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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

#161

Post by m4rtink »

pfdietz wrote: post #148
thrownthatway wrote: post #115

Earlier quoted context omitted.

90 minutes is a low earth orbit period. A suborbital craft won’t be travelling at that speed.

Unless a suborbital trip is nearly at orbital velocity, it will involve a high, arcing trajectory. This will make the deceleration at the end unacceptably (lethally) high for all but short arcs. Some of the Mercury suborbital missions involved deceleration of 15 gees, if I recall correctly.

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.

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

#162

Post by emptyfile »

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…

[dead]

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

#163

Post by fancyfredbot »

octaane wrote: post #151
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…

My take is also a missile, but as an interceptor, not offensive purposes. North Korea has shown that they can deliver a payload to Japan if they want. If the NKs do decide to launch something at Japan, it's not going to be tipped with conventional explosives. It'll be a nuke. Hypersonic interceptor seems the more likely application is this tech to me.

I think that hypersonic interceptors would use a rocket motor and not a ramjet, but I'm not sure.

I think this is for offence because I understood the advantage of this engine (compared to a rocket engine) is that you don't carry oxygen so you can carry more fuel and get more range. I think range is much more useful for offence than defence.

I am possibly making myself look foolish now as I'm not an expert on either rockets or ramjets and I might have incorrectly dismissed defensive applications.

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

#164

Post by phire »

pfdietz wrote: post #148
thrownthatway wrote: post #115

Earlier quoted context omitted.

90 minutes is a low earth orbit period. A suborbital craft won’t be travelling at that speed.

Unless a suborbital trip is nearly at orbital velocity, it will involve a high, arcing trajectory. This will make the deceleration at the end unacceptably (lethally) high for all but short arcs. Some of the Mercury suborbital missions involved deceleration of 15 gees, if I recall correctly.

That was only an issue because they were fired pretty much straight up; They only went 500km down range.

You can also reduce peek deceleration forces by using aerodynamic lift to stretch out the reentry over a longer period.

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

#165

Post by rafram »

atoav wrote: post #116
rafram wrote: post #66

Earlier quoted context omitted.

Really? Obviously it varies by country, but there’s no customs/immigration when leaving the US, and security usually takes <5 minutes with PreCheck. Sometimes immigration takes a while on the other side, but it’s quick at airports with biometric gate systems. You still hear people talk about airport buffer time in units of hours, but I think that’s increasingly out of date.

So how long before the actual flight departure will you be at the airport? If I catch a train that is 10 minutes before the train departs on a metropolitan train station in Europe. With planes in my experience arriving two hours before the actual departure is not uncommon at bigger airports, since there are more insecurities involved like how crowded security checks are, where your gate is, etc.

In the US, generally one hour no matter whether it's domestic or international. In Germany, like three hours because security and immigration is insanely slow and inefficient. In the UK and other countries I'm less familiar with, two is usually fine.

If I come earlier, it's with the expectation that I'll waste some time hanging out in a lounge.

(Train situation is similar in the US, in places where we actually have those. Generally fine to show up right before departure.)

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

#166

Post by pfdietz »

phire wrote: post #164
pfdietz wrote: post #148

Earlier quoted context omitted.

Unless a suborbital trip is nearly at orbital velocity, it will involve a high, arcing trajectory. This will make the deceleration at the end unacceptably (lethally) high for all but short arcs. Some of the Mercury suborbital missions involved deceleration of 15 gees, if I recall correctly.

That was only an issue because they were fired pretty much straight up; They only went 500km down range. You can also reduce peek deceleration forces by using aerodynamic lift to stretch out the reentry over a longer period.

No, it's an issue for most arcing trajectories. Lift doesn't help much if you're coming in at a steep angle. Reentry from orbit only works well because the entry is almost flat; there even a little lift helps a lot.

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

#167

Post by pfdietz »

m4rtink wrote: post #161
pfdietz wrote: post #148

Earlier quoted context omitted.

Unless a suborbital trip is nearly at orbital velocity, it will involve a high, arcing trajectory. This will make the deceleration at the end unacceptably (lethally) high for all but short arcs. Some of the Mercury suborbital missions involved deceleration of 15 gees, if I recall correctly.

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 turning is v^2/r; for v = 5000 m/s and r = 10 km this is 250 g.

Acceleration also limits how rapidly one can reenter from beyond Earth orbit. At > LEO velocity, the vehicle has to use (downward) lift to stay in the atmosphere, and if v is too high the required acceleration is too high.

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

#168

Post by mckn1ght »

throwaway2037 wrote: post #158
fragmede wrote: post #68

Earlier quoted context omitted.

Shorter, no, but having a private cabin with a shower, and a lounge with a bartender on the plane, not to mention Starlink, would make those 12 hours a lot more bearable vs 12 in an economy seat.

> having a private cabin with a shower AFAIK: Showers are only available to first class customers flying via the major Gulf carriers. I checked Google flights for business class and first class tickets between Tokyo and London. Business is about 5,000 USD and first class is about 10,000 USD. Assuming that we are talking about first class here (to satisfy your shower requirement), what kind of developer is hacking cod…

Wasn’t Concorde like 20-50% more expensive than a normal first class ticket for the same itinerary?

So any hacker considering a SST flight should also be able to afford the first class cabin.

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

#169

Post by bobthepanda »

mckn1ght wrote: post #168
throwaway2037 wrote: post #158

Earlier quoted context omitted.

> having a private cabin with a shower AFAIK: Showers are only available to first class customers flying via the major Gulf carriers. I checked Google flights for business class and first class tickets between Tokyo and London. Business is about 5,000 USD and first class is about 10,000 USD. Assuming that we are talking about first class here (to satisfy your shower requirement), what kind of developer is hacking cod…

Wasn’t Concorde like 20-50% more expensive than a normal first class ticket for the same itinerary? So any hacker considering a SST flight should also be able to afford the first class cabin.

If it ever actually gets off the ground, Boom Supersonic is allegedly targeting a $5000 business class trip for transatlantic.

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

#170

Post by lonelyasacloud »

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…

> 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.

Case of China's got them, and can't rely on the Orange Emperor and his heirs to have their backs.

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