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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

#181

Post by trhway »

sfifs wrote: post #92
darkteflon wrote: post #6

Cool science. But the article fails to take even a cursory stab at contextualising the plan against the economic, environmental and political backdrop - doesn’t even mention that there’s already been one failed supersonic commercial flight programme. This is as pie-in-the-sky as it gets.

Concord was very old technology. I am quite sure a clean sheet now 1. Would have much lower sonic booms thanks to recent research (quite a bit of it by NASA on wing geometry) and more importantly computer simulation available now 2. The engines would be far more fuel efficient 3. The flights would be able to have better efficiency in the subsonic regime as well. Just see what winglets and the like have done to fuel e…

>2. The engines would be far more fuel efficient

not really. In supersonic regime Concorde engines were pretty good, and you'd not beat them today by much.

Concorde was using afterburners to accelerate to supersonic and this is where it burned a lot of fuel. Designing engines which would give you good thrust at subsonic speeds without afterburners and would still perform well in supersonic is still much unsolved. Just look at the best military engines today - they all under Mach 2 and can't give even 3000 miles range.

And without increasing efficiency we can't really get much beyond the Concorde's 4500 miles. I.e. unfortunately there seems to be no current tech (or coming right tomorrow morning) that will allow Trans-Pacific.

It looks more feasible to me that Starship suborbital SFO-to-Shanghai will come well before a new Concorde on that route. Especially considering that Starship's ballistic trajectory is more fuel efficient on such long distances than supersonic plane flight.

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

#182

Post by Ngraph »

AIorNot wrote: post #97
Ngraph wrote: post #91

First time I heard the word "ramjet" was as a kid watching the Goliath episode of Knight Rider. Definitely not a documentary, but the word stuck. Then the Blackbird showed up in some plane book, and that was that. Ramjets back in the news. Kid me is having a great morning.

Yes it looks a lot more cheesy now than I remember as a kid https://youtu.be/SpEO-jIKhE8?si=89Qw1_AOXYow9PfR But ramjets have been promised to us for years

So nostalgic. AI, self-driving, ramjets — they packed it all in. And the thing that dates it isn't any of that, it's that nothing is a touchscreen. The future used to be chunky buttons.

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

#183

Post by Ngraph »

testing22321 wrote: post #106
Ngraph wrote: post #91

First time I heard the word "ramjet" was as a kid watching the Goliath episode of Knight Rider. Definitely not a documentary, but the word stuck. Then the Blackbird showed up in some plane book, and that was that. Ramjets back in the news. Kid me is having a great morning.

“Roger ramjet he’s our man, hero of the nation!! https://m.youtube.com/watch?v=E7SqSNQeAFM

Roger Ramjet! Now I've got that theme stuck in my head. Pretty sure that's where "ramjet = unstoppable" got hardwired in me.

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

#184

Post by flohofwoe »

trhway wrote: post #179
flohofwoe wrote: post #128

Earlier quoted context omitted.

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

> https://en.wikipedia.org/wiki/Kronach_Lorin coal burning ramjet! "It was initially proposed that a wire-mesh basket holding coal be mounted behind a nose air intake, protruding slightly into the airflow and ignited by a gas burner. [...] The air passing through the ramjet would take the gases from the burning coal ..."

Yes, not because it would be any better than the alternatives, but because this was one of countless "last ditch" efforts.

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

#185

Post by flohofwoe »

belviewreview wrote: post #178
flohofwoe wrote: post #128

Earlier quoted context omitted.

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

Ok, but the question still remains, how is it going to get up to the required speed? And in a way that is practical for a passenger plane?

I'm no aircraft engineer, but I guess it would use traditional jet engines to get up to some low Mach 1+ speed until the ramjet gets enough air to bite on.

My bet is that this hasn't been done yet simply because it wouldn't be economical (the technology itself is a century old and has been tried over and over again), and that the 'civilian ramjet aircraft' is just a feel good story for what will end up as purely military usage, and most likely not in an airplane, but in missiles (there are a couple ramjet engine missiles in use already, like the European Meteor).

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

#186

Post by flohofwoe »

Gravityloss wrote: post #127

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 miss…

> Ramjets were developed right after the second world war

Development already started during WW2 as one of many German last-ditch experiments, for instance:

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

...it never went into an actually flying airplane though (apparently there were test flights with Lorin tubes attached to propeller planes, but only to test the Lorin tube behaviour under flight conditions, not as an engine replacement).

The idea and patent itself is over a century old by now:

https://en.wikipedia.org/wiki/Ren%C3%A9_Lorin

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

#187

Post by flohofwoe »

throwaway2037 wrote: post #153
emptyfile wrote: post #130

Earlier quoted context omitted.

Well here's an economic application without nuclear tipped warheads. https://en.wikipedia.org/wiki/Meteor_(missile)

The Wiki pages says top speed is about Mach 4. There are already multiple rockets from US, Russia, and China that can achieve the same (or more) but with a solid-fuel rocket motor. What is the advantage of a ramjet here? It just seems way more complex and much less well tested (in labs and in combat). Also, has this missile (Meteor) been used in any combat scenarios? To be clear, the max speed for any fighter jet is…

You really need to play combat flight sims (like DCS) to understand why a ramjet AA missile makes a lot of sense ;)

It's not mainly about top speed, but about endurance (e.g. flying under power for the entire flight time of the missile).

The gist ist that traditional BVR AA missiles are only powered at the start of an engagement (and a lot of that power is used to gain height) until their rocket engine runs out of fuel. For a large part of its flight, traditional AA missiles glide without power towards the target, meaning the missile will lose speed from the moment the rocket engines are switched off, and even more for each required maneuver that needs to be performed afterwards (that's why it is a valid strategy for the targeted airplane to evade the missile by forcing it into a turn during its unpowered flight phase - e.g. instead of doing a 180 and flying straight away from the missile, fly a roughly 90 degree course to the incoming missile to force it into a wide turn, which means the missile will lose more energy than it would when remaining on a straight course).

A ramjet powered missile on the other hand flies under power for the entire engagement, it can 'cruise' towards the target and then for the final phase of the engagement speed up and home in on the target (or generally do complex maneuvers) without losing speed, which gives the target airplane much fewer options to evade the attack.

> I read some funny commentary once about how to shoot down a modern fighter jet: Two missiles. They can dodge the first one, but sacrifice so much speed, that the second one can easily find its target.

With a ramjet missile you don't need a second missile to exploit the target's depleted energy. And the two-missile strategy also doesn't really work when the other aircraft fires a single Meteor from a greater distance first ;)

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

#188

Post by seabass-labrax »

pfdietz wrote: post #167
m4rtink wrote: post #161

Earlier quoted context omitted.

If the capsule/rocketplane has some lift & preferably steerable aerosurfaces then you can compensate the purely ballistic deceleration somewhat. But yeah, if it is going down almost vertically then this will not be enough.

And all but rather short ballistic trajectories (well below orbital speed) will come in at a steep angle. Unless one has seriously variable aerodynamics, the vehicle will have to swerve to nearly horizontal over a distance of about 1 scale height of the atmosphere, which is about 10 km. The exponentially thinning atmosphere goes from "too thin to matter" to "brick wall" over a short distance. The acceleration for tur…

It would still be possible to fly a predominantly ballistic trajectory, yet use rocket propulsion to decelerate whilst still outside the atmosphere. It would require a huge amount of extra fuel compared to a purely ballistic trajectory, but perhaps still less than achieving a full orbit and de-orbiting again for some destinations.

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

#189

Post by laughing_man »

throwaway2037 wrote: post #180
laughing_man wrote: post #87

Earlier quoted context omitted.

If it stays in the realm of the ultra wealthy I don't see how it will succeed in the end. Commercial aircraft are really expensive to design and qualify, and you need to have a lot of sales to justify a new model. Ultra wealthy people are willing to pay more, but they also demand luxuries that take up a lot of space. The only reason Concorde did as well as it did, economically speaking, is the respective governments…

> respective governments footed the bill for development I just looked up development costs on Wiki: "£12–16.7 billion in 2025". Yikes. And "the market forecast was 350 aircraft", but only 20 were built. What a waste.

Yeah. But to be fair, it was the first supersonic airliner, so they were feeling around a bit in the dark when it came to estimating demand. They would have all looked like geniuses if enough demand to build 700 air frames had materialized.

I remember when the aircraft first went into service. Everybody thought subsonic air travel, at least over the ocean, would become a thing of the past.

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

#190

Post by pfdietz »

seabass-labrax wrote: post #188
pfdietz wrote: post #167

Earlier quoted context omitted.

And all but rather short ballistic trajectories (well below orbital speed) will come in at a steep angle. Unless one has seriously variable aerodynamics, the vehicle will have to swerve to nearly horizontal over a distance of about 1 scale height of the atmosphere, which is about 10 km. The exponentially thinning atmosphere goes from "too thin to matter" to "brick wall" over a short distance. The acceleration for tur…

It would still be possible to fly a predominantly ballistic trajectory, yet use rocket propulsion to decelerate whilst still outside the atmosphere. It would require a huge amount of extra fuel compared to a purely ballistic trajectory, but perhaps still less than achieving a full orbit and de-orbiting again for some destinations.

At global distances a fraction orbital trajectory would use less total rocket delta-V.

More practical would be a trajectory that was a series of small suborbital arcs with skipping off the atmosphere (perhaps with some airbreathing propulsion during the skips.) The thermal protection can cool by radiation between the skips.

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