoing engagements with potential service partners have identified a wide variety of use cases that indicate the utility of the concept. Examples of potential mission areas include:
Expeditionary Advanced Base Operations (EABO)
Distributed Maritime Operations (DMO)
Distributed logistics and logistics under threat operations
Combat Search and Rescue (CSAR), on-site triage, mass casualty rescue
Unmanned vehicle operations
Low payload, long duration arctic patrol flights
DARPA is exploring ideas to help frame potential future program investments in this new concept. Existing platforms are unable to effectively support distributed operational constructs and ongoing studies and concept exploration activities have identified several key challenges a future concept must overcome.
Specific technical challenges include:
Low Cost Development and Manufacturing Methods: Current aircraft manufacturing methods will result in an exquisite solution that will be too expensive to effectively allow the purchase quantities desired. What innovative manufacturing techniques can be applied to the concept to reduce overall system cost from standard $/lb. estimates for large aircraft?
High sea state takeoff/landing: High sea state takeoff and landing will be required for high operability in oceans around the world. What key technologies and design features are required for high sea state takeoff and landing operations?
Flight control in high sea states: High operability for transoceanic flights necessitates the capability to fly in ground effect in high sea states to maximize system efficiency. What sensing and control solutions are required to maintain ground effect flight with acceptable ride characteristics, handling qualities, and crew workload near highly dynamic surface waves?
Payload load/unload capabilities: To efficiently support distributed operations, considerations for payload loading and unloading must be accounted for in the design. What mechanisms and design features are required to load/offload cargo? How can the vehicle interface with existing systems and logistics operations (on water, at pier, ship to ship, ship to shore, etc.)?
Extended on water operations and maintenance: The envisioned system will spend a majority of its time on water. What unique technologies or design considerations can be utilized to decrease life cycle costs associated with salt water/salt fog exposure?
Maritime and Air Vehicle Demonstrator Design: The envisioned system will operate extensively in the air and on the water, requiring a blend of maritime and aircraft design methods. What unique skillsets and design methodologies can be applied to effectively develop a low cost, full-scale demonstrator vehicle?
Vehicle size and Performance Capabilities: To effectively support future Navy and USMC operations, the vehicle must be sized appropriately to carry relevant payloads or mission sets. What size platform will provide the most disruptive capability to the services?
The agency’s solicitation states that conversations with the services show this new aircraft would be useful for the Navy’s two keystone concepts of operation: Distributed Maritime Operations and Expeditionary Advanced Base Operations. The RFI also lists combat search and rescue, distributed logistics, unmanned vehicle operations and “low payload, long duration arctic patrol flights” as viable missions.
Chris Bassler, a senior fellow for the Center for Strategic and Budgetary Assessments, told Breaking Defense the military has considered using WIG vehicles in the past, as have Russia and China for both civilian and military applications. The problem is those efforts have often resulted in “the worst of most design parameters.” The vehicles end up being slower than planes and less cost effective than ships, and, as DARPA’s solicitation explained, they cannot operate in even mildly rough sea state conditions.
“Various studies and technology development efforts have commenced over the decades to see if designs can be developed which can carry more, go faster, and increase the environmental conditions where it can operate,” Bassler said. “This is a good opportunity for a ‘DARPA-hard’ problem, to push some of the technologies which may also be used for unmanned systems, sealift, and tilt rotors.”
Bassler posited a fleet of these new WIG vehicles could prove particularly useful in the Indo-Pacific, where they could shuttle supplies to Marine Littoral Regiments and other special forces operating dispersed among the island chains.