I wasn't sure if this should go in "Advance Concepts" or "Commercial" with the main SABRESkylon thread, but it's not meant to be a product and it' would certainly be advanced. REL have talked about the idea of a "Flight Test Vehicle" on a couple of occasions. Earlier ideas were for a scaled down Skylon, running LOX/Methane rockets while the current design, resembles the D-21 M3 reconnaissance drone designed to launch off the back of a couple of modified SR71s in hte late 60's. then modified with a booster longer than the drone, was tested off a modified B52, before the whole project was cancelled. However looking through the archives I located this. https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20000004765.pdfand this.https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19990110312.pdfBasically a late 90's plan to modify a couple of D-21 to demonstrate the "DRACO" Rock Based Combined Cycle engine some NASA centers were working on. This system has multiple mode transitions in its flight trajectory and also featured a moving inlet spike to accommodate the speed changes. In the process the second one discusses the D-21 in some detail, along with the LM Advanced Projects "Experimental Prototype" approach to cutting the development cost by about 1/3 (page 35 if you're interested).Interestingly they reckoned you could add a LOX tank between the fuel wing tanks and the engine duct, and they didn't think it would have thermal issues, although once you got above M3.5 the titanium skin and duct leading edge looked doubtful. Interestingly the issue around the LOX tank was not temperature related but pressurization. The D-21 was designed to operate its fuel tanks (there were 3, front, middle and back cross ways) at 1.5psi above the ambient pressure. Pressurizing the tanks to make the engine pressure fed was viewed as too dangerous. On the upside the REL FTV is a clean sheet design with a thrust about 29x bigger than the D-21 ramjet. (Marquardt RJ43-MA-20S4) and recovery and reuse will be designed in from day one. Beyond that we have a few data points.The SABRE test engine is expected to have a thrust of 20 tonnes (44 000lbf) and according to the SEI study on the USAF TSTO design thrust needs to be at least 70% of GTOW, giving about 28500Kg of mass. SABRE's T/W ratio is expected to be 14:1 so engine mass is say 1430Kg. The D21 dry mass 5500lb vs fully loaded at 11200lb means it was 49% structure. It was stressed to withstand -2/+5g in both axial and directions normal to axial. So a lower peak acceleration should give a lighter structure.28,500-1,430kg is a total mass of 27,070Kg. A 15% mass growth allowance means the maximum mass (structure and propellant) is 23,539Kg. To put this in perspective 30tonnes is a small(ish) regional airliner or a large(ish) fighter aircraft. My instinct is this layout is not a good fit to the issues around LH2 as a fuel, hence my interest in wheather it would be possible to make 2 engines and go with a "Mini Skylon" airframe. Given the D-21 is going to be REL's FTV design to test inlet design and spike schedule what does that say about its capabilities?My instinct is REL can go one of two ways on this. A "bare bones" X-plane approach.This is totally focused on flying SABRE through as much of its trajectory as possible and refining the inlet and spike performance to meet its goals. The vehicle structure is as simple as possible to do that. Not intended to be anywhere close to deliver a substantial payload to orbit, or a 2nd stage to release.A "Skylon risk retirement" approach.This implements the FTV in technologies more like those planned for Skylon. IE a truss framework with appropriate levels of MLI and the SiC reinforced ceramic skin fabricated in corrugated panels. Both options can help retire a number of operations features of a Skylon as well. EG fully automated fueling and de-fueling, although that would not be necessary for early tests. Likewise early tests could treat it as an RPV flown from a ground station, before moving to fully AGV status. the big question would be what else could it be used for ? What sort of things would 3rd parties like to test, and what sorts of instrumentation would they want to install to do so?
BAE are the steering force now in this, their actual percentage is pretty irrelevant but it’s big enough to do what they want to do. Also why do you think they are working with DARPA in the US, they only have one purpose and it sure isn’t civilian.
The form a test vehicle takes will depend on the requirements behind the funding.REL worked on FSPLUK which if funded may provide a flight tested vehicle that could fly a SABRE. But I can't see anyone funding a pure SABRE test vehicle until SABRE has been tested. BAe's initial estimates for a test vehicle was 1 billionThe Darpa funding has a potential phase 3, which covers flight testing (It also explicitly mentions dual use - civilian and military).
Quote from: Katana on 05/05/2018 06:06 amTwo booster engines to be symmetrical like conventional rockets with strap on boosters, nothing related to X7.Are you saying you think REL would build two flight engines or two rocket engines? Quote from: KatanaThe X7 airframe may work up to M6, but would be infeasible for rocket mode operation to M10.I'm talking about the X7 layout which is basically the same as the M2 Firebee II drone and Hound Dog missiles. Quote from: KatanaEven without VTOL, the vehicle need to be symmetrical in rocket mode, which exclude X7 and favors BOMARC/ SR71/ original Skylon.There have been a number of asymmetric thrust rocket concepts, IIRC one of the NLS designs for example. I think everyone would prefer a symmetric vehicle wheather it looked like Skylon or not. Thrust is more balanced, there are more engine placement options and you have redundancy, which is important given the new engine has unknown reliability statistics (something else flight testing will discover). It's wheather the budget will be available to allow it. The minimal assumption is there will be enough for one engine, not two, so what can you do with that one engine? Incidentally it turns out that through the 1970's and 80's NASA ran a number of studies for such an aircraft in the 40-60 000lb range as the "High Speed" or "Hypersonic Speed" Research Aircraft, partly to try out the various possible structural concepts they had seen on a scale that would give them a realistic test of the structural issues of a large aircraft. They reckoned you could build a baseline aircraft out of fairly conventional Aluminium with active water/glycol cooling good at least to M6. My instinct is for a passive heat pipes to move heat, eliminating the need for pumps and the large numbers of fluid connectors that have to stay fluid tight over a very wide range of temperatures and pressures covering the wings and fuselage. I don't think their complexity was ever really addressed and it's a non trivial problem to solve.
Two booster engines to be symmetrical like conventional rockets with strap on boosters, nothing related to X7.
The X7 airframe may work up to M6, but would be infeasible for rocket mode operation to M10.
Even without VTOL, the vehicle need to be symmetrical in rocket mode, which exclude X7 and favors BOMARC/ SR71/ original Skylon.
Why you think REL can't afford to build two engines , for a test vehicle? Building several more copies per batch only add minor cost to R&D. In fact they are really needed for backup, in case of damaging.Solving the asymmetrical thrust problem needs additional procedures, which becomes really expensive.
BAE works on military funding scales, if they say it will cost a billion, a non military contractor probably could so it for a fraction of that price. The vehicle only have to be something similar to SpaceshipOne,. Which cost around a 100 million dollars, even taking inflation into account it hard to get to BAE figure of a billion quid for a demonstrator vehicle.
The UK has just announce it building a new fighter the tempest. I think Reaction Engine can squeeze a bit of money out of this program. It could provide a continuous revenue stream by getting rolls royce to adopt it pre coolers for the fighter engine. Reaction Engine do claim they offer a lot of advantages, https://www.reactionengines.co.uk/sabre/pre-cooled-turbojet. This is Roll Royce video on the new engine Could the guy fit any more buzz words in this video! Improve thermal management is one of Reaction Engine claims through. Also nearly all the partners involve in Tempest are now also actively involved in Reaction Engine. I'm taking a little guess here but to be a truly next gen aircraft the Tempest will be base on a all electrical system. incorporate electrical landing gears and replace most of hydraulic systems with electrical systems, which should produce plenty of transferable knowledge to incorporate those technologies into skylon. Also could reaction engines take advantage of Project Magma https://www.baesystems.com/en/article/first-magma-flight-trials to further lighten skylon?Project Tempest if the UK truly wants a true 6th gen aircraft, should mature all of these technologies making them cheaper to integrate them into Skylon and produce a even lighter vehicle and may be even a simpler spacecraft to build as well.
The UK has just announce it building a new fighter the tempest. I think Reaction Engine can squeeze a bit of money out of this program. It could provide a continuous revenue stream by getting rolls royce to adopt it pre coolers for the fighter engine. Reaction Engine do claim they offer a lot of advantages, https://www.reactionengines.co.uk/sabre/pre-cooled-turbojet. Could the guy fit any more buzz words in this video! Improve thermal management is one of Reaction Engine claims through.
Also nearly all the partners involve in Tempest are now also actively involved in Reaction Engine. I'm taking a little guess here but to be a truly next gen aircraft the Tempest will be base on a all electrical system. incorporate electrical landing gears and replace most of hydraulic systems with electrical systems, which should produce plenty of transferable knowledge to incorporate those technologies into skylon.
Also could reaction engines take advantage of Project Magma https://www.baesystems.com/en/article/first-magma-flight-trials to further lighten skylon?Project Tempest if the UK truly wants a true 6th gen aircraft, should mature all of these technologies making them cheaper to integrate them into Skylon and produce a even lighter vehicle and may be even a simpler spacecraft to build as well.
Fluidic controls are even more problematical if you've already gone to electric actuators. Where you draw the line is a very tricky question. Necessary innovation (because you can't make the design work without it) versus unnecessary innovation, that adds cost, technical risk and potential delays.
I'm no expert but it just seemed like thrust vectoring a rocket nozzle with airflow would be a huge research project of its own and why would you want to do it for a launch vehicle?
As for replacing ailerons etc they mentioned that it got more challenging with larger aircraft but that the fact that large modern engines (as opposed to their model aircraft ones) had more compressors which might compensate. That's all I could get - I leave you to judge if anything's applicable to SABRE-powered vehicles.
Would fluidic nozzles win versus gimbals and associated structure to accommodate gimbaling? I get a sneaking suspicion that the mass and performance trades are real murky here.
For instance, is there enough bleed air from the SABRE compressor to run fluidics? On a more conventional rocket engine, would turbine exhaust work?
Shades of the TAN augmented nozzle work in a sense?
For Skylon, the nacelles have a serious bend to them, trying to matching between airflow flight angle and ideal thrust angle, which is probably not insignificant in terms of drag. Could one cheat with fluidics to effectively get more of the nozzle inline with the airflow and have variable thrust angle/trim?
Doing a web search I found this item from the British space agency. It's the planning for the flight test vehicle to test SABRE.Interesting points. It's funding comes from ESA through its general support programm for future technology. It's for both an FTV and a road map for a new full scale launch vehicle (single or two stage) for the European market in c2030.
I assume this would be funding that is not yet paid. If this is the case, would it be only available to EU members going forward, which might in some cases cause problems for BSA/Reaction.