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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

#111

Post by sigmoid10 »

mytailorisrich wrote: post #109

It seems to me that hypersonic engines are the fusion power of aeronautics. Always 10 years away.

Building a ramjet that is more efficient than rockets while travelling at several times the speed of sound is the easy part. The hard part is getting up to that speed first, because they give basically no thrust at low speeds. So you always need a two component engine and fuel system, with each component being useless at either launch or in-flight. Basically a similar reason why only the military uses VTOL planes. The military has no problem strapping a rocket booster on a ramjet missile.

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

#112

Post by m4rtink »

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…

90 minutes is a full low Earth orbit cycle. For a suborbital hop it should be about half of that at maximum for any 2 points on Earth.

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

#113

Post by m4rtink »

sigmoid10 wrote: post #111
mytailorisrich wrote: post #109

It seems to me that hypersonic engines are the fusion power of aeronautics. Always 10 years away.

Building a ramjet that is more efficient than rockets while travelling at several times the speed of sound is the easy part. The hard part is getting up to that speed first, because they give basically no thrust at low speeds. So you always need a two component engine and fuel system, with each component being useless at either launch or in-flight. Basically a similar reason why only the military uses VTOL planes. Th…

And once you do all that, you will need to also handle the massive atmospheric heating from friction, so that the whole thing does not melt during flight.

Again, not that problematic for missiles due to shorter flight times and single-use ablative heatshields being viable.

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

#114

Post by petterroea »

m4rtink wrote: post #112
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…

90 minutes is a full low Earth orbit cycle. For a suborbital hop it should be about half of that at maximum for any 2 points on Earth.

I didn't initially believe these numbers, but if you look at some real life stats, you are probably right.

Nominal SECO for the last starship mission was at ~8 minutes and it took ~20 minutes from deceleration started (well, from air resistance outweighed the forces of acceleration) to landing. So basically 30 minutes of flight is just the "getting up to speed" and "slowing down" part. Both account for some distance traveled, but still. ~45 minutes is probably a good bet.

Do note however that you may have to go around the world "the wrong way" to get some places due to launch constraints. But living in a world where going around the world "the wrong way" is the easier path is interesting. Imagine that.

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

#115

Post by thrownthatway »

m4rtink wrote: post #112
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…

90 minutes is a full low Earth orbit cycle. For a suborbital hop it should be about half of that at maximum for any 2 points on Earth.

90 minutes is a low earth orbit period.

A suborbital craft won’t be travelling at that speed.

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

#116

Post by atoav »

rafram wrote: post #66
atoav wrote: post #4

The actual time to skim off IMO is all the airport procedures.

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.

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

#118

Post by adev_ »

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…

> you might as well just switch to a suborbital hop concept.

One is not exclusive to the other.

Skylon was expected to use air breathing engine up to Mach5+ and switch to rocket engine beyond it.

You can probably do the same for a suborbital airliner if you are insane enough.

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

#119

Post by inglor_cz »

Insimwytim wrote: post #29

> At that elevation at Mach‑5, air around the nose and leading edges can reach temperatures exceeding 1,000 degrees Celsius (1,832°F), a challenge the U.S. Air Force has struggled to overcome with its own hypersonic jets. > To handle that level of heat, engineers constructed an advanced thermal‑protection system that maintained the aircraft's interior near normal operating temperature, allowing the onboard avionics a…

We have a lot of experience with heat shields from cosmic reentries now, though. This is probably doable.

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

#120

Post by notahacker »

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…

It'd be far more efficient than the 50 year old tech, but so is the baseline tech they're comparing it with, and the market has optimised heavily for price competition (and has a lot more private jets doing exactly the route and time executives with Concorde money want) and needs speed somewhat less when it's a lot easier to stay in touch with a business whilst inflight. Ultimately there's not much to draw lessons from that suggests it's going to sell enough aircraft to recover the investment of building and certifying it (even comparatively simple niche aircraft like the A380 struggled there), which is why even Boom is now reinventing itself as a provider of turbines for AI datacentres to try to fund its development costs...
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