# I Built the FIRST VENTURI ROCKET ENGINE Source: https://www.youtube.com/watch?v=qY9fpU8Vpig Recap page: https://rapidrecap.app/video/qY9fpU8Vpig Generated: 2025-12-11T17:11:47.214+00:00 --- ## Quick Overview The creator successfully built and tested a functional hybrid rocket engine nozzle using a 3D-printed aerospike design, proving that the design works effectively when fed with a proportional mix of liquid (isopropyl alcohol) and gaseous (propane) propellants, despite the challenges of the custom-machined injector being difficult to throttle. **Key Points:** - The creator successfully tested a custom-built hybrid rocket engine featuring a 3D-printed aerospike nozzle design. - The propellants used were isopropyl alcohol (liquid fuel) and propane (gas oxidizer), mixed at a ratio intended to create a 'rocket fuel' that burns like rocket fuel. - The initial test of the custom-machined injector resulted in poor combustion quality, leaving residue and a blast that looked like 'molten sugar' (05:16). - The creator then switched to a 3D-printed nozzle design, which performed significantly better, although the final test with the new nozzle produced a purple flame, indicating an issue with the fuel-to-oxidizer ratio. - The narrator admits to lying about the impossibility of controlling the thrust on hybrid rockets, noting that the design allows for throttling the fuel flow (03:04). - The video heavily features the use of an Onshape CAD simulation to visualize the fluid dynamics (Venturi effect) within the injector, showing how the high-pressure air draws in the lower-pressure liquid fuel. - The creator used a $10 stainless steel 3D-printed nozzle (purchased from JLCPCB) as a superior alternative to the initial, poorly performing machined injector. ![Screenshot at 00:00: A close-up shot of the custom-built rocket nozzle test firing, producing a bright, intense yellow-orange flame against a dark background, showcasing the raw power of the combustion test.](https://ss.rapidrecap.app/screens/qY9fpU8Vpig/00-00-00.png) **Context:** The video documents the process of designing, manufacturing, and testing a custom hybrid rocket engine injector, contrasting the performance of a traditional machined injector with a new 3D-printed aerospike design. The creator uses both physical tests (igniting small amounts of propellant) and CFD simulations in Onshape to validate the fluid dynamics principles, specifically the Venturi effect, which is crucial for properly atomizing and mixing the liquid fuel (isopropyl alcohol) and gaseous oxidizer (propane). ## Detailed Analysis The video details the creation and testing of a custom hybrid rocket engine injector, focusing on an aerospike nozzle design. The creator first shows an initial test using a custom-machined injector (00:05), noting that this design failed to achieve clean combustion, resulting in residue resembling 'molten sugar' (05:15). The narrator explains that hybrid rockets require both a fuel (solid or liquid) and an oxidizer (gas or liquid), unlike solid rockets which are pre-mixed (05:31). To improve performance, the creator designed and 3D-printed a new nozzle in Onshape (09:57) and ordered it in stainless steel from JLCPCB for $10 (10:14). The creator also simulates the fluid dynamics using SimScale within Onshape (11:18), demonstrating the Venturi effect where the high-speed air flow creates a low-pressure zone that effectively sucks in the liquid fuel (isopropyl alcohol) from its side port (14:03). The narrator admits to previously lying about the inability to throttle hybrid rockets, stating that the design allows for adjusting the flow rate of the gaseous fuel (propane) (03:04). After printing the new nozzle (16:15), a test is conducted where the aerospike design successfully ignites the mixture (16:42), producing a powerful flame, although the initial test with the new nozzle yielded a purple flame, suggesting an incorrect fuel-to-oxidizer ratio (16:51). The creator concludes that the aerospike design is superior because its geometry naturally creates the necessary low-pressure zone to draw in the fuel efficiently, unlike the air gun demo where the resulting low-pressure zone was not filled with the injected liquid (13:28). ### Hybrid Rocket Concept - Demonstrates solid rocket (pre-mixed propellant) vs. hybrid rocket (separate fuel/oxidizer) vs. liquid rocket (separate tanks) (02:17). ### Custom Injector Failure - Initial test with a machined injector fails to burn cleanly, leaving residue and poor performance (05:11). ### CFD Simulation & Venturi Effect - Uses Onshape/SimScale to model fluid dynamics, showing how high-speed air flow through the constricted nozzle creates a vacuum that draws in the liquid fuel (11:18). ### 3D Printed Nozzle Success - The creator 3D prints a custom aerospike nozzle from stainless steel via JLCPCB ($10) (10:04, 16:15). ### Final Test & Conclusion - The 3D-printed nozzle successfully ignites the fuel mixture, proving the design works, though the first test showed a purple flame requiring ratio adjustment (15:32, 16:42). ![Screenshot at 00:05: A close-up, high-speed capture of the initial test firing of the custom-made rocket nozzle, showing a bright yellow-orange flame erupting forcefully.](https://ss.rapidrecap.app/screens/qY9fpU8Vpig/00-00-05.png) ![Screenshot at 08:08: The creator reviewing the 3D CAD model of the fuel/air injector in Onshape, highlighting the complex geometry that enables the Venturi effect.](https://ss.rapidrecap.app/screens/qY9fpU8Vpig/00-08-08.png) ![Screenshot at 10:17: A screenshot from the JLCPCB quoting interface showing the selection of 'SLM Metal' 3D printing technology for the custom nozzle part made of 'Stainless Steel' costing €9.31.](https://ss.rapidrecap.app/screens/qY9fpU8Vpig/00-10-17.png) ![Screenshot at 11:22: A CFD simulation visualization inside the Venturi tube showing high-speed \(orange/red\) flow accelerating through the constriction and creating a low-pressure \(blue\) zone behind the central post.](https://ss.rapidrecap.app/screens/qY9fpU8Vpig/00-11-22.png) ![Screenshot at 15:11: A high-speed, slow-motion capture of the successful test firing of the 3D-printed aerospike nozzle, characterized by an intense, bright yellow exhaust plume and visible sparks.](https://ss.rapidrecap.app/screens/qY9fpU8Vpig/00-15-11.png)