Beyond Supersonic

Imagine the convenience of traveling 10 times the speed of sound. You could make it from Los Angeles to Tokyo in two hours, to New York in 30 minutes.

A new design for a hypersonic plane has made this scenario a little less fanciful, a little more feasible. Dubbed HyperSoar, the plane would be capable of far outpacing current aircraft of supersonic capability--defined as one to five times the speed of sound. Go above Mach 5 and the rating jumps to hypersonic.

The man behind the concept is Preston Carter, an aerospace engineer at Lawrence Livermore National Laboratory. By linking advances in engine technology and aerodynamics with theories in flight pattern dating back to World War II, Carter came up with a design that is capturing the imagination of the public as well as those in the industry.

Not only would the plane get from point A to point B in record time, says Carter, but--size and weight being equal--a HyperSoar plane could carry twice the load of a Boeing 747-400. HyperSoar could also be used to launch other vehicles into space.

“It’s a very good airplane,” Carter said, “but it’s one heck of a good launch vehicle. We could put payloads into space at three to five times the efficiency of anything we’ve got now.”

Still, Carter acknowledges that the idea of HyperSoar as a plane might hold more glamour for the public. But this allure would be tempered by a flight plan that calls for taking the passenger from weightlessness back to gravity force every two minutes for the entire course of the trip.

HyperSoar would take off just like a typical airliner. The plane would “skip” above the atmosphere to 200,000 feet, then descend to 115,000 feet before starting up again.

Why skip? Jason Speyer, professor of mechanical and aerospace engineering at UCLA, says the skipping, known technically as a periodic trajectory, helps deal with a longtime bane of supersonic flight: heat. The faster an object flies through space, the more it slows and compresses the air around it. The more the air is compressed, the hotter it gets.

“If [the plane] stays in the atmosphere, you are constantly absorbing heat,” Speyer said. “With periodic motion, you go outside the atmosphere.”

Because HyperSoar would spend up to two-thirds of its time in space, heat could dissipate, giving the plane a needed cool-down period.

Passengers would feel the pull of gravity weakening to zero as the plane rose into space. The engine would shut off during the crest of the wave, and for about 100 seconds, everything inside the plane would be weightless.

As the plane descended, gravity would take hold again at about 1.5 Gs, the same force one might feel at the lowest point in a child’s swing. The engine would start up again to help boost the plane out of the atmosphere, and the cycle would start again.

In one skip, the plane could travel 250 miles. Going to Asia? Get ready for 24 more skips.

People With Weak Stomachs: Beware

Those with weak stomachs might be cringing at the plane’s trajectory, but Carter thinks many people would be willing to tolerate the unconventional flight path if it meant valuable time saved. “I would ask, do you want an hour and 50 minutes between L.A. and Tokyo and maybe getting airsick, or a 12-hour flight” on a conventional jet, Carter said.

The plane’s shape would increase lift by taking advantage of the same aerodynamic principles that generally increase drag at high speeds. The sharp leading edges of a “waverider” plane such as HyperSoar would give the vehicle lift from the high-pressure air behind the shock wave created by breaking the sound barrier, said Mark Lewis, associate professor of aerospace engineering at the University of Maryland and a consultant on the HyperSoar project.

In addition, the velocity, as the plane descended into the atmosphere, would provide enough lift to actually reverse the flight path and create the “skip.” On each cycle, the HyperSoar’s engines would turn on for a quick boost, keeping the bounce going and extending the plane’s traveling distance.

Carter said most of the materials needed to withstand the heat and pressure of hypersonic flight exist today. But what may ultimately make or break the HyperSoar concept, experts say, is the success of its engine, which is still in development.

So-called ramjet engines are used in today’s fastest manned plane, the SR-71 Blackbird of the U.S. Air Force, capable of traveling three times the speed of sound. Air flows into the engine, where it is compressed, mixed with fuel and shot out the back for thrust.

“Scramjet”--supersonic combustion ramjet--engines work similarly but for speeds higher than Mach 6. Scramjets would be used for the Hyper X, another hypersonic research vehicle that is being developed by Boeing.

However, George Orton, manager of hypersonics at Phantom Works, Boeing’s research and development unit in St. Louis, said scramjets are not yet operational in an airplane.

It is possible to package a rocket engine with the ramjet and scramjet engines, creating a system powerful enough to accelerate the plane to Mach speeds. But this would almost certainly sacrifice fuel-efficiency and add too much to the engine’s weight.

The answer, manufacturers hope, is the rocket-based “combined cycle”--or RBCC--engine, which integrates the three types of engines into one of relatively light weight, allowing the plane to fly at many speeds without sacrificing fuel-efficiency or weight.

The concept is still experimental and has only been tested in wind tunnels. One such system is under development at NASA’s Marshall Spaceflight Center in Huntsville, Ala.

One of the biggest challenges is making sure the correct cycle of the engine switches on at the correct Mach speed, said Mel Bulman, chief engineer for advanced propulsion projects at GenCorp Aerojet Propulsion Division, which is testing its own version of a combined-cycle engine called StrutJet.

For instance, when air reaches a certain speed, the engine needs to switch from a ramjet mode to a scramjet mode. Air traveling faster than Mach 6 going through a ramjet engine would be compressed too quickly, creating unacceptable temperatures and pressure.

“Even if the engine is strong enough not to blow up, the air gets so hot it doesn’t want to burn,” Bulman said. “It’s getting close to the temperature of the surface of the sun.”

Carter said that using liquid hydrogen as fuel may help keep the temperature down. Not only is liquid hydrogen cold enough to turn gaseous nitrogen into liquid, it contains a tremendous amount of energy for its weight. Another plus is that most of the emissions created by liquid hydrogen fuel are environmentally friendly water vapor.

$500 Million Needed to Build, Fly Prototype

How long will it be before the first HyperSoar rolls off the assembly line? Much depends on the pace of research. “[HyperSoar] is an incredibly complicated vehicle,” said Gen. Robert Behler of the Air Force Strategic Command. “This is so avant-garde, it’s still a ways away.”

Carter estimates that $500 million would be needed to build and fly the first HyperSoar prototype within the next five years.

Until then, he may refine the plane’s design, perhaps more to suit a potential occupant’s tastes than any specific engineering requirement. For instance, the plane’s original design lacked windows, which would get extremely hot at hypersonic speeds.

“Pilots like to have windows,” said Behler, who used to fly the SR-71 Blackbird as a test pilot. “It’s part of our psyche. You’ve got to be able to look outside. You’re just a Spam in a can if you can’t look outside.”

David L. Mumme, NASA research pilot at the Johnson Space Center, pointed out that Boeing 737s have been flown by computer monitors in the back of the plane, but that pilots would still only “reluctantly” accept a windowless aircraft.

Carter has since sketched a plane that includes overhead windows, along with passenger seats and a cargo area. Recent questions posed by international reporters have also made Carter think of more mundane, yet important, considerations, such as the location of the restrooms.

“I had never thought of that question,” Carter said with a smile. “To be quite honest, I don’t know.”

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Moving on Another Plane

A new design for an airplane called HyperSoar could allow it to fly 10 times the speed of sound, reach the outer edge of Earth’s atmosphere and carry twice the load of a Boeing 747-400, according to the airplane’s engineers.

HyperSoar could deliver passengers and cargo anywhere on the globe within hours. Engineers are engine that would incorporate rocket-power capabilities and a runway launch. The plane also could be used to help launch space vehicle.

Hauling bigger loads

According to its designers, HyperSoar would be capable of carrying more weight over a greater distance than planes of similar size and mass.

Skipping through space

The plane would apply propulsion in bursts, helping it “skip” along the upper atmosphere like a stone skimmed across water. It would remain at basically the same angle relative to the earth. The tremendous heat built up while speeding through the atmosphere would dissipate while the plane is in space.

Source: Lawrence Livermore National Laboratory.

Note: Scale is compressed

DRS (No Caption), MATT MOODY / LOS ANGELES TIMES