"I have read many of the documents at the REL site, but not yet found the documents you refer to that address this and my other points. If you have them handy, please post the links."There are no documents that discuss you questions from your POV. Some of your questions indicated you did not understand Skylon's structure. This would be the place to start. http://www.reactionengines.co.uk/downloads/JBIS_v57_22-32.pdf"Shuttle data gives you good confidence. (But Concorde burst tire data is less rosy.)" I fatal crash in 27 years is pretty good by many yardsticks."However, in the "commercial" promotional video at the REL web site, they depict a fleet of Skylons at what appears to be a commercial airport - there are A380s there."
Did Reaction Engines evaluate the possibility of using some kind of catapult for liftoff? It would work exactly the same way as it works on the aircraft carrier. Would it make some difference in fuel consuption?
Quote from: yamato on 07/17/2011 05:57 pmDid Reaction Engines evaluate the possibility of using some kind of catapult for liftoff? It would work exactly the same way as it works on the aircraft carrier. Would it make some difference in fuel consuption?Skylon at takeoff has an ISP on the order of 20 km/s. Takeoff speed is on the order of 0.1 km/s, so fuel burned during takeoff is on the order of 0.5% of takeoff mass. A catapult launch would save carrying that extra fuel, decreasing dry mass by a similar percentage. That's certainly not negligible, but presumably not worth the trouble of designing and building a catapult.If the catapult supported the vehicle instead of the landing gear one could reduce the size of the landing gear somewhat. This would save a significant amount of dry mass, but why add more risks and development cost for a marginal gain?
Have "convoy" of 40 dump truck/lorries which have capacity of 20 ton load, giving total max load of 800 tons [1.6 million lbs]. So a line of 20 trucks and two columns and spaced so their outside perimeter is about 30' and 600' long. Have these vehicles support a deck which also about 30' wide and 600'. Have this deck weight around 100,000 to 200,000 lbs.Have Skylon on an elevated structure the same height as 40 truck platform. Using tow vehicle used with airline planes, tow the fueled Skylon on to truck platform. Truck platform accelerates to say 30 mph [and continues up to 60 mph] but at 30 mph, Skylon accelerate and takes off around same time truck platform has reaches 60 mph.[cut]Oh, these vehicles would controlled remotely.
Quote from: gbaikie on 07/18/2011 12:00 amHave "convoy" of 40 dump truck/lorries which have capacity of 20 ton load, giving total max load of 800 tons [1.6 million lbs]. So a line of 20 trucks and two columns and spaced so their outside perimeter is about 30' and 600' long. Have these vehicles support a deck which also about 30' wide and 600'. Have this deck weight around 100,000 to 200,000 lbs.Have Skylon on an elevated structure the same height as 40 truck platform. Using tow vehicle used with airline planes, tow the fueled Skylon on to truck platform. Truck platform accelerates to say 30 mph [and continues up to 60 mph] but at 30 mph, Skylon accelerate and takes off around same time truck platform has reaches 60 mph.[cut]Oh, these vehicles would controlled remotely.For some reason I'm reminded of the first episode of Thunderbirds, though that was landing, not takeoff.Also that's a lot of things to go wrong for a small fuel saving.
What is the take off speed of Skylon?
our rotation speed is around 590 km/hr
Skylon at takeoff has an ISP on the order of 20 km/s. Takeoff speed is on the order of 0.1 km/s, so fuel burned during takeoff is on the order of 0.5% of takeoff mass. A catapult launch would save carrying that extra fuel, decreasing dry mass by a similar percentage. That's certainly not negligible, but presumably not worth the trouble of designing and building a catapult.
Operational simplicity was judged to be more important. A kilometers long powered launch trolley is not simple or cheap.
Quote from: Hempsell on 07/06/2011 03:35 pmQuote from: tnphysics on 07/03/2011 04:05 amOther question: What about transferring heat from the heated (post-precooler) helium to the high pressure (pre-turbine) hydrogen via another heat exchanger? The idea is to allow far higher hydrogen outlet temps, and thus allow less of it to be used.I am afraid (like your previous proposal) without diagrams I am not quite sure what you mean. The hydrogen does not drive the main compressor turbine (it did in the old HOTOL RB545 engine). It does drive its own (i.e. the hydrogen pump) and the He circulation pump; an arrangement that means the engine can be started (which we judged to be an important feature of a operational engine). But this is already after we have exchanged heat with the helium.Well, let me describe it in detail.After the turbine, the helium passes through a heat exchanger that heats the hydrogen. The hydrogen exits this heat exchanger at a certain temperature.The idea is actually quite simple, at least in theory (though I am sure not in practice). The idea is that some of the helium (instead of entering the turbine) is shunted into another heat exchanger and then into the last He compressor stage. This heat exchanger heats the hydrogen a second time. The hydrogen then enters its turbine in the usual way.The net result is that some more heat is shunted from the air to the same amount of H2 -> less H2 needed for a given cooling effect ->higher Isp.
Quote from: tnphysics on 07/03/2011 04:05 amOther question: What about transferring heat from the heated (post-precooler) helium to the high pressure (pre-turbine) hydrogen via another heat exchanger? The idea is to allow far higher hydrogen outlet temps, and thus allow less of it to be used.I am afraid (like your previous proposal) without diagrams I am not quite sure what you mean. The hydrogen does not drive the main compressor turbine (it did in the old HOTOL RB545 engine). It does drive its own (i.e. the hydrogen pump) and the He circulation pump; an arrangement that means the engine can be started (which we judged to be an important feature of a operational engine). But this is already after we have exchanged heat with the helium.
Other question: What about transferring heat from the heated (post-precooler) helium to the high pressure (pre-turbine) hydrogen via another heat exchanger? The idea is to allow far higher hydrogen outlet temps, and thus allow less of it to be used.
Suppose the ramjet Isp turned out to be better than expected. What would be the improvement in payload?