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The difficulties of providing 110-volt power to your airline seat

theatlantic.com

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Re: The difficulties of providing 110-volt power to your airline seat

#61

Post by bonzoesc »

yread wrote: post #37
vilhelm_s wrote: post #19

"I wondered whether, as a technical matter, an airliner could actually produce enough power to keep a planeful of laptop users plugged in through a whole flight. [...] Short answer: No, you probably couldn't make this work." Given that the power output of the engines of a Boeing 747 is 140MW [1], enough to power 15 copies of the Empire State Building at peak business hours[2], I find this impossibility a bit depressi…

The APU power is more relevant. THe 737 can have 90kW APU which should be enough for 1000 laptops under full load (while 737 cannot carry more than 215 passangers) http://www.b737.org.uk/apu.htm

The APU doesn't run during normal flight, since the engine generators more than handle the electrical load.

Re: The difficulties of providing 110-volt power to your airline seat

#62

Post by bonzoesc »

Yaggo wrote: post #39

Interesting article, but a whopping quarter of kilowatt to every seat? Isn't that a bit overkill? Assuming that typical laptop charger drinks 80 joules of energy per second at most, and since laptops luckily have built-in energy sources for couple of hours, the power output could be time-divided, eg. every output is powered half of the time in 30 minute intervals. Assuming not everyone needs power at all, two power o…

The OEM DC adapters for Apple laptops prevent battery charging, because some in-seat DC outlets don't provide that much power.

I've had trouble connecting a laptop that wants to charge to inverters before, so this isn't without reason.

Re: The difficulties of providing 110-volt power to your airline seat

#63

Post by Retric »

For anyone who was wondering over a 12 hour flight the fuel cost would be aproximatly:

(240 watt) * 12 hour * 500 people / 45 MJ (energy dencity per gallon) / .35 energy effecency = 330 gallons * 6.8 lb / gallion = ~2244 pounds. Granted this is probably +/- 30% depending on the fuel, engine effecency, transmission losses etc.

For comparison a 12 hour flight would burn ~ 43,000 gallons or 292,000 lb of fuel.

Re: The difficulties of providing 110-volt power to your airline seat

#64

Post by bradleyland »

varjag wrote: post #42

Makes you wonder how they even manage to power those 500 Watt aircraft headlight bulbs, tens of KW in avionics, coffee machines and kettles, ovens, in-flight entertainment system per every seat etc etc

The reason none of those are a problem is pretty straight forward. Each of those systems were designed to be powered by the aircraft's gen-sets, rather than the other way around.

When designing an aircraft and its sub-systems, the engineer provides power availability specifications. The people who make the headlights, avionics, and coffee machines are all aware of the common power configurations and design their equipment to work with that specification directly. I used to work on light aircraft (private), which all used 24 VDC. Everything in the plane was designed to run on 24 VDC. Commercial airliners likely have more than one voltage specification available, but I'd imagine it's all DC.

Any time you have to convert voltage, you're going to lose some efficiency. Inverters (DC to AC) have some particularly nasty characteristics that make them undesirable on an aircraft. A DC voltage converter would work, but you still introduce some degree of inefficiency. A good switching DC voltage converter can exceed 90% efficiency, but so can an AC inverter. Neither operates at that efficiency all the time though. I know that AC inverters perform best when run at close to nominal load. At lower current levels, efficiency drops. I don't know enough about DC converters to say.

Add to this the fact that inverters and converters are heavy, and you can begin to understand why a power outlet at each seat is problematic.

Re: The difficulties of providing 110-volt power to your airline seat

#65

Post by varjag »

paol wrote: post #52
varjag wrote: post #51

Earlier quoted context omitted.

Boeing 747 was designed in 1960s.

Yes and no. The 747 is still in production and has been revised many times since. A 747 bought today will have relatively little in common with one bought in 1970.

It is still roughly the same energy requirements to lift one in the air and keep it there. Electricity intake is a tiny part of that.

Yes there was no in-flight entertainment in mid-60s, but avionics back then were still to a great extent valve-based and consumed gobs of power.

Re: The difficulties of providing 110-volt power to your airline seat

#66

Post by orborde »

quellhorst wrote: post #43

Since every laptop has a battery, you could do "rolling blackouts". The laptop doesn't need power the whole flight. I know from going to conferences sometimes just plugging in once in the middle of the day allowed me to make it without being plugged in for the rest of the day.

You might have failed to consider conservation of energy here. The laptops use a steady amount of energy whether plugged in or not (more or less), and if they're unplugged for a while, then they'll draw more power during the time they are plugged in as they recharge their batteries. In fact, if the batteries are not perfectly efficient and thus don't provide the same energy that was used to charge them, you're now using more energy per time by running it through the batteries first.

Of course, doing the rolling blackouts might encourage less use of devices, reducing power use.

Re: The difficulties of providing 110-volt power to your airline seat

#67

Post by sokoloff »

bradleyland wrote: post #64
varjag wrote: post #42

Makes you wonder how they even manage to power those 500 Watt aircraft headlight bulbs, tens of KW in avionics, coffee machines and kettles, ovens, in-flight entertainment system per every seat etc etc

The reason none of those are a problem is pretty straight forward. Each of those systems were designed to be powered by the aircraft's gen-sets, rather than the other way around. When designing an aircraft and its sub-systems, the engineer provides power availability specifications. The people who make the headlights, avionics, and coffee machines are all aware of the common power configurations and design their equi…

I took 737 mini (two day) ground school about 10 years ago. I believe the commercial jets' main electrical buses are 3-phase 110/200 volt 400Hz AC, created by the starter-generators on the turbines. It's relatively straightforward to tap across two of the terminals and get 110VAC, but it'll be at 400Hz, meaning not everything designed for 110VAC/60Hz will be able to handle it.

(Also, some older private aircraft, such as mine, use a 12VDC standard.)

Re: The difficulties of providing 110-volt power to your airline seat

#68

Post by gaius »

varjag wrote: post #65
paol wrote: post #52

Earlier quoted context omitted.

Yes and no. The 747 is still in production and has been revised many times since. A 747 bought today will have relatively little in common with one bought in 1970.

It is still roughly the same energy requirements to lift one in the air and keep it there. Electricity intake is a tiny part of that. Yes there was no in-flight entertainment in mid-60s, but avionics back then were still to a great extent valve-based and consumed gobs of power.

It's not just the power - it's the weight of the transformer, inverter, etc.

Re: The difficulties of providing 110-volt power to your airline seat

#69

Post by pavel_lishin »

nostrademons wrote: post #30
evgen wrote: post #26

Earlier quoted context omitted.

It is all about costs. Those engines are producing energy to keep the plane flying at 500mph. If you pull some power to spin an alternator then you need to run the engines faster and burn more fuel (which means you need even more fuel on board at takeoff to lug all of this extra fuel to the destination.) Add in the weight of the various inverters and equipment necessary to make this system safe on an airplane and I a…

Some math: 120V * 2A = 240W * 300 passengers = 72 kW. That's 1/50th of a percent of the existing power output of a 747. If you figure a $600 plane ticket, I'd gladly pay 1/50th of a percent ($0.30) of that for electrical power on the flight. The numbers get a bit more complicated when you figure in the weight for transformers, alternators, inverters, etc. But fuel is not a major component of this. The math really doe…

Sure. But don't forget that adding a new feature to an airplane is going to take work. People have to figure out how all of this works, then other people have to test it, other people have to make sure it passes safety inspections, etc., etc., etc. Plus, then you have to retrofit old planes - or build new ones.

It's more than just fuel costs.

Re: The difficulties of providing 110-volt power to your airline seat

#70

Post by quellhorst »

orborde wrote: post #66
quellhorst wrote: post #43

Since every laptop has a battery, you could do "rolling blackouts". The laptop doesn't need power the whole flight. I know from going to conferences sometimes just plugging in once in the middle of the day allowed me to make it without being plugged in for the rest of the day.

You might have failed to consider conservation of energy here. The laptops use a steady amount of energy whether plugged in or not (more or less), and if they're unplugged for a while, then they'll draw more power during the time they are plugged in as they recharge their batteries. In fact, if the batteries are not perfectly efficient and thus don't provide the same energy that was used to charge them, you're now us…

Actually, in OS X my laptop will use less power when on battery power. The clock speed goes down, the display dims, the hard drive goes to sleep faster, the display adapter switches to the less powerful one.
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