AirSpaceMag.com

Eurocopter's X3 (Photo: Patrick Penna)

Helicopter speeds have traditionally been limited by a phenomenon called “retreating blade stall,” which describes what happens to the main rotor at high speed. The relative wind on the retreating blade is reduced by the forward speed of the helicopter to a point where it no longer generates lift, and the helicopter rolls off to the side with reduced lift.

Tilt-rotor vehicles like the Bell Boeing Osprey turn the rotor blades into propellers. Now a less complex solution that dates back several decades is re-emerging: the compound helicopter, which uses a dedicated propulsor to produce forward speed. The Piasecki X-49A modified a Sikorsky UH-60 with a lifting surface made up of two wings, plus a ducted fan in the tail to push the aircraft to speeds of around 200 mph. The wings take up part of the lift load so the main rotor doesn’t have to provide as much at high speeds, and blade stall no longer matters as much.

The Eurocopter X3 is a modified EC155, itself a derivative of that company’s Dauphin (the U.S. Coast Guard operates one version). The X3 has achieved speed bursts as high as 267 mph, propelled by two tractor propellers driven by the main engines and mounted on stubby wings just beneath the main rotor. At high speed, the six-blade main rotor is slowed to reduce the drag of the advancing blade, while the wings provide necessary lift.

Sikorsky’s X-2 has advanced far enough to become the proof-of-concept for a prototype military aircraft  now designated the S-97 Raider, a high-speed attack and scout helicopter. The X-2 proved the efficacy of a coaxial main rotor blade in which both sides of the helicopter have advancing blades opposite retreating blades, providing a symmetrical lift that requires no wing. Forward thrust is provided by a pusher propeller in the tail, an arrangement that took the experimental craft to a top speed of 290 mph, and, in a descent, to 300 mph. There is no tail rotor à la the traditional helicopter, and the X-2 maneuvers about the yaw axis by applying differential torque to the two main rotors. The little X-2 (it weighed less than 8,000 pounds on takeoff) was retired after only 22 hours of flying.

The X-2 is not Sikorsky’s first compound helicopter. Its S-72 employed a fixed wing and two turbofan engines to achieve a design speed of up to 345 mph. The wing generated enough lift to allow the craft to fly without a main rotor, which it actually did during testing. The X-Wing, another 1980s experimental craft, employed large, rigid main rotor blades that were intended to be stopped inflight to form an X-shape wing that supplemented lift from a conventional wing. Two turbofans provided thrust.

The closest the U.S. military came to buying and operating a compound helicopter was when it launched the Lockheed AH-56 Cheyenne with a contract in 1966 for 10 prototypes. Problems and delays during development led to cancellation of the Cheyenne, but the Army followed that with the AH-64 Apache, which is not a compound helicopter but is in operation today.

Here’s a demo of Eurocopter’s X-3 at last summer’s Paris Air Show:

DARPA's Space Surveillance Telescope in White Sands, New Mexico. Photo courtesy DARPA

At a little after 10:00 EST this morning, a “bus-size” asteroid will give us a little buzz. It isn’t big enough to do damage, even if it were to hit our atmosphere, but its a reminder that there are objects out there that we might want to be worried about, if only we knew where they were.

Now an innovative new telescope is getting into the asteroid hunting game. DARPA’s Space Surveillance Telescope (SST) had its first light early in 2011, and is now officially online and going through its first demonstration, seeking out potentially Earth-threatening asteroids.

It’s not the first asteroid hunter. Among others, NASA’s WISE (Wide-field Infrared Survey Explorer) space telescope found over 33,000 new asteroids during its all-sky survey in 2010 (the team will be publishing their official results this March). There’s also the Panoramic Survey Telescope & Rapid Response System (Pan-STARRS) on top of Mount Haleakala in Maui, Hawaii. The team’s goal since they started operations in 2010 is to complete a survey of all asteroids over 1 km wide.

DARPA hopes the SST will fill out that catalog further by seeing even smaller, but still potentially dangerous, asteroids. Commissioned in 2002, the SST is unique in that its “mirrors are some of the steepest aspherical curvatures ever to be polished, and allow the telescope to have the fastest optics of this aperture class.” It’s short focal length and wide field-of-view allow it to be moved rapidly. By seeing smaller objects, it can help protect not just Earth, but satellites in orbit — military satellites, that is, as SST is primarily run by the U.S. Air Force at the White Sands Missile Base in New Mexico.

January 22, 2012 solar flare. Photo courtesy NASA/SDO/AIA.

Despite being the strongest solar storm since 2005, this week’s flareup appears to have caused few disruptions on Earth. (As Space.com reports, the Coronal Mass Ejection “hit Earth at an angle, so the electromagnetic burst was largely shielded by the planet’s magnetic field.”)

But the storm did lead some airlines—including Delta, Qantas, and Air Canada—to alter their transpolar routes to reduce potential disruptions to high-frequency radio communication along the way. At least one Qantas flight, reports AvWeb, carried an extra five tons of fuel in order to fly a less southerly route.

We may have gotten off easy. The remarkable electrical effects of solar storms have been recorded in newspapers since British astronomer Richard Carrington noticed a solar eruption in 1859 while sketching sun spots seen through his telescope. Just days later, the northern lights—seen as far south as Cuba—damaged telegraph systems, even setting offices on fire and melting wires. On August 30, 1859, the New York Times included this observation from the superintendent of the Canadian Telegraph Company:

I never, in my experience of fifteen years in the working of telegraph lines, witnessed anything like the extraordinary effect of the Aurora Borealis, between Quebec and Further Point last night. The line was in most perfect order, and well-skilled operators worked incessantly from 8 o’clock last evening till 1 o’clock this morning, to get over in even a tolerably intelligent form about four hundred words of the steamer Indian‘s report for the Associated Press, and at the latter hour so completely were the wires under the influence of the Aurora Borealis, it was found utterly impossible to communicate between the telegraph stations, and the line was closed for the night.

Another solar storm, nearly as strong as what has come to be known as the Carrington event, occurred in 1921. On May 16, 1921, the Los Angeles Times reported that “electrical influences exerted by the Aurora Borealis…continued today to play havoc with telegraph traffic throughout the United States…. For more than an hour before midnight Saturday nearly every telephone wire leading from New York and Chicago was out of condition.”

The New-York Tribune hoped to calm its readers by noting that the sun would soon “turn [its] spotted face away and end earthly wire troubles,” while the New York Times reported disturbances in France: “The operators at the central transmission stations came to the conclusion that a strange force had got into their instruments, for nothing would go right. Morse instruments, instead of making dots and dashes, recorded one long line. Hughes instruments produced words in what might have been an unknown language, and Baudot, of which French telegraphers are proud because it is very intricate, seemed possessed by evil spirits.”

Newcomb Carlton, president of the Western Union Telegraph Company, was quoted in the New York Times as saying: “The magnetic disturbances were much the worst ever experienced. A great many fuses were blown out on our land lines and we had great difficulty with the submarine cables.” The story also reports that the solar storm burned out a telephone station in Sweden, which then contributed to a short circuit in the New York Central signal system, which was followed by a fire in the Fifty-seventh Street signal tower.

In 1989, the Washington Post reported on December 18 that a solar storm—or “titanic temper tantrum”—set off radiation alarms aboard the supersonic Concorde in flight, damaged orbiting satellites, and caused a nine-hour power blackout in most of Canada’s Quebec province.

In comparison, Space.com reports, this week’s solar flare caused “minor disruptions to spacecraft and power grids.”

Screenshot from UAVForge submitted video for a concept by team GremLion

The Defense Advanced Research Projects Agency (DARPA) is trying out innovation the 21st century way: crowdsourcing. The agency, along with the Space and Naval Warfare Systems Center Atlantic and Northwest UAV Propulsion Systems, wants to build an advanced unmanned aerial vehicle, so it asked engineers and designers to submit their ideas.

The initiative, called UAVForge, received submissions from more than 1,400 teams, who were encouraged to share ideas and problems they’ve encountered in the hope that they would build on each other’s ingenuity and create something they might not have by working in secret. It’s still a competition, though; whichever team creates the best product will take home a $100,000 prize. UAVForge is currently in the process of voting for the top 10 ideas.

This isn’t the first crowdsourcing project by the Department of Defense, which has experimented with software and, last summer, unveiled a particularly hideous but — DARPA hopes — extremely versatile and inexpensive combat support vehicle, the FLYPmode.

Crowdsourcing is certainly one way to cut way back on parts of the defense budget. And though the idea is probably not well-received, generally speaking, by defense contractors, it’s not all bad news — Northwest UAV has already been awarded a contract to manufacture the winning idea. One has to wonder how the 1,400-plus teams can integrate classified military do-dads — which one might assume an “advanced” UAV would have — not to mention keeping whatever they come up with themselves a secret.

Lufthansa tested biofuel in this Airbus A321, operating one engine on Jet A and the other on a 50-percent blend of Jet A and a fuel made from processed plant and animal-fat hydrocarbons.

Jet A, the fuel that civil jets use (the military’s are designated JP), comes from crude oil that’s been distilled and standardized to meet a chemical specification. While many turbines can run on almost any light oil or liquid hydrocarbon, jet aircraft fly very high where it’s cold, and Jet A has to resist solidifying up there in the stratosphere, among other requirements.

In recent years, synthetic jet fuels have been created by processing coal and by using biological methods, which produce so-called “bio-fuel.” Although crude oil – petroleum – technically comes from plants, the crude was formed eons ago, and is considered “fossil fuel.” The first bio-fuel to appear in quantity, and the most common one available to consumers, is a blend of gasoline and ethanol in various proportions. The ethanol is made by fermenting the sugars in corn, cane or sugar beets. Ethanol reduces the energy density of the blends compared to gasoline, and researchers are looking for ways to produce butanol instead, because it has better energy density.

Synthetic bio-jet fuel has to closely resemble kerosene and Jet A in its energy density and other properties, and small quantities have been made to be blended with traditional fuels – with some success. Lufthansa recently completed trials using some bio-jet fuel in a roughly 50 percent mix with standard Jet A. But the reason Lufthansa halted the trials highlights a problem posed by bio-fuels generally: They’re not available yet in sufficient quantity or at an affordable price.

Doing demonstrations is one thing; operating large fleets of airliners using even a modest blend of bio-fuel and Jet A will require enormous capital investment in an infrastructure that can produce the fuel. Algae-based oils from bioengineered plant cells, for example, would require huge quantities of water and tanks in which to hold the algae. Right now, the energy it takes to produce biofuels usually exceeds the energy yield. Petroleum flows out of wells and through pipes to refineries, and while the price of oil occasionally spikes in response to market demands, the actual cost of producing it will probably continue to undercut the cost of making fuels from renewable sources. Nonetheless, the U.S. Air Force continues to pursue synthetic fuels to ensure it can continue to operate if crude oil were to be unobtainable.