During the 2012 ILA Berlin Show, A German aerospace research firm Bauhaus Luftfahrt unveiled its concept for a zero-emissions 190-seat airliner that may enter service by 2035. The airliner is powered by two electric engines using a large bank of batteries, up to 16 containers with an energy density estimated to be 2kWh/kg. Comparatively, a Chevy Volt’s Li-On battery has energy density of 0.09 kWh/kg.

Bauhaus projected that battery technology will advanced to a state such that such airliner can achieve a range of about 600nm by 2030, but it will only cover 59% of the routes similar sized aircraft flies today. By 2035, it could reach a range of 900nm, and by 2040, up to 1400 nm. While the projected range is astounding for an electric powered aircraft, it is still has a range less than half of a 737-800 today.

To squeeze out every last percentage of efficiency, the Ce-liner utilizes a unconventional non-planar c-wing configuration. This allows the aircraft to still retain the conventional tube fuselage design and minimize operational complexity associated with other configurations such as blended wing body (BWB).

The prospect of zero-emissions commercial airliner is exciting, but there are still questions that need to be answered, aside from progression of battery technology. For example, the required recharge time would be longer than a regular turn-around time. Bauhaus Luftfahrt claims that one can just switch out the batteries, which is feasible. But now an airline would need purchase huge quantities of batteries to support its fleet, in proportion to the charge time.

A picture of this cool looking airplane is located below.

(Source: Aviation Week)

I had the pleasure of attending this year’s Farnborough International Airshow in jolly ol’ England. While the weather did not cooperate; apparently the United Kingdom is experiencing a rare bout of early summer monsoon, with minor flooding in various spots in the location. Despite the weather, the show went on without any problems.

This year’s show, as before, showcased the latest in aerospace achievement. On the commercial side, Boeing brought in the 787-8 Dreamliner (powered by GEnx engines), in full Qatar livery. Airbus responded with a brand new A380 in Malaysia Airlines colors, and even the A320 with “sharklet” winglet made a brief appearance. On the military side, it was the battle of the gen 4.5 fighters, featuring a trio of Boeing F/A-18E Super Hornet, Saab JAS-39 Gripen, and Eurofighter Typhoon. The contrast between the latest military and civil aircraft is apparent during the airshow, while the crowd is energized by the roar of the jet fighters, they were equally marveled by the quietness of the latest airliners.

From the order book perspective, this year is truly the year of the max, 737 MAX that is. The latest generation of the venerable 737 family received some sizeable orders, including 75 firm orders from Air Lease Corporation and 100 from United Airlines. Of course, all these aircraft will be powered by the latest CFM LEAP-1B engines.

GE Aviation had a strong presence at the show, with a chalet on the flight line and an interactive booth in the exhibition hall. The GEnx engine was a popular attraction, where countless visitors stopped to take pictures. Other interactive displays, which showed various engine and systems products, were also well received. The future visions video, which talked about Aviation Systems vision of the future in ATM, IVHM, and integrated electrical power system, resonated with many of the visitors. Finally, the Nexcelle IPS nacelle display gave people a glimpse of what is possible in propulsion integration.

Here are some snapshots and clips of the airshow. Enjoy!

Farnborough Video 1

Farnborough Video 2

Recently, a team composed of Boeing, GE, and Georgia Tech completed an 18-month study on future commercial airplane concepts under the NASA N+3 Program. The goal of the program is to explore revolutionary aircraft concepts aimed at entry into service date of 2030 and beyond, with aggressive noise, emissions, and fuel burn targets. The program looked at both subsonic and supersonic aircraft concepts. The Boeing-led team looked at five different subsonic concepts as part of the Subsonic, Ultra Green Aircraft Research (SUGAR) project. Concepts ranged from a conventional tube and wing design (SUGAR Free and Refined SUGAR) to a high span, strut-braced wing aircraft (SUGAR High and SUGAR Volt), and a hybrid wing body configuration (SUGAR Ray). To read more about Boeing’s technology research and the future of aircraft design, click here.

While not all concepts met the ambitious goal set by NASA, the SUGAR Volt concept, which adds an electric battery gas turbine hybrid propulsion system, can reduce fuel burn by greater than 70%. It also reduces overall energy use by 55% when battery energy is included. With the fuel burn improvement, the aircraft has an added benefit of large reductions of CO2 and nitrous oxide emissions.

What’s preventing engineers from designing such aircraft today? One major challenge is battery technology. While there are rapid advancements in battery technology, a level of energy density suitable for aerospace application is still years away.  Will a hybrid electric open rotor propulsion be the game changing technology the industry is seeking? We hope so. There have been many innovative aircraft concepts that were not adopted due to either the infrastructural or operational constraints. As the price of fuel continues to increase, the industry will hopefully be more acceptable to these innovations.

Image credit: NASA/The Boeing Company

In my previous blog from Oshkosh, I talked about Sikorsky’s ambitious Firefly project, an all-electric helicopter powered by batteries. Sikorsky had planned for first flight sometime in 2012, but apparently someone has beaten them to the punch! Pascal Chretien, a French electrical/aerospace engineer and helicopter pilot, has designed and built a fully electric coaxial rotor helicopter by himself (almost) and took his machine into the air for a two minute flight.

The challenges for electric fixed-wing flight are well documented, and they are even greater for electric rotary-wing flight. For a fixed-wing aircraft, it will only require max power during takeoff, but once in flight, the power requirement is reduced. On the other hand, a helicopter requires high power throughout its flight profile, so it will require a tremendous amount of energy to stay in the air.

For Pascal, he had to design a helicopter with minimum weight, so he had to adopt a different configuration than the standard single main rotor. He picked the coaxial design so all the power is going toward lifting the vehicle off the ground, versus a 90:10 split with the conventional helicopter. Instead of cyclic for directional control, he uses a weight shifting system. This design is particularly dangerous for two reasons. The first reason is that you are shifting the C.G. of the vehicle, which could be catastrophic if the weight is shifted beyond design envelope. The second reason is that the control is now backwards compared to the regular cyclic.

As a throwback, perhaps homage, to the early aviation pioneers, Pascal did not recruit a test pilot to fly his contraption. Instead, he took it to the air himself. So far the flight testing has been limited to within ground effect while he makes final tweaks. Eventually, Pascal and his sponsor, Solution F, is targeting 10 to 12 minute flight time, which is similar to the Firefly.

Back on June 30, 2011, DLR of Germany demonstrated electric taxiing using a novel fuel cell-powered electric landing gear (press release here and video link here). The premise of electric taxiing is to postpone engine start and using it as the source for propulsion and electricity while the airplane is still on the ground, turning the engine on once the aircraft is ready to take off. By doing so, this would help reduce fuel consumption and wear on the engine while the aircraft is sitting in queue waiting to takeoff, and now days the queue seems to get longer and longer.

This concept sounds great at first glance, but let’s dig a bit deeper. Fuel burn savings during taxi are really dependent on the proportion of time spent on ground taxi relative to the entire mission. For example, a 737 flight involves around 20% of its mission time on ground taxiing, while a 777 flight involves only 6%. Therefore, electric taxiing creates more value for a 737 versus 777 because the fuel consumption reduction due to electric taxi is greater on a 737 (~16%) than a 777 (~5%). The savings is not 20% for 737 because you still have to burn some fuel to power the electric motors, either through an APU or in the future, a fuel cell.

While ~16% savings is pretty significant, there are tradeoffs to consider. To start, one will have to offset the gain with the added complexity and weight of adding motors and related controls robust enough to handle the rigorous landing environment. Also, aircraft engines need to warm up prior to takeoff, depending on ambient temperature and whether it is the first flight of the day, so the real savings might be less than the 16%.

Are there other ways to achieve the same results? What about using ground tugs to tow aircraft to the runway? What do you think?

In my earlier blog on the 787, I talked about the dramatic increase (5X) in electrical power on board the aircraft versus its predecessor due to increased demand. With all that power, the weight of the electrical power system is sure to go up and at some point, the electrical power system weight will drive decisions and compromises in aircraft design. A step change in technology is needed to overcome the weight challenge.

Current power electronic components are silicon (Si) based and as power devices are forced to achieve higher efficiency, the silicon core is operating closer to its temperature limit. Extra cooling packaging is required to maintain reliability, which becomes a key driver of the weight increase. A breakthrough in reduced cooling requirements is anticipated with the introduction of silicon carbide (SiC) based devices. Key advantages of SiC are that they can operate at higher temperatures (more than 50% higher than Si-based devices) and at faster switching speeds, especially at high voltage (> 600V). However, fundamental challenges associated with reliability and yield of the SiC devices are preventing mass adoption in many markets.

Many leading power electronics manufacturers are focusing on the SiC device area. Cree has launched the first commercial SiC-based MOSFET.  The product’s performance is slightly better than Si-based devices, and more companies will join suit in the next two to three years with more capable devices. Why the focus? The industry is anticipating the next generation hybrid-electric and pure-electric vehicles to adopt SiC technology, making the vehicles more efficient than current generations. Companies are jockeying for a piece of this huge market.

GE is certainly not standing still on the sideline in SiC development. GE Aviation Systems, in collaboration with GE’s Global Research Center (GRC), has a an industry leading  cooperative project with AFRL at Wright Patterson AFB to develop an advanced solid-state primary power distribution technology using Silicon Carbide (SiC) high power switches. GE also announced introduction of a new line of SiC-based power conversion devices at the 2011 Paris Air Show. GE anticipates that its proprietary SiC technology will be world class, addressing fundamental challenges of gate oxidation and switch reliability. Once the technology matures, we can imagine that the next generation of aircraft will have electrical power equipment that enables aircraft manufacturers to continue up the power curve without lumbering heavy electrical power systems.

Click here to see GE’s SiC MOSFET.

 Click here to see lower switching loss of GE’s all SiC module vs. hybrid Si-SiC module.

In part one, we talked about Pipistrel’s achievement with its Taurus G4, flying for 200 miles in less than two hours. While this is a phenomenal milestone, it is still not practical for general aviation applications. Compared to Pipistrel’s own LSA class aircraft Sinus, which has a cruise speed of 110 knots and a range of 540 nautical miles, Taurus G4’s performance falls way short.

So what can be done to extend Taurus G4’s range? One possibility is to take out the batteries and replace them with fuel cells, such as Proton Exchange Membrane (PEM) fuel cells, to generate electricity.

From various reports, the Taurus G4 uses a 450 pound (134 kg) Li-Ion battery with energy of 100kWhr. If we assume the best in class PEM fuel cell has a power density of 1.2 kW/kg, the fuel cell needed to power the motor will weigh around 121 kg and it can carry 13kg of compressed hydrogen. The amount of energy 13 kg of hydrogen contain is 3.5 times that of the battery pack, which means in theory a fuel cell powered Taurus G4 can fly for 7 hours!

Of course, this is all in theory right now because of a couple technical issues. First, PEM fuel cell durability is still a major challenge. You certainly don’t want the fuel cell to fail during flight. Another issue is that, while compressed hydrogen weighs little, it takes a lot of space. 13kg of compressed hydrogen will take up almost 150 liters, which will take up 5 cubic feet!

Recently, Pipistrel won $1.35 million for placing first in the NASA Comparative Aircraft Flight Efficiency (CAFÉ) Green Flight Challenge, sponsored by Google. The goal of the competition is to make a step change in the efficiency of aircraft. Pipistrel designed and flew their Taurus G4, a futuristic 4-seat all-electric aircraft, for almost 200 miles in less than two hours.

Click here to read EAA’s story on Pipistrel, and view photos.

This is a HUGE advancement in electric flight. Current all-electric aircraft would either have short flight time, which are less than one hour, or low speed to increase their range and flight time. Either way, it was impractical to fly electric aircraft beyond recreational flying. It’s also important to note that Tauras G4, as well as the second place e-genius, beat out hybrid powered competition by a wide margin.

While the range, speed and payload performance of Pipistrel’s Taurus G4 doesn’t quite match up to their avgas powered counterparts, it’s not hard to envision electric powered LSA or even GA aircraft in the not-so-distant future. What would help make electric aircraft viable? Could fuel cell be the solution? We will take a deeper look in part two.

As the Boeing 787 gets ready to enter service at All Nippon Airways (ANA) in September, Let’s take a look at this “more electric” aircraft.

Over the years, the demand for electrical power increases as new technologies such as fly-by-wire (FBW), digital avionics, and in-flight entertainment (IFE) systems are introduced.  This is in addition to other power demand increases, such as the on-going change from hydraulic and pneumatic systems to electrically powered systems. When you look at 787, which is a replacement for a Boeing 767-sized aircraft, it’s amazing to see that it will generate five times the electrical power than its predecessor!

The source for the electrical power data is from Frost & Sullivan

When Boeing started designing the 787, they decided to depart from the traditional architecture and go with a “no-bleed” design. Boeing claims that the new system would provide improved fuel consumption, reduced maintenance costs, improved reliability, and reduced number of components

Boeing achieved this by removing bleed air extraction from the engine (making it more efficient!), and instead driving the environmental control system (ECS) and anti-ice system electrically. Boeing also removed air turbines that traditionally drive part of the hydraulic system, so the hydraulic system is all electrically driven. Finally the auxiliary power units (APUs) on the 787 provide only electricity, as opposed to pneumatic and electrical power from other APU’s.

It is interesting to note that when Airbus launched the A350 XWB, they decided not to follow suit and retained the more conventional bleed architecture. Did Boeing make the right decision by adopting the no-bleed system, or did Airbus make the right move by staying with the current system? Given that both Airbus and Boeing have decided to re-engine rather than design a new narrowbody aircraft, we will have to wait to see the verdict.

For more details, you can take a look at this article form Boeing.

-Jimmy

The great annual gathering of aviation enthusiasts known as Oshkosh Air Show successfully wrapped up on July 31^st. I was there first half of the week to observe the latest innovation on electric flight.

Part of my assignment was to man the GE Aviation Systems booth at the Innovations Center, helping out at the popular all electric aircraft simulator. Luckily for me, I was surrounded by pioneers of electric flight. In the same hangar we have the all-electric Sonex and a PC-Aero, who plans to put solar panels on the Elektra-One electric sailplane.

I had the opportunity to talk to Jonathon Hartman, Research Engineer and project manager of the Sikorsky Firefly project – the all electric helicopter powered by batteries. Jonathon providing updates on the project:

During Oshkosh, many enthusiasts expressed their excitement on the prospect of flying an all-electric airplane. We agreed that there are still a few challenges ahead. The first one is energy storage – flying for only ten minutes doesn’t make the aircraft practical. The other is certification of electric aircraft. For an electric aircraft to become main stream, it has to move beyond the experimental category.  Check out this story (link) from Flight Global on the topic.

For pictures from the show, click here.

-Jimmy