Does anyone have enough knowledge of commercial aviation to explain why this hasn't been done before? To an outsider, it seems like kind of an obvious feature.
Airbus 320 pilot here. This is something I've wondered myself for a long time. This same idea of a electric motor on the wheels powered by the APU(auxiliar small turbine for electricity and air presure, is the loud noise you hear when boarding the plane), is what some other pilots and myself have talked about for a long time.
Just taking in to account that it makes you autonomous when pushing back and taxing, the long times you spend waiting for take of at the runway, it makes a lot of sense for this kind of planes that spend a lot of the daily time taxing on congested airports.
I don't know exactly the reason why it hasn't been done before, I don't think is a weight or technology reason. It surely has seated on a TODO list for a long time, just take into account that in aviation we are way behind in aplication of the latest technology. For example we are still using single chanel radio for comunications with control( this is terribly frustrating and ineficient, it's pretty common to have comunication jams due to excess of traffics on the same frequency).
Airplane computers even in new models are still 90s models (very slow but i suppose that stability is worth the boredom). There are a lot of other vintage technologies in aviation, after all every single release to production must be tested and approved by the FAA and EASA. It's the same for all major changes in systems and procedures. That makes all changes and improvements very slow and expensive.
Weight added to the aircraft (660lb). Another factor is reliability. Wheel or tire damage can bring down an airliner. The Concorde crash. Also a DC-8 crash in Jeddah in 1991 was due to a fire in the wheel well.[1] Even things like entertainment systems cause risk. Swissair Flight 111 went down due to a fire that started in the entertainment system rack, behind the cockpit. [2]
Since aviation became an industry, adding more "things" is always circumspect. If you think about it, that makes sense since every new feature, by virtue of being "new", still has to go through a gauntlet of testing, retesting and independent verification (plus Aviation Authority approval from several different countries).
There may have been previous attempts that were possibly abandoned until now when technology has finally caught up to the expected reliability.
Well, we shall see. If the Boeing battery problems[1] are a hint, it will take actual major use to bring out any bugs. But I'm still hopeful.
I'm guessing the added weight of electric engines and batteries/generators weren't worth the fuel savings until now, thanks to advances in batteries and rising fuel costs.
I think I like the sound of the Taxibot over installing electric engines which weight 660 lbs on the wheels. It's like a Roomba for push backs :-)
I assume the bot autonomously 'docks' with the plane, then the pilot takes over control and pushes back. Then the bot autonomously returns back to its docking station by the jet bridge.
I suppose a single bot could do push backs for 3 or 4 neighboring jets, if they're just doing the push back. If it's taxing the jet all the way down the runway, I guess it's more of a 1:1 ratio, and probably a lot more complicated to work the returning units into ground traffic control, to the point where you need to work it into the overall airport design?
Does this take away from being able to warm the engines up to prevent thermal shock and/or ensure give them enough run time before takeoff to ensure they are running well?
Wouldn't they also have to place an electric air conditioning system on the plane as well? When they disconnect the shore power at the terminal, the air does not come back on until the engines spin up.
Air conditioning and electricity are suplied by the APU, not only by the ground units. For engine start up you must use the air presure(the startup motor is pneumatic not electric), that's why you don't have air conditioning till the engines are running, but you can have it till the moment that you begin pushing back.
Also low cost companies try to save every cent so they don't use the APU till they have to start the engines. This can be pretty unconfortable when you have more than 28C inside, but they don't care too much.
The APU was a nice advance in that it enabled getting rid of the ground cart - which provided power to the airplane when its engines were off, and also provided the electric power needed to start the engines.
I wonder if they could spin up the tires before they hit the tarmac on landing? Think about it: the landing gear tires go from 0 rpm to spinning rapidly enough to carry the plane going about 140 mph in a fraction of a second. That puts the tire under enormous strain, which causes them to blow out all the time. A pre-landing spin-up system might be able to save a lot of petroleum by conserving synthetic rubber.
They don't blow out "all the time," that's why you've never experienced a landing with a blow out. Any way this is a FAQ and has been investigated before:
> While I was in college at the University of Cincinnati, I was watching television and saw a shot of an aircraft landing. There was the normal boil of tire smoke at touchdown. I had the same thought as your reader. Thinking that I had a great invention on my hands, I did some research in the library. I found some U.S. Government (Air Force or Navy) documents that addressed this issue. They were complete with photographs of a very elaborate test sled designed to accelerate a test tire over various surfaces and measure the effects of load and spinup time. Tests were done also of pre-spinning the tires. Much to my surprise, tire spinup was not a significant factor in tire wear.
> Flight crews did not like having almost 1000 lb. of spinning mass ~15 ft below the center of gravity. The special tires made the aircraft very hard to turn, especially at low airspeeds associated with the approach and landing phase. The crews wanted gyroscopes in the cockpit, not under the wings. But it seemed like a good idea at the time.
I believe the US air force did extensive studies on this back in the 60's and found that tire ware from spinup only accounted for ~<10% of overall wear on the tires. They found most of the stress comes from the act of braking and turning. Also I believe they found the gyroscopic effects of the spinning wheels actually made it more difficult to land the plane... although that may not be an issue anymore with modern avionics and autopilots.
The Taxibot system, where a small tug vehicle positions itself under the plane's front wheels, would be very promising if it could be self-driving and fully automated.
And think of the cost saving when we get rid of the pilot and cockpit. And heck, let's get rid of the landing gear too, and have the plane drop into a cradle running along underneath the plane on a track to catch the plane. The cradle would also provide a lot of the acceleration of liftoff, and the cradle's liftoff track could climb a few hundred feet like a roller coaster, so maybe the plane's engines could be smaller.
We could get rid of those pesky complaining meat sacks too. I never quite understood the fiscal arguements for pilotless passenger aircraft. It's not like a single seat fighter jet where you can ditch the pressurisation gear, you've got to still keep the cargo alive no matter how much noise that they make.
Been also watching WheelTug[1] as a result of Andrew Tobias' interest (and investment) in it[2]. Sounds like they have more customers lined up, but competition already in this market should be a good thing!
I wonder how much weight this adds to the plane. A full jet is often right at the edge of it's envelope and adding a few hundred pounds of electric motors could mean that they lose a row of seats. I would love it if extra leg room was an unintended consequence of electric ground propulsion.
"The companies claim the result is a potential savings of more than 150 gallons during a multi-flight day for an airplane like the A320 or Boeing’s 737. Overall an airplane equipped with the EGTS could cut fuel consumption by four percent over the course of a year."
Another step to help reduce the costs of air travel. Follows the trend of airlines and manufacturers choosing to provide more efficient air travel vs faster air travel to consumers: https://medium.com/lift-and-drag/7885a299bca2
It's a pretty funny trend since, as both articles suggest, speed is the cooler/sexier technology. Goes to show that it isn't always the cooler inventions that have the greatest impact.
As we've agreed, this is not a new or novel idea, but it does illustrate why the patent system is broken. A quick, cursory search yields a patent from 1994 for the exact same thing. " Preferably, a motor (27, 44) powered by the auxiliary power unit of the aircraft is used to drive the wheels of the landing gear."
I think the Concorde was the worst offender when it comes to taxing to the runway, if I remember correctly, because its jet engines were hugely inefficient at low speeds, it would burn almost 2 tonnes of fuel just to get to the runway
> if I remember correctly, because its jet engines were hugely inefficient at low speeds
Yes, turbojet vs turbofan. Turbojet only become efficient over Mach 1.
> the Concorde was the worst offender
No, I the SR 71 was worse, it literally leaked fuel:
"Similarly, the fuselage panels were manufactured to fit only loosely on the ground. Proper alignment was achieved only when the airframe heated up and expanded several inches. Because of this, and the lack of a fuel sealing system that could handle the thermal expansion of the airframe at extreme temperatures, the aircraft would leak JP-7 jet fuel on the runway."
That was the next logical steps after Boeing electrifying most of the 787 functions (I'm still wondering why Airbus didn't go with bleedless engines for the 350).
My impression was that Airbus quite consciously decided to be a bit more conservative with the A350 after seeing all the problems Boeing had with the 787 switching to a zillion new technologies, all at once...
Could they also use he motors to spin the wheels up to speed right before landing? I always see a puff of smoke when the wheels first touch the runway. I imagine that wears down the tires pretty quickly?
[+] [-] kevincennis|12 years ago|reply
[+] [-] omegant|12 years ago|reply
[+] [-] neurotech1|12 years ago|reply
[1] http://en.wikipedia.org/wiki/Nigeria_Airways_Flight_2120
[2] http://en.wikipedia.org/wiki/Swissair_Flight_111
[+] [-] eksith|12 years ago|reply
There may have been previous attempts that were possibly abandoned until now when technology has finally caught up to the expected reliability.
Well, we shall see. If the Boeing battery problems[1] are a hint, it will take actual major use to bring out any bugs. But I'm still hopeful.
[1] http://en.wikipedia.org/wiki/Boeing_787_Dreamliner_battery_p...
[+] [-] standeven|12 years ago|reply
[+] [-] unknown|12 years ago|reply
[deleted]
[+] [-] unknown|12 years ago|reply
[deleted]
[+] [-] zaroth|12 years ago|reply
I assume the bot autonomously 'docks' with the plane, then the pilot takes over control and pushes back. Then the bot autonomously returns back to its docking station by the jet bridge.
I suppose a single bot could do push backs for 3 or 4 neighboring jets, if they're just doing the push back. If it's taxing the jet all the way down the runway, I guess it's more of a 1:1 ratio, and probably a lot more complicated to work the returning units into ground traffic control, to the point where you need to work it into the overall airport design?
[+] [-] rodgerd|12 years ago|reply
These units go where the jets goes, and are available for exactly the utilised capacity of the airport.
[+] [-] jerrya|12 years ago|reply
[+] [-] marcosscriven|12 years ago|reply
[deleted]
[+] [-] mehmehshoe|12 years ago|reply
edit Read the comments on the article page and a reply stated the APU powers the ac. http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Auxilia...
[+] [-] omegant|12 years ago|reply
Edit: redaction.
[+] [-] WalterBright|12 years ago|reply
[+] [-] stcredzero|12 years ago|reply
[+] [-] nether|12 years ago|reply
> While I was in college at the University of Cincinnati, I was watching television and saw a shot of an aircraft landing. There was the normal boil of tire smoke at touchdown. I had the same thought as your reader. Thinking that I had a great invention on my hands, I did some research in the library. I found some U.S. Government (Air Force or Navy) documents that addressed this issue. They were complete with photographs of a very elaborate test sled designed to accelerate a test tire over various surfaces and measure the effects of load and spinup time. Tests were done also of pre-spinning the tires. Much to my surprise, tire spinup was not a significant factor in tire wear.
> Flight crews did not like having almost 1000 lb. of spinning mass ~15 ft below the center of gravity. The special tires made the aircraft very hard to turn, especially at low airspeeds associated with the approach and landing phase. The crews wanted gyroscopes in the cockpit, not under the wings. But it seemed like a good idea at the time.
http://archives.sensorsmag.com/articles/0300/14/index.htm
[+] [-] Element_|12 years ago|reply
[+] [-] anonfunction|12 years ago|reply
http://tires.about.com/b/2013/05/20/spin-doctor.htm
[+] [-] nealabq|12 years ago|reply
And think of the cost saving when we get rid of the pilot and cockpit. And heck, let's get rid of the landing gear too, and have the plane drop into a cradle running along underneath the plane on a track to catch the plane. The cradle would also provide a lot of the acceleration of liftoff, and the cradle's liftoff track could climb a few hundred feet like a roller coaster, so maybe the plane's engines could be smaller.
[+] [-] thedrbrian|12 years ago|reply
[+] [-] WalterBright|12 years ago|reply
Of course, the Me-163 had other problems like blowing up on the ascent, or worse, dissolving the pilot if it developed a fuel leak.
[+] [-] rdl|12 years ago|reply
[+] [-] carleverett|12 years ago|reply
[+] [-] X9|12 years ago|reply
[1] http://www.wheeltug.gi/
[2] http://andrewtobias.com/column/hot-brakes/
[+] [-] olympus|12 years ago|reply
[+] [-] smoyer|12 years ago|reply
[+] [-] jljljl|12 years ago|reply
Another step to help reduce the costs of air travel. Follows the trend of airlines and manufacturers choosing to provide more efficient air travel vs faster air travel to consumers: https://medium.com/lift-and-drag/7885a299bca2
It's a pretty funny trend since, as both articles suggest, speed is the cooler/sexier technology. Goes to show that it isn't always the cooler inventions that have the greatest impact.
[+] [-] savrajsingh|12 years ago|reply
https://www.google.com/patents/EP0756556B1?cl=en&dq=electric...
Search Google Patents for "electric taxi airplane". Even so, there are many subsequent patents on the same overall concept. A broken system.
[+] [-] bconway|12 years ago|reply
[+] [-] gambiting|12 years ago|reply
[+] [-] ghshephard|12 years ago|reply
[+] [-] dorfsmay|12 years ago|reply
Yes, turbojet vs turbofan. Turbojet only become efficient over Mach 1.
> the Concorde was the worst offender
No, I the SR 71 was worse, it literally leaked fuel:
"Similarly, the fuselage panels were manufactured to fit only loosely on the ground. Proper alignment was achieved only when the airframe heated up and expanded several inches. Because of this, and the lack of a fuel sealing system that could handle the thermal expansion of the airframe at extreme temperatures, the aircraft would leak JP-7 jet fuel on the runway."
http://en.wikipedia.org/wiki/Lockheed_SR-71_Blackbird
[+] [-] dorfsmay|12 years ago|reply
[+] [-] snogglethorpe|12 years ago|reply
[+] [-] tocomment|12 years ago|reply