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Published January 30, 2008 09:20 AM

Hydrogen-Burning Hypersonic Airplane: Going Green at Mach-5

The proposed future of air travel is quite a marvel. Seems unfathomable compared to the pollutant, oil-guzzling airliners of today. With the endless and testing delays, the awkward security, and greenhouse gas-emitting beasts, it’s a wonder why solutions have not yet come to fruition.

It just so turns out, it is all happening rather quickly behind the scenes. One proposed aircraft that seems wildly impossible is actually on the slate for possible funding for testing. The concept hypersonic jet has been developed by Reaction Engine and it is aptly called the A2. It is a Mach-5 (3,400 mph) wicked aircraft capable of holding 300 passengers and produces, get this, ZERO emissions!

The project has been supplemented in part through funding from the European Union’s Long-Term Advanced Propulsion Concepts and Technologies project, otherwise known in short as (Lapcat). Lapcat is in search for an airliner that can cruise from Brussels to Sydney in less than 4 hours. The A2 can meet the expectations without leaving its footprint behind.


Engineers have been re-working the A2 with the Concorde’s short comings in mind. The technical director of the project, Richard Varvill, believes that the Concorde was trashed for a few major reasons, limitations rather. First, it could not fly far enough, the limited range kept it from flying trans-Pacific routes. These routes are where the biggest market potential is for these hypersonic jets. Second, the Concorde’s power plant was only efficient up to its Mach-2 cruising speed. The problem with that was when the jet was restricted to cruise at Mach-0.9 to avoid producing sonic booms; its gas mileage took a dive.

Because of these limitations that sank the Concorde, the A2 has compensated and improved upon the shortfalls. The A2 engine has two modes for efficient cruising which is a combination of ramjet and turbojet propulsion systems. These systems will allow the A2 to be efficient at slow speeds and also give it the power necessary to produce hypersonic very high speeds.

Some interesting twists include the lack of any windows in the design due to the heat the jet will have to mitigate and weight of space shuttle type windows that would be required. Although passengers like to have windows for viewing pleasure and comfort they might be willing to bend on that luxury to get from point A to B in 4 hours rather than the current 22 hour flight time.

The A2 will reach hypersonic speeds in the following manner:


Mode 1- The jet’s four Scimitar engines send incoming air through the bypass ducts to the turbines. These turbines will produce thrust similar to today’s jet engines. The turbine compresses incoming air and mixes it with fuel to generate combustion which is enough to push the jet off the runway and propel it up to Mach-2.5.

Mode 2- Once Mach-2.5 is achieved the A2 switches into high gear and begins to reach its value. The incoming air is rerouted into the engine’s core with enough pressure to sustain combustion at speeds of up to Mach-5. This is the principle behind all ramjet designs, but the A2’s Scimitar system kicks it up a notch by adding a turbine compressor to squash the air far more intensely.

The problem that has foreshadowed this idea is that air-breathing engines cannot use turbines due to the super heated air that enters the blades, some 1,800 degrees F. The Scimitar hopes to overcome this problem with the addition of a cooling system enveloped within the engine which will cool the air enough to allow it to run through a turbine.

The most astounding aspect of this concept is the ZERO emissions footprint. The A2 is hydrogen powered so that it discharges only water vapor and nitrous oxide through the exhaust. Even though hydrogen still sounds dangerous to most folks, the fuel is actually no more explosive than normal jet fuel.

Hypersonic propulsion experts say that there is nothing fundamentally unsound in the A2’s plans. However, accomplishing the goal of making it happen is another story. Many obstacles will have to be overcome to perfect the design to the point of production. The heat exchange system is a serious issue and a massive engineering feat. Perhaps one of the biggest challenges is producing large amounts of hydrogen fuel without emitting carbon to do so. This leaves the A2 as not a truly green flying wonder because carbon-free hydrogen production is still a far ways off just yet but it is a radical start in a new direction.

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