Pochari Hydrogen’s CHP701 is the world’s first liquid hydrogen powered turbine helicopter. Development will begin in the early 2020s. Pochari Hydrogen utilizes hydrogen stored in “cryogenic” state in carbon fiber tanks lined with an aluminum liner to minimize permeation. The liquid hydrogen is pumped via a “cryopump” from the liquid tank into a heat exchanger connected to the exhaust pipe from the turboshaft engine. Once the liquid has vaporized it immediately rises in pressure to up to 1000 psi where is it injected into modified combustors designed for hydrogen’s unique combustion characteristics. A small helium tank is used to store sufficient quantities of helium gas that serves as a pressurant. The liquid hydrogen tanks needs to maintain a minimum pressure of approximately 30 psi. Due to the nature of cryogenic systems, a very elaborate insulation system is required to minimize excessive “boil-off”. The insulation used is a state of the art vacuum insulated panel system that is lined around the outside of the tank. The insulation is formed in two large uniform shells that are joined in the middle. The middle seam is sealed with a recessed strip of vacuum panel. The uniform shell design is meant to minimize thermal conductivity by eliminating gaps and seams. The tank is fully “modular” meaning it is detachable and can be easily replaced, refilled and maintained. The modularity also allows for the pilot to release the tank in flight in the case of an emergency event that could lead to an impact violent enough to cause a potential detonation. The tank wall is 0.15″ thick aerospace grade carbon fiber reinforced polymer. The tank is designed as a semi-monocoque structure, providing excellent rigidity. “Bulkheads” or formers are placed every 18″. The tank both suspends from the upper cantilevered structure and bears at the bottom section of the airframe. The tank is attached to the airframe via UHMWPE straps wrapped underneath the insulation. The tank is isolated from the vibrations of the rotorcraft via multiple small air isolation mounts. The tank can be easily released and carried with a special dolly cart. The estimated cost of the modular tanks is $100,000. The tanks have a lifetime of around 4-5 years. A forward facing tank is the ideal configuration to minimize structural weight and to allow clamshell doors in the rear of the aircraft which is highly useful for air medical operations. This unorthodox configuration requires a “virtual” flight control system as the tank is placed directly where the cockpit would be. Since autonomy and remote control appear to be the future, this not a significant issue. Three smaller tanks can be installed externally, under the fuselage, and on both sides similar to auxilary fuel tanks on the UH-60. Pochari Hydrogen has considered this configuration but due to the lower volume/surface ratio (a number very important for cryogenic hydrogen aircraft) is much lower resulting in tanks approximately 30-40% heavier than fuselage mounted tanks. Thus we have concluded this is an unattractive option.
Advanced Energy Systems 