London to Sydney in 2 hours!
Last month, more than 70 years since the dream of sustained hypersonic flight was first born out of Nazi designs for a manned bomber with a global reach, the US Air Force's latest experimental hypersonic aircraft was lost during an attempt to maintain Mach 6 for merely five minutes. Hypersonic (high supersonic) speeds are those greater than Mach 5, or 3,500mph.
Despite the crash of the unmanned X-51 A Waverider last month, scientists from across the world are in a series of experimental test flights racing to be the first to develop a propulsion system that will crack the secrets of sustained hypersonic flight. This is about more than flying from London to Sydney in four hours, as the headline writers would have it. This is about space.
"So hypersonic travel may be the dream, but aircraft-like space access is the prize," Ben Gallagher says. Gallagher is business development manager for Reaction Engines Ltd, whose revolutionary and privately financed Sabre and Skylon spaceplane are Britain's champions in the hypersonic race. "And we are not talking Concorde frequency and cost, we are talking Ryanair. That's why it is now attracting more resources ," Gallagher says.
The challenge that today's engineers face is to develop a propulsion system and then an airframe that can sustain these very fast speeds for the much longer period of time necessary to fly into space or cruise to Sydney. The key to flying at hypersonic speeds for any length of time is the ability of an engine to manage the exponential jumps in temperature for small increases in speed beyond Mach 5.
Traditionally, engineers have looked to the air-breathing scramjet as the propulsion system to deliver such sustained hypersonic flight, as it can fly as fast as Mach 10 (London to Sydney in two hours). However, a major disadvantage of scramjets is that they can start to operate only at Mach 4 or 5, so any scramjet space-plane would need one, two or even three other propulsion systems to get them up to near Mach 4.
In contrast, the reusable Sabre engine can function as both a jet and a rocket engine. In its jet mode it can reach a speed of around Mach 5, sucking in oxygen from the atmosphere and using very lightweight pre-cooler heat exchangers to cool the air before it enters the engine, thus avoiding the problem of overheating . The same engine then switches into rocket mode when it enters space.
"Twenty years ago we were real voices in the wilderness and now we are being taken seriously," says Richard Varvill, chief designer of Reaction Engines, whose revolutionary hypersonic engines are now being taken seriously .
-- The Independent