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A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft
131–140 of 196 posts
Re: A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft
#132Earlier quoted context omitted.
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.
Like, you could do a partial orbit & then drop down over the destination. But it would need much more delta-v & an orbital class heat shield.
It was proposed as nuclear warhead delivery method though: https://en.wikipedia.org/wiki/Fractional_Orbital_Bombardment...
Re: A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft
#133We had Concorde - it was too expensive to operate safely.
We just didn‘t have enough billionaires back then. Today the Thiels and Musks and Bezos will be able to afford this.
Agree that this is a matter of economic viability rather than technology. Presumably somebody could just go back and resurrect the Roles Royce IP
There would be the nice side benefit of maybe having all these guys in one place, upon an experimental aviation platform.
Re: A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft
#134As a Canadian who travels to Europe about once per month I am very excited for this :D
Wait 20 years to save a few hours :)
Re: A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft
#135> 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…
> Hindenburg 2.0 waiting to happen
Fortunately there's no hydrogen in that plane.
Re: A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft
#136I imagine passengers will be exposed to very high noise levels during flight.
I don't have a good intuitive feel for that. At 25km altitude, with 1% of normal atmosphere, maybe you're close enough to vacuum that it can get really quiet?
This effect would help mitigate the noise heard by people outside of the plane (but I suspect that noise is negligible compared to the sonic boom), but in the plane the sound would mostly be propagated though the fuselage of the plane, not through air, so it's not going to help.
Re: A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft
#137Earlier quoted context omitted.
12 hours on a plane is 12 hours on a plane. And there's currently no amount of ticket money that can make that shorter.
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.
Sure, but it would also make it much more expensive than a supersonic flight…
Re: A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft
#138Is 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 comp…
The individual aircraft could be operationally viable on certain routes, but the whole program was not commercially viable.
Re: A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft
#139For 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…
I find fast missiles with AI to be pretty scary. Heck a slow drone with AI targeting chasing me is bad enough...
Re: A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft
#140Earlier quoted context omitted.
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?
And you’d need the conventional jet to survive