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A Kludge

Is this the future of air travel?

Engineers created the A2 with the failures of its doomed supersonic predecessor, the Concorde, very much in mind. Reaction Engines's technical director, Richard Varvill, and his colleagues believe that the Concorde was phased out because of a couple major limitations. First, it couldn't fly far enough. "The range was inadequate to do trans-Pacific routes, which is where a lot of the potential market is thought to be for a supersonic transport," Varvill explains. Second, the Concorde's engines were efficient only at its Mach-2 cruising speed, which meant that when it was poking along overland at Mach 0.9 to avoid producing sonic booms, it got horrible gas mileage. "The [A2] engine has two modes because we're very conscious of the Concorde experience," he says.

Those two modes--a combination of turbojet and ramjet propulsion systems--would both make the A2 efficient at slower speeds and give it incredible speed capabilities. (Engineers didn't include windows in the design because only space-shuttle windows, which are too heavy for use in an airliner, can withstand the heat the A2 would encounter.) In the A2's first mode, its four Scimitar engines send incoming air through bypass ducts to turbines. These turbines produce thrust much like today's conventional jet engines--by using the turbine to compress incoming air and then mixing it with fuel to achieve combustion--and that's enough to get the jet in the air and up to Mach 2.5. Once it reaches Mach 2.5, the A2 switches into its second mode and does the job it was built for. Incoming air is rerouted directly to the engine's core. Now that the plane is traveling at supersonic speed, the air gets rammed through the engine with enough pressure to sustain combustion at speeds of up to Mach 5.

A combination turbofan/ramjet. Hokay.

If I understand this properly, the idea is to fly fast subsonic over land to avoid breaking windows, and then to go like a bat out of hell over the water. When I look at that design, I have to wonder how they can really get the range, with all of the drag that is implied from those huge delta wings, not to mention the wave drag at Mach 5. I also wonder where they put the hydrogen--that stuff is very fluffy, and needs large tanks. It's probably not wet wing (it would be very structurally inefficient), which is why the fuselage must be so huge, to provide enough volume in there for it.

Sorry, but I don't think that this will be economically viable. As is discussed in comments and the article, hydrogen is not an energy source--it's an energy storage method, and it's unclear how they'll generate it without a greenhouse footprint. Moreover, it's not as "green" as claimed, because dihydrogen monoxide itself is a greenhouse gas. I'll bet that this thing has to fly at sixty thousand feet or more to get itself sufficiently out of the atmosphere to mitigate the drag problem, and that's not a place where you want to be injecting a lot of water.

This concept doesn't learn the true lessons of Concorde: like Shuttle, a lot of people have learned lessons from Concorde, but the wrong ones. The correct lesson is that we need to get rid of shock waves and drag. Once we do that, we'll be able to cruise at reasonable speeds (say, Mach 2.5) everywhere, over both land and water, so we won't have to build the vehicle out of exotic materials and eliminate windows. We'll also be able to have fast transcontinental trips (two hours coast to coast) which is another huge market that this concept doesn't address at all. Finally, it has to do it with a reasonable lift/drag ratio, so that ticket prices will be affordable. And I think that the fuel issue is superfluous--Jet A will be just fine for the planet, as long as fuel consumption is reasonable, which makes the vehicle design much easier, with much more dense fuel.

Fortunately, I've been working for over a decade with a company that thinks it knows how to do this, and I'm hoping that we'll be able to start to move forward on it very soon.

[Via Clark Lindsey]

[Update in the late afternoon]

In response to the question in comments, there's not much publicly available on the web about shock-free supersonics, but here's a piece I wrote a few years ago on the subject.


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Patrick wrote:

Hey, it's the Myasishchev Bounder!!!

K wrote:

Has anyone noticed that they just took the wing configuration from an old Russian supersonic bomber, the M-50 Bounder?

K wrote:

Bah! Someone beat me to it!

anon wrote:

Ah, the Hydrogen Religion again.

Project SUNTAN all over again. Pity Kelly Johnson isn't around to send the money back this time.....

Erik Anderson wrote:

What it is, is the Skylon air-breathing launcher, apparently without any changes. Not a swell idea for launching stuff into space, but it's got to be even worse for intercontinental passenger service.

Brock wrote:


I'll understand if you can't divulge anything on your particular business venture at this time, but can you point to any articles or research on how one would (in theory) get rid of shockwaves and/or drag? I am not an aeronautics engineer so I'd be interested in a basic introduction to the concept.

Thanks for any links!

Dennis Ray Wingo wrote:

One thing to comment on here.

Hydrogen is no more an energy storage method than gasoline is. The only difference is that the energy stored in the gasoline was done a long time ago.

Also, H2O is a greenhouse gas, 20 times more powerful than CO2. However, the persistence of H2O in the atmosphere is measured in days or weeks, not decades. H20 has a tendency to precipitate when its density reaches a certain level.

Paul F. Dietz wrote:

However, the persistence of H2O in the atmosphere is measured in days or weeks, not decades. H20 has a tendency to precipitate when its density reaches a certain level.

This is true -- in the troposphere. As Rand pointed out, this plane would fly at 60,000 feet, where the relative humidity is normally quite low. The residence time of water at that altitude is considerably longer, and the natural rate of water injection there is considerably lower. So, anthropogenic effects would be easier to produce there than down here near the surface.

Paul Milenkovic wrote:

On the subject of all of this, anyone have any insights or knowledge of the outcome of the XB-70 project with regard to supersonic aerodynamics.

The way the story was told, the Air Force let it be known that they wanted a supersonic or perhaps even a supercruise (supersonic the whole way over, not just evading air defenses) bomber, and they got a number of impractical proposals owing to the fuel consumption problems of supersonic flight. On proposal was for a plane that had some ridiculously large drop tanks, and General Curtis LeMay was heard to exclaim, "That is not a bomber, that is a three ship (as in aircraft) formation!"

North American came along with a radically-different proposal, one in which the drag-inducing shock wave could be put to a good purpose -- generating lift. The concept was called compression lift and supposedly a supercruise aircraft could have higher (?) L/D ratios than a subsonic one.

The embodiment of compression lift in the XB-70 was 1) having the engines in one big pod under the wing, and 2) a variable geometry wing where enormous wing tip sections would droop downward -- these two features were supposed to channel the shock wave and create the compression lift. Sort of the aerodynamic version of the fictional Star Trek Warp Drive where the Warp Drive pods create a bubble of space-time that scoots the ship along.

They built two XB-70s. While these were designed as Mach 3+ aircraft, Ben Rich of Skunk Works fame derides the accomplishment to claim the SR-70 as the only Mach 3 supercruiser and claims the XB-70 to be Mach 2.5. In actuality, XB-70 #1 could go Mach 3, but it had the tendency to melt off the bonding of the steel honeycomb structure and injest part of the inlet structure into those very expensive engines, so they slapped a Mach 2.5 speed limit on it. XB-70 #2 was supposed to have been bonded so it didn't have that problem, but it had flight control problems stemming from a dihederal wing that was supposed to solve flight control problems of XB-70 #1. XB-70 #2 was lost in an accident resulting from a stupid photo op, killing chase pilot Joe Walker, one of the XB-70 crew and maiming the other.

So it is not clear how much test flight took place at Mach 3 supercruise or whether they got anywhere near the predicted fuel economy from compression lift -- anyone know? Two things were revealed by the XB-70 -- like the Mach 3+ SR-70, the XB-70 had serious issues with control of the engine inlets and something called an "unstart" where the shock wave didn't stay put. It was said that these unstarts were always major inflight emergencies that got your attention by uncommanded yaw that could slam your helmeted head against the side of the cockpit, and some remarked that a Mach 3 SST was a non-starter on account of un-starts.

The other thing they figured out was that Mach 3 supercruise would generate huge sonic boom swaths. Was this a feature of the compression lift or just of that big and that fast a plane?

The final thing was that while the XB-70 was used to get test data on the SST flight profile, the Boeing SST didn't look like it had any of the compression lift features -- the single engine pod with multi engines, the wing tip droops. Was compression lift one big "unstart" based on unmet expectation in the XB-70 program?

Dale Amon wrote:

Hmmm. Is shockfree for public discussion?

Dale Amon wrote:

Note that the repeats were due to getting error pages back from commment.cgi and then retrying. You might still have some debugging to do :-)

Rand Simberg wrote:

Is shockfree for public discussion?

I've been discussing it publicly for years. The patents are in place.

Note that the repeats were due to getting error pages back from commment.cgi and then retrying. You might still have some debugging to do :-)

Yes, that's why I have the warning, right under "Leave a comment..."

Shockfree - a bit of googling turns up this project from Vehicle Research Corporation. Dale and Rand, is this what you're referring to?

Rand Simberg wrote:

Yes, that is the concept. I hadn't realized that that paper was on the web. We'll have to add it to the reference list. Note however that it's not VRC work--it's a review of VRC work, and only a cursory analytical one.

Jeff Mauldin wrote:

I seem to be developing the habit of injecting sci-fi short stories and novels into these threads.

A few months (a year or two?) ago I read as story in analog that was about (and may have been titled) a supersonic blimp. The idea was, as Rand mentions, to have a non-shock wave producing wing/fuselage, which would unfortunately provide no lift. Lift, then was to be provided using helium. It was a humor piece, full of exaggerated bureaucrats and skunk work operations, and quite a good read. I was left with "I hadn't known before that you could go supersonic without a shock wave" and "that couldn't possibly work--could it?"

Peter wrote:

Clever idea using a jet curtain to reflect shock waves from the wing to reduce sonic boom and improve wing performance. But it seems to me that running your engines to produce such a curtain, multiple Mach factors faster than the aircraft, would use a lot of power, unless the curtain was very thin to use a small fraction of jet reaction mass.

Rand Simberg wrote: seems to me that running your engines to produce such a curtain, multiple Mach factors faster than the aircraft, would use a lot of power, unless the curtain was very thin to use a small fraction of jet reaction mass.

Calculations indicate that you need about ten percent of the bleed air off the compressor, and you get thrust out of it, so the only losses are entropy getting it from the engine to the jet nozzle. These are relatively low, because it occurs at low velocity and high pressure.

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This page contains a single entry by Rand Simberg published on February 16, 2008 8:13 AM.

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