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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The Lockheed HTV-3X vehicle itself has been superseded by the DARPA Blackswift hypersonic program DailyTech has covered before.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: Is that fast enough to reach orbit?
By RabidDog on 6/26/2008 2:27:05 PM , Rating: 2
Nope. At Mach 4, you are still about 10,000mph short to reaching orbit. To orbit you must go about 17,500mph.


RE: Is that fast enough to reach orbit?
By Mojo the Monkey on 6/26/2008 2:52:01 PM , Rating: 2
well wouldn't it depend on the specific orbit speed of the space station vs the atmospheric entry point of the second ship? Is the space station geo-sync'd? -just curious


By Curelom on 6/26/2008 3:29:05 PM , Rating: 2
It would depend on the speed of the space station, which is orbiting, thus going at or faster than the 17,500 specified in the previous post.
The space station is not ge-sync'd. Occasionally you can see it fly across the sky.


By masher2 (blog) on 6/26/2008 5:04:17 PM , Rating: 3
> "At Mach 4, you are still about 10,000mph short to reaching orbit"

Mach 4 is the minimum ignition speed for the ramjet, not the maximum velocity. We've had test Scramjets that broke Mach 30, IIRC.


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