Liquid Air Tandem Biplane

I previously proposed a liquid air-powered VTOL aircraft for domestic transportation. However, after evaluating STOL (Short Take-Off and Landing) requirements, I have determined that a STOL configuration is superior. Vertical takeoff requires immense thrust, necessitating the rapid gasification of large volumes of liquid air, which reduces the energy available for cruise. STOL solves these energy density challenges with minimal additional airport real estate.

Propulsion is achieved through the expansion of liquid air via ambient heat exchange. The flat-bottom fuselage serves as the primary evaporator, using copper-finned heat pipe arrays—scaled-up versions of high-performance CPU evaporators—to transfer thermal energy from the atmosphere to internal expansion chambers. Liquid air is stored in vacuum-insulated tanks integrated into the floor structure.

Like the VTOL variant, this STOL version utilizes a tandem biplane design to maximize the lift-to-drag ratio. The upper wings are positioned slightly forward of the lower wings for pitch stability. These wings are interconnected with vertical studs to form a box-wing configuration, providing structural rigidity that reduces wing weight and thickness. The upper wings provide passive lift, while the lower wings, extending from the flat belly, feature integrated liquid air engines.

The engines utilize trailing-edge slits across the entire wingspan to provide distributed thrust and create a virtual wing effect, increasing the effective chord. Leading-edge slits on the lower wings utilize the Coanda effect to maintain attached flow at high angles of attack. These are engaged during takeoff and landing to reduce stall speed, enabling operations on runways as short as 100 meters.

The tandem box-wing geometry negates the need for a tail stabilizer, reducing weight and drag. This configuration eliminates wingtip vortices and maintains a lift-to-drag ratio between 22 and 25. During the takeoff roll, a 1-meter clearance between the flat belly and the runway surface creates a high-pressure ground-effect cushion. The aircraft cruises at 400 kilometers per hour at altitudes between 900 and 1,500 meters, with acoustic emissions remaining below 70 decibels.