Crashworthy Hydrogen-Powered Aircraft Retrofit Preliminary Design

Abstract

Design methodologies for retrofitting are devised, and the retrofitted fuselage configuration designs were developed and tested for crashworthiness using finite element analysis in this thesis. These retrofits aimed to install hydrogen tanks within the fuselage, contributing to an efficient transition of the aerospace sector towards hydrogen-powered aviation.
Liquid hydrogen is chosen as the fuel source for hydrogen tanks due to its high density compared to other forms of hydrogen storage. However, storing the same amount of energy as traditional fuel still requires four times as much volume. Therefore, installing hydrogen tanks within the fuselage is necessary due to the low volumetric density and the relatively high flammability of liquid hydrogen.

The retrofits were carried out on a typical fuselage, the most common tube and wing aircraft section. The chosen aircraft type was the single-aisle/short-haul aircraft, and the typical section designed for was the F28. The designs aimed to maximize the fuel capacity within the fuselage, ensuring the retrofitted aircraft could achieve the maximum range. The design methodology was based on practical packing solutions commonly used in the logistics sector to transport as much fuel volume as possible within the constraints imposed by the available volume. This approach is especially beneficial for liquefied hydrogen tanks, considering their low volumetric density and the resulting demand for a large volume.

The design methodology is based on packing solutions popularly employed in the transportation and logistics sector to transport large containers of a specific shape in a constrained volume. Packing solutions utilize tessellation, in which a plane of a certain shape is covered or filled by another shape. This method is beneficial for hydrogen tanks since all of them will be of the same shape in a plane, namely, a circle.

Three designs were devised based on two tank orientations. Two designs are in the lateral direction,
while the other is in the longitudinal direction. All three designs use different packing solutions to
design the tank configuration with the fuselage, with the tank supports designed accordingly.
Some tank design choices were influenced by other fuel tanks and liquefied hydrogen tanks related to regulations such as API 620. Five crashworthiness tests were conducted based on criteria outlined in certification standards such as CS-25 or FAR-25. All designs passed the crashworthiness and fuel system criteria, indicating their ability to meet crashworthiness certification. The crashworthiness results for each design were compared and discussed, and observations were noted.

By loading the tanks onto the frames, longitudinal circle packing (LCP) can alter the load path
and facilitate significant friction dissipation. This helps avoid issues with a lighter fuselage, which may not produce enough plastic deformation in the lower fuselage to correspond with the designed crash sequence. On the other hand, LHP lacks this mechanism, leading to extreme acceleration on the tanks. Lateral square packing (LSP) closely resembles the designed loading, follows the crash sequence as intended, and shows the lowest average DRI despite necessitating the highest energy dissipation.

Finally, a trade-off study was conducted to compare the designs based on the retrofitted aircraft’s range, inspectability, crashworthiness, and retrofit cost estimation. LCP was selected as the best design due to its advantage in range and crashworthiness.