Ethanol Trimaran VTOL

I had previously proposed a trimaran VTOL aircraft using hydrolox as the propellant. That proposition contained so many radical changes from classical designs that it would be very difficult to implement directly. Additionally, liquid hydrogen fueling infrastructure will not be universally available around the world. After re-evaluating ethanol's proven capabilities in rocketry and recognizing how cleanly it integrates into my trimaran VTOL architecture, I am proposing the ethanol-fueled variant of my VTOL design as a low-CapEx, high-density stepping stone.

Nose Rocket and Core Propulsion

My VTOL plane requires a dedicated mini-rocket engine beneath the nose of the pontoons to provide longitudinal vectoring, vertical takeoff, pitch-up authority, and high-thrust aerodynamic braking during landing. Ethanol has been used in rocketry for decades, and such a compact, high-efficiency nose engine operating at a proper stoichiometric mixture ratio can be easily designed and manufactured using standard copper and alloy techniques.

Thermochemical Separation and Power Generation

Another critical feature of ethanol is that it can be catalytically decomposed or thermally cracked into molecular hydrogen and acetaldehyde (ethanal, CH₃CHO). My VTOL relies on high-power-density electric motors for fuel pumping. By generating hydrogen directly onboard via catalytic dehydrogenation using waste heat from the engine core, the aircraft can run an onboard fuel cell to power its electric pumps using hydrogen and oxygen—just like the hydrolox variant.

Decomposed ethanol produces a hot gas mixture of acetaldehyde vapor and gaseous hydrogen. Hydrogen is cleanly isolated from this mixture by using the cryogenic temperature of onboard LOX in a flash heat exchanger to condense the acetaldehyde into a liquid at +10°C to +20°C, leaving dry, pure hydrogen gas for the fuel cell stack. The condensed liquid acetaldehyde is then drained directly into the entrainment duct.

Fluidic Entrainment and Secondary Autoignition

Acetaldehyde’s autoignition properties are exceptionally favorable: its low autoignition temperature (∼ 175°C) allows it to spontaneously ignite upon contacting entrained ambient air inside the top-fed ejector shroud, driving secondary air-breathing afterburning without requiring complex electrical igniters.

Due to the higher molecular mass (44 g/mol) and higher primary jet density of the acetaldehyde/steam exhaust compared to pure steam/hydrogen, momentum transfer inside the duct is more efficient. This higher mass density pulls harder on the upper-deck Boundary Layer Ingestion (BLI) scoops, generating a strong static pressure drop across the upper pontoon hull that offloads up to 22% of the aircraft's weight during cruise. It also allows the 4-sided divergent air entrainment duct to be significantly shorter and more compact than in the hydrolox variant.

Density, Dry Mass, and Pumping Work

Even though ethanol has a lower specific impulse (I_sp) than hydrogen, its 11× higher liquid density (∼ 0.79 g/cm³) and the lack of bulky vacuum insulation lower the aircraft's structural volume and dry mass, which offsets the lower I_sp. Because liquid ethanol and LOX are far denser than liquid hydrogen, the volumetric displacement required to feed the engines is drastically lower. This means smaller combustion chambers, smaller pumps, and a much lower electrical power draw from the fuel cell. Furthermore, without the 20 K temperatures needed for MgB₂ superconductivity, standard copper-wound BLDC pump motors can be used, sub-cooled by the cold LOX feed line to reduce electrical resistance by up to 80%.

Manufacturability and Environmental Advantages

From a manufacturing perspective, eliminating high-speed rotating turbomachinery in favor of static composite ducts, 360-degree aft vectoring leaves, and tiled fluidic injectors eliminates the multi-billion-dollar development cycles of traditional turbofans, making the airframe modular and easy to scale.

Environmentally, ethanol is an advanced renewable fuel that burns cleanly with zero sulfur oxides (SOₓ), dramatically lower NOₓ, and an 80%-95% reduction in soot and particulate matter compared to Jet A-1. This eliminates persistent contrail formation at high altitudes. When derived from sugarcane or 2G cellulosic agricultural waste, it delivers a 65%-90% net reduction in life-cycle greenhouse gases, exempting flight operations from carbon taxes and qualifying for global green aviation incentives.

Global Accessibility

Compared to liquid hydrogen, ethanol is far easier to store, handle, and transport, and it can be found almost anywhere on Earth without boil-off losses. Installing an on-demand LOX generator at a VTOL pad is straightforward and inexpensive. This allows Ethanol VTOL airports to be deployed almost anywhere on Earth, bringing the benefits of high-speed, blade-free VTOL flight to the masses worldwide.