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?

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