X-106 "Christa", the Hyper Dart

[mlorrey]

And I've stated that even if I add a few thousand lbs of TPS, the wing loading of the X-106 (currently 18.3 lb/ft^2) will still be significantly less than the X-33 (30 lb/ft^2), and hugely less than the STS Orbiter (95.6 lb/ft^2). For this reason, I have no need to use extensive TPS beyond RCC nose and leading edges, with titanium aluminide on the rest of the surfaces. While TiAl is slightly more dense than standard aircraft aluminum alloys, the RCC is less than 1/4th the density of the steels used in the nose and leading edge of the stock F-106, and the existing leading edges have a more dense structure than would be needed with RCC, so any use of TiAL behind the RCC, or even silica, would likely be less than the steel structure being eliminated, while still gaining significant structural strength over the steel with the RCC.<br /><br />One thing you are ignoring with my weight program is that I'm eliminating the two largest masses in the 106: the turbojet engine, and the weapons system. The turbojet engine is 5700 lbs. The weapons system, including weapons bay hardware, weapons avionics, wiring, radar, amounts to a minimum of 1,000 lbs. Plus, in addition to the turbojet, we are getting rid of the electrical generator, the hydraulic pump(s) and the compressor bleed air ducting to the ECS. We are getting rid of the 1950's turbocompressor-based ECS and replacing it with a peroxide driven system that supplies O2 and power, and will do CO2 scavenging.<br /><br />While the RCC will be significantly lighter than the steel and aluminum it is replacing, the real weight savings is eliminating old technology that won't be needed by this vehicle. After all, we are not going to be bombing anybody... The weapons system was built to launch a nuclear armed Genie missile into bomber formations and carry a vulcan cannon along with six AA missiles.

 

[mlorrey]

"In an earlier post you said the ramjet would consume 3/5 of the fuel. So I ran the numbers; using the remaining fuel and all the LOX and assuming the vehicle starts the Merlin burn at Mach 8, a final weight at burnout of 18,300 lbs, and an ISP of 457, I get a final result a little better than 8.5 km/s. <br /><br />I don't see any excess margin for using the Merlin below speed Mach 8. "<br /><br />My 3/5 statement was obviously a rough guesstimate. You should use the official O/F ratio of 2.52:1. This means for using all the LOX, you'd use about 9800 lbs of the fuel in the Merlin. You also need to consider the use of the peroxide in the ramjet. I haven't calculated the flow rates and total consumption required for simple MIPCC cooling, though I suspect it will be significantly less than the amount of peroxide that will fill the wing tanks. Any excess would be usable in the ramjet in a rocket mode once the zoom maneuver begins with the Merlin. This will of course require that the ram scoop be capable of sealing off, but this mechanism is well demonstrated by the RBCC engine.<br /><br />BTW: Please post your equations w/ numbers you are using, so everybody can check and compare.

 

[gunsandrockets]

"The RASCAL had a much higher GLOW in the reference design than 80k, more lik 180k...but you are also wrong on the RASCAL vehicle, it was intended to reach mach 5-6."<br /><br />Hey go complain to Aviation Week & Space Technology. It was from their article I found the figures I used. The same article I posted a link to.<br /><br />"The difference is that the 50,000 original estimate of mine is low. Going by the RBCC performance, one should figure about 10,000 lbs thrust per square foot of ramjet cross sectional area, which comes out to 100,000 lbs thrust."<br /><br />Well which is it? 50,000 lbs of thrust or 100,000 pounds of thrust? I take it then you admit 50,000 pounds of thrust could not push the X-106 up to a speed of Mach 6?

 

[gunsandrockets]

"One thing you are ignoring with my weight program is that I'm eliminating the two largest masses in the 106: the turbojet engine, and the weapons system."<br /><br />Nope. I've never questioned that part of your mass calculation. My question was always about the claimed reduction of mass of the airframe, despite it's enlargement in size.

 

[gunsandrockets]

"My 3/5 statement was obviously a rough guesstimate. You should use the official O/F ratio of 2.52:1. This means for using all the LOX, you'd use about 9800 lbs of the fuel in the Merlin. "<br /><br />I thought the ratio looked way off, but I didn't bother taking that into account and assumed a proper ratio and a total propellent mass of 24 tonnes. With the new figure you provided the total propellent for the Merlin is only 15.5 tonnes! That's gonna be real bad.<br /><br />So here we go. X-106 final mass to orbit 8.3 tonnes (18,300 lbs). Propellent mass 15.5 tonnes. Mass ratio 2.86 (about as good as a V-2). Start speed Mach 8 (2.57 km/s at sea level! Slower higher up). Rocket ISP 457 seconds. Rocket exhaust velocity 4.48 km/s.<br /><br />According to the graph of mass ratio and rocket exhaust velocity the Merlin would add about 4.5 km/s to the X-106. That plus the 2.57 km/s from the ramjet add up to a total of 7.07 km/s for the X-106 at best.<br /><br />V = c log(subscript e)R<br /><br />V = final velocity<br /><br />c = exhaust velocity<br /><br />R = mass ratio<br /><br />mass ratio = (initial mass of rocket)/(final mass of rocket after burning fuel)<br /><br />My math skills suck so I just use the graph instead of the equation.

 

[tap_sa]

<font color="yellow">" X-106 final mass to orbit 8.3 tonnes (18,300 lbs). Propellent mass 15.5 tonnes. Mass ratio 1.86 (not even as good as a V-2). Start speed Mach 8 (2.57 km/s at sea level! Slower higher up). Rocket ISP 457 seconds. Rocket exhaust velocity 4.48 km/s. "</font><br /><br />A minor correction: Mass ratio is (8.3 + 15.5)/8.3 = 2.87 . Better but still not good enough.<br /><br />4480m/s*ln(2.87) = 4723m/s

 

[gunsandrockets]

Yeah I caught the error and was correcting my post at the same time you were posting. Oops.

 

[tap_sa]

I wonder what the actual dv requirement for the rocket propulsion part would be. That info would tell the required MR. Anyway I'd swag the MR to be at least 4. And that with somewhat utopistic hydrocarbon engine 'on boroids'. If adding hundred seconds Isp to ordinary HC engine would be just a matter of mixing some boron dust into the fuel then why aren't everyone doing just that?

 

[gunsandrockets]

"I wonder what the actual dv requirement for the rocket propulsion part would be. That info would tell the required MR. Anyway I'd swag the MR to be at least 4. And that with somewhat utopistic hydrocarbon engine 'on boroids'. If adding hundred seconds Isp to ordinary HC engine would be just a matter of mixing some boron dust into the fuel then why aren't everyone doing just that?"<br /><br />Dude I salute your wit. 'On boroids'! Perhaps boron dust is related to pixie dust? PFM, Pure effing magic.<br /><br />There is much that seems magical about the X-106. Magic fuel, magic engines, and magic TPS.

 

[mlorrey]

I try to look up more authoritative sources than AvLeak. For example, the original DARPA pages, or proposal papers. For instance, the Georgia Tech study of the program did a pretty good job, though it turns out you were closer to actual mass: 90,000 lb for 1st stage, though the RASCAL carries little fuel for the zoom maneuver, so its acceleration time is brief. It simply doesn't have enough fuel to go very fast, and carries a 16,000 lb upper stage. The MIPCC and F-100 engines operate to 85,000 ft and Mach 4, whereupon they shut down and the vehicle coasts to apogee at 200,000 ft. The RASCAL vehicle carries less than 30,000 lb of JP-4 and H2O2, and takes up a lot of mass (15,000+ lb) on the four F-100 turbofan engines. This gives it a mass fraction of less than .30. The X-106 has a significantly higher mass fraction, more than 2.5 times higher.<br /><br />http://pweb.ae.gatech.edu/labs/ssdl/Papers/Technical%20Papers/AIAA-2005-3241.pdf<br /><br />It oddly enough directs a lot of its fuel to a 250 mile circular range to the launch point, plus a half hour of loiter time to wait for the launch window. This is excessive and IMHO a boat anchor intended to scuttle the feasibility of the vehicle. You don't see rockets loitering about between stages. It is an impossible mission requirement. Either all systems check out at take-off or you scrub the mission.<br /><br />as for TPS, the RASCAL program proposed the following:<br /><br />"As this plot shows the maximum stagnation temperature on both the wing and nose does not exceed 1300 degrees F. Unfortunately, Aluminum’s reuse temperature is only 300 degrees F. Therefore TPS is needed on the first stage. MA-25 was chosen due to its availability, and will be used as a spray-on ablator which would be reapplied on every flight [10]. This ablator is used extensively in the shuttle program and can withstand one time uses exceeding 1,2

 

[mlorrey]

Okay, I'm convinced we need more LOX so the Merlin can run longer. I imagine that given the much higher Isp of the ramjet that it would likely not need all that extra fuel, so the LOX tank can be longer, and extend deeper into the intake region. Lets work out what amount of LOX would be needed to get from mach 8 to mach 24 on the Merlin, then figure the amount of fuel to go with it, and figure out how much fuel we'd need for the ramjet to get from 450 kt to mach 8 (incl MIPCC coolant/oxidant) at the higher effective Isp comparable to LH2 (as the boronated RP-1 has).

 

[mlorrey]

""I wonder what the actual dv requirement for the rocket propulsion part would be. That info would tell the required MR. Anyway I'd swag the MR to be at least 4. And that with somewhat utopistic hydrocarbon engine 'on boroids'. If adding hundred seconds Isp to ordinary HC engine would be just a matter of mixing some boron dust into the fuel then why aren't everyone doing just that?" <br /><br />Dude I salute your wit. 'On boroids'! Perhaps boron dust is related to pixie dust? PFM, Pure effing magic. <br /><br />There is much that seems magical about the X-106. Magic fuel, magic engines, and magic TPS. "<br /><br />Nice term, boroids. Everybody doesn't do it because it makes smokey contrails, boron is expensive, and everyone has been hypnotized by the NASA LH2 agitprop.<br /><br />Turbine engines don't need more Isp for normal passenger service, not with the potential particulate emissions, however with a rarely flown space plane (1-3 flights/wk, max), the minor amount of pollution it produces is easily compensated for in lower value economic functions that provide emissions credits.<br /><br />What magic engines? The Merlin? Its proven and tested. Ramjets are proven and tested, with the RBCC providing 10klb/x-section ft^2. Sounds to me like you are jumping on the NASA train.<br /><br />And last I checked, RCC was 30% less dense than aluminum, so getting a lighter airframe from exchanging acft Al alloy for RCC should be a no brainer.<br /><br />Your use of STS TPS numbers is disengenuous, because you didn't show what the mass of the aluminum sheetmetal underlying the TPS is on the orbiter, and add that to the mass of the various TPS types.<br /><br />You've also totally ignored the vehicle density issue, as shown in the wing loading numbers. The X-106, like the X-33, simply will never experience Shuttle-like reentry temps, so demanding STS level TPS is unreasonable and absurd.

 

[gunsandrockets]

Enough nitpicking, here is what might really work.<br /><br />1) Use aided launch which effectively makes the vehicle a two-stage system. I favor towed air-launch such as the Kellyspace system. That way the vehicle can launch at the best possible lattitude (good for an extra 450 m/s) and benefit from the airspeed at launch (good for an extra 240 m/s). The rocket engine exhaust bell can also use an idealized size for high-altitude operation and maximum ISP.<br /><br />2) Ditch the mixed-mode propulsion, become a pure rocket-glider. Lingering in the soup of the atmosphere is more pain than gain. Accelerating in the air a vehicle has to fight not only it's mass but also drag and heating as well.<br /><br />3) Use CH4/LOX for the rocket engine propellent. It has only slightly less ISP than LH2/LOX while avoiding the horrible density and super-cryo storage problems of liquid hydrogen. With this fuel a vehicle with a mass ratio of roughly 8 should get the vehicle to orbit. (Drop tanks may be needed to achieve as high a mass ratio as 8, effectively adding a half-stage and making the vehicle a 2-1/2 stage to orbit system.)<br /><br />4) Use transpiration active cooling for the primary reusable TPS. It's never been done before, but has great potential. t/Space plans to use transpiration cooling for it's reusable CXV manned capsule.<br /><br />5) What is it good for? The margins of such a vehicle are so narrow, it's hard to see what it's good for. About the only thing I can think of would be orbital tourism 'gee-whiz' flights lasting less than 24 hours. Flying to any kind of higher orbital inclination than zero would probably require the addition of an expendable JATO stage to the vehicle (now we are up to 3.5 stages to orbit), and even then there is no ability to transfer crew to a hab in orbit short of using EVA. (Payload, one dude in a vac suit strapped into an MMU?)

 

[mlorrey]

<blockquote><font class="small">In reply to:</font><hr /><p>1) Use aided launch which effectively makes the vehicle a two-stage system. I favor towed air-launch such as the Kellyspace system. That way the vehicle can launch at the best possible lattitude (good for an extra 450 m/s) and benefit from the airspeed at launch (good for an extra 240 m/s). The rocket engine exhaust bell can also use an idealized size for high-altitude operation and maximum ISP. <p><hr /></p></p></blockquote><br />I'm open to a towed launch. The wing loading is low enough for it to work. <br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>2) Ditch the mixed-mode propulsion, become a pure rocket-glider. Lingering in the soup of the atmosphere is more pain than gain. Accelerating in the air a vehicle has to fight not only it's mass but also drag and heating as well. <p><hr /></p></p></blockquote><br />Disagree here. The Isp advantages way more than make up for the aerodynamic issues. Getting the average Isp above 500 secs is the magic number to SSTO. Just need to figure out the right ratio of total LOX and fuel tankage. If we're going to air launch, we're not going to see heating issues til above mach 2.5, and by then the vehicle will be above 50,000 feet and rising, so there really shouldn't be any real heating problems. The aircraft has 74 degrees of sweep from nose to wingtip, so it will be able to fly up to mach 5 before any nose-shock impingement on the wings. I don't plan on any loiter time or other BS like they put in the absurd RASCAL reference mission.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>3) Use CH4/LOX for the rocket engine propellent. It has only slightly less ISP than LH2/LOX while avoiding the horrible density and super-cryo storage problems of liquid hydrogen. With this fuel a vehicle with a mass ratio of roughly 8 should get the vehicle to orbit. (Drop tanks may be needed to achieve as high a mass ratio as 8, effectively adding a half-stage and making the</p></blockquote>

 

[gunsandrockets]

Magic fuel - RP sprinkled with boron dust.<br /><br />In a different thread I asked you to produce any information with links about the use of such a fuel in a rocket engine and any test results. To date I have heard nothing in response and my own searches have been fruitless.<br /><br />So Tap_Sa's question "If adding hundred seconds Isp to ordinary HC engine would be just a matter of mixing some boron dust into the fuel then why aren't everyone doing just that?" is extremely relevant.<br /><br />Your response, "Everybody doesn't do it because it makes smokey contrails, boron is expensive, and everyone has been hypnotized by the NASA LH2 agitprop", is inadequate.<br /><br />Smokey contrails has nothing to do with common rocket engine practices which employ poisonous and polluting propellents with abandon. And no dark 'NASA LH2' conspiracy can explain the non-use of boron by the Soviets during the space race who didn't use any liquid hydrogen engines until the 1980's.<br /><br />You have made extravagant claims for boron fueled rocket engines and not backed any of it up. Sounds like magic to me.<br /><br />Magic engines - engines with increased ISP yet they still maintain the same thrust.<br /><br />I've knocked this down before.<br /><br />Magic TPS - reusable passive thermal protection system that instead of adding weight reduces weight while increasing structure at the same time.<br /><br />You can't escape the difficulties of thermal issues no matter how much you try. An airframe can always be constructed with lighter materials and that will save some weight. But TPS is added dead weight and there is no way around it, and it can't be ignored. Like ignoring thermal insulation.<br /><br />The most efficient combined airframe structure + thermal protection system I am familiar with is the Gemini reentry capsule, and I'm not refering to the ablative main heat shield. It's very instructive about the issues and possibilties involved in spacecraft construction. I'm talking about t

 

[mlorrey]

http://www.freepatentsonline.com/6652682.pdf<br />http://www.freepatentsonline.com/5837930.pdf<br /><br />http://www.grc.nasa.gov/WWW/retf/textFiles/museumDisplay_displays.html<br />"Advanced Chemical Propulsion<br />Researchers at NASA Glenn are continuing research into the advanced fuels and rocket-engine technologies that will improve the performance of chemical rockets. One technology uses a high-energy, gelled propellant with a higher-density aluminum additive mixed into the fuel. (The above image shows a rocket engine with this propellant firing in Glenn’s Research Combustion Lab). The gelled propellant makes the fuel safer if it is accidentally spilled, and adding metal to the fuel makes the fuel denser and more compact, allowing the fuel to be stored in a more compact space. Other advances that researchers are investigating include safer fuels, such as ones that can be handled without special protective suits, and high-performance atomic chemical fuels that hold atoms of boron, carbon, or hydrogen in solid-hydrogen particles. These atomic chemical fuels could one day be the highest performing fuels ever created. "<br /><br />If you'd cared to read the Onera page I cited previously, the RJ-5 and RJ-9 rocket fuels were boranes and boron slurries.<br /><br />It really shouldn't matter, the Isp chart I showed for boron slurries in ramjets is directly proportional, you need to scale only for the fact that you have a bottled oxidizer rather than using atmospheric mass. It should be obvious that Isp gains of 20-30% for a low percentage boron slurry with RP-1.<br /><br />As for the use of ramjet: this image:<br /><br />http://www.onera.f

 

[tap_sa]

For the record, I don't doubt boron slurry's ability to produce 450+ second Isp. Boron does have exceptionally high heat of combustion. What I do doubt is Merlin's ability to cope with burning that stuff without melting in a split second.<br /><br />The amount of boron additive would be relatively small meaning that most stuff coming out of business end of the vehicle would still be the same as in ordinary Merlin, CO2 and water. But in the boroids engine they would be coming out at ~50% higher speed. Let's simplify things a bit and assume the exhaust gases behave like ideal gas whose temperature is directly proportional to the average <i>kinetic energy</i> of individual gas molecules. 1.5 times higher exhaust gas speed means those molecules have (1.5)² = 2.25 times the kinetic energy. This means 2.25 times higher temperature inside the reaction chamber! We'd shift from relatively bening conditions into SSME class, I doubt such change could be tackled just by adding some more ablative.<br /><br />I agree that H2 is overhyped. Great Isp but bloated tanks aren't good for SSTO. I suspect we both have read Dunn's great propellant article <img src="/images/icons/wink.gif" /><br /><br />I'd try to work the design to increase rocket-flight MR enough to allow more mundane RP-1/methane/propargyl alcohol(=toxic, suspect carcinogen <img src="/images/icons/frown.gif" />) etc.<br /><br />For instance:<br /><br />Jettison ramjets when they flame out. Recovery by parachute. Perhaps combined ramjet-fueltank-RATO modules so that the vehicle itself contains only propellants for the rocket engine. If the vehicle is towed/air dropped then no need for RATO, but personally I like the idea of the thing getting off the ground all by itself. One might be tempted to use the Merlin for takeoff but that may not work well because a) the engine may need to be covered with some aerodynamic tail cone during the ramjet

 

[mlorrey]

I agree that there should be concerns about combustion chamber pressures on the Merlin. Given the higher heat of combustion and pressure, the thrust of the Merlin should also be higher with boroids, shouldn't it? If so, detune it to 80klbf again, which should mean the chamber temp and pressure will be within design margins for the nozzle. As for the bell nozzle itself, it seems like the boron will be coating the nozzle with boron oxides and boron carbides. Do not know the rate of deposition, if it would be faster or slower than the rate of ablation, but this will likely be a significantly mitigating effect.<br /><br />Jettisonable ramjet would be a nice idea. Mounting two, one on each wing weapons hardpoint, would be doable, though they'd have to be low enough that the exhaust doesn't mess up the wing flaps. This would also allow the aircraft to take-off up to the F-106 specced max T-O AOA, one thing I had been concerned about with the underbelly/behind main gear location. However, this would mean the vehicle is once again a glider after reentry, with limited crossrange and no landing abort or loiter capability.<br /><br />The dolly is a good idea, though that means you'd have to either get a dolly to the landing airport too, if you aren't going to reenter and go directly home. A problem with the dolly is that it eliminates your ability for an intact abort if your main gear can't handle your gross weight on a abort landing. Intact aborts are a primely important thing with minimizing launch costs. I also foresee possibly suborbital point to point executive transport with this thing too...<br /><br />The Merlin is tuned for ground level, since it's the first stage engine of the Falcon1.<br /><br />Deltav: we need to go from 0-450 kt, then 450 kt-mach8 on ramjet, then mach 8-25 on the Merlin. Actual delta v is going to need some calculating, as different vehicles have different dv requirements having to do with T/W, Isp, Cd, launch altitude, etc Mitchell Clapp has done some g

 

[tap_sa]

<font color="yellow">"Given the higher heat of combustion and pressure, the thrust of the Merlin should also be higher with boroids, shouldn't it?"</font><br /><br />If propellant feed rate (dot-m) is kept the same as in original Merlin then yes. The thrust equation:<br /><br />F = dot-m*v_exhaust + (p_exit - p_ambient)*A_exit<br /><br />First term on the right side is the momentum thrust which shows that if you increase v_exhaust (= directly proportional to Isp) then thrust increases too. Second term is the pressure thrust caused by pressure difference between exhaust gas and outside world at the nozzle exit. Note that this second term may go negative if an engine tuned for high altitude/vacuum operation is fired at sealevel! That' one reason why thick atmosphere is such a pain in the butt for pure rocket propulsion.<br /><br /><br /><br /><font color="yellow">"detune it to 80klbf again, which should mean the chamber temp and pressure will be within design margins for the nozzle."</font><br /><br />Pressure, yes. Temperature, no. The simplified equation for exhaust velocity tells why:<br /><br />v_exhaust = sqrt( 2k/(k-1)*R*T_chamber*[1 - (p_exit/p_chamber)^(k-1)/k] )<br /><br />(Sorry but don't know how to make it any prettier than that using plain html)<br /><br />k is the ratio of specific heats and R is gas constant, both depend on the choice of propellants and mixture ratio. R is interesting because it is inversely proportional to the molecular weight. That's part of the reason why hydrogen offers better Isp than RP-1, CO2 is heavier molecule than H2O. And this is also the reason why NTRs boast 900+s Isps, they vent pure H2, very light molecule.<br /><br />Note the 1 - (p_exit/p_chamber part. We wish to keep this pressure ratio as small as possible so that value of one minus it remains high. If we lower the chamber pressure we'll take a Isp

 

[mlorrey]

Okay, so we'll be able to return to a normal chamber pressure, depending on what the exit pressure is vs. ambient pressure. Given that we're lighting it off at altitude, rather than ground level, the standard nozzle should easily have positive exit pressure even at a lower feed rate and bring chamber pressure well within design limits (which we don't know yet, so this is all hand waving).<br /><br />Ablation: a) BOx deposition should at least mitigate some of the ablation losses, if not negate them entirely. Whatever the design ablation rate is at the normal RP-1 pressure and temp range, this rate is designed for a specific burn time for the engine as well. How much mass is lost by ablation (thus increasing T/W ratio as well as mass fraction) is another question to ask. So there are multiple issues that need to be answered wrt this choice of fuel.<br /><br />As for flying circles around the orbiter, I suspect you are right, the wing loading is quite low, and while not in the range of a glider, I suspect it will allow for very comfortable landing conditions esp without the mass of the ramjet. Still, I am leery of design features that result in dumping expensive equipment in the ocean. The second largest cost factor for the STS is the recovery and refurbishment of the SRBs, and those are capable of positive bouyancy. Droppable ramjets will require parachutes and inflatable floats, gps and transponders, plus a ship and recovery crew. The extra mass of the recovery system and the extra expense of the recovery infrastructure are big negatives to me.<br />Keeping the ram on the vehicle, so it can land anywhere, be refuelled, towed back to the air, and can ramjet propel itself back to home base if need be, or simply start another mission from its first mission landing location. THis vastly increases its market utility and reduces operations costs to a large degree.<br />While you are right that its a glider below 450 kt, w/ 500 lb of fuel it can fly a long way at 450 kt, and

 

[mlorrey]

RE: droppable ramjet pods:<br /><br />Actually, I've a better idea: rather than ramjets on droppable pods under the wings, keep it where it is. Add droppable turbofans/turbojets to the wing hard points. This solves the take-off and 0-450 kt issue with a very high Isp solution, which again ups the vehicle average Isp while not increasing weight to orbit. To reach 450 kt, I expect a T/W ratio of about .20, so two engines of 8600 lb thrust each on A/B should do the trick. Add 40-50% on top for insurance sake (and to allow flyback of the whole vehicle if one engine quits).<br /><br />The F404-GE-100D engine is a non-afterburning derivative of the F404-GE-400. GE and Singapore Aircraft Industries replaced the J65 engine in the Boeing A-4 Skyhawk with the F404-GE-100D to create the A-4S Super Skyhawk.<br /><br />Single-engine safety features are incorporated into the engine for this application. The F404-GE-100D engine provides the Super Skyhawk with higher dash speed, better acceleration, improved turn performance and increased fuel efficiency.<br /> <br /> Physical Dimensions <br /> Fan/Compressor Stages 3/7 <br /> Low-Pressure Turbine/ <br />High-Pressure Turbine 1/1 <br />Maximum Diameter (Inches) 35 <br />Length (Inches) 89 <br />Dry Weight (Lb.) 1,820 <br />Application A-4S Super Skyhawk<br /><br />Power Specifications <br />Specific Fuel Consumption<br />at Maximum Power 0.8 <br />Max. Power at Sea Level (Lb.) 11,000 <br />Overall Pressure Ratio <br />at Maximum Power 24 <br />Bypass Ratio 0.37 <br /><br />If each pod has its own deployable swing wing and tail fins, it could fly back home on idle and internal fuel rather than parachute into the ocean, too. Shouldn't be any more complex than an R/C aircraft or UCAV.

 

[argosy]

I have a couple of questions and possibly suggestions.<br />First of all, lets say that this (space)plane menages to reach orbit. I am intrested how would you control it in space? How would you adjust yourself to a reentry angle with only rear nozzles? The other question would be what is the estimated energy(heat) produced while entering the atmosfere? If you'd keep the old f-106 airframe, would it melt or atleast stretch out of heat and thus cause the plane to become less manueverble(if at all) and non-reusable. Don't get me wrong, I like the concept, but I think it would be possibly better to use concepts like this to achieve suborbital speeds and heights. For going to orbit, I think you should start with a clean sheet. But I aint no pro, so i might be wrong

 

[mlorrey]

Okay, I didn't draw in RCS thrusters, but I did include RCS mass in the system, and if you'd read the thread, we've discussed RCS mass already. The green tank up in the nose is RCS fuel.<br /><br />That being said, one technique I developed with my Lorrey Ballistijet in X-Plane was to develop a slight amount of roll before exiting the atmosphere. This put a bit of rifle-like spin on the vehicle that ensured that one always had a nose first reentry so that even with less than 100 kt IAS around 300kft, you could rapidly reorient even if upside down in time for reentry. <br /><br />As for thermal heating, if you'd read the thread, you'd see we've had extensive discussions over heating. Heating is a function of ambient pressure, mach speed, and cross sectional area presented to the airstream. With angles of attack of 40 degrees, which is typical, this cross sectional area is derived from the horizontal cross section of the whole vehicle, and thus one quick and dirty way to compare heating on various vehicles is to compare wing loading figures.<br /><br />STS Orbiter has a wing loading of 95.6 lb/ft^2. The X-33 was designed with a 30 lb/ft^2 wing loading. The X-106 has a 18.3 lb/ft^2 wing loading. Given that the X-33 was intended to operate with a metallic based thermal system, outside of a small nose cone and fin leading edges of RCC, not the high temp silica tiles and thermal blankets of the STS Orbiter, it is evident that the X-33 would operate in a much lower thermal regime than the shuttle. Proportionately, the X-106 would have less than 2/3 the thermal stress of the X-33, thus even less of a problem.<br /><br />While there is still risk to the aluminum portions of the 106 airframe, with proper techniques, stress and damage to these should be preventable.

 

[torino10]

It looks good to me but then again I'm no expert.<br /><br /> I was wondering however if it would be more prudent to mount the ramjets on the hardpoints and mount the turbofans where the ramjet would be?<br /><br />I tend to think that the turbofans would be able to give more low speed control at take off and landing. The turbo fans are off the shelf tech while the ramjets in question are not.

 

[mlorrey]

No. The ramjet is being carried to orbit and back, and needs the thrust ramp below the merlin to generate a large chunk of the thrust. You can't have such a structure on the wings. The turbojets are going to be dropped after takeoff.<br /><br />Nor are ramjets not 'off the shelf' tech. They are not new, they've been pretty well understood since WWII, used in the Navaho, BOMARC, other US missiles, and tested on the X-15. Another was developed for the XF-103. They've been tested up to mach 5.5. Final design work on this will be based on a well developed database of prior tests and research.<br /><br />I have been thinking about turning the ramjet into an annular ram-ejector that would surround the merlin nozzle and be dropped at mach 8 during the shift from air breathing to 100% rocket propulsion. This would improve the Isp performance of the rocket engine as well to above 500 secs, allow it to be used on takeoff while giving a low speed start to the ramjet function. The downside of the concept is it would be hanging off the back end 10' or more, which could mess up the CG, assuming that it doesn't counterbalance all the fuel up in what was once the weapons bay. After that fuel is burned would be the right time to time dropping the ram-ejector structure, thus recentering the CG.