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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 coul

by olympus 13y ago

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.

smoyer 13y ago
"And that includes the 660-pound weight penalty of installing the system on an airplane."
- fishtoaster 13y ago
  The context makes it sound like they included the extra weight in fuel calculations, but it's not clear whether they included overall weight capacity. As the parent points out, this probably isn't worth it if they have to cut a row of paying passengers to do it.
  - mikeash 13y ago
    Just carry a bit less cargo. I don't think passenger airplanes are typically limited by weight, but rather volume, when it comes to the number of passengers.
  - olympus 13y ago
    Guessing that an A320 carries about 150 passengers, losing 3-4 of them would still make this worth it, and if they weren't flying 100% full in the first place the lost seats don't cost them anything. It's a neat idea, seems like a relatively safe mod and a way to catch some low hanging fruit. smoyer, thanks for catching the weight. Seems like I have gotten a little too "efficient" with my reading.
  - jmharvey 13y ago
    An A320 burns about a half pound of fuel per second when taxiing. [1] So it seems plausible that the amount of weight you save on fuel could go a significant part of the way toward offsetting the weight penalty from carrying the extra motors. I suppose if you're pushing the envelope precisely, and push back overweight, count on the taxi burn to get you down to max take-off weight, and plan to land with the legal minimum fuel reserve, then yeah, you'd still pay the full weight penalty. But I'm guessing that most airlines, as a policy, anticipate a range of possible taxi times in calculating their weight and fuel budgets, so significant weight savings should be realized. [1] http://www.mit.edu/~hamsa/pubs/KhadilkarBalakrishnanGNC2011.pdf http://www.mit.edu/~hamsa/pubs/KhadilkarBalakrishnanGNC2011....
- WalterBright 13y ago
  Airframe companies know exactly what a pound of extra weight on an airliner is worth. It's large, well into the 6 figures. 660 pounds needs a lot of fuel savings to make up for it. Remember, it takes extra fuel to hold that 660 lbs up in the air. I'm sure this has all been carefully costed out.
  - apendleton 13y ago
    The article says a 4% savings per year, after accounting for the additional weight of the motors. So yes, already thought out.

by olympus 13y ago

smoyer 13y ago

"And that includes the 660-pound weight penalty of installing the system on an airplane."

fishtoaster 13y ago
The context makes it sound like they included the extra weight in fuel calculations, but it's not clear whether they included overall weight capacity. As the parent points out, this probably isn't worth it if they have to cut a row of paying passengers to do it.
- mikeash 13y ago
  Just carry a bit less cargo. I don't think passenger airplanes are typically limited by weight, but rather volume, when it comes to the number of passengers.
- olympus 13y ago
  Guessing that an A320 carries about 150 passengers, losing 3-4 of them would still make this worth it, and if they weren't flying 100% full in the first place the lost seats don't cost them anything. It's a neat idea, seems like a relatively safe mod and a way to catch some low hanging fruit. smoyer, thanks for catching the weight. Seems like I have gotten a little too "efficient" with my reading.
- jmharvey 13y ago
  An A320 burns about a half pound of fuel per second when taxiing. [1] So it seems plausible that the amount of weight you save on fuel could go a significant part of the way toward offsetting the weight penalty from carrying the extra motors. I suppose if you're pushing the envelope precisely, and push back overweight, count on the taxi burn to get you down to max take-off weight, and plan to land with the legal minimum fuel reserve, then yeah, you'd still pay the full weight penalty. But I'm guessing that most airlines, as a policy, anticipate a range of possible taxi times in calculating their weight and fuel budgets, so significant weight savings should be realized. [1] http://www.mit.edu/~hamsa/pubs/KhadilkarBalakrishnanGNC2011.pdf http://www.mit.edu/~hamsa/pubs/KhadilkarBalakrishnanGNC2011....
WalterBright 13y ago
Airframe companies know exactly what a pound of extra weight on an airliner is worth. It's large, well into the 6 figures. 660 pounds needs a lot of fuel savings to make up for it. Remember, it takes extra fuel to hold that 660 lbs up in the air. I'm sure this has all been carefully costed out.
- apendleton 13y ago
  The article says a 4% savings per year, after accounting for the additional weight of the motors. So yes, already thought out.