Friday, August 31, 2007

Led Zeppelin

I have typically not been alarmed by the prospects of oil running out. Europe has shown that railroads can work, so personally I couldn't care less if driving a car becomes 10x more expensive. The only issue is --- I really want my airtravel. And I'm sure most researchers, living the conference life, will agree.

Now, I have always assumed that balloons will provide a solution. Sure, we'll take it slower, and spend more time in the air (never mind those students), but we'll continue to get there. Unfortunately, it seems I was wrong...

Zeppelin NT (Neue Technologie) seems to be the most efficient commercially available "balloon" today. It is a semi-rigid design, german-engineered to optimize fuel-efficiency and speed. It can:

  • carry about 6 passengers in addition to 1 pilot, if you want to go up to 2000m~6600ft (which you do, because there are mountains on most interesting routes).

  • cruise at 80 km/h ~ 50mph, relative to the wind
To understand that this thing is really built with great care, consider that it costs about $7M a piece (around 100x more than the highend blimps on American skies).

Now, let's say you want to travel BOS->SFO to collaborate with the Berkeley people.
  • the distance is 4339 km
  • ... which takes you 54 hours (which has the positive effect that you're actually going to read their papers before asking them questions). NB: this assumes no wind, so you may able to do slightly better by finding a nice altitude with good wind.

  • according to these technical specifications, the thing needs 60 kg of gas/hour at cruising speed, plus 50kg for takeoff and landing, so you spend 3304 kgs of gas.
  • with gasoline density 737.22 kg/m3 this is 4481 liters ~ 1184 gallons.
  • at current gas prices of $2.7/gallon, the trip costs $3197
  • ... that is, $533 USD / person. Of course, I am ignoring the cost of the pilot, investment in the zeppelin, airport taxes etc --- which for current airlines are more than half of the cost.
Economy of scale. Of course, this calculation is missing the economy of scale. Right now we don't have huge zeppelins because nobody will pay to build them. But what if we did? Well, the useful load grows proportional to volume, i.e. like the cube of the radius. On the other hand, the drag force (which is what the engines are fighting) grows like the area, i.e. like the square of the radius. So this is sublinear growth!

For instance, if we carry 27 times more people, the price per person will drop by roughly 3 (yes, yes, I'm ignoring the pilot). Note that 162 passengers is really a lot for a BOS->SFO flight today; US airlines learned that US travellers are very spoiled, and the recipe for success is frequent small flights.

In any case, this means you should pay on the order of $178 USD / person. That is not bad, but it's about what you're paying today for a regular airline, with sevices included. This means the zeppelin is not actually saving gas, and has the same oil bottleneck.

Seems like there no Stairway to Heaven, and we might have to sell our soul.


Anonymous said...

Maybe you'll just need to wait for Zeppelin XP.

Anonymous said...

Wouldn't it be ironic (in the Alanis sense) if the most energy-efficient way to get from New York to Delhi was via hypersonic sub-orbital scramjet?

But after you've built Transdichotomous Industries, LTD, into a global empire, maybe you'll take the time to sit back, relax, and enjoy a quiet Kefir as you travel in the luxury of your own private aeroscraft.

-Ken Clarkson