Hey, I saw a documentary about the first Nitrogen powered plane. It was being developed in Germany and is more a prototype than anything else. They said one of the problems is that the tank is insanly expensive for liquid nitrogen but "Cheap" for nitrogen gas. Well I don´t understand why it is so expensive and why they need to insulate the tanks. I mean considering you kept the liquid nitrogen under preasure it could not turn into gas until it is being burnt. Am I right?