I have walked into the melt down crater when the bird literally burned down into the shelter.

Ramjets: I was not aware of the runaway Ramjet, it may have happened after I departed.
We routinely sent a dmg to blow the bird after the mission.
The thumbnail tuning for that point in history was the Ramjets could take a frame to MACH 10. We knew when and what would fail before it reached 10.

Most cases kept the bird at about the speed of the F4 of the day. Remember, the gulf of mexico at the time was full of “Fishing Boats” for all over the world. I am sure some of them were collecting data.

What happened with the C Bird?

While “technically” correct I still like to ask, and thanks for the compliment :o)

Oh and I posted this on nasaspaceflight.com but I figured I’d ‘cross-post it here too :o)

On the subject of ‘ideas’ this has apperantly come up before as witnessed by this 1989 “final” report on a study on a Hypersonic Business Jet concept study called “HyBuJet”

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19910000727_19...

Randy

It’s easy to see that ramjets could already operate at quite low speeds. The first ramjet airplane, the Leduc 010-01 was released from a propeller carrier aircraft and climbed under pure ramjet power in 1949 already.

More about the excellent and fascinating yet little known story here:
http://aerostories.free.fr/constructeurs/leduc/page8.html

Of course, turbojets with afterburners made ramjet aircraft obsolete in the mid fifties. I don’t know what the efficiency (thrust, ISP) of these ramjets was through varying speed ranges either.

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Regarding combined rocket and turbine engine technologies, there are a variety of possible solutions.
Basically, turbofan is best for low speeds, turbojet for intermediate and turbojet with afterburner for even faster.

At sufficiently fast speeds the turbine blades will melt. There are principally two ways to avoid putting the turbine in the main air stream.

One can run a small fuel rich gas generator with lox-kerosene and use that to spin a separate small turbine that spins the compressor. Then just have an “afterburner” (i.e. no turbine after it) for the turbine exhaust and put some additional fuel straight there too. This can be called gas generator air turborocket.

One can do without a gas generator if one uses the idea from the expander rocket cycle. Use the heat of the combustion chamber to heat up hydrogen fuel, and use that hot hydrogen to drive a turbine that spins the compressor. Then inject the fuel into the chamber and burn it in an afterburner. This is an expander air turborocket.

Of course, with even faster speeds even the compressor blades start getting into trouble. I don’t remember offhand when this starts to be the case. One can anyway then possibly close the “front door” air intake completely and just inject liquid oxygen (if you are accelerating for space). Or one could bypass the compressor and use the engine as a ramjet (if you cruise in the atmosphere). All these moving surfaces of course will be big, heavy and expensive and limit efficiency.

The expander RBCC engine wouldn’t work with kerosene. I don’t know about methane or ethane though. It could be the best of both worlds, or it could be the worst.

Oh, and Randy, of course I have no say on where else you post your stuff. It’s nice that you comment here.

Also there are a number of ways to bring ramjets “up-to-speed” as it were if you design them to operate more efficiently towards the upper Mach ranges; most of these types of engines being some type of “combined-cycle” propulsion system.

Examples would include using turbine engines to augment the ramjet for low speed operations, the turbo-ramjet J58 engines developed by Pratt-&-Whitney for propulsion on the A-12/SR-71 aircraft are a good example of this.
Below Mach-1 the turbojet operates as normal using the ramjet ducting as an afterburner but as speed increases more and more air is ‘by-passed’ past the turbojet and directly into the duct until at cruising speed over 75% of the thrust provided for the aircraft is by the ramjet ducting alone.

(Note: P-&-W has been working with NASA on a more advanced turbo-ramjet called the “Hyperburner” engine: gltrs.grc.nasa.gov/reports/2005/TM-2005-213803.pdf which is less complicated than the J58 was, and won’t require the special jet fuel blend that in the SR/A aircraft was used for everything from the engine hydraulics to lubricant before being fed into the combustion section :o)

The ‘downside’ of this type of engine is that they most often need either some sort of complicated ducting to bypass the turbojet sections during high-speed flight or some sort of active cooling of the turbojet components to survive the temperature extremes generated during high speed flight.

Another turbine based combined cycle engine uses cryogenic fuel in a similar manner to that used in the “expander” cycle rocket motor; by allowing the cryogenic fuel to warm the expanding fuel is used to turn a turbine which is connected to a compressor. The compressor operates like that in a normal jet-engine and compresses air and forces it into a combustion section though in this process that section is separate from the compressor/turbine section.

This allows the compressor/turbine to operate without being directly in the path of the air flow which at high speeds can become quite hot. Another advantage is that the cryogenic fuel can be circulated through heat exchangers in the compressor inlet to cool and densify the incoming air negating the need for added complications of active cooling within the compressor/turbine themselves and eliminates the need for ducting around the turbojet sections though you’ll still need ‘plumbing’ to get the compressed air into the combustor.

The cryogenic fuel can also be circulated around the ‘hot’ sections of the vehicle during boost/cruise and then pumped into the combustor as a gas which allows more thorough mixing and more efficient combustion.

Downsides? Well one of the most often brought up ‘faults’ is Liquid Hydrogen is bulky which increases your vehicle size, drag, etc. That of course ‘assumes’ one uses LH2 :o)
While LH2 engines have high ISP the bulk and extreme cold needed to liquefy it make it difficult to work with, cryogenic fuels such as Methane, Propane, or Ethylene are preferable.

(In my preference Ethylene or Propane are probably preferable because when cooled to LOX temperatures they are densified enough to almost match Kerosene with a much higher ISP :o)

Lastly there are the Rocket-Based Combined Cycle engines which use fuel rich rocket exhaust to ‘entrain’ air into the ramjet duct where they mix and are ignited creating thrust. Though most often based on ‘pure’ rockets using internal LOX until the ramjet engine can run on its own, research has also been done on using expander cycle compressor/turbines to inject air with the fuel in the rocket combustor which have yielded good results.
(http://caius.utias.utoronto.ca/rbcc.html)

One of the ‘neater’ things about RBCC engines is they usually require less powerful engines than a pure rocket would due to the mass of entrained air in the exhaust, so that (using the original example given :o) instead of using a Merlin one could probably use a Kestrel engine run fuel rich exhausting into a ram-rocket duct to still achieve vertical take-off and acceleration to ramjet take-over speed.

I should also mention another aspect of the last engine; Liquid Air-Cycle Engines or LACE. These usually use a highly cryogenic fuel such as Liquid Methane or Liquid Hydrogen, (as opposed to the ‘softer’ cryogenic fuels such as Ethylene or Propane which only require LOX temperatures) to liquefy part of the incoming airstream burning some in the rocket combustor with fuel for thrust but also storing some as LOX for later use as a pure rocket. There have been variations suggested that use more mechanical liquefying process but the time required to ‘fill’ vehicle LOX tanks using these methods usually limit those to being used in some sort of Air-Launch scenario where the vehicle takes off with only fuel and collects its LOX while flying to the launch position or altitude.

Randy
(GL: I hope you don’t mind but I’m going to cross-post this to the V-Prize thread over at nasaspaceflight.com forums? :o)

Yeah, this is harder to analyze. Let’s still assume 3000 seconds and 6000 km for the trip (600 s was reserved for launch and landing where not much distance is covered).

That would mean 4000 km at slow speed, say, mach 5.5. The time taken would be 2500 s.

So 500 s left for the first 2000 km. That would mean 4 km/s or mach 14 at 20 km altitude.

So in essence dropping the speed by 20% in the latter two thirds doubles the speed needed in the first third. In fractions of total time:
tfirst=1 - 0.67/0.8 = 0.1625. Compare to the normal 0.33.

This seems actually pretty feasible, better than I expected!

Since 4 km/s is half of orbital velocity, it only offsets a quarter of the Earth’s gravity (again a = v^2 / r) meaning it it was a ballistic arc, it wouldn’t be much shallower than low horizontal velocity one.

It’s also fun to note that Earth’s rotation at Wallops’ 37 degrees is about 0.36 km/s. That means the trip is easier to do from USA to Europe than the other way.

I don’t know if the prize rules will allow staging.

I have a suggestion for the prize rules that would make it more feasible for a reusable non-staging craft, but more about that later.

I’ll answer more comments later.

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Turning radius at some speed and acceleration is a simple mechanical relation, centripetal acceleration:
a = v^2 / r

r = v^2 / a

So Mach 6 is about 6*300 m/s = 1800 m/s. And with a 2 gee acceleration of 20 m/s^2 we get
r = (1800^2 / 20) m = 162 000 m = 162 km. That’s about 100 miles.
With 4 gee acceleration, 80 km or 50 miles. Etc…

Halving the speed drops the radius to one quarter.

Bank angle is not related to this, it’s a different order phenomena.

Neither I nor my sources that I’ve been able to access can find the citation for the BOMARC speed I listed. Though I’ve found my notes recalling such an incident I can’t find anything to actually VERIFY the statement so I’ll apologize and withdraw THAT one.

I will however draw anyone interested in the V-Prize and the possibilities of ramjets to this website:
http://www.alt-accel.com/

The site owner, Mr. Glenn Olson has done a good bit of research on the promise and possibilities of ramjet propulsion. Specifically his “Ramjet Primer” (http://www.alt-accel.com/ramjet2.htm) is worth reading and his Pogo, and ARLA (Amateur Rocket Launch Assist) papers are highly recommended.

I will note here some points that he makes;

-There is an often quoted ‘fact’ that ramjet engines can’t be started at speeds of less than Mach 1, this is incorrect as is another often quoted figure of 200mph. The actual “fact” is that ramjets cannot produce thrust at zero speed, but are capable of useful operation at any speed above zero.

- Since the majority of ramjet engines have been employed in ‘niche’ applications the majority of information is difficult to come by leading to an assumption that such applications are ‘all’ they can be used for.

- Generally Subsonic Combustion ramjets have been designed for either Subsonic or Supersonic speeds bur rarely for both applications. This has been a DESIGN limitation used for simplicity purposes to allow the use of fixed or ‘simple’ inlet design, and optimized performance at one or two, (occasionally three) “optimal” speeds. (The ASALM missile which had an optimized “fixed” inlet designed for a best-speed point of around Mach 4.5 but was accelerating beyond Mach 5.5 when its fuel ran out)

- Many of the constraints on ramjet operations are design trade-offs made in attempts to constrain the ramjet to optimal speeds at specific altitudes. A properly designed subsonic ramjet engine, with some type of variable inlet system, (types would include ‘ramp’ inlets such as the F-15, or the moving spike type inlet of the SR-71) should be capable of speeds from under 200mph to at least Mach 7, if not more.
(Starts from ‘zero’ speed can be achieved through the use of ‘assists’ such as the turbojet engines on the ‘turboramjet’ SR-71 engines to injection of compressed or bleed air into a ramjet intake)

There are charts, data, and performance specifications on ramjets able to travel at Mach 6.5 enough for it to be a logical conclusion that someone has tested them at speeds at least this high. Speeds in excess of Mach 7 are only bound by the ability to continue to shock the air down below supersonic for feeding to the ramjet compressor section.

(Generally it would be easier and more efficient at Mach 7 to switch to supersonic combustion or ‘scramjet” engines

There are many more data points in the listed threads and articles but the bottom line is this:

Ramjets can be used if designed and constructed with proper design techniquies to operate from zero to speeds of around Mach 7 with little difficulty.

Randy

Uhm, I suppose “rather large” just won’t cover it will it? :o)

I found the following with a quick search using:
“Turning Radiaus’ At Mach Speed”
http://www.physicsforums.com/archive/index.php/t-141112.html

The thread is entitiled “Supersonic Turning Radius” and has some posts with the relevent formula and various variations there-of your looking for.

Another possible helpful site is this one:
http://www.temporaldoorway.com/ufo/analysis/belgianradar/index.htm

though dealing with formula and mathmatics for a UFO incident it also provides some data that might prove useful.

Lastly this site:
http://www.answers.com/topic/centripetal-force?cat=health

has the basics for figuring Centipetal-force which should give you the basic answers for each of the speeds listed.

My take? After about Mach2 you’re probably looking at adapting something akin to the neat little “saying” taut to Cadets at Star Fleet (via “Voyger) “Faster-Than-Light No Left-or-Right” :o)

From what I gather reading, trying to turn and stay at or around 2gs in a turn will run somewhere between 20-50 kilometer for radius at above Mach 1, but below Mach 2.

Hope that helps :o)

Randy