Quote from: john smith 19 on 09/23/2017 05:58 pmIt remains astonishing how fixated US aeroenging designers remain with supersonic combustion. It's even more astonishing how the USG continues to fund them. Maybe because they know more than you.
It remains astonishing how fixated US aeroenging designers remain with supersonic combustion. It's even more astonishing how the USG continues to fund them.
Quote from: Jim on 09/23/2017 08:03 pmQuote from: john smith 19 on 09/23/2017 05:58 pmIt remains astonishing how fixated US aeroenging designers remain with supersonic combustion. It's even more astonishing how the USG continues to fund them. Maybe because they know more than you. Well Jim so do fusion engineers and after almost 50 years of trying it's about time they get it out of the lab... Unfortunately as we know things are different outside the lab and it would seem what they 'know' still remains "it works great in theory..." and that if they keep promising it 'soon' they will continue to get money to keep trying.Now none of this is especially "bad" as we eventually get advances out of this research, it's inevitable. The BAD thing is very often, (especially in the realm of supersonic combustion research) is that more near-term, often vastly more viable technology gets ignored or overlooked due to the aforementioned "fixation" (and that's what it is) on a single aspect of research and development.Do we "need" SCramjets? No, that's rather obvious as there are other method of reaching and cruising at the speeds of interest. In fact researchers actually admit that the speed range of interest is LOW for supersonic combustion, but it is the 'default' technology. Truth is hypersonic flight has never been hampered by PROPULSION it has ALWAYS been dependent on materials technology for the airframe. Hypersonic 'cruise' flight is VERY tough on the airframe but propulsion to get a vehicle to cruise at hypersonic speeds has been around for over 40 years.The main issue with hypersonic flight still remains justification for the trouble and expense to build and operate a hypersonic airframe not the need for SCramjet propulsion.Randy
The cross-section of the proposed engine is almost identical to the J67+RJ55 powerplant in the old Republic F-103. They studied that plane from 1951 to 1957, but couldn't make it work. There is a good account in Dennis R. Jenkins' book on the XB-70. Everything old is new again.The basic problem with these combined engines is that the area and geometry of the intake and exhaust have to vary a lot to accommodate different speeds and Mach numbers. You need complex variable intakes with powerful actuators at a place suffering maximum airflow heating. Even plain turbojet planes like MiG-23/MiG-27 and B-1A/B-1B switched to fixed inlets in the 1970s at a considerable loss of speed in order to reduce the maintenance burden. The Chinese have recently made the same switch in J-17. When you add supersonic combustion the problems multiply.
When LM are reportedly already flying a sub scale model of a hypersonic vehicle so this matter has rather moved on. It’s been clear the USAF wants such vehicles and they have an administration with both the former and current presidents who will give them the money to achieve these vehicles. The materials needed to build such vehicles appear to be in process. No doubt such craft will be very expensive to build but they are seen as a key component of global strike so I am sure those costs will be met.
Quote from: Arch Admiral on 10/19/2017 09:48 pmThe cross-section of the proposed engine is almost identical to the J67+RJ55 powerplant in the old Republic F-103. They studied that plane from 1951 to 1957, but couldn't make it work. There is a good account in Dennis R. Jenkins' book on the XB-70. Everything old is new again.The basic problem with these combined engines is that the area and geometry of the intake and exhaust have to vary a lot to accommodate different speeds and Mach numbers. You need complex variable intakes with powerful actuators at a place suffering maximum airflow heating. Even plain turbojet planes like MiG-23/MiG-27 and B-1A/B-1B switched to fixed inlets in the 1970s at a considerable loss of speed in order to reduce the maintenance burden. The Chinese have recently made the same switch in J-17. When you add supersonic combustion the problems multiply.I imagine that’s why LM & AJ took 4 years ground testing one.
That's part of the reason why the SR-71 with it's conical inlet worked so well: it is a simple forward/backward translation on a an internal pole/actuator.
Quote from: Star One on 10/19/2017 08:41 amWhen LM are reportedly already flying a sub scale model of a hypersonic vehicle so this matter has rather moved on. It’s been clear the USAF wants such vehicles and they have an administration with both the former and current presidents who will give them the money to achieve these vehicles. The materials needed to build such vehicles appear to be in process. No doubt such craft will be very expensive to build but they are seen as a key component of global strike so I am sure those costs will be met.1) LM flew a subscale model of a fly-back rocket booster, (two years after a university student project did the same thing for 1/10th the budget) yet they didn't get a contract to build an actual vehicle. "Moved on" is relative in government projects, doubly so for defense projects. The key question would be did they fly a subscale vehicle at hypersonic speeds or are they just repeating the various prior projects and calling it "progress"?2) Actually the USAF has "talked" about wanting a hypersonic vehicle bu they still don't have a definite mission or have defined operational usage of such a vehicle. "Global Strike" has often been suggested but the actual utility of such a vehicle has been questioned just as often and the Air Force has not been able to justify it as a requirement. Support of Presidental administrations and/or Congress does not constitute the ability to actually justify and fund a proposal. More often than not it actually just manages to funnel research funding to certain areas without resulting in working (operational) hardware. This is of course 'progress' but that's about it.3)You misunderstand what I was getting at on materials vis-a-vis propulsion; We've had the propulsion since the 50s. we've actually had the materials as well. Combing the two to produce a viable hypersonic cruise vehicle should be fairly straightforward but has not been done mostly because programs gets sidetracked from that into cul-de-sacs like SCramjets. That obviously should not be enough to fully prevent the construction and use of a hypersonic vehicle and it is of course not the only factor. The MAIN factor is no one really "needs" a hypersonic cruise vehicle and that is as true today as it was in the 1960s. Therefore the funding and actually requirement to build and operate a hypersonic vehicle remains unavailable.4) A hypersonic vehicle is only "key" to Global Strike when the Air Force needs it to be to get research funding. it tends to be 'lacking' when an operational requirement is asked for. Why? Simply you don't need a hypersonic cruise vehicle to perform Global Strike. "Nice to have" does not equate to an actual requirement and every time the Air Force attempts to build a requirment on those grounds it falls apart. The fact that SCramjes inevitably get tacked on to the "requirement" don't help. (The Air Force pointed this out to itself with the AFL study on the SABRE cycle. You can have a hypersonic cruise vehicle without SCramjets at which point the Air Force calls on LM to design a hypersonic cruise vehicle that uses SCramjets...)We've had working SCramjets, (not that good but they at least 'worked' out of the lab) but not operational ones. We've had working materials and techniques to have a hypersonic cruise airframe, again just not an operational one. We've had working combined cycle engines, (up to an including a dual mode ram/SCramjet but not outside a lab) just not operational ones. We've had working hypersonic inlets and exhausts but not operational ones. Nothing in the current LM/Air Force offering would lead me to believe this iteration is any more likely to lead to an operational vehicle than previous projects. The inclusion of a requirement for an operational dual mode SCramjet in fact by the airframe designer in fact bias' it heavily in the direction of "only" another research project which will not end in actual hardware to me. The fact that the Air Force does not have a clear requirement or mission for such a vehicle pretty much seals the deal.YMMV of course...Randy
Well Jim so do fusion engineers and after almost 50 years of trying it's about time they get it out of the lab...
To expand on RanulfC's comments on the A-12/SR-71: This aircraft's designed mission (flying regular illegal peacetime recon missions over the USSR a la U-2) went away before it even flew. The CORONA and GAMBIT spacecraft did the same job better, cheaper, and in accordance with international law. Their weak point was the time it took to return the film, which made them useless for tactical intelligence in wartime. It seems clear that the SR-71 fleet was retained to provide a faster recon capability during a major conventional war with the USSR. All the "operational" missions were really training exercises for WWIII.Even this capability withered away as the Sovs provided the S-200 [SA-5] missile system and the MiG-25/31 interceptor to most of their puppet states. The Blackbird was dead meat to these systems (one was damaged by an old S-75 [SA-2] over Vietnam). They lasted as long as they did only because of their coolness factor. Any "SR-72" would have to face late-model S-300s or S-400s or even tactical ABMs for which speed and altitude are no defense at all. There is no chance that this airplane will actually be funded.
To expand on RanulfC's comments on the A-12/SR-71: This aircraft's designed mission (flying regular illegal peacetime recon missions over the USSR a la U-2) went away before it even flew. The CORONA and GAMBIT spacecraft did the same job better, cheaper, and in accordance with international law. Their weak point was the time it took to return the film, which made them useless for tactical intelligence in wartime. It seems clear that the SR-71 fleet was retained to provide a faster recon capability during a major conventional war with the USSR. All the "operational" missions were really training exercises for WWIII.
Any "SR-72" would have to face late-model S-300s or S-400s or even tactical ABMs for which speed and altitude are no defense at all. There is no chance that this airplane will actually be funded.
Quote from: Arch Admiral on 10/26/2017 09:17 pmTo expand on RanulfC's comments on the A-12/SR-71: This aircraft's designed mission (flying regular illegal peacetime recon missions over the USSR a la U-2) went away before it even flew. The CORONA and GAMBIT spacecraft did the same job better, cheaper, and in accordance with international law. Their weak point was the time it took to return the film, which made them useless for tactical intelligence in wartime. It seems clear that the SR-71 fleet was retained to provide a faster recon capability during a major conventional war with the USSR. All the "operational" missions were really training exercises for WWIII.Satellites other weak point is they fly predictable tracks, and can be avoided if you have their orbital parameters. The fact that low speed, high latitude drones continue to be used by the US suggests they are not the perfect solution. Quote from: Arch AdmiralAny "SR-72" would have to face late-model S-300s or S-400s or even tactical ABMs for which speed and altitude are no defense at all. There is no chance that this airplane will actually be funded.It does seem to be niche target. People who are sophisticated enough to threaten the current generation of subsonic high altitude drones but couldn't shoot this down?This sounds like a fairly selective choice of enemies.
I doubt those missiles would be able to successfully engage a vehicle such as the SR-72. The SR-71 after all successfully avoided increasingly sophisticated SAMs over its long life
Quote from: Star One on 10/27/2017 01:08 pmI doubt those missiles would be able to successfully engage a vehicle such as the SR-72. The SR-71 after all successfully avoided increasingly sophisticated SAMs over its long lifeI thought so too, but as others have pointed out it was fairly early banned from overflying the USSR, who would rank as the #1 in terms of altitude and speed of their air defense systems. I suspect no client state was allowed their most advanced SAM's for fear of copies finding their way into the wrong hands.
The RQ-180 is rumoured to rely on very high levels of stealth and using the same trick as the U-2 that’s flying virtually on the edge of space and having sideways looking sensors. It can probably get closer in than the U-2 being a lot more stealthy. I assume though that’s not an option that will be open to the SR-72.
Did the acquisition of Orbital ATK by Northrop Grumman in June 2018 affect the DARPA Advanced Full Range engine contract awarded to Orbital ATK in 2016, especially considering that the Valkyrie hypersonic aircraft concept envisaged in 2018 by Boeing (which co-partnered with Orbital ATK on the DARPA Advanced Full Range Engine study) has evolved in terms of design over the span of a few years?