No, not the sensation you get when you have gulped your ice cream too fast. SUGAR Freeze is the a new propulsion concept developed by Boeing that aims to revolutionize air travel. Standing for Subsonic Ultra Green Aircraft Research, the NASA-commissioned project (codenamed "N+4") looks at immature technologies in the hope of kickstarting research for the future. It's reportedly 60 percent more efficient than the equivalent Boeing 737-800, thanks to a
