The Woracle

Airbus has flown an A380 from Bristol in the UK and Toulouse in France on alternative fuel. The synthetic jet fuel was supplied by Shell and produced from natural gas in Qatar using the Fischer-Tropsch process. It's the first test of gas-to-liquid (GTL) fuel in an airliner, but similar synthetic jet fuel is already being qualified by the US Air Force across all of its aircraft.

So what was the point of the flight, other than to steal some thunder from Boeing and the much-hyped Virgin Atlantic biofuel demonstration planned later in February? A cynic would say Airbus is trying to convince a concerned public it is going green, but there is almost no difference in the CO2 produced by GTL jet fuel and kerosene. Okay, it does burn cleaner, cutting NOx, sulphur and soot emissions, and a slightly higher energy content should trim the fuel consumed per trip.

But when it comes to tackling aviation's evironmental impact, GTL is a bit of a non-starter - or, at best, an interim step. Cleaner-burning jet fuel is a good thing, but CO2 is the issue haunting the industry and only biofuel appears to offer a long-term solution. But bio-jet fuel is years away, whatever Sir Richard Branson might claim after his 747-400 flies from London to Amsterdam with one of its GE engines running on processed pond scum, or whatever it is.

GTL will be useful in diversifying the sources of jet fuel, and it may stimulate the development of "designer" fuels with better properties than kerosene, but aviation needs to keep up the pressure to develop sustainable, renewable sources of bio-jet fuel.

I am thinking of starting an occasional series on "visual aerodynamics" - images that show the air at work, creating lift and generating drag. What better way to start than these stills from high-speed video of the US Naval Research Organisation's January 31 test of the world's most powerful electromagnetic railgun. Not aviation perhaps, but aerodynamics certainly. As the projectile leaves the railgun with a muzzle velocity almost Mach 7.5 you can see the "lens" effect caused by the shockwave. Remember, the projectile is unpowered - the flames are generated by friction...

Northrop's E-2 Hawkeye is operated by seven customers, only two of which have aircraft carriers. More countries operate the "Hummer" than any one of the other AEW platforms, but the E-2 is regarded as a niche player within a niche market. Almost every other aircraft flies faster, goes higher and stays up longer, but for its operators the Hawkeye was the best - sometimes only - AEW option available at the time.

But time moves on, and the airborne early warning and control market has bloomed. Where there was once just the big-jet E-3 AWACS and twin-prop E-2 Hawkeye, there are now the Boeing 737 AEW&C, Embraer EMB-145SA, IAI/Gulfstream G550 CAEW and Saab Ericsson Erieye. And there are others.

The Hawkeye's hold to the market has been eroding. Israel retired its E-2Cs, selling them to Mexico, and is replacing them with G550s. Singapore has ordered the Israeli-equipped CAEW to replace its Hawkeyes. Now Northrop thinks it can get back into the market with the E-2D Advanced Hawkeye under development for the US Navy.

Rotorhub has just posted an odd story. Conservationists in Alaska are seeking bids for removing rats from Rat Island in the Aleutians by using helicopters to broadcast poisoned grain pellets "from buckets guided by differential GPS". Precision-guided rodenticide - dashed clever, these conservation types! They want to get rid the rats so the seabirds will return. Two helicopters are needed, with "aerial rat baiting" to begin in October. If they succeed, what will they call the place, I wonder - the "Island Formerly Known As Rat"?

Gotta take precautions when there's rats around... (US Army photo)

How's this for timing? The day after the Pentagon says it will try again to cancel the General Electric/Rolls-Royce F136 alternative engine for the F-35, the Lexington Institute defence think-tank publishes a study arguing "one engine is enough" to power the Joint Strike Fighter. Either the Institute's Loren Thompson worked through the night or he knew what was coming. Knowing Loren, it was the latter.

The Pentagon tried to cancel the F136 last year, but Congress put the money back into the budget. So eliminating funding for the GE/R-R engine (right, in afterburner) from the defence department's FY2009 budget request sets the stage for another showdown with the lawmakers. It will be interesting to see what influence the Lexington Institute's report has on this year's debate.

No one argues that annual competitions to power the JSF would bring down the purchase price of the engines, or that having two powerplants would avoid the potential for an engine-related grounding of the entire F-35 fleet. But do the advantages outweigh the extra cost of developing, producing and supporting two engines over their service lives? Most DoD studies - and the Lexington report - say no.

So it comes down to the emotive issue of industrial base and keeping GE in the fighter engine business. Citing GE's domination of the commercial engine market, Loren Thompson argues that keeping the alternative JSF engine would probably cement the company's dominance over domestic rival Pratt & Whitney "until mid-century, of not forever".

F-35 keeps flying on Pratt power as argument continues

The Pentagon boffins have been keeping mum, but the DoD's fiscal year 2009 budget request lifts the lid on Blackswift - DARPA's prototype hypersonic aircraft. Formerly the Falcon HTV-3X, and being designed by Lockheed's Skunk Works, the unmanned Blackswift is intended to take off conventionally on turbojet power, transition to scramjets, cruise at Mach 6 for an extended period, then return to a runway landing. If it succeeds, Blackswift will be a worthy successor to the Skunk Works' Blackbird.

Sharon Weinberger at Wired's Danger Room was first to blow Blackswift's cover, and in January alerted us to an InsideDefense story that DARPA was to seek $750 million for the demonstration programme. DARPA's FY2009 request is for $70 million on top of the $35 million to be spent in FY2008. Here's what DARPA's budget documentation has to say:

"The Blackswift Test Bed program will develop an extended duration hypersonic test bed which will allow for the study of tactics for a hypersonic airplane that includes a runway take-off, Mach 6 cruise and runway landing. This test bed is an evolution of the reusable Hypersonic Cruise Vehicle developed under the Falcon program.

"Key technologies that will be demonstrated include efficient aerodynamic shaping for high lift to drag, lightweight and durable (reusable) high-temperature materials and thermal management techniques including active cooling, autonomous flight control, and turbine-based combined cycle propulsion.

"It is envisaged that flying this hypersonic aircraft test bed in a relevant, flight environment will permit the futire development of enhanced-capability reusable high-speed vehicles for intelligence, surveillance, reconnaissance, strike and other national need missions. This program will transition to the Air Force following completion of flight-testing."

DARPA's Falcon programme continues, with two unpowered, rocket-boosted HTV-2 hypersonic test vehicles scheduled to be flown in FY09 to pave the way for Blackswift. The Skunk Works, meanwhile, is to complete the Blackswift preliminary design and ground test the integrated high-speed turbojet and scramjet propulsion system by the end of FY09. No news yet on when Blackswift might fly, but it should look like this...

I've taken the bullet on your behalf and ploughed through DARPA's fiscal year 2009 budget request to look for goodies. Here's what I've found.

New programmes for FY09:

Multi-Modal Missile - manportable surface-to-surface and surface-to-air weapon with direct and indirect fire modes against vehicles, bunkers, helicopters and UAVs.

Small UAV Strike Munition - inexpensive, lightweight precision-guided submunition to be delivered by a loitering weapon launched from an unmanned aircraft.

Stealthy, Persistent, Perch and Stare (SP2S) - a VTOL micro air vehicle based on the Aerovironment Wasp that will land on a perch, collect data and fly home.

FY09 funding for existing programmes:

Heliplane - $16m to demonstrate the tipjet-driven rotor for Groen Brothers' high-speed gyroplane (assuming they succeed in FY08 in cutting tipjet noise by more than 10dB)

Oblique Flying Wing - $29.6m to begin construction of the unmanned X-plane demonstrator for Northrop Grumman's supersonic, tailless variable-sweep asymmetric flying wing.

CASTLE - $7.5m to complete preliminary design of a persistent, unmanned gunship to be armed with electromagnetic guns, directed-energy weapons or vertical-launch missiles.

Rapid Eye - $15.9m to complete preliminary design of a rapid-reaction HALE UAV to be rocket-deployed from the US to anywhere in the world in 1-2h for ISR and comms missions.

Vulture - $11m to begin building a subscale demonstrator for a "pseudo-satellite" ISR UAV able to stay on station for more than five years. The demonstator goal is a year-long flight.

Someone was going to say it, so Cessna's sales boss Roger Whyte got in first, calling today (February 6) Cessna's "Columbus day" (after a US holiday). Why? Because today the company unveiled its Citation Columbus large-cabin bizjet in Washington, DC. The name was picked by Cessna because this is the first Citation designed to take its passengers overseas - London to Dubai, Munich to New York, Singapore to Sydney, Sao Paulo to Miami - nonstop.

It will be a big aeroplane - bigger than I realised. It will be bigger and fly further, faster than its competitors, the Bombardier Challenger 605 and Dassault Falcon 2000EX. At $780 million to develop and $27 million to buy, it will be the most expensive Citation yet. It won't enter service until 2014, but there is no doubt Cessna can deliver this aircraft - just look at the Citation X.

One interesting factoid from today's press conference: there are 5,100 Citations now flying - by the time the Columbus enters service, there will be 8,000...

Timing is everything. Bad timing is breaking your engine on the very day your customer tries for a third time to cancel your rival and a new report rubbishes the benefits of competing engines. But that's what happened to Pratt & Whitney on February 4, when a turbine blade on an F135 Joint Strike Fighter engine broke during "proof testing". That was the day the Pentagon told Congress it still intends to cancel the General Electric/Rolls-Royce F136 alternative engine.

The blade problem is not news. That's why the engine was being proof tested, to see if it was susceptible to a unique blade vibration that causes high-cycle fatigue. This follows a blade failure on a test stand in August last year. What is news is that this latest incident will delay the first flight of Lockheed Martin's F-35 STOVL JSF, which was scheduled for mid-year.

The two blades that have failed so far were in STOVL F135s - Pratt thinks the problem is tied to the heavier load on the third turbine stage in the STOVL engine, because the low-pressure turbine has to work harder to power the shaft-driven lift fan. The latest engine to fail was to power the first F-35B - aircraft BF-1 - now Pratt will have to proof-test a replacement engine, which will delay the start of STOVL ground testing by a month - maybe more, they don't know yet.

The US Marine Corps has just released this rare image of an MV-22 Osprey tiltrotor operating in Iraq - there are green rotor-tip lights, the Marines now tell me. (US Navy photo)

When a test flight lasts only minutes and ends in a fiery plunge into the ocean, you want to make sure the radios work - to ensure telemetry data is safely sent to the ground. So Boeing is testing the antennas for the US Air Force Research Laboratory's X-51A Scramjet-Waverider hypersonic demonstrator in the anechoic chamber at Edwards AFB.

Powered by a Pratt & Whitney Rocketdyne scramjet that uses the fuel to cool itself, the first X-51A is scheduled to fly in August 2009 - dropped from a B-52 50,000ft over the Pacific, boosted to Mach 4.7, where the scramjet will light and run for 5min, accelerating the vehicle to Mach 6.7 before the tanks run dry and it plunges into the ocean. Those radios had better work.

I'm no expert on Chinese defence, or on the trustworthiness of the various websites that cover Chinese defence, but there is an interesting analysis on two possible new Chinese air-to-air missiles by Richard Fisher at the International Assessment and Strategy Center, which describes itself as a think-tank on security issues.

China's AIM-9X-class short-range AAM? (from wforum.com)

The two missiles are the short-range, infrared-guided PL-ASR, or PL-10, which resembles South Africa's Denel R-Darter, and the PL-13, a ramjet-powered derivative of the medium-range, active-radar PL-12. The PL-13 (or is it PL-21?) looks roughly equivalent to Europe's MBDA Meteor.

If their existence is confirmed, these missiles - like the Chengdu J-10 and Shenyang J-11B fighters they will arm - look pretty competent. Check out Chinese Military Aviation and decide for yourself.

After some positive press in the past week, when the Marine Corps praised the tiltrotor's performance so far in Iraq, the week ended on a down note when an MV-22 was forced to land near Greenville, NC, after a panel fell off an engine nacelle. No damage was done and the aircraft returned home to MCAS New River the next day.

Meanwhile, the Marines' first progress report since the Osprey deployed to Al Anbar province in October makes clear most of the Thunder Chickens' 1,400-plus sorties and 2,000-plus flight hours in theatre have been "battlefield circulation" and "governance" missions - in other words transporting officers, Iraqi leaders and others around the area of operations. Not surprisingly, the tiltrotor's speed is appreciated by its passengers.

Only recently have the MV-22s begun roving aeroscout missions to hunt for insurgents and the tiltrotors had taken part in one pre-planned raid by the end of January. So, for now, the Osprey gets a passing grade.

Lockheed has posted this new video on youtube, entitled "F-22: Operational, Relevant, Revolutionary". I don't remember relevant as being one of the defining characteristics of a fifth-generation fighter, but maybe it needs to be. After all, US defence secretary Robert Gates did a pretty good job of damning the F-22 with faint praise last week when he told Congress:

"The reality is we are fighting two wars, in Iraq and Afghanistan, and the F-22 has not performed a single mission in either theatre. So it is principally for use against a near peer in a conflict, and I think we all know who that is. And looking at what I regard as the level of risk of conflict with one of those near peers over the next four or five years, until the Joint Strike Fighter comes along, I think that something along the lines of 183 is a reasonable buy."

The US Air Force wants 381 Raptors, but Gates and his deputy Gordon England think somewhere around 183 is the right number. "My concern is that the F-22 is $140 million a copy and the Joint Strike Fighter will be about half that, about $77 million a copy. And so my worry is that if the F-22 production is expanded, that it will come at the expense of the Joint Strike Fighter," Gates told Congress.

Sensible words, I think. Meanwhile my colleague Steve Trimble over the The DEW Line is taking a closer look at those questioning Gordon England's motives in trying to kill the F-22...

"Miss you" (US Navy photo)

Despite its engine glitch, Lockheed thinks the F-35B will fly before the end on June, maybe a month later than originally hoped for, but still within its "mid-2008" window for the first flight of the STOVL JSF. It will take Pratt & Whitney about a month to deliver a replacement flight-test F135 engine, and it should arrive in March, allowing Lockheed to get on with hover pit testing.

The hiccup happened when the original engine for aircraft BF-1 failed a proof test designed to reveal if it was susceptible to high-cycle fatigue of the third-stage turbine blades (it was!). P&W is proof testing the replacement engine, and probably has its fingers very tightly crossed. So far three F135s have been proof-tested: two CTOLs passed and one STOVL failed.

Meanwhile, thanks to Steve Trimble on The DEW Line for finding this video of the STOVL F135's three-bearing swivelling nozzle being tested in aircraft BF-1. I am still fascinated to watch this nozzle working...

VLJ developer Adam Aircraft has suspended operations - hard on the heels of ATG, which hit a similar wall when it came to funding. Before I have my say here's Adam's statement, issued on Feb 11:

"In a difficult but necessary move, Adam Aircraft Industries suspended operations today at its facilities in Colorado. This measure was required due to the inability of the company to come to terms with their lender for funding necessary to maintain business operations. The company is currently exploring all of its alternatives and will provide further guidance when decisions are made, which is expected to be later this week."

I can't say I'm surprised. I've been sceptical of Adam from the outset, when it retained Rutan's Scaled Composites to design a new-generation all-composite piston twin (the M309). An admirable goal, but no-one had successfully taken a Rutan design through certification and into production. To give Adam its due, it has come closer than anyone, acheiving partial certification and slow-paced production.

But, for me, Adam stretched its credibility a shade too thin when it launched development of a VLJ before finishing the job on its piston twin. Okay, so that was the way the market was going. Okay, so the A700 VLJ was a derivative of the A500 piston twin. But aircraft manufacturers have walk before they can run and Adam was barely crawling.

Adam has recently begun to behave like a real aircraft manufacturer, bringing in experienced management and establishing proper production discipline. But meanwhile the money has run out. Inevitably, the credit crunch will be blamed for for Adam's troubles, but I would look further back for their origins.

Frank Piasecki, who flew the USA's second successful helicopter, died on February 11. Born in 1919, Piasecki might not have been quite as well known as the guy who got there first - Igor Sikorsky - but the helicopters his company designed certainly are, particularly the CH-47 Chinook. Lately Piasecki Aircraft has been getting attention for its X-49A SpeedHawk - the latest incarnation of a compound-helicopter dream Piasecki pursued for five decades.

"He was one of the original inventors of the helicopter and a pioneer in establishing the helicopter industry," his son, John Piasecki, told the Philadelphia Inquirer. "He was the last of that generation that really created an entirely new industry."

Piasecki's PV-2 first flew in April 1943, with Frank at the controls, but it was with the tandem-rotor HRP and HUP that the Philadelphia-based company made its fortune. Renamed Vertol Aircraft, the firm was acquired by Boeing in 1960 and continues to build the Chinook. Piasecki Aircraft was then formed to develop compound helicopters, the company's 16H-1A Pathfinder II reaching an impressive 225mph in 1966.

The compound dream was not realised, but with the flight of Piasecki's X-49A in June 2007, the concept and the company returned to prominence. With backing from the US Army and Boeing, Piasecki plans to push the SpeedHawk - a modified Sikorsky SH-60 - beyond 200mph. Thankfully. Frank lived to see his dream rekindled.

Piasecki's pioneering PV-2......tandem-rotor HRP.....and compound Pathfinder II

My colleague John Croft was invited to Wilmington, Delaware last year to watch the X-49A fly and help Piasecki celebrate its founder's 88th birthday. He took this picture of Frank with the Pathfinder II, flanked by two of his five sons (there are also two daughters):

Helicopter pioneer Frank Piasecki is remembered by his family in the attached obituary. The family requests any contributions be made to the American Helicopter Museum & Education Center's “Frank Piasecki Memorial Fund”, 1220 American Boulevard ,West Chester, PA 19380; or the “Piasecki Fund for Math and Science Education”, St. Malachy School, 1419 N. 11th Street, Philadelphia, PA 19122. Both worthy causes.

I've been waiting for the axe to fall. Every analyst call, every press briefing, I've been braced to hear the boom is over, and the bust has begun. I'm talking about business aviation. Today (12 February) it was the General Aviation Manufacturers Associations' opportunity to burst the bubble at its annual industry review in Washington, DC.

It didn't.

The US economy may be tanking (sorry, slowing), dragged down by dodgy loans and pricey fuel, but business aircraft manufacturers believe their record backlogs remain secure for now. Largely because 50% or more of the aircraft on order are for customers outside North America. As long as the US economic malaise is not catching, deliveries should hold up.

Clearly the US downturn is hurting some sectors of the GA industry - witness the funding woes of VLJ hopefuls Adam and ATG.And the decline in piston-singles sales to private fliers and flight schools suffering the credit crunch. But so far, as GAMA's figures show, business users are hanging in there.

"Final Countdown anyone?"

Another example of "visual aerodynamics", although usually the condensation cloud caused by the low pressure behind shockwaves is photographed from the side...

It's been a contentious week in the US fifth-generation fighter business, with the Department of Defense and US Air Force taking diametrically opposed positions on whether more F-22s are needed. The DoD has made clear it thinks 183 F-22s are enough (plus another 4 in the FY09 war supplemental). The USAF is adamant it needs 381, and can find a way to pay for them.

Steve Trimble over on The DEW Line calculates, at $150 million a copy, it will cost the USAF almost $30 billion to buy the Raptors it wants. That money will have to come from other programmes - and the DoD's fear is it will come from the F-35 Joint Strike Fighter, which is intended not only for the Air Force, but also the Navy and Marine Corps (not to mention lots of US allies!).

Raptor - endangered species?

It emerged during the week that the DoD sees the F-35, and not the F-22, as the likely replacement for any F-15s that have to be retired because of structural problems. Quite a turn-around given the F-22 was designed to replace the "high" F-15 and the F-35 the 'low" F-16. The USAF disagrees, of course, but the argument casts the DoD's opinion of the JSF's capability in an interesting light.

Here are some of the competing statements made over the past week:

It ended up in a hangar covered in bird crap, that's what. A remnant of an unhappy time in NASA's recent history, the Orbital Sciences-built X-34 was photographed by Ashley Wallace in storage at Edwards AFB in California. The X-34 was built as a flying testbed to demonstrate technology for future low-cost reusable launch vehicles.

(Picture by Ashley Wallace, from airliners.net)

The unmanned X-34 was intended to be air launched from Orbital's Lockheed L-1011 mothership and accelerated to Mach 8 by a NASA-built oxygen/kerosene rocket engine. The vehicle was designed to land on a runway and fly up to 25 times to test composite structures, resuable propellant tanks and thermal protection systems, and autonomous flight operations.

Orbital got as far as captive-carry tests on the L-1011 before the X-34 was cancelled in 2001, along with Lockheed Martin's mightily ambitious X-33 single-stage-to-orbit RLV technology demonstrator (video). Spiralling costs and changes in NASA's RLV thinking were blamed. Two completed X-34s and parts for the third were transferred to the US Air Force.

In an aviation community as cosy, and as busy, as that of Wichita, Kansas, it's inevitable people will move from company to company, between Cessna, Learjet, Beechcraft, Boeing and Spirit. But here's one move that's worth noting: Hawker Beechcraft has just hired Russ Meyer III as its director of new product development. He is the son of famed Cessna boss Russ Meyer, and most recently he was programme manager for the Citation Mustang.

"If you would have told me six months ago that I was leaving Cessna, I would have said: 'You're crazy,' " Meyer tells the Wichita Eagle. Meyer says his father, who is chairman emeritus of Cessna, took the news well: "He takes things pretty businesslike." What next, a Boeing taking over at Airbus?

On the eve of its annual winter get-together in Orlando, the US Air Force has finally cleared all of its much-grounded, much-inspected, much-speculated-about F-15s to return to flight. All bar the nine out of some 440 A- to D-model Eagles found to have the same longeron cracks that caused an F-15 to break up in flight in early November.

The USAF argues it was justified on safety grounds in keeping the Eagles grounded for so long, although it has finally released even those with suspect longerons for flight without repair, without restrictions and with only the requirement for recurrent checks every 400h (provided they pass one last inspection).

Safety is essential, and the USAF has lost three F-15s since they began returning to flight in January - two on 19 February when they collided over the Gulf of Mexico - none of them to structural failure. But it's hard to shake the belief the Air Force stretched this grounding out to make a point about its aging fleet, and its need for more F-22s to replace the F-15s.

On that very subject, the USAF has been forced to disavow the recent comments of a senior officer who said what many believe to be true - that the Air Force will get its 380 Raptors by hook or by crook. "The Air Force wholeheartedly supports the President's budget request for the F-22 program," the statement says.

Well no surprise there, because what that budget request does is not close the F-22 line, so leaving the decision on whether to buy more to Congress and the next Administration. But the statement also says: "The Air Force and the DoD share the same desired end state." Well the DoD's idea of an end state seems clear - 187 Raptors.

It was always an unusual-looking bird, but Scaled Composites' Ares had a certain style. Not any more. Mojave-based photographer Alan Radecki has captured the long-stored Ares taxiing under its own power and boy does it look ugly now, covered in lumps and bumps of unknown purpose.

Ares then... (Bernard Klein Collection photo from 1000aircraftphotos.com)

...and now (Alan Radecki photo)

It's conference season again, and last week it was the Air Force Association's winter symposium in Orlando - where I grabbed 5min with Frank Mauro, vp advanced systems development at Lockheed Martin's Skunk Works. Here's some of what he said.

Polecat (video) - LM has decided against building a replacement for the P-175 Polecat flying-wing UAV that crashed in December 2006. Polecat was mainly about low-cost composites, Mauro says, and that work is continuing under the US Air Force Research Laboratory's Advanced Composite Cargo Aircraft programme - Skunk Works with fly the highly modified Dorier 328Jet late this year.

VARIOUS (video) - Mauro says a lesson learned from the private-venture Polecat was a need to get governent partners on board to share the cost and risk, so the Skunks are working to get backers for the VARIOUS VTOL UCAV demonstrator. This is mainly an engine integration challenge, he says. The VARIOUS has three small Teledyne gas turbines, one for cruise and two driving fans embedded in the wing.

Hybrid airship (video) - The Skunk Works is preparing to fly its P-791 hybrid airship demonstrator again, and Mauro says Lockheed is looking for a partner to commercialise the aircraft, having decided against entering the commercial market itself. An unmanned version is being proposed to Raytheon for the JLENS cruise-missile defence system, as an alternative to tethered aerostats.

RATTLRS (video) - The Mach 3-plus missile demonstrator could still fly this year, but more funding will be required, Mauro says, after Rolls-Royce suffered foil bearing failures in the YJ102R high-Mach turbine engine. An Office of Naval Research programme, RATTLRS is designed to cruise above Mach 3 for 5min.

Morphing UAV (video) - Lockheed's DARPA funding ran out before the Skunk Works could fly its folding-wing morphing wing UAV. Mauro says the problem was the lack of a 150lb-thrust engine. All the engines delivered said 150lb on the box, he says, but only produced about 75lb - not enough to get the UAV off the ground.

It's not every day a new form of propulsion makes its first flight: the turbojet in August 1939 (Heinkel He178), the ramjet in April 1949 (Leduc 010), the scramjet in July 2002 (University of Queensland HyShot). Now it's the turn of the pulsed detonation engine (PDE) - a simple, lightweight powerplant that promises efficient operation over a wide range of speeds from 0 to Mach 4.

In a PDE, combustion is supersonic (detonation) rather than subsonic (deflagration), resulting in the more efficient conversion of fuel into thrust. PDEs have few moving parts. A fuel/air mixture is injected into a tube and ignited, creating a supersonic detonation wave that travels down the tube and is expelled, producing a pulse of thrust. Grouping several tubes together and firing each many times a second produces constant thrust.

It's taken a few years longer than planned, but the US Air Force Research Laboratory and partners ISSI and Scaled Composites finally accomplished the first PDE-powered flight in late January. The modified Long-EZ was powered by a four-tube PDE, each tube firing 20 times a second, producing 200lb peak thrust. The flight was short, just a few tens of seconds, taking place within the length of the Mojave runway, but it was a first.

(Pictures by Alan Radecki)