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A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft

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Re: A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft

#121

Post by numpad0 »

phire wrote: post #110

Is a Mach-5 passenger aircraft actually the goal of this project? Seems more likely that Japan is designing this engine for a hypersonic cruise missile program, and the passenger aircraft concept is somewhat of a cover. IMO, there is no point in a Mach-5 Aircraft (other than cruise missiles). There is potentially some point in Mach 2-3 aircraft, (not that we have ever made them commercially viable) but at the boundar…

Air breathing engines don't need the oxidizer tank, so like the 2/3 of a rocket just goes away before even touching Tsiolkovsky math. That improves payload mass fraction massively.

Also, this doesn't scale down to Mach 3-4 and under. This thing uses scramjet, or supersonic combustion ramjet. It REQUIRES intake air to be at high supersonic speeds for it to work.

Re: A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft

#122

Post by numpad0 »

brandelune wrote: post #70

Two news items in one : Japan is getting ready for hypersonic missiles, and Japan’s elite does not give a damn about global warming.

Next generation of. The Type 25 HVGP just entered service few months ago. That one is just a two-stage Scud, but the Block 3 or NG or Type 35 or whatever of that could have this tech.

Re: A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft

#123

Post by avadodin »

The original submission didn't mention ramjet.

I always thought it was an underutilized design that could be improved for practical applications.

Improved enough, it could become cheaper and more environmentally-friendly than current aviation whereas regular supersonic jets are never going to achieve that.

Re: A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft

#124

Post by MrMikardo93 »

phire wrote: post #110

Is a Mach-5 passenger aircraft actually the goal of this project? Seems more likely that Japan is designing this engine for a hypersonic cruise missile program, and the passenger aircraft concept is somewhat of a cover. IMO, there is no point in a Mach-5 Aircraft (other than cruise missiles). There is potentially some point in Mach 2-3 aircraft, (not that we have ever made them commercially viable) but at the boundar…

> (not that we have ever made them commercially viable)

Concorde was commercially viable at Mach 2.2 in supercruise (although there's a common misconception that it was not).

However, its overheads were very high, and its applicability was severely limited by fears around the sonic boom (most particularly in the US, which banned supersonic flight overland, possibly largely because they wanted to kill off foreign competition).

Re: A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft

#125

Post by MrMikardo93 »

numpad0 wrote: post #121
phire wrote: post #110

Is a Mach-5 passenger aircraft actually the goal of this project? Seems more likely that Japan is designing this engine for a hypersonic cruise missile program, and the passenger aircraft concept is somewhat of a cover. IMO, there is no point in a Mach-5 Aircraft (other than cruise missiles). There is potentially some point in Mach 2-3 aircraft, (not that we have ever made them commercially viable) but at the boundar…

Air breathing engines don't need the oxidizer tank, so like the 2/3 of a rocket just goes away before even touching Tsiolkovsky math. That improves payload mass fraction massively. Also, this doesn't scale down to Mach 3-4 and under. This thing uses scramjet, or supersonic combustion ramjet. It REQUIRES intake air to be at high supersonic speeds for it to work.

> It REQUIRES intake air to be at high supersonic speeds for it to work

This is why I am highly sceptical it can be part of a commercial supersonic passenger jet: how do you get from subsonic -> supersonic without also tacking on some kind of conventional jet engine?

Re: A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft

#126

Post by fancyfredbot »

For many many reasons this engine only has one economic application - delivery of a nuclear payload in a way which is very hard for missile defences to stop.

ICBMs can go faster than this already but as I understand it they go higher allowing for earlier detection and they follow a more predictable trajectory which makes interception more realistic.

I find super fast missiles far scarier than advanced AI. I suppose they maintain the "mutually assured destruction" which might be the main reason there hasn't been a nuclear war since WW2, but it's not a huge comfort.

Re: A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft

#127

Post by Gravityloss »

Ramjets were developed right after the second world war and Mach 4+ was reached in the fifites. It's complicated but not extremely. See Antonio Ferri or Lockheed X-7.

It turned out out solid fuel rockets are operationally more practical for the use cases like air defence, long range missiles that are ballistic instead of cruising in the atmosphere and so on. And jet engines are more efficient for subsonic cruise missiles. Ramjets are still used in some missiles like the long range mach 3 air-to-air Meteor.

Re: A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft

#128

Post by flohofwoe »

belviewreview wrote: post #86

Interesting, but assuming they can get the engine to work as intended, the question still remains how the passenger jet would get up to Mach 5 so the engine can start working. A solid-fuel rocket booster that would then drop off?

I may be wrong but I think a ramjet doesn't need Mach 5 to ignite, Mach 3 to 6 is just where it is most efficient at high altitudes.

E.g. early German experiments during WW2 based on the Lorin tube (https://en.wikipedia.org/wiki/Ren%C3%A9_Lorin) only had to get to 320 km/h to start working:

https://en.wikipedia.org/wiki/Kronach_Lorin

Re: A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft

#129

Post by abbadadda »

I actually learned about what a ramjet is after looking up the definition of “scramjet” when watching the _Top Gun: Maverick_ movie with my son. This is at the beginning of the movie when he is flying the Dark Star plane designed in conjunction with Skunk Works from Lockheed Martin. Well, we are obviously a ways away from Mach 10 reached in the film by the SR-71 Blackbird descendant, the new technology pushing Mach 5 and into high hypersonic is pretty impressive.

> A scramjet is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow. As in ramjets, a scramjet relies on high vehicle speed to compress the incoming air forcefully before combustion, but whereas a ramjet decelerates the air to subsonic velocities before combustion using shock cones, a scramjet has no shock cone and slows the airflow using shockwaves produced by its ignition source in place of a shock cone - Wikipedia

Re: A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft

#130

Post by emptyfile »

fancyfredbot wrote: post #126

For many many reasons this engine only has one economic application - delivery of a nuclear payload in a way which is very hard for missile defences to stop. ICBMs can go faster than this already but as I understand it they go higher allowing for earlier detection and they follow a more predictable trajectory which makes interception more realistic. I find super fast missiles far scarier than advanced AI. I suppose t…

Well here's an economic application without nuclear tipped warheads.

https://en.wikipedia.org/wiki/Meteor_(missile)

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