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Impact of air transport of Roadster gliders

Discussion in 'Roadster' started by bolosky, Dec 30, 2010.

  1. bolosky

    bolosky Member

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    Back when I was waiting for my Roadster to arrive and I had more time to think (due to spending no time driving it), I worked out a rough cut at the amount of fuel that is used in moving the gliders by plane from London to SJC. This is a very loose estimate, so at best you should trust only the order of magnitude. In addition, I had to make a number of assumptions. I tried to make them in a way that overstated the impact of the trip, so I'll wind up with more of an upper bound than a correct result. In particular, I assumed that the plane makes the trip with a full fuel load, which is almost certainly not true since it's not all that close to its max range. I also assumed that flying the plane to its max range results in burning all of its fuel, which is wrong because there is always a pretty ample fuel reserve. I also assumed that the plane capcity would have been used if the Roadster hadn't taken it up. I used Wikipedia for my information source, with all of its attendant hazards. With those caveats, here is my math:

    A Roadster weighs 2700 lbs, of which 900 lbs is the battery. If the rest of the powertrain is only 100 lbs (I'm sure it's more, since the motor alone is this heavy, not to mention the tranny and PEM), then the glider is 1700 lbs.

    A 747-400 has max gross weight of 875 k lbs, of which 390 k lbs (= 220 k L max fuel capacity x 0.82 kg / L kerosene * 2.2 kg /lb) is fuel, and 394 k lbs is the empty weight of the plane, leaving a cargo capacity of 91 K lbs. Therefore, a Roadster glider is a little less than 2% of the capacity of a 747-400. The plane's max range is 7300 nm (nautical miles, not nanometers :)), so if it uses all 220 k L of fuel it consumes about 30 L / nm. London to SJC is about 4700 nm, so the trip takes 141 k L of fuel. 2% of that is 2800 L, or about 800 gal of gasoline. A 30 mpg car would go 24,000 miles on that amount of fuel (assuming that jet A/kerosene and gasoline are equivalent).

    So, even with my over estimations and giving gasoline cars credit for completely free transport, after a couple of years of driving the Roadster, you've make up for the plane flight.
     
  2. tennis_trs

    tennis_trs 2010 2.0 Roadster Sport

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    It doesn't affect the final result but I believe (typo)
    should instead be
     
  3. bolosky

    bolosky Member

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    Yes, that was a typo, but I did the arithmetic right, so it doesn't affect the result.

    It's also worth saying that in my case I was driving an RX-8 that got maybe 16MPG about 15,000 miles per year, so my breakeven point was 10 months, not 2 years.
     
  4. Tdave

    Tdave Member

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    I think your 2% figure is way off. It is a percentage of the cargo capacity, right? Since the fuel is used to transport the plane's empty weight (and the fuel itself), as well as its cargo, you need to figure your percentage relative to the gross weight, not the cargo weight. That means your final calculation is off by quite a bit. How much? Let's figure out the gross weight transported by that fuel usage...

    That trip is 64% of its range, so it needs 251 k lbs of fuel for the trip. If it's half full of cargo, that means the take off weight is 691 k lbs, and it lands at 440 k lbs, or an average weight of 565 k lbs during the trip. The Tesla, at 1500 lbs (*see below), is therefore 0.27% of the weight of the plane, not 2%.

    That puts the gals used for the Tesla transportation at 99 gals, not 800.

    Am I right on this point? It's pretty significant.

    (*) The battery pack weighs 990 pounds by itself, not 900. I'm pretty sure the glider is more like 1500 pounds, at most.
     
  5. tennis_trs

    tennis_trs 2010 2.0 Roadster Sport

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    I had initially thought along the same lines, but I decided that I thought bolosky's way is essentially right: transporting the cargo is the reason the trip happens at all, transporting the rest of the plane and fuel is overhead and the overhead "costs" should be shared against the cargo.

    Did a thread somewhere say that some gliders were sent in the cargo area of passenger planes? I assume then that passengers pay a significantly larger portion than just the weight they add to the plane, which would also make bolosky's upper estimate higher relative to the actual.
     
  6. PeterW

    PeterW Member

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    I am confused regarding the whole plane discussion(which may belong in a different thread). Are we talking about the environmental impact of transporting a glider by plane? Or are we talking about the cost in dollars?

    If we are talking about the environmental cost then the answer is the extra amount of fuel used because of the weight of the glider. If the gliders were transported on a cargo plane and the entire load of the plane was Tesla Roadster gliders; then the cost of one glider would be the quantity of fuel used for the trip divided by the number of gliders transported. If half of the cargo were Tesla Roadster gliders(by weight) then it would follow to take half of the fuel used and divide it by the number of gliders.

    The question is; does it get to a point where you can say “This plane was taking off with or without the gliders.”?

    If you can say that then one could argue that the fuel cost should be worked out in relation to the weight of the entire plane. In essence the difference between the amount of fuel used if the gliders were not on board, and amount of fuel used if the gliders were on board.
     
  7. bolosky

    bolosky Member

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    I did roughly what you describe in the first paragraph, and I explicitly said that I was assuming that the cargo space would be used for something if the glider wasn't transported. If you're willing to assume that it would be otherwise empty, then you'd come up with a much lower number, because there's a whole lot of overhead that doesn't depend on the weight. That is, the marginal cost of an extra 1700 lbs is a lot lower than the cost of the flight times the percentage of the cargo capacity that a glider occupies.
     
  8. dsm363

    dsm363 Roadster + Sig Model S

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    I believe Tesla piggy-backs on a cargo plane that is already flying to the US to they don't hire a plane just to transport a few gliders which would be a waste. So basically, if I have this correct, the plane was going to fly with or without the Roadsters on it.
     
  9. vfx

    vfx Well-Known Member

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    This whole thing just seems ridiculous. A car is not a vegetable.
    Name a car that all the raw materials and parts are made within a 400 mile radius.

    Now say that magical car company wanted to stay in business. The car would have to ship by some means since no one would want a new car that has driven across country. Even an EV.

    If the argument is plane VS ship you would have to calculate every raw material and every single part origin Dust to Dealer.

    Someone did that with the Prius once to mock it's green cred.
     
  10. dsm363

    dsm363 Roadster + Sig Model S

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    I was at a restaurant the other day and while I was away from the table, the waiter mentioned to my friends (who were talking about the Roadster) that it's like the Prius and more polluting than an SUV. Gotta love the misinformation sometimes.
     
  11. strider

    strider Active Member

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