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Two methods can be used to achieve the Vulcan hypersonic engine

DARPA held an industry day where it outlined some of its plans for hypersonic aircraft of the future. The program being shown off at the industry day was the DARPA Vulcan project. The project centers around developing an aircraft that uses a constant volume combustion (CVC) engine capable of flight at speeds from a standstill to Mach 4 and over.

Aviation Week’s Ares blog reports that the first part of the program was an introduction to the problem the program faces -- how exactly to accelerate an aircraft from a stop to speeds fast enough to activate a supersonic-combustion ramjet.

The program has some interesting slides and information (PDF) from the famed Lockheed Skunk Works HTV-3X flight demonstration vehicle that was conceived as part of the DARPA Falcon program. One of the slides gives an idea of the size of the HTV-3X vehicle by comparing it to the Have Blue aircraft that ended up being about 60% of the F-117 stealth fighter.

The Lockheed HTV-3X vehicle itself has been superseded by the DARPA Blackswift hypersonic program DailyTech has covered before. The engine that DARPA envisions for the Vulcan project is a CVC and turbojet combination.

According to Ares two methods can be used to achieve this type of engine. In one method a common air inlet would be used for both the turbojet engine that is to carry the aircraft from a stop to Mach 4 and higher speeds and the CVC that would take over at propel the aircraft to Mach 6 and over. This method is called turbine-based combined cycle.

The second method to achieve the engine needed is called an annular approach and would embed a turbojet inside a CVC ramjet engine. The big challenge here is that the turbojet would have to be cocooned when the CVC is active to protect it from the high heat produced inside the Vulcan engine over Mach 2.

Because a turbojet capable of propelling a aircraft over Mach 4 would be large and expensive to develop, DARPA instead wants to take a conventional Mach 2 turbojet and combine it with a CVC to get an engine capable of high Mach speeds, but at much cheaper development costs.



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RE: What no Pulse Detonation Engines
By US56 on 7/1/2008 5:22:20 AM , Rating: 2
After looking through the slides referenced in the article it seems as if the Vulcan may primarily be a jobs program for government employees and contractors. If there is/was no Aurora then there hasn't been any significant improvement on the 50 year old J58 design. What have they been doing all those years and why the big deal now? If Aurora exists then the Vulcan and some of the other programs cited may be disinformation or covers for classified advanced propulsion technology programs.

It should be possible to do something much more sophisticated with current technology than siamese a conventional turbojet with a CVC or ramjet engine. Above Mach 2 the turbojet would be dead weight. That wastes a lot of fuel when efficiency seems to be a major goal and works against using that approach for a low-cost orbital launch system. Based on some personal experience, it should be possible to build a single multi-mode engine which can transition smoothly from pulse to pulse detonation or continuous detonation mode or alternately pulse to ramjet operation. It would rely heavily on the kind of digital processing capability available now which wasn't even imagined when the J58 was designed in order to automate fuel management, inlet and exhaust nozzle variable geometries, and possibly combustion aids specific to each operational mode. That would seem to be the kind of technology investment which would be a worthy successor to the J58.


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