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In the US, a rotating detonation rocket engine takes flight

arstechnica.com

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Re: In the US, a rotating detonation rocket engine takes flight

#51

Post by Voultapher »

K0balt wrote: post #21
zdragnar wrote: post #14

Earlier quoted context omitted.

The point is reduced fuel use and faster response times (either emergencies or warfare). Maintaining a detonation (as opposed to deflagration) is quite a technical challenge. If nothing else, it pushes mechanical engineering and material science forward.

At supersonic speeds, the efficiency of an engine like this can be very high, and at high altitudes, travel is very efficient. People don’t seem to get that there is potential for more efficient transport at supersonic speeds/ hypersonic speeds. The ultimate example of this a satellite. How many times does it circle the world every 45 min, all on that initial fuel it took to get it up there? It seems wasteful, but it…

What about noise? So far all we have gotten is companies trying to build planes that still are very loud and produce audible booms all the way along their travel path. Pitched to the empathetic heros that are billionaires. And to sway public opinion they fly test planes at slightly over mach one in specific weather and altitude setting that avoids having the sonic booms reach the ground. While marketing and selling the idea of not mach 1.1 but mach 2-3 supersonics. Which is AFAIK completely impossible without the boom issue, even if made less bad - but arguably still bad - by fancy wing shapes. So all I see is selfish people trying to build something at expense of everyone else, including the environment.

Re: In the US, a rotating detonation rocket engine takes flight

#52

Post by Symmetry »

kragen wrote: post #45
Symmetry wrote: post #12

Earlier quoted context omitted.

To be a bit more clear, the detonation is racing around a circular track in one plane, but the net thrust is in the direction perpendicular to that plane. Fuel and oxidiser are continuously pumped in all along the track, dropping to ~0 after a detonation and rising afterwards until the detonation front arrives again. Since you don't have to pump into a continual high pressure deflagration like in a conventional rocke…

By "chock" do you mean "impact"? In English a chock is a rubber wedge you put under a wheel to keep it from rolling, or various similar objects, or the act of using one to keep something from moving: https://en.wiktionary.org/wiki/chock

Oops, that should have been "choke".

Re: In the US, a rotating detonation rocket engine takes flight

#53

Post by magicalhippo »

growlNark wrote: post #50
lupusreal wrote: post #41

Earlier quoted context omitted.

It's not a new term, and it exists because there are unique practical engineering problems associated with high mach numbers so having a term for this regime is useful even if the distinction seems arbitrary from a pure theoretically perspective.

Sure, but "hyper"? Is there any reason other than that it sounds cooler than "super"? What are we going to do when we hit mach 11, start talking about "hyperhypersonic"? "superhypersonic"?

It's a distinct regime, so useful to give it a distinc name. Super and hyper are roughly synonyms, but super was already taken.

There was also some precedence from wave research back in 1938 which suggested hypersonic and ultrasonic for high frequency waves[1].

At this point it's a well-established term, with 60 years of history[2].

[1]: https://www.ias.ac.in/public/Volumes/seca/007/03/0163-0176.p...

[2]: https://secwww.jhuapl.edu/techdigest/Content/techdigest/pdf/...

Re: In the US, a rotating detonation rocket engine takes flight

#54

Post by growlNark »

magicalhippo wrote: post #53
growlNark wrote: post #50

Earlier quoted context omitted.

Sure, but "hyper"? Is there any reason other than that it sounds cooler than "super"? What are we going to do when we hit mach 11, start talking about "hyperhypersonic"? "superhypersonic"?

It's a distinct regime, so useful to give it a distinc name. Super and hyper are roughly synonyms, but super was already taken. There was also some precedence from wave research back in 1938 which suggested hypersonic and ultrasonic for high frequency waves[1]. At this point it's a well-established term, with 60 years of history[2]. [1]: https://www.ias.ac.in/public/Volumes/seca/007/03/0163-0176.p... [2]: https://sec…

> Super and hyper are roughly synonyms

Perhaps you're right in terms of how they're leveraged in today's society. I'll drop my pedantry.

Re: In the US, a rotating detonation rocket engine takes flight

#55

Post by K0balt »

hermitcrab wrote: post #33
K0balt wrote: post #21

Earlier quoted context omitted.

At supersonic speeds, the efficiency of an engine like this can be very high, and at high altitudes, travel is very efficient. People don’t seem to get that there is potential for more efficient transport at supersonic speeds/ hypersonic speeds. The ultimate example of this a satellite. How many times does it circle the world every 45 min, all on that initial fuel it took to get it up there? It seems wasteful, but it…

Presumably, you have to be travelling quite a distance before hypersonic/high-altitude flight becomes more efficient than current commercial airliners.

Certainly not for short hops, but if regular aviation is any indication, it’s more efficient even if you don’t even reach cruising altitude before beginning to descend, so I’d imagine any flight that currently is around 4 hours or more would potentially benefit. (Given full technology maturity) that said, we are a long, long way from having efficient engines for that wide of a speed envelope.

Re: In the US, a rotating detonation rocket engine takes flight

#56

Post by magicalhippo »

growlNark wrote: post #54
magicalhippo wrote: post #53

Earlier quoted context omitted.

It's a distinct regime, so useful to give it a distinc name. Super and hyper are roughly synonyms, but super was already taken. There was also some precedence from wave research back in 1938 which suggested hypersonic and ultrasonic for high frequency waves[1]. At this point it's a well-established term, with 60 years of history[2]. [1]: https://www.ias.ac.in/public/Volumes/seca/007/03/0163-0176.p... [2]: https://sec…

> Super and hyper are roughly synonyms Perhaps you're right in terms of how they're leveraged in today's society. I'll drop my pedantry.

They roughly have the same meaning in the languages they were borrowed from, Latin[1] and Greek[2] respectively.

Yeah it's random, but established at this point. The radio bands aren't much better[3] with their Very High Frequency (VHF), Ultra High Frequency (UHF) and Super High Frequency (SHF) and Extremely High Frequency (EHF).

[1]: https://www.etymonline.com/word/super-

[2]: https://www.etymonline.com/word/hyper-

[3]: https://en.wikipedia.org/wiki/Radio_spectrum#ITU

Re: In the US, a rotating detonation rocket engine takes flight

#57

Post by K0balt »

Voultapher wrote: post #51
K0balt wrote: post #21

Earlier quoted context omitted.

At supersonic speeds, the efficiency of an engine like this can be very high, and at high altitudes, travel is very efficient. People don’t seem to get that there is potential for more efficient transport at supersonic speeds/ hypersonic speeds. The ultimate example of this a satellite. How many times does it circle the world every 45 min, all on that initial fuel it took to get it up there? It seems wasteful, but it…

What about noise? So far all we have gotten is companies trying to build planes that still are very loud and produce audible booms all the way along their travel path. Pitched to the empathetic heros that are billionaires. And to sway public opinion they fly test planes at slightly over mach one in specific weather and altitude setting that avoids having the sonic booms reach the ground. While marketing and selling t…

Flying it the high limits of the atmosphere reduces sonic boom intensity due to both the extremely low density of the air and the distance from the ground. Ultimately, sonic boom is a sign of wasted energy, so if (big if) we can make aircraft that conform to the required aerodynamic ideals for efficient hypersonic flight, they will be relatively quiet.

Just like with regular air travel, though, I would expect a few decades of practical application for specialized service before it was commodified to be really useful for large amounts of passengers.

Re: In the US, a rotating detonation rocket engine takes flight

#58

Post by jasrys »

ColinWright wrote: post #2

From the article: "In contrast to a traditional rocket engine, in which a highly pressurized propellant and an oxidizer are injected into a combustion chamber where they burn and produce an energetic exhaust plume, a rotating detonation engine is different in that a wave of detonation travels around a circular channel. This is sustained by the injection of fuel and oxidizer and produces a shockwave that travels outwa…

NASA tested one at Marshall about a year ago: https://www.youtube.com/watch?v=UShD03eG9IU

Re: In the US, a rotating detonation rocket engine takes flight

#59

Post by lupusreal »

growlNark wrote: post #50
lupusreal wrote: post #41

Earlier quoted context omitted.

It's not a new term, and it exists because there are unique practical engineering problems associated with high mach numbers so having a term for this regime is useful even if the distinction seems arbitrary from a pure theoretically perspective.

Sure, but "hyper"? Is there any reason other than that it sounds cooler than "super"? What are we going to do when we hit mach 11, start talking about "hyperhypersonic"? "superhypersonic"?

The term has been in use since the 1940s, pretty much as soon as it was sensible to think about making something that can go that fast. Does your modern perception of "hyper" being a cool word reflect how the word was perceived 80 years ago, or does your perception of the word being cool come from the way the word has since been used to describe such extreme things?

Maybe it was considered cool back then, but I wouldn't be sure of that. Maybe it was just an obscure latin term nerds used. I guess you could search comic book archives for clues. In any case, really fast things are cool, but only figuratively speaking.

Re: In the US, a rotating detonation rocket engine takes flight

#60

Post by twic »

xeonmc wrote: post #43
twic wrote: post #24

Earlier quoted context omitted.

What i've never understood is how detonation can be more efficient than deflagration. What does that mean? Both types of engine take a mix of fuel and oxidiser and turn it into hot combustion products. The hot combustion products then expand through a nozzle to produce thrust. How is that process different between the two? Does a deflagration engine leave some fuel unburnt, that a detonation engine burns? Does the co…

Just think in terms of the P-V diagram, you want the pressure increase curve to be as vertical as possible to maximize the area enclosed by the cycle

This doesn't help at all. Diagrams are diagrams, what does it actually mean physically?
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