A successful Japanese trial of a ramjet engine designed for Mach‑5 aircraft
A Japanese test of a ramjet engine for proposed Mach‑5 passenger aircraft is prompting skepticism about whether hypersonic civilian travel is technically, economically, and environmentally realistic. Commenters note that while hypersonic air‑breathing propulsion is advancing, materials, heat management, noise, and certification for reusable aircraft remain major hurdles, and past efforts like Concorde struggled to be commercially viable. Many see the most likely near‑term uses in missiles or ultra‑premium business jets rather than mass passenger transport, especially given growing concern over climate impact and limited time savings once airport logistics are factored in.
Technical feasibility of Mach‑5 flight
- Commenters stress that an engine alone doesn’t make 2‑hour transpacific flights feasible; materials, thermal management, and airframe design are major unsolved issues.
- Hypersonic air‑breathing propulsion (ramjet/scramjet) is described as much harder than rocket-based hypersonic flight: internal shockwaves and heat loads inside the duct are key constraints.
- Some think hypersonic air‑breathing is “nowhere near” solved; others point to rumored programs (e.g., SR‑72, Meteor missile) as evidence the puzzle may be cracked for military-scale craft.
- Noise and structural vibration are expected to be significant for passengers, even at high altitude, due to transmission through the fuselage.
Passenger travel vs. missiles
- Many argue the obvious first application is hypersonic missiles, not passenger jets, given complexity, heat, and startup-speed requirements.
- Ramjets need high initial speeds; practical designs likely require separate propulsion (e.g., rockets or conventional jets) to get to ignition speed.
- Several posts suggest the “Mach‑5 passenger jet” narrative is partly cover or aspirational; the real driver is seen as cruise-missile tech and advanced fighters/interceptors.
Economics and market
- Concorde is repeatedly cited: technically impressive but economically marginal, with limited routes, high fuel burn, and sonic boom restrictions.
- Some say today’s world—more ultra‑wealthy, more long‑haul Asia–Pacific traffic—could support a boutique supersonic/hypersonic market, especially for business jets and key executives.
- Others argue there are no economies of scale; certification, maintenance, training, and separate fleets make commercial viability unlikely, even with high ticket prices.
Alternatives: suborbital and existing air travel
- Suborbital hops are proposed as more sensible for extreme speed: shorter global travel times, avoidance of sustained hypersonic heating, and a brief weightless experience.
- Discussion highlights that door‑to‑door time is dominated by ground logistics and airport security; some see this as the real bottleneck, others say trusted-traveler programs already minimize this for the target clientele.
Environment, safety, and politics
- Environmental impact is a major concern; some see hypersonic passenger travel as incompatible with climate goals.
- Several view this primarily as part of a broader hypersonic weapons race and missile defense ecosystem, not a civil aviation revolution.