[belviewreview]

Interesting, but assuming they can get the engine to work as intended, the question still remains how the passenger jet would get up to Mach 5 so the engine can start working. A solid-fuel rocket booster that would then drop off?

[credit_guy]

It is a safe bet that the first applications will be missiles and there won't be any passengers to worry about.

[jandrewrogers]

Interns provide the guidance.

[flohofwoe]

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

[trhway]

>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 ..."

[flohofwoe]

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

[belviewreview]

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?

[flohofwoe]

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).