Talk:Ram accelerator

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Is there a distinction in literature between "ram accelerators" and "scram accelerators"? My understanding is that these devices were originally built to study _scramjet_ design (easier to send a projectile down a tube filled with air/hydrogen mixture than to build a hypersonic wind tunnel). --Christopher Thomas 17:28, 28 Feb 2005 (UTC)

Check out http://www.physicsforums.com/archive/t-51528_Ram_Accelerator.html and http://www.aa.washington.edu/AERP/ramac/detailed/prop_modes.html. Ramjets operate with subsonic/transonic flow in the combustion chamber, and scramjets operate with supersonic flow in the "combustion chamber"--in most scramjet designs I've seen, the "jet" is just a bump or angle with a fuel injector behind it, with the shock wave providing one combustion chamber wall (sort of like the linear nozzle engies) and the compression heating of the air providing the ingition source. The problem is, to get a scramjet to work, you need to be going Mach 4+. Ramjets kick in at around Mach 1, and can run up to Mach 5 or so. Basically the differentiation between ram and scram acceleration is whether or not the projectile hits speeds high enough to transition to supersonic combustion. It may also be possible to make a projectile that will only scram, but not ram, by not truncating the rear cone. I read an article in Discover Magazine 10+ years ago about a scram cannon, and I think it had a projectile that was pointed at both ends. It was not like the Washinton U gun, it used gunpowder for initial acceleration, not a light gas gun. It may well have skipped subsonic combustion completely and gone right to scram. I do also wonder if the ram projectiles need an ignition source in the base. The old ramjet cruise missles used a flare sticking out of the flameholder as an ignition source. scot 18:32, 28 Feb 2005 (UTC)

I am aware of the operational difference between a ramjet and a scramjet; my point was that I had understood that the term "ram accelerator" covered cannons that operated both in subsonic and supersonic combustion regimes (among other things, this is what that Discover article you mention described). I had never heard the term "scram accelerator", and the description on the combustion modes page you link doesn't mention it either, which makes me leery of considering it a technical term. Google turns up a handful of hits for papers that used it, but "ram accelerator" is far more common. Please don't take this as an attack; it just strikes me as a term that is not in common use among academics discussing this type of device. --Christopher Thomas 22:24, 28 Feb 2005 (UTC)

Yeah, I think you're right. The term "scram cannon" appears to be far more common, especially in SF references to the technology's potential military uses. That's also the term that stuck when I read the Discover article, but "scram accelerator" just seemed to be a more correct term, but, as you pointed out, it's just not that commonly used. How about changing the note in the article to "scram cannon" and changing the redirect as well? Or leave in "scram accelerator" and add "scram cannon"? scot 04:27, 1 Mar 2005 (UTC)

I'll tweak the wording a bit, and make a note of "scram cannon" as a science fiction term for the supersonic combustion version. The redirect from "scram accelerator" isn't doing any harm, so as far as I'm concerned it can be left as-is (and a few people may search for it based on the paper and forum links that are out there). I'll also fold in your reference links into the main article (thanks for the research!).--Christopher Thomas 04:49, 1 Mar 2005 (UTC)

Tweaking complete. If you feel up to starting a "scram cannon" page to describe the fictional weapon, go ahead; you probably have a much better handle on where the term has been used than I do.--Christopher Thomas 05:05, 1 Mar 2005 (UTC)

I'm adding the scram cannon page now. I might be reading too much into Heinlein's gun in "If this goes on-", as there had been attempts to make staged guns in the 1940s, but I think that the description he used doesn't rule out a ram accelerator, and certainly the ram accelerator would achieve the same goal--the maximum energy possible from a kinetic energy projectile. scot 16:33, 1 Mar 2005 (UTC)