Aviation LNG Tank

One of the primary hurdles in public acceptance of LNG powered plane is the mental image of automotive LPG or CNG tanks. Most people view a pressure tank as a "dumb" steel bottle that either holds or explodes catastrophically. In a car, safety is achieved through brute force; the tank is simply made thick enough to survive a crash. However, in aviation safety must be intelligent.

Automotive tanks (LPG/CNG) are designed for a "worst-case" collision. They have excessive wall thickness to prevent any rupture at all. Because they are uniform cylinders, if the pressure exceeds the material's limit, the tank can fragment in any direction, potentially toward the passengers.

On the other hand, the LNG tank I propose for my VTOL plane would have active geometry and controlled failure path. Instead of making the tank equally strong everywhere, I utilize Aero-Structural Fusing. Engineered composites with integrated weak points and protective cage. Just like the crumple zones of a car to protect the cabin by sacrificing the engine bay, aviation LNG tank would utilize controlled failure paths. By engineering specific frangible sections (structural fuses) on the bottom of the tank facing away from the passengers to dictate the terms of a failure. If the pressure relief valves are overwhelmed, the tank does not explode in the traditional sense. Instead, it punctures at a pre-calculated point. This ensures that the energy, cryogenic liquid, and debris are vectored downward into the atmosphere, while the passenger cabin remains a protected, uncompromised zone.

Additionally, methane gas is very light compared to the air. As a result, any released liquid natural gas would rapidly evaporate and move away the plane without leaving a residue. On the other hand, on a traditional plane if the jet fuel is leaked, it would cling to the fuselage and crawl along the skin toward other areas due to Coandă effect. As a result, in case of an emergency landing, the belly of the plane would be covered by flammable jet fuel and the high temperature turbofan engines nearby would ignite it. That's why planes burst into flames when they emergency land. With LNG, which is at cryogenic temperatures, such scenario would be very unlikely. More importantly, LNG tank can be easily emptied before emergency landing. The specially placed vents on the belly of the plane would double as cold gas thrusters and keep the plane airborne longer. Since LNG expands about 600 times its volume when it turns into gas, that "thruster" effect would actually be quite significant. A "Safety Cushion" of thrust during the most critical moments of a forced descent!