Electric cars are a hot topic these days but I recently have read some interesting stuff about electric aircraft.
Airbus thinks that they may be able to field a large electrically powered commercial aircraft in the next 20-30 years.
Airbus E-Fan. Could this be the future of aviation?
Airbus recently began test flying its E-Fan demonstrator aircraft. While there have been electric conversions of existing aircraft, this little guy was designed to be electrically powered.
Unique variable-pitch ducted fans.
Its driven by a pair of 30 kilowatt electric motors driving variable-pitch ducted fans. Each one produces 337 pounds (1.5 kN) of thrust. Power comes from 250 volt lithium ion batteries. They say it carries enough charge for 45 to 60 minutes of flight. Top speed is 118 knots. Cruise speed is a leisurely 86 knots. This puts it at least in the ball park of primary trainer aircraft like the Cessna 152.
Electric ducted fans have driving model aircraft for a while now but I think this may be the first use on a full size aircraft.
Electrically driven main gear can hit 38 mph without using the fans.
What I found rather interesting is that it moves on the ground by powering its main landing gear electrically without using the main motors. It can also accelerate up to 38 mph on the take-off roll using just the landing gear. I'm guessing the reason they did that is it's more efficient to move something on the ground by driving the wheels. This is why our cars don't have propellers. They must have felt the added weight was worth the trade off.
It actually flies.
Obviously it's a long way from the E-Fan to something like an all electric Airbus A320. I don't know how well this technology will scale up from 337 pound of thrust to say 52,000 pounds from a GE CF-6. The E in GE does stand for "Electric" so who knows?
So what would the advantages of an electric airliner be? The obvious one would be less dependence on fossil fuels and a lower carbon footprint. Of course the electricity is only as clean as its source but we'll assume that in 20-30 years we're using more renewable sources.
Efficiency would be a big one. Fuel is a huge cost for airlines. Airline profit margins are exceedingly slim, frequently pennies per passenger-mile. Just as an electric car costs much less per mile driven than its gasoline counterpart, an electric airliner might be equally efficient.
Rolls Royce concept of a ducted fan powered by a superconducting motor.
Noise is another advantage. European airports are especially noise sensitive. And electric airliner would probably be quiet enough to be exempt from noise restrictions. They could possibly fly at any hour even at the most restrictive airports.
Reliability and ease of maintenance would be much improved. No fuel pumps or fuel control units to maintain. Electric motors are pretty simple devices. I have an Emerson electric fan from the 1930s that still hums along quite nicely. Modern jet engines are amazingly reliable but an electric motor is more reliable yet.
Sounds great but do I have a few reservations. For one, I'm leery of flying around with large numbers of lithium-ion batteries. There's a reason that shipments of Li batteries are marked "cargo aircraft only". They've been known to burn up. UPS lost a 747 a while back and we're pretty sure it was due to a shipment of Li batteries catching fire. It may sound weird that I'd rather fly around with 5000 gallons of highly flammable Jet-A but at least Jet-A is predictable.
The second issue would be recharge time. I'm curious just how long it would take to charge that many batteries. We can refuel a jet airliner in 20 minutes or so. It wouldn't be as much of a problem for cargo outfits. Our planes don't fly as many legs in a day as a passenger hauler does. They could probably take on a pretty good charge during the 4 hour "sort". I could see it being an issue for someone like Southwest, however. Part of their business model is turning their planes quickly.
Then there's weight. An aircraft that burns fuel takes off heavy and gets lighter as it goes. If I fly the 757 from coast to coast, we're going to land 30-40 thousand pounds lighter than when we took off. An electric aircraft is going to weigh exactly the same when it lands as when it takes off. That means its maximum takeoff weight will be limited to its landing weight.
With jets we can trade off range for payload. If we're only going a short distance we can put more cargo on because we don't need as much gas. I don't see that kind of flexibility in an electric aircraft. I suppose it would be possible to make modular battery packs that could be added or removed as necessary.
I would say that the key hurdles to overcome would be energy density and weight. Can we make a battery pack with enough energy to move an airliner? If so, can we keep it light enough to not only fly but also carry a meaningful payload? That sounds like a tall order but who knows where battery and motor technology will be in 20 years?
Before we see a pure electric airliner we may see a hybrid airliner. Airbus wants to build a regional jet that uses a single gas turbine to generate electricity for six electric fans. The reason for this is efficiency. The gas turbine can be optimized for thermal efficiency while the fans can be optimized for thrust. Current turbofan engines are a compromise on both.
EADS wants to have this hybrid airliner flying by 2030.
The gas turbine would be optimized for cruise efficiency and a battery pack would provide extra power for takeoff. Once airborne the turbine-driven generator powers the fans and recharges the batteries. It would retain the ability to go a certain distance on battery power alone if the gas turbine failed. The fans could windmill on descent to top off the batteries.
Will we actually see it? I don't know. So many of these "airliner of the future" designs have come and gone over the years. The technology may exist to build it but it still has to pass government certification. Then they have to convince an airline to actually buy it. That's always the biggest hurdle.
Meanwhile I'll imagine what the checklist for an electric airliner would be like.
"Before start checklist"
"ON/OFF Switch - ON"
"Before start checklist - complete"
I'm curious what we would use for a thrust setting on an electric ducted fan. On jets we either use EPR (Exhaust Pressure Ratio) or N1 (Fan RPM). I guess it doesn't matter all that much. I'm a pilot. If they tell me to set 50,000 "turtle power" then I'll set the turtle gauge to 50,000 and off we go!
I'm glad somebody is at least looking into this. Oil is a finite resource and it won't last forever. Yes, we seem to have cheap oil as of late but at some point supply won't be able to keep up with demand and the price will go back up. Maybe new fracking technology will let us get those last few barrels out of the ground but at what environmental cost? Perhaps instead of using technology to get more oil we can use it to not use so much oil in the first place.