Hypersonic Cruise for the V Prize

The Virginia Spaceport at Wallops (east coast of USA, south from New York) advocates want to create a prize to foster use for the spaceport, and have floated an idea of a “one hour to Europe” style prize, the V Prize, but the rules aren’t yet finalized.
The requirements are quite tough. About 6000 km in one hour implies a speed of over Mach 6. There’s some discussion here too.

It’s probably a useless exercise but fun nevertheless, so I propose a notional atmospheric (as opposed to purely ballistic ICBM style) vehicle design for the prize.

Hypersonic Cruiser Slug Silhouette

First of all, out of the assumed 3600 seconds available from runway start to runway stop we reserve 600 seconds for takeoff, acceleration, deceleration and landing, and 3000 s for the 6000 km cruise. This means a cruise speed of 2 km/s, at an altitude of 10 to 20 km this means Mach 6.7.

We can ditch air breathing propulsion, it’s just too hard at such speeds as you’d have to use a scramjet, which is beyond the state of the art. Ramjets top out around Mach 5-6. These air breathers would also need a separate acceleration system.

We will also use a vehicle with wings, because that helps (we will see later). We won’t look at any of the massive literature because where would be the fun in that?

Cruise

Now, we can examine the cruise problem with a few huge simplifications. We assume a constant lift to drag ratio, L/D, heretofore referred to as B. Now, at level flight, the lift equals the weight and thrust equals drag. Thus

mg=FB \Leftrightarrow F=mg/B \Rightarrow a_{virtual} = g/B \Rightarrow \Delta v=\Delta t g/B

That was easy! The virtual acceleration a is just like the gravity g in a normal hovering rocket, where, with a stationary vehicle you have gravity losses \Delta v = g \Delta t.

We can solve further: \Delta t = \Delta x / v_{cruise} \Rightarrow \Delta v = \frac{g}{B}\frac{\Delta x}{v_{cruise}}

Now, we can make the trajectory drop somewhat, to reduce the required delta vee. Delta vee from vertical is of course \Delta v_{y}=\sqrt{g\Delta y} and thus total cruise delta vee is

\Delta v_{cruise} = \frac{g}{B}\frac{\Delta x}{v_{cruise}} - \sqrt{g\Delta y}

Boost

This is simple, we accelerate to cruise velocity and altitude, delta vee is

\Delta v_{boost} = v_{cruise} + \sqrt{g\Delta y}

Total

\Delta v_{tot} = \Delta v_{boost} + \Delta v_{cruise} = v_{cruise}+\frac{g}{B}\frac{\Delta x}{v_{cruise}}

Note that the vertical movement cancels out.

With Data

If we assume a very good lift to drag (remember this is hypersonic where the drag is a very large problem) of B=7, distance of 6E6 m distance, cruise velocity of 2E3 m/s, we get:

\Delta v_{tot} = = 2E3 m/s + \frac{9.81 m/s^2}{7}\frac{6E6 m}{2E3 m/s} = 6.2E3 m/s = 6.2 km/s

That kind of delta vee could perhaps be in the realm of possibility for a winged single stage.

Here’s a graph for different L/D ratios:

Needed hypersonic Delta vee with different L/D ratios

Point Design

Ok, now we have some requirements. Let’s make a grand design. Take a SpaceX Falcon 1 and stick it on a delta wing platform. From the payload bay user’s guide:

Falcon 1 E first stage

  • Empty mass 1.8 t
  • Propellant 31 t
  • Vacuum ISP 304 s
  • We guesstimate sea level ISP 256 s
  • Vacuum thrust 510 kN
  • Sea level thrust 450 kN
  • Length 27 m with interstage, upperstage and fairing. We estimate 17 m for the first stage alone.
  • Material Aluminium
  • Diameter 1.7 m
Most of the Delta vee is high altitude, thus we can use a v_ex estimate of 2900 m/s. With the 6.2 km/s Delta vee, we need a mass ratio of 8.8. The 31 t of propellants, if tank size is kept original, gives a total dry mass for the vehicle of 4.0 t, leaving only 2.2 t for wings, control surfaces, cockpit and landing gear. This is clearly too little, and the Merlin could push a heavier craft easily. Also the thrust vectoring can be eliminated, shortening the rocket stage and freeing mass for adding strength for the new loads it experiences in horizontal flight. If we double the tank volume by increasing its diameter but keep a single Merlin, we have a vehicle that has
  • Empty mass 8 t
    • Falcon-derived “stage” mass (800 kg engine included) 2.8 t
    • Wing, landing gear, control surface, cockpit mass of 5.2 t
      • Landing gear is an aggressive 2% of total mass and thus 1.4 t
      • Wings with stabilizers are 1 t a piece
      • The rocket stage’s cradle is 0.5 t
      • The front body and nose is 1 t
      • The TPS for the wing leading edges and front is 0.8 t
  • Propellant mass 62 t
  • Total gross liftoff mass 70 t
  • Thrust at sea level 440 kN yielding a T/W of 0.66
This would be a roughly MD-82-sized craft in mass, but instead of 150 people it would carry only perhaps one to three. Note that the MD-82 has only 100 kN of thrust, although it has a much better L/D.
Further dimensions can be guesstimated:
  • Stage length 14 m
  • Stage / fuselage diameter 2.4 m
  • Nose length ~10 m
  • Total fuselage length ~24 m
  • Wingspan ~8 m (fuselage width + 1:7 Mach 7 hypersonic half triangle shape)
  • Wing area 40 m^2 ?

Compare this to the delta-winged Mirage 2000:

  • Length 14 m
  • Wingspan 9 m
  • Wing area 41 m^2
  • Max takeoff mass 17 t
  • Thrust 95 kN
  • T/W 0.57

And F-106 Delta Dart:

  • Length 22 m
  • Wingspan 12 m
  • Wing area 62 m^2
  • Loaded mass 16 t
  • Thrust 109 kN

The hypersonic plane would probably need deployable low speed canards for takeoff since the center of gravity would be so far forward. The wing and control surfaces could be quite separate from the monocoque aluminum main stage, minimizing heat transfer and easing construction. The heat load would mainly be from the front and underside and thus only affect the underbelly, nose cone, wing leading edge and vertical fins, which would all have high temperature materials. The landing gear could retract in the wing – main fuselage interface space.

Let’s call the design Slug.

Slug - Hypersonic Sketch

It’s weird how the thing practically designed itself to turn out pretty much like X-24C-L301, a Lockheed design for a hypersonics testbed from the seventies. The dimensions are pretty similar, but the Lockheed plane used three propellants and very many different shaped tanks.

Lastly, I included a hasty sketch, comparing the cruiser to the few relevant craft. Scale should be mostly right:

Comparison of the hypersonic cruiser Slug to some other craft

This proposal is not serious but rather overoptimistic. I didn’t research background literature at all really, but it was fun to write nevertheless. The constant L/D of 7 at various speeds and angles of attack (with heavy mass at the start of the cruise you need more lift hence higher AoA) is where it already assumes the majority of the magic to happen. For example the L/D numbers for Concorde are: Low speed- 3.94, Approach- 4.35, 250 kn, 10,000 ft- 9.27, Mach 0.94- 11.47, Mach 2.04- 7.14. So the aerodynamics over a wide speed range seems like a very big challenge. Also the variable thrust and long duration of the burn probably require at least two propulsion systems, which was completely glossed over.

There’s a lot of material available on the net to examine stuff more closely, here’s one example of hypersonic shapes. Here’s NASA’s report about the design of X-24C, a 30 ton vehicle dropped from a B-52, having a payload of 2 t and providing 70 seconds of cruise at Mach 7.

Offer your criticisms. 🙂

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20 Responses to Hypersonic Cruise for the V Prize

  1. Randy Campbell says:

    Just a point but “standard” ramjets can operate up to around Mach 8. The ASLAM ramjet cruise missile (1980s) ran up to Mach 8 with an inlet and ramjet that was design-point for only Mach 4 because a fuel valve jammed open.
    A BOMARC missile with a similar problem during a test flight hit over Mach 6 before they blew it up with the range safety charges and it was still accelerating. (Designed for cruise at Mach 3)

    I have not finished your article yet, (at work and they are locking me in :o) but felt I should point this out since you dismissed ramjets early on.

    I’d also suggest as something to look ‘up’ on the net a proposal for a “home-built” Mach-6 aircraft called the “Forerunner” that was designed as a ‘thought-experiment’ at one point in time.
    The ‘designer’ has assured me he wants to eventually get backc and update the article but it still has some good information in it.
    (As does most of his “the joys of high tech” articles :o)

    Randy Campbell

  2. gravityloss says:

    The ASALM only ran to Mach 5.5
    http://www.designation-systems.net/dusrm/app4/asalm.html

    Also, the BOMARC engines made a speed record at Mach 4.5 which was fast for it’s time (late fifties). Do you have a reference to a Bomarc actually reaching mach 6?

    From my sources, mach 7 is just beyond ramjet tech and needs a scramjet. Which are notoriously hard.

    That’s why I stuck to rockets, to see what would be required…

    I’ll check out the Forerunner. It seems like an air breather and is slower, mach 6. Thanks for the link!

  3. Bob Steinke says:

    How about a rocket powered vertical takeoff and ballistic arc covering about a third of the distance at a speed faster than mach 7 and then the final two thirds cruising under ramjet power at mach 5-6 so that the average speed still comes in fast enough? This would also solve the problem of accelerating to ramjet speed. But it’s harder to analyze from first principles.

  4. Randy Campbell says:

    GL wrote:
    >The ASALM only ran to Mach 5.5
    >http://www.designation-
    >systems.net/dusrm/app4/asalm.html

    Thank you for the correction I was going from memory, however this still points out (as noted in several articles around the net on ramjet design, construction and uses) that even specific FIXED inlet ramjets are quite capable of higher speeds than specific engineering would usually show.

    >Also, the BOMARC engines made a speed record at Mach
    >4.5 which was fast for it’s time (late fifties). Do you have
    >a reference to a Bomarc actually reaching mach 6?

    My “original” source which I actually questioned was from this site:
    http://www.lorrey.biz/x-106/conversion.html#specs

    Specifically:
    “It was a BOMARC missile with a stuck throttle that achieved the fastest ramjet speed prior to the first launch of the X-43A, clocking a blistering mach 5.5 with two extremely crude uncooled ramjet engines that were designed for a maximum speed of only mach 3.5.”

    Which is quite embaressing as “I” pointed out to the website owner that the ‘referenced’ stuck fuel throttle and Mach 5.5 flight was in fact from the ASLAM :o)

    Further research, (lots of it) finally turned up a mention in several places of a malfunction in a BOMARC test flight that resulted in the vehicle being self-destructed at a speed of Mach-6 while still accelerating. Further Marquart Company tests showed that subsonic combustion ramjets with fixed inlets but variable exhausts could be flown up to speeds around Mach-8 with little performance loss.

    Unfortunatly all I currently have is some various ‘notes’ on this and nothing to actually ‘reference’ other than sites such as this which reference various other sources than your using I assume :o)
    http://www.alt-accel.com/ramjet2.htm
    http://www.alt-accel.com/arla/arla-int.htm

    Additional information here:
    http://www.alt-accel.com/arla/arla-ram.htm

    Which note from various sources that according to test data and experiments with very high speed ramjet engine design there is no physical reason a subsonic ramjet engine can’t be used out to around Mach-10 even using hydrocarbon fuels.
    It is also intersting to note that along with the idea that subsonic combustion ramjets being limited to low supersonic speeds the OTHER “assumption” that grew up around supersonic combustion ramjets was that they would only work with a ‘fast’ burning fuel such as liquid hydrogen which has also been proven incorrect with supersonic combustion of JP series fuels in airstreams up to Mach 15 in various scramjet test rigs.

    (The “sad” part here is I’ve spent the last few hours searching my notes and various internet resources for information while STILL not having completed YOUR article. Me thinks I should at least do that much before I get to much further but since I’m approaching 2am here and need sleep before work tomorrow I think I’ll finish up tomorrow morning :o)

    A note though: Rocket/Ramjet are NOT mutually exclusive for applications such as suggested point-to-point hypersonic service!

    Air-Augmented Rockets, Ejector-rockets, Ducted-Rockets or RamRockets is a concept that has been around for quite a while:
    http://en.wikipedia.org/wiki/Air-augmented_rocket
    http://stinet.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA142043
    http://caius.utias.utoronto.ca/rbcc.html

    http://www.peroxidepropulsion.com/article/17

    There are also article available on Methanol Ejector rocket motors that have been tested though flight test data is still lacking in many cases a LOT of research has been done on combining ramjets with other propulsion systems for horizontal take off modes to multi-mach speed also.

    Anyway enough for the moment, let me get some sleep, your article fully read and quit embaressing myself. (Mostly with my current spelling and inability to see the screen or keyboard very well :o)

    Take care.

    Randy

  5. Randy Campbell says:

    Added note:
    The link provided to the Aerospaceweb waverider page seems broken. Here is the proper link:
    http://www.aerospaceweb.org/design/waverider/

    Randy

  6. Jim Knight says:

    Can anyone tell me what the turning radius would be for a 30 and 60 degree level turn at 2.5 Gs for Mach 3, 4, 5, 6, 7, 8, 9, and 10?

  7. Randy Campbell says:

    Jim Knight asks:
    >Can anyone tell me what the turning radius would be
    >for a 30 and 60 degree level turn at 2.5 Gs for Mach
    >3, 4, 5, 6, 7, 8, 9, and 10?

    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

  8. Randy Campbell says:

    I’m figuring that this ‘thread’ is probably not on the priority list but, I feel the need to apologize;

    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

  9. gravityloss says:

    I’ll reply to the rest of the comments later… It also seems that comments with links still have to be moderated.

    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.

  10. gravityloss says:

    Bob Steinke wrote:
    “How about a rocket powered vertical takeoff and ballistic arc covering about a third of the distance at a speed faster than mach 7 and then the final two thirds cruising under ramjet power at mach 5-6 so that the average speed still comes in fast enough? This would also solve the problem of accelerating to ramjet speed. But it’s harder to analyze from first principles.”

    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.

  11. gravityloss says:

    Boost-cruise addendum:
    Assuming no atmosphere for the boost and 4 km/s horizontal velocity, 500s time and 2000 km horizontal distance, the arc is shaped very roughly like this (doesn’t take into account Earth’s atmosphere or curvature or ending up at cruise altitude):
    g = 0.75*g_0 = 7.4 m/s^2
    height = 0.5*g*(t/2)^2 = 230 km
    v_y0 = 1.8 km/s.
    So a launch angle of 24 degrees.

  12. Randy Campbell says:

    Oh another thing I “forgot” to mention on ramjets is that beyond Mach 7 you have to start ‘engineering’ solutions to keep the flow inside the engine subsonic which is where your complexity begins to creep up pretty quick.

    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)

  13. gravityloss says:

    Okay, replying more to Randy’s posts.

    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.


    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.

  14. Randy Campbell says:

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

    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

  15. 4751 ADSM Florida says:

    Randy, spent a few years in the Florida Panhandle working with Vitreo and USAF, in uniform, on the Bomarc A and B bird. Primarly in the telemetry side of the house.

    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?

    • randy campbell says:

      4751 ADSM Florida wrote:
      >Randy, spent a few years in the Florida Panhandle
      >working with Vitreo and USAF, in uniform, on the Bomarc
      >A and B bird. Primarly in the telemetry side of the house.

      I hear that 🙂
      My first assignment in the USAF was Eglin, test side in 1980. (Munitions 🙂
      I got lucky a couple of times on-the-job and got to look over some of the Bomarc launch sites and other missile test stands that are (or were) still in-place. Everyone always seemed to “take-it-in-stride” while I was always struck by the fact I was walking through history.

      >Ramjets: I was not aware of the runaway Ramjet, it
      >may have happened after I departed.

      That seems to be what EVERYONE says about this story 😉
      Heck I got more information, easier about the SNARK test launch site than I could get about most of the BOMARC program. (Including a look at the launch site for the SNARK we “lost” when the bird had a total communications failure and ended up flying down into South America before it ran out of fuel and crashed 🙂
      {Google search: “The Day They Lost A Snark”}

      >We routinely sent a dmg to blow the bird after the
      >mission.

      “dmg”? Destruct signal? My Acronym-Fu is not what it used to be 😉

      >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.

      Thanks, that jibes with information I’ve been able to get ahold of saying that in most cases the ramjets were capable of more thrust and acceleration than the air-frames of the day could handle.

      Randy

  16. sicsok says:

    About the engine I would check (among others) US Patent US 7111449!
    No startup and no speed limits. Serious work too and all this with higher than currently known efficiencies in all but start up speed regime.
    Not included but the nozzle can accomodate rather simle thrust-vectoring method too.
    Sounds too good. But too good compared to what?

  17. Alexwebmaster says:

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  18. Nik says:

    http://www.reactionengines.co.uk/

    Allan Bond & Co seem to have solved the heat-exchanger issues, and are designing a simplified version of the engine for a very fast civilian jet-liner…

  19. Mike Lorrey says:

    Yes Randy, it was the ASALM, not the BOMARC, that hit mach 5.5 with a stuck throttle, but they both used the exact same Marquardt fixed inlet ramjet, in fact they basically ripped some ramjets off mothballed BOMARCs to engine the ASALM for the test program.

    To make a ramjet work up to mach 8, you essentially need the inlet, combustor, and exhaust to use active cooling or some high temp materials like hafnium diboride (SHARP materials). You need inlet and exhaust to have variable geometry (not hard either), and you should use LOX based MIPCC. I prefer a design that cools the inlet with LOX and bleeds excess LOX into the airstream to cool and condense it at high speeds.

    I would suggest a small rocket motor in addition to the ramjet, once you reach mach 6-7, I’d light the rocket and drop the ramjet (ramjets are simple, cheap, and easily mass produced) to get some ballistic boost, then skip glide the rest of the way to Britain. I built such a design in X-Plane simulator that could be skipped all the way around the planet.

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