I think Giz has missed the point..
Aircraft using their main Thrust engines for Taxying is about 99% inefficient..
Using the APU (already generating power for the plane or an upgraded APU) to electrically power the wheels for slow taxying is a huge leap in efficiency...
For short haul operators (lots of taxying realtive to the time in the air) there are gains to be made, also not having to be pushed out from a terminal will mean faster turn around times (will still need ground crew to guide the reversing part)...
For Long haul operations, carrying the extra weight for the whole trip may cut into any benefits.. who cares if 500kg of fuel are saved on the ground if 2000kg extra are burned in flight due to the weight of the system...
Same with using batteries for the power, using a Jet fuel powered efficient APU will be lighter and more cost effective than carrying batteries to be topped up with imaginative green power... more weight, means more fuel burnt, more whales extincted... Simpler lighter system, has some merit.. (of course a super capacitor for regen-braking on landing would be interesting, but to actually capture any significant part of the braking energy, would need a wheel generator as big as the thrust power-turbine... probably not doable, as then extra fuel burn carrying the load will negate any benefits...
They have not explored ground based take-off acceleration (catapult or cable tow), that has more possibility of reducing pollution, as it could use \"green\" power, and capture landing energy (using arrestor cables), allowing the aircraft to have a lighter takeoff weight, not needing the fuel for the initial acceleration from rest to Rotation speed..... fanciful, well so is wheel motors in airliners, not impossible.
10th February, 2012 @ 7:34 a.m. (California Time)
I wonder have they considered electric planes. Sure it may seem wierd at first but energy storage is getting better and better, and the weight is stable compared to jet fuel, also with the huge surface area on planes, solar recharing during the day is an almost given. just think of the green advantages to going to electric...
10th February, 2012 @ 9:27 a.m. (California Time)
I\'ve heard of alternative taxiing methods being suggested before, but I was expecting a ground based tow vehicle. Surely you could come up with something efficient that took the equipment and the weight out of the aircraft?
In the same vein, aircraft on the ground could be powered from umbilicals from the airport terminal rather than using the aircraft APU.
10th February, 2012 @ 5 p.m. (California Time)
spot on MD! Excellent concise post
10th February, 2012 @ 8:24 p.m. (California Time)
If the plane has thrust reversers it can back away from the terminal under its own power. Granted it was uncomfortably loud inside the shaking terminal but I watched it happen.
No matter how energy dense the batteries get they don\'t get lighter as the energy is consumed. The cargo weight that an airplane can carry is the difference between the weight of the airplane and reserve fuel load, and the maximum total landing weight. So aside from the reserve fuel load every gram of fuel displaced by a battery is a gram of cargo that can not be carried. Many airliners burn greater weight of fuel per flight than the weight of the cargo.
While solar might be equal in weight for axillary power the planes will also fly at night so the extra weight will require more fuel to move than the APU burns.
Electrical storage will have to either get far more energy dense than jet fuel or a safe, practical broadcast power system will have to be created for electrically powered airliners to be feasible.
If you built wind turbans that could be raised and lowered at the ends of the runways so that you could power them by the jet exhaust as they wind up for takeoff you could harvest a great deal of predictable electricity from the wasted energy.
10th February, 2012 @ 10:37 p.m. (California Time)
High altitude air travel is inherently inefficient. For travel over land, high speed trains would be much more energy-efficient. Transoceanic travel would be better served by ground effect vehicles, which are more fuel-efficient than airliners. They also don\'t require dedicated runways, of which most airports have only a few. If a seaplane terminal is temporarily at capacity, just land and wait in the water a few thousand feet away instead of going into a ridiculous holding pattern for a few hours, burning fuel all the while.
11th February, 2012 @ 1:22 p.m. (California Time)
Trains wreck at a much higher rate than planes crash.
You forgot to calculate the value of time lost to transit. A high subsonic altitude plane can take you half way around the world in less than a day.
Ground effect vehicles AKA air cushion vehicles AKA hover craft like helicopters use power to simply stay aloft are less efficient than fixed wing aircraft.
Also flying boats are known to burn half their fuel taking off. It is fare more efficient to fly a holding pattern for hours than to land and take off in a seaplane.
12th February, 2012 @ 1:06 a.m. (California Time)
gadgeter : were you thinking of Ekranoplane (?) from Russia ?
looks like a plane but \"flies\" only a few feet above the water, and can fly # 500 kph
only available in Black Sea, and I think something like \"operational prototypes\"
(sorry for my \"foreigner english)
13th February, 2012 @ 2:26 a.m. (California Time)
why doesn\'t easyJet make the passengers walk to the plane waiting close to the runway? they could offer it as \"keep fit and fly\" and save even more money!! (speaking as a former passenger)
13th February, 2012 @ 6:06 a.m. (California Time)
Gadgeteer - A little research on aerodynamics will reveal why airliners fly as high as they do, it\'s because of the air density - lower density at higher altitude results in lower drag, which means higher speeds can be achieved with less thrust. Ekranoplans and Trains are sea-level vehicles, and will always experience higher drag, and thus require more fuel to reach the same speed. This is why it\'s such a challenge to break the sound barrier at sea level.
13th February, 2012 @ 8:22 a.m. (California Time)
\"flying boats are known to burn half their fuel taking off\"
Don\'t you think that\'s a bit
That\'s nowhere close to accurate.
If the gpm IS double what inflight consumption is,
takeoff still takes place in less than five minutes.
Even counting climbout,
a plane with 4 hours range would half to be burning something like 16x the burn rate of cruise consumption.
13th February, 2012 @ 8:32 a.m. (California Time)
If they rig this system to spin up the tires prior to landing, it would save on tire wear VS the way they hit the runway stationary and leave a bunch of rubber behind as they have to nearly instantly spin up to speed.
There should be some way to mount air deflectors on the landing gear so airflow would make the wheels spin before landing. I bet landing with spinning wheels would reduce stress on the landing gear.
13th February, 2012 @ 2:49 p.m. (California Time)
Flying burns massive amounts of fuel and is expensive. Solution is cheaper renewable method of fuel production, or nanotechnology for a higher density energy storage, before this commitment and removal of interest groups is required . I don\'t agree with faster more efficient travel of super efficient important people, no such thing. Trips\' objectives and duties can be planned, work can also be done while travelling and work or study or entertainment while travel industry flourishes. Technology has reduced requirements of travel too, so one can have a holistic view.
13th February, 2012 @ 3:36 p.m. (California Time)
The drag of water on a hull ridiculous the Pam Am flying boats flew at cruising speed with the engines running at less than 40% power. flying boats were abandoned commercially because they are so massively inefficient. The Ekranoplane known as the Caspian Sea Monster has Two jet engines on the tail for propulsion and eight larger jets up front just to get it out of the water.
Just as an aside. Generally the higher you fly the safer you are because it gives the pilots more time to fix what goes wrong before you hit.
13th February, 2012 @ 7:09 p.m. (California Time)
re; Dawar Saify
Some people get motion sick no matter what they do, others get motion sick if they do anything but look at the horizon. For them transit time is always lost time.
19th February, 2012 @ 9:26 a.m. (California Time)