Quite a bit. I could probably figure out a first-order estimate by hand.
Maybe Aero's claim that basic theory will get you to 3Km/s (about M8.8 ) is correct but given the results of the X30 programme what I'm suggesting is a flight programme.
Quote from: john smith 19 on 08/16/2014 11:28 AMMaybe Aero's claim that basic theory will get you to 3Km/s (about M8.8 ) is correct but given the results of the X30 programme what I'm suggesting is a flight programme.And really what DOES air-breathing to @Mach-5+ get you if its "cheap" and "easy" enough over the alternatives?(I'd suggest hitting up the "Ex-Rocketman's Take" blog to see some of the work he's done as one of "those" engineers )
I have downloaded the copy of the Glen Olson's site, including the ramjet design tool (although working out how to use it looks tricky. I'm guessing it's imperial units, but I'm not sure ).
My suggestion is a pure research project to settle an apparently simple question (it's one of the outstanding question's on Olson's site). In the same way the X1 was designed to answer the question "could you build a vehicle big enough to carry a person that could exceed M1".
My impression is that it seems that historically a missile requirement has been stated and people have built a ram jet to meet it but no one seems to checked how fast can such an engine go before you have to start looking at full supersonic combustion or pure rocket systems. In the US upper speeds have only been established by stuck open valves (and I'll note they seem to have been still accelerating so thrust > drag and lift > mass) while the French report you cited indicated that a 10 flight M5 test programme seemed to be fairly straight forward.
Olson suspected the operating range of 3 Mach numbers of most actual missiles was a convenience for the designers (and a perfectly valid trade off in a weapon system). The implication being that with more attention to detail and possibly accepting you'd lose some payload that range could be much wider.
I'll note the Russian/Indian "BraMos" anti ship missile is good to M2.8-3.0 and their planned 2nd generation is to M7. They don't seem to be talking about supersonic combustion to do it but they do seem to want liquid fuel.
As a side note I will note that M7 is 1/4 of the velocity to orbit including losses and M13 (using M1=340 m/s) is about 1/2 to orbital velocity.If LEO is "half way to anywhere" then I guess at 1/2 LEO velocity you'd be a quarter way to anywhere?TBH that's beyond what the comments of the people Olson talked to thought possible but the truth is that despite the first one running in the early 1930's we still don't know.
I'm still playing with it when I remember I have it
Anyway, in some of his notes Glenn mentiones that during his research there was enough written data to support the conslusion that "someone" had flown a subsonic ramjet engine at speeds to around Mach-8 and most seemed confident that Mach-10 was possible and still generate thrust. But as you note, we really don't KNOW what the limits are.
As far as I know there were only a few actual "test" ramjet vehicles the best known one being the X7. Most engines were "point-designs" specifically designed to operate at a restricted range speeds.
I got from his site and other sources that if you're willing to put up with the expense and compelxity of moving inlets and exhaust AND intergrate into the vehicle (the majority of early work concentrated on podded engines as experiance with imbedded jet engines hadn't been as good as hoped, turns out different engines have different operational experiances... Who knew ) then you're main barrier should JUST be generating thrust.Of course that in itself can cause some issues to be worried about... (below)A LOT of folks "talk" SCramjets but operationally its all been ramjets and everything I've seen so far points to subsonic combustion ramjets being perfectly capable of doing the job.
Mach-7 with a subsonic combustion ramjet seems dooable, Mach-13...The main point as you say is we simply don't know. Designing a vehicle to be able to test up to such speeds isn't easy and the need for variable intake/exhaust system drives up the system cost. I like Glenn Olson's idea of "cheap" testing of subscale ramjets but the need to intergrate them works very hard against the "cheap" part.Something along the lines of the X7 test vehicle (wikipedia I know but, for general info: http://en.wikipedia.org/wiki/Lockheed_X-7) that's both robust but able to take a variety of engines to test.(Funny finding, again its wikipedia so take it with a grain of salt but I'd actually heard the "target-drone" version of the X7 was almost impossible to shoot down even with the advanced systems of the day. http://en.wikipedia.org/wiki/AQM-60_Kingfisher)But probably something more along the lines of the "ASTROX" RBCC booster (http://forum.nasaspaceflight.com/index.php?topic=22610.0) or the more "sugar-scoop" inward-turning design so that the exact nature of the "active" inlet and exhaust systems are less of an overall design issue?Might be "nice" to have take-off and landing capability but in general I'd settle for the "job" being the main point of the design so "flight" rather than being able to land and take off from a certain point.
Finding the actual speed limit of a conventional ramjet powered vehicle.Sorry, but the clarification must be asked... African or European?
He (Olson) mentions that there are enough old documents with graphs running up to M6.5 to suggest someone had flight tested something up to that speed. "Aero" suggested the thermodynamics of the fuel suggested M8.8 was possible (if you ignored drag, which would be a very silly idea). Checking the...
That's what I suspected. On the upside it demonstrates that ramjet designs at multiple point speeds and altitudes are viable.
The designs I suggested in the OP were just outlines. My starting view would be a "simplest possible" approach with fixed geometry, which got the French and the US designs to M5. My instinct is for a reusable design to allow (relatively) gradual expansion of the flight envelope and the ability to reuse the basic structure. OTOH a fully expendable design skips the landing gear and could be built more lightly. I think modern materials open up some interesting options. PICA demonstrates high temperature entry. There are also various ceramic materials that can offer light weight(ish) high temperature protection.
You seem to have cut off there
One of the reasons I mentioned the X7 was when looking at the "inward-turning" ASTROX design I noted the twin "horns" on the front an thougth "a duel spike X7" and imagined a very robust "recoverable" test vehicle using the X7 landing method
I want to see an actual flight vehicle to anchor some of those CFD predictions.
Quote from: john smith 19 on 08/27/2014 07:02 AMI want to see an actual flight vehicle to anchor some of those CFD predictions.No super-/hypersonic wind tunnel tests in between?
Quote from: R7 on 08/27/2014 09:55 AMQuote from: john smith 19 on 08/27/2014 07:02 AMI want to see an actual flight vehicle to anchor some of those CFD predictions.No super-/hypersonic wind tunnel tests in between?I'll quote 2 data points on that.1)The Navaho cruise missile was designed to fly with a pair of 40 000lb ramjets in cruise at M3 in the late 1950's. IOW the people of the time were confident enough of their ability to deploy this tech that they could fit it to a large operational vehicle and make it work.
I think wind tunnel tests up to about M3 should be used to test the separation dynamics but I think by then the test ramjet should also have ignited.
And lest we forget there was PLUTO (http://www.merkle.com/pluto/pluto.html)Unshielded nuclear reactors at 300ft AGL at Mach-3 for the win! (And by "win" I mean in the same sense anyone "wins" a game of Nuclear War )
Seperation of what? And where?
Quote from: RanulfC on 08/27/2014 05:49 PMSeperation of what? And where?One of the outlines in my OP was the idea of a 2 stage Parent/Child design. The parent being a small RPV designed specifically to carry the test vehicle (whatever it turned out to be) to launch height, accelerate to launch speed and release it.
The firebee supersonic drones showed that if your thurst is more like 50% of your GTOW rather than 30% powering through the sound barrier is not that difficult. What I have in mind is a small vehicle big enough to carry the main test vehicle whose design is driven by the requirements to make it easy to control (especially during the separation phase) with AFAP minimal danger of the test vehicle hitting any control surfaces.
Conceptually I'm thinking of a low supersonic White Knight 2, although I'd expect the actual layout to be very different. No crew should allow significantly larger payloads or smaller engines (as an aside does anyone make pure turbojets these days which aren't for expendable drones or missiles?) and only enough structural endurance to survive at M1+ (probably nearer M2) to get the ramjet firing and separated.
I'll note that WK2 has had quite a successful life hiring out to various people who want to drop test stuff off it. Perhaps VG are already in profit on their operations? Sadly I doubt the ramjet carrier would be so popular.
Oh sure, like "I" ever read what you actually wrote.. My bad I missed that. Beside one of the reasons I keep bringing up the ex-rocketman's blog is he's done a lot of work, (given it was his "real" job for a long time) on hybrid rocket-ramjets using solid boosters inside the ramjet that transition to ramjets engines using liquid fuel for the rest of the flight.
And my own idea was that the vehicle could be launched using a liquid/solid/hybrid booster vertically before switching to ramjet power.
The above mentioned Crossbow ALV isn't a bad idea for something of a similar nature:http://thehuwaldtfamily.org/jtrl/research/Space/Launch%20Vehicles/Air%20Launch/Air%20Launch%20To%20Orbit%20-%20ALTO%20-%20Crossbow-concept,%20MSFC.pdf
"Biggest" issue for seperation is the carrier vehicle having a postive lift factor after release, the more the better which argues towards something like a box or joined wing. Since the ramjet is just running flat-out (pun-intended) there's no need for fancy manuevers at seperation.
Subsonic would require some sort of booster to get the ramjet up to speed I'm thinking. (And "yes" technically the ONLY folks that make small jet engines these days make "pure" turbojets but they're pretty much all centrifugal compressors and turbines coupled with one or more "fan" blades for added cruise efficiency. The problem is they are all pretty small and what you'd need comes closer to a small fighter engine like a J85 or some such: http://en.wikipedia.org/wiki/General_Electric_J85. However I'll point out there are a number of studies on usign the "standard" cruise missile type engines, the F107/F112 types, http://en.wikipedia.org/wiki/Williams_F107/http://en.wikipedia.org/wiki/Williams_F112, and fitting them with afterburners to get supersonic performance out of them similar to early centrifugal turbojets)
Depends on what people want to use it for The ALTO/Crossbow study mentioned above was partially refined and driven by the idea of an RPV space launch vehicle after all according to some folks here
Quote from: john smith 19 on 08/16/2014 11:28 AMMaybe Aero's claim that basic theory will get you to 3Km/s (about M8.8 ) is correct but given the results of the X30 programme what I'm suggesting is a flight programme.I think I noted that Glenn Olson (of the old alt-accel website) had spoken to enough ex-ramejt engineers to come away pretty confident that a well-designed subsonic combustion ramjet could reach speeds in a bit excess of Mach-8 and for the most part (unlike many of the folks riding "theory" till it auguered into the ground in the form of the SCramjet ) couldn't see many "good" reasons to go faster even if most of them thought Mach-10 was possible given the right propellant and design And really what DOES air-breathing to @Mach-5+ get you if its "cheap" and "easy" enough over the alternatives?(I'd suggest hitting up the "Ex-Rocketman's Take" blog to see some of the work he's done as one of "those" engineers )Randy