Comment by spectramax | Hacker News Reader

Comment by spectramax | Hacker News Reader

I have a bit of a polarizing view about the fascination for things such as aerospike engines, wenkel car engine, etc. While I think it’s cool, what’s cooler are technologies that are optimized across many dimensions from manufacturability to cost, performance to durability, across the entire spectrum. While I understand and appreciate the author’s passion, hard work and his ability to explain things so clearly; I find the fascination, almost fetishization of outlier technologies that have been proven suboptimal for many reasons, to be unexplainable. As an engineer, I am personally fascinated by practical technologies that are simple, cost effective, manufacturable, durable, etc etc, technologies that are optimized across a wide domain to be useful... such as Traditional rocket engines and Piston IC engines to be equally “cool” if not cooler.

But it’s good to learn why certain technologies don’t work and why they haven’t taken off. There is definitely something to learn from failures as much as to learn from optimal designs.

Overall, I applaud the author for this amazing video.

As supporting technologies improve and materials science marches on, fringe technologies can sometimes leap quite suddenly into the mainstream. For example: the Stirling-cycle engine. It was a suboptimal technology compared to steam and IC engines for nearly 200 years, until Sweden found a use for it in their Gotland-class submarines. As it turns out, subs built with free-piston Stirling engines can run even more silently than their nuclear-powered competitors:

https://en.wikipedia.org/wiki/Gotland-class_submarine

Nuclear powered submarines can be as quiet. They aren't typically as quiet as they could be, because they have pumps to circulate coolant around the reactor spaces, and they typically have the prop being directly driven by a turbine (through a gear train).

Both of those have solutions: natural circulation, and turbo-electric drive. Natural circulation is seen on the Ohio class submarines[0], in which the heat gradient inside the reactor is enough to cause it to circulate without powering a pump to move it around. It only works well at low power, but if you're trying to make a good imitation of a hole in the water, that's enough. And it's not like the Gotland-class is any better at going fast.

Turbo-electric propulsion was seen on the USS Tullibee[1]. It definitely was an advantage, in terms of making the submarine quieter. But it had a disadvantage in being heavier than the machinery required for geared drive.

And the USN wants nuclear submarines. A Gotland had a pair of 75kW generators onboard for power/propulsion. A S9G reactor drives a 30MW pumpjet on a Virginia class. SSNs can go faster when necessary, and have more power available to run all their systems.

[0] https://en.wikipedia.org/wiki/S8G_reactor [1] https://en.wikipedia.org/wiki/USS_Tullibee_(SSN-597)

> what’s cooler are technologies that are optimized across many dimensions

That sounds boring to me - there's no room for improvement. The aerospike and wenkel engines and ramjets are exciting exactly because they have not been explored so well and there may be a lot of improvements yet to be discovered.

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