Operating from water: Testing and optimisation for a game-changing capability

We are bringing an aircraft to market that operates differently to current aircraft. Airlander is able to operate away from airports and runways thanks to its ability to land and take off from any relatively flat surface, including water. Unlike many of the aircraft we see in the skies today, Airlander’s unique hybrid design enables it to be set free from the constraints of infrastructure. This means Airlander could take passengers much closer to their end destination, such as landing on bodies of water close to city centres, significantly reducing total journey times (when considering the city centre to city centre journey as a whole) and providing flexibility.

Our team of highly experienced engineers are always working to develop, test and enhance Airlander’s design. The team have recently carried out testing on Airlander’s water operation capability to further optimise the design of the landing gear and better understand how it behaves in a wide variety of conditions.

Paul Macey, our Principal Engineer for concept design, and Steven Groeneveld, our Senior Flight Sciences Engineer, have led this work. Paul Macey is responsible for evaluating new ideas and technologies that will enhance the capabilities of the Airlander aircraft. He works closely with the wider engineering team to perform investigatory tests that allow us to understand our aircraft better and enhance the design further. Steven works in the Flight Sciences team and analyses aerodynamic data from wind tunnel or CFD (computational fluid dynamics) sources to build the aerodynamic database for simulation and determination of loads. Steven conducted the water operation testing and analysed the results which guided the design of the landing gear for water operation.

Below we take a closer look at the work Paul and Steven have led and the outcomes of this important development.

Still water testing

The production team built a water tank at our facilities to undertake preliminary work and refine the design of the Airlander 10 landing gear with in-house testing. The Airlander 10 landing gear consists of six stud like shapes. To continue to optimise the shape the engineering team designed and created a range of models to test at a scale-equivalent pressure to reproduce the efficient shock-absorbing characteristics of the full-size Airlander landing gear. These conical shaped models, representing a single aircraft landing gear, were mounted on a tow trolley pulling the models through the still water. When the tow trolley is pulled at speed, four components of longitudinal force act on the model, together with heaviness, buoyancy, and hydrodynamic lift forces.

The outcome of this testing was an optimised landing gear shape. The testing showed that some of the shapes exhibited excellent planing characteristics, combining substantial hydrodynamic lift with low drag. This performance was achieved with minimal volume immersion and the observed behaviour was stable across the range of incidence angles needed to facilitate aircraft take-off and landing on water.

Following this work, the team then took the optimised Airlander landing gear design to an external specialist hydrodynamic test facility, to introduce the effect of waves.

Testing in an environment up to sea state level three

We selected HR Wallingford because we regard them as the best facility in the UK for this type of testing. HR Wallingford specialise in helping the world understand the changing influence and impact of water, usually working in the marine and coastal sectors.

The testing focused on the effect of waves on waterborne operations. The team created a large test rig that was used to measure wave forces coming into contact with a stationary aircraft. This is representative of when Airlander is moored on the water or holding position while readying for take off. Testing was undertaken in one of HR Wallingford’s large wave basins that generates a range of scaled wave conditions around a stationary test rig in different depths of water. The opposite end of the wave basin has a gradually sloping section of floor that functions like a beach to break up and diffuse the energy of the oncoming waves in the same way it would work in real life. Two variants of the landing gear model were tested, configured to represent the landing gear inflated in take-off and moored modes. The model was tested in a range of wave heights and frequencies.

This testing showed that the peak vertical forces measured at HR Wallingford were virtually identical to those encountered in previous land-based drop testing. The corresponding horizontal forces were found to be substantially lower than those generated when landing on high friction surfaces (e.g. asphalt or concrete) and so are comfortably within the capabilities of the Airlander aircraft. The two phases of testing validate that the Airlander 10 landing gear is suited to water operations up to and including sea state level three. Moving forward we will be extending the investigation to take-off and landing testing in a much larger water tow tank utilising a partial aircraft model that incorporates the full landing gear, rather than one section of it.