Date:21 August 2013
We’ll board trains that turn into planes. Whir aloft under planet-friendly electric power. And we’ll take off from a runway, soar into space under rocket power and land thousands of kilometres away in an hour or two – without any need for booster tanks.
In an era in which air travel has become commonplace, developments in materials and technologies have pushed the envelope for conventional fixed- and rotor-wing aircraft to the limits. Currently, propulsion systems are a significant area under scrutiny as never before as we grapple with the challenges of sustainability and efficiency. Weighing heavily on manufacturers’ minds: the Advisory Council for Aeronautics Research in Europe, ACARE, aims to halve CO2 emissions by 2020. By mid-century, according to the EC’s report Flightpath 2050 – Europe’s Vision for Aviation, we’ll need to have cut current C02 emissions by 75 per cent, NOx emissions by 90 per cent and noise by 65 per cent.
But innovative thinkers are moving beyond this. They are brainstorming new concepts that will transform air travel within the next few decades. New designs that harness the new tech and the imagination in completely different approaches to the job of getting from Point A to Point B by air.
Admittedly, these flights of fancy range from the far-sighted to the frankly far-fetched. And, even if they pass the airworthiness test, there’s no guarantee of commercial acceptance. Then again, even the Wright brothers had their detractors…
Skylon: Long-haul blues no more
Spearheading a new breed of spaceplanes for long-haul flights, the pilotless 85-metre Skylon clearly makes a convincing case. Potentially able to take off from a runway, fly into orbit and return without the need for booster tanks, this spaceplane was recently boosted by the British government’s go-ahead for a £60 million (about R900 million) investment.
A research project, jointly funded by the European Space Agency (ESA) and UK company Reaction Engines, last year successfully tested key technologies in the Skylon’s Synergistic Air-Breathing Rocket Engine (SABRE). Designed by Reaction Engines, the SABRE (see graphic below) will use atmospheric air in the early part of the flight before switching to rocket mode for the final ascent to orbit.
According to ESA, the concept paves the way for true spaceplanes. Unlike existing shuttles, these will be lighter, reusable and able to fly from conventional runways. It has the potential, they say, to revolutionise access to space.
During the next four years the SABRE’s technical design will be refined. The big push will be construction and ground testing of a complete prototype.
It’s early days yet, says Mark Ford, head of ESA’s propulsion section. “An entire Skylon vehicle development would cost billions of euros. But the success so far puts Europe in a good position for any future international collaboration. We have something here that is really unique.”
The SABRE is a Supersonic Combustion ramjet (scramjet), in which the airflow is never lower than supersonic, a principle known since the dawn of the jet age. In the lower atmosphere it flies like a normal air-breathing jet engine up to “about Mach 5” and then operates like a rocket, switching to liquid oxygen to burn its liquid hydrogen fuel for the rest of its flight to orbit. A big benefit of the scramjet principle is that it doesn’t have to drag along quite as much oxygen as a conventional rocket. Getting it all to work is the problem.
At Mach 5, intake air needs to be slowed to burn it in the engine, and doing so will raise the temperature of the air to above engine material temperature limits, says Ford. Translation: stuff starts melting. Last year’s successful test involved a precooler to chill the hot air entering the engine at hypersonic speed. “Ambient air comes in and is cooled down to below freezing in a fraction of a second,” explained Ford. The actual figures are from about 1 000 degrees to 150 degrees. “These types of heat exchangers exist in the real world, but they’re the size of a factory. The key part of this is that Reaction Engines have produced something sufficiently light and compact that it can be flown.”
Clip-Air: Train to plane
“Attention all passengers: Flight 023 to Paris is now departing from Platform 5… ” The thinking behind Clip-Air is a modular aircraft concept that marries trains and planes. At a railway station, you’d board a 30-metre 30-ton capsule that would travel to your take-off point by rail. From there, the capsule would be hitched to the airborne equivalent of a locomotive: A flying wing able to carry up to three such capsules, each housing up to 150 passengers. The wing would contain engines, cockpit, fuel and landing gear.
Once at the other end, the capsule would take you to your final destination by rail. All of this would happen without any need to disembark en route or (even better) not to be subjected to what many consider to be the least enticing part of air travel: the airport.
Switzerland’s Cole Polytechnique Fédérale de Lausanne (EPFL) has been developing Clip-Air since 2009. According to EPFL, the concept allows a glimpse at the air transportation of tomorrow, which is meant to be more flexible, closer to our needs, more efficient and less energy-consuming. At this year’s Paris Air Show, a model of the Clip-Air plane was shown for the first time.
“More than a new type of flying device, its innovative concept could revolutionise the airports of the future,” EPFL says.
The project’s backers point to its potential for more efficient and flexible fleet management, plus savings in maintenance and storage. Then there’s the potential for addressing environmental concerns: it is estimated that Clip-Air aircraft could carry as many passengers as three A320s while using half the number of engines. The modular concept is also suited to alternative fuelling, for example by exchanging one passenger capsule for a hydrogen one.
Project leader Claudio Leonardi concedes that they have to break down barriers with a concept so at odds with current aircraft technology. Aerodynamics, weight distribution and logistics at each end could be significant problem areas. Capsules that are robust and safe enough for rail transport would be too heavy for flight. Also, there appears to be no way for crew to move between units, preventing them from acting as backup.
Then, some might say that the easy solution would simply be to have more trains running straight to airports. It’s a fact that, in many regions, notably Europe, convenient inter-city trains have superseded short-haul flights. In any case, who would gladly spend more time cooped up in Economy class?
Tropospheric airship concept: Long-distance runner
An innovative hybrid designed for flights lasting up to 40 days, the Tropospheric Airship concept is envisaged as a primarily unmanned observation platform for polar regions.
According to EADS, its roles will range from environment monitoring to security. Its extended “loiter time” and minimal environmental impact are also ideal, the company says, for an aerial platform used to keep track of shifting ice patterns – and the growing number of ships expected to use the open-water routes opened up as climate change effects melt the ice cap.
You’ll notice that it is a lot more streamlined than a traditional airship. That’s because its catamaran design is said to combine aerostatic lift with helium gas. Helium will take the airship up to 5 000 metres and the wings will provide the additional lift to get to its operating altitude of 7 000 metres. Significantly, this will reduce the amount of helium needed – and, as a result, hull volume. The wings will also boost manoeuvrability during landing; EADS says that the “negative lift” they can provide will make it easier to moor, especially when it’s windy. A novel buoyancy concept involves manipulating the individual helium cells. Extending them lowers internal gas pressure, increasing buoyancy; retracting them does the reverse. The effect can be used to finetune the craft’s pitch and roll and could come in useful for manoeuvring when it is used to carry cargo.
eConcept: Hybrids en route to 2050
A complete rethink of commercial aviation, the eConcept is a showcase for some amazing ideas that we can expect to see by 2050, but its creators concede they will not necessarily appear together in a single aircraft. Hybrid electric power that will save fuel while cutting emissions and noise is just one of the features of this vision of mid-century commercial aviation.
At the Paris Show, the Airbus eConcept was on display in model form. It uses EADS’ E-Thrust Distributed Propulsion system, which in concept is like a typical diesel-electric drivetrain. So, the eConcept uses an engine burning fossil fuel to drive an array of electric fans. At the same time, a battery bank will be charged. Like hybrid cars, this is being touted as a transition phase on the way to full electric operation.
Pre-charging the electric drive system would provide the extra thrust needed at take-off, meaning that a modestly sized gas turbine could be adequate during flight. As the aircraft glides during descent, the fans could provide power regeneration.
As it stands, E-Thrust needs some technological leaps before it can be considered viable. Battery energy density is just one of these, with EADS considering lithium-air technology.
The eConcept’s other tech features that we could be seeing in aircraft in the not too distant future include wings specially designed for improved efficiency, new lightweight load-sensing “smart materials”, innovative manufacturing methods to take advantage of new advanced materials and shapes, and quieter and more reliable engines that can be incorporated into the aircraft body because easy access is not needed. Fuselages will be no longer a simple tube, but will be shaped to combine optimum internal space and aerodynamics. According to EADS, because new, more reliable engines obviate the need for a vertical tail for its stabilising effect in the event of engine failure, the concept has a more optimal U-shaped empennage (tail section) that reduces noise pollution.
Solar Impulse: Pioneering record-setter
When Solar Impulse touched down in New York City at 11.09 pm on July 6, it had written another memorable chapter in the 7-year story of this pioneering solar-powered aircraft. The spindly craft had just crossed the USA from west to east entirely powered by the Sun.
Swiss pioneers Bertrand Piccard and André Borschberg, founders of the Solar Impulse mission, are now looking ahead to an even greater challenge: a round-the-world tour in 2015.
The cross-USA trip, begun in San Francisco, California, was covered in five stages. Total flying time was 105 h 41 min and the distance of 5 649 km was covered flown at an average speed of 53,3 km/h.
Like many pioneering machines, Solar Impulse is a testbed for technologies that might be of use in the future. Built of carbon fibre, it has the 60-metre wingspan of a Boeing 747 and weighs 1 600 kg. According to its makers, a plane so big and yet so light has never been built before.
Its wings house 12 000 solar cells, powering four 7,5-kW electric motors while recharging the 400-kg lithium batteries that allow the plane to fly at night.
Saker S-1: Top Gun style
What looks like a fighter jet, flies at a hair under the speed of sound and seats two in tandem… plus their designer suitcases? The Saker-S1, that’s what. With a design inspired by military fighter jets, it’s the aviation counterpart of the supercar.
Top speed is quoted as a pedantic-sounding Mach 0,99, with a cruise of Mach 0,95. Fortunately, although it looks the part, it won’t need a military-sized airstrip. Equally, despite the S-1’s racy looks, it is said to need no special training to fly. In the event that you do run out of ability, though, you’ll be pleased to know that ejection seats are available as an option.
According to its designers the S-1 will be able to take off and land in under 500 metres. Its two Williams FJ44-4 engines and internal 1 890-litre fuel tank provide a range of 2 575 km. Add-on tanks will extend the range by about 1 000 km. Climb rate is specified at 14 000 ft/min and it will have a ceiling of 45 000 ft (13 720 m). For the budget-conscious, Saker has pointed out that the engines and aerodynamics make the S-1 a massive 20 per cent more economical than competitors. The projected asking price is reported to be between $5 million and $7 million; deliveries should start in 2019.
Terrafugia TF-X: Is this the future of flight?
Meet the Terrafugia TF-X, a futuristically styled vertical take-off and landing (VTOL) hybrid-electric flying car with a host of revolutionary features, including the ability to land by itself. Before you dismiss this as just another pie-in-the-sky digital creation, it’s worth remembering that the company behind the concept has actually built and demonstrated a flying car, the street-legal Transition (see Inset).
Their new flying machine, say the people at Terrafugia, will feature fly-by-wire controls and employ powerful electric motors in combination with parallel power and control system architectures to achieve a higher level of safety than modern cars. Standard equipment includes a vehicle parachute system that can be activated in an emergency should the pilot believe it be incapable of auto-landing. Should the pilot become unresponsive for whatever reason, the TF-X will take control and automatically implement an emergency auto-land at the nearest airport.
Carrying four passengers in car-like comfort, the TF-X will be able to take off vertically from a level clearing just 30 m in diameter, and has a range of about 800 km. With the wings folded, it would fi t into an ordinary single-car garage. Don’t haul out your cheque book just yet, though. The TF-X is expected to remain in development for anything from 8-12 years.
US-based Terrafugia (terra-foo-gee-ah) is a growing aerospace company founded by pilot-engineers from MIT and supported by a network of advisers and investors.
Sagita Sherpa: Not just hot air?
Simpler, more efficient, more reliable, cheaper… and runs on hot air. What’s not to like about this compact Belgian helicopter with a fuselage a fraction under 5 metres long?
Sagita says that the Sherpa’s engine drives a compressor that draws in air from the rear of the fuselage (right). Here’s how the product brochure describes the process: “Part of the compressed air feeds the engine. The balance bypasses the engine, collects the heat of the cooling system and is eventually mixed with the engine’s exhaust gases to raise the temperature to 100 degrees.
“The hot compressed air is then sent to the rotor and expanded in two contra-rotating turbines. Each turbine directly drives one of the two contra-rotating coaxial rotors. The air exits the turbine through a circumferential gap between the two rotors.”
According to Sagita, the transmission needs no lubrication, no cooling and no tail rotor drive, and operates at an efficiency of about 85 per cent. There are no specifics about the Sherpa’s power unit itself.
Claimed benefits are no tail rotor, reduced maintenance through fewer moving parts, more direct flight control thanks to rigid blades, a faired hub and advancing blade on each side for high-speed flight, and increased power at high altitude. The Sherpa is said to be able to lift a 171 payload and fly 400 km at a cruising speed of about 160 km, with a ceiling of 2 000 metres.
This is all in theory at the moment; a full-sized model was on display at the Paris Air Show, though an electric-powered one-fifth scale model has flown trials. It’s been reported that there are hopes for a maiden flight in about two years’ time and an on-sale date a year later; expected price is about R2 million.