This post details a rocketry project gone wrong, focusing on the pitfalls of a two-stage design. The author attempted to build a two-stage rocket using cardboard tubes, 3D printed components, and commercially available motors. Key failures included inadequate staging separation (the second stage ignited while still inside the first), overly complex electronics, and insufficient testing of individual components. The chosen recovery method, a single parachute for both stages, proved ineffective. Ultimately, the project highlighted the importance of thorough planning, rigorous testing, and simplifying design complexity, particularly when dealing with staged rocketry.
The "Whoosh Rocket" is a simple experiment demonstrating Newton's Third Law of Motion (for every action, there's an equal and opposite reaction). A plastic bottle, partially filled with water and pressurized with air, launches upwards when the air is released. The compressed air exerts force equally in all directions inside the bottle. When the stopper is removed, the air rushes out the opening, creating thrust. This downward force of the escaping air creates an equal and opposite upward force on the bottle, propelling it skyward. The amount of water affects the rocket's performance – too little and there isn't enough mass to be propelled efficiently; too much and the extra weight hinders its flight.
The Hacker News comments on the NASA "Whoosh Rocket" article largely focus on the surprising amount of thrust generated by this simple demonstration. Several commenters express fascination with the physics involved and the counterintuitive nature of the thrust being independent of the surrounding air pressure. Some discuss the educational value of the experiment, highlighting its simplicity and effectiveness in illustrating fundamental principles of rocket propulsion. One commenter provides further context by linking to a video demonstrating the experiment in a vacuum chamber, reinforcing the concept of thrust being generated solely by the expelled propellant. Another points out the historical significance of the experiment, linking it to a similar demonstration performed by Robert Goddard, considered the father of modern rocketry. There's a brief discussion comparing this type of rocket to other propulsion systems, and one user asks a clarifying question about the relevance of nozzle shape.
Summary of Comments ( 25 )
https://news.ycombinator.com/item?id=43669981
Hacker News users generally praised the article for its clear explanation of common mistakes in amateur rocketry, particularly regarding staging. Several commenters shared their own experiences with similar issues, echoing the author's points about the importance of proper separation mechanisms and stable flight. One highlighted the danger of hot ejection charges igniting the upper stage prematurely. Another emphasized the value of simulations and pre-flight testing. Some users suggested additional resources for aspiring rocketeers, including OpenRocket for simulation and various online forums. The overall sentiment was positive, with the article seen as a valuable resource for avoiding common pitfalls in rocketry.
The Hacker News post "How to not build a two stage model rocket" (linking to a GitBook page detailing a rocketry project) generated a moderate amount of discussion, with several commenters focusing on specific technical aspects and offering advice based on their own experiences.
One of the most compelling comments highlighted the potential danger involved in using PVC for rocket bodies, especially for larger rockets. The commenter emphasized that PVC is not designed for pressure vessels and can shatter explosively, posing a significant safety risk. They suggested exploring alternative materials like fiberglass or phenolic tubing, which are more commonly used in mid-power rocketry and offer better structural integrity.
Another commenter focused on the staging mechanism, questioning the use of black powder for stage separation. They pointed out that black powder is messy and unreliable, often producing inconsistent results. They recommended using a more reliable pyrotechnic device specifically designed for rocket staging, such as commercially available separation charges. This, they argued, would ensure a cleaner and more predictable stage separation.
Several commenters discussed the importance of proper motor retention, expressing concern that the method described in the article might not be sufficient to withstand the forces involved during launch and stage separation. They suggested incorporating a more robust retention system, possibly using a positive retention mechanism rather than relying solely on friction.
One commenter with experience in larger-scale amateur rocketry mentioned the regulations surrounding high-power rocket motors and the need for certification. They recommended that the author familiarize themselves with the relevant regulations and seek certification if necessary, emphasizing the importance of safety and legal compliance in rocketry.
A few comments also addressed the issue of stability, advising the author to carefully consider the rocket's center of gravity and center of pressure to ensure stable flight. They suggested using a flight simulator or performing stability calculations to optimize the rocket's design and prevent uncontrolled tumbling.
Finally, some commenters offered general advice on rocketry resources and communities, pointing the author towards organizations like the National Association of Rocketry (NAR) and Tripoli Rocketry Association, which provide valuable information, guidelines, and support for rocketry enthusiasts. These comments underscored the importance of learning from experienced rocketeers and following established safety practices.