Abstract:

This video details the experimental design and construction of a novel "spinning rocket" concept, drawing inspiration from Heron's Aeolipile to rotate a propeller. The project focuses on an internal combustion engine fueled by butane, later upgraded to propylene, designed to expel exhaust gases sideways to generate rotational thrust. Key engineering challenges addressed include managing extreme heat, leading to the use of graphite for both the engine's nozzles and a custom ball bearing cage. A thermodynamic innovation involves coiling a copper pipe around the engine to utilize the expansion and cooling properties of liquid butane, simultaneously cooling the engine and increasing fuel pressure. While initial tests with butane yielded limited RPMs, the accidental use of propylene significantly boosted performance to 2840 RPM, producing a kilogram of thrust. The video concludes with the next objective: integrating an air compressor driven by the engine for self-contained flight.

Propeller Rocket Engine: From Ancient Inspiration to Modern Experimentation

• 0:00 Heron's Aeolipile Inspiration: The video begins by introducing Heron's Aeolipile, an ancient steam turbine, and reinterprets its rotational principle to create a "spinning rocket" designed to drive a propeller.
• 0:32 Efficiency of Moving Air Slowly: The creator explains the principle that moving a large volume of air slowly (like a propeller) is more energy-efficient than moving a small volume of gas very fast (like a rocket) for sub-supersonic applications, due to the quadratic relationship between energy and velocity.
• 1:00 Rocket Engine Construction: The core of the project is a compact combustion engine that burns butane gas and expels it through a small hole to generate thrust, based on Newton's Third Law.
• 1:18 Graphite Nozzles: The engine's nozzles are crafted from graphite, chosen for its excellent heat resistance and ease of machining. The creator empirically tests three different nozzle sizes based on NASA-derived equations.
• 2:03 Sideways Thrust for Rotation: To achieve rotation, the exhaust gases are redirected sideways through brass tubes, a design inspired by the Aeolipile's rotational motion.
• 3:33 Ball Bearing Heat Failure & Graphite Solution: An initial zirconia ceramic ball bearing failed due to its plastic cage melting under high temperatures. This was remedied by fabricating a new, heat-resistant, low-friction cage from graphite.
• 6:39 Propeller Protection & Butane Cooling System: Recognizing that the carbon fiber propeller's resin binder would burn, an ingenious cooling system was devised: a copper pipe coiled around the engine carries liquid butane. As the butane vaporizes and expands to fuel the engine, it simultaneously absorbs heat from the engine (cooling it) and increases its own pressure, enhancing fuel delivery.
• 9:00 Challenges in Butane System Optimization: Achieving stable operation required precise adjustments to the fuel reservoir's placement and the exact amount of butane charged into the system, balancing cooling and fuel supply.
• 9:41 Initial Performance with Butane: With butane as fuel, the engine reached up to 1280 rotations per minute (RPM). However, performance was limited by the butane's relatively low vapor pressure of 4 bar.
• 10:42 Accidental Discovery of Propylene Fuel: The creator inadvertently switched to propylene (mistaken for butane) from a welding kit, which naturally has a higher vapor pressure.
• 11:56 Dramatic Performance Boost with Propylene: The use of propylene led to an "insane" increase in speed, reaching 2840 RPM and generating approximately 1 kilogram of thrust.
• 12:08 Future Goal: Self-Contained Flight: The next phase of the project involves integrating an air compressor, powered by the engine's rotation, to eliminate the need for an external air supply and enable autonomous flight.