Hans D. Baumeister

Hans D. Baumeister

End of quality Journalism at Scientific American?

Wow, have a look at this article by Scientific American regarding advancement in electric-powered aircraft.

I held SciAm in quite high regard as to their journalistic quality, so I hope this is a one-off.

A couple of comments:

1) The picture in the sidebar doesn’t show an “unmanned aerial vehicle” but rather a two-seater, electric sailplane with both seats filled. These are actually becoming halfway common at airshows in Germany.

2) The article indicates that the term “passenger miles per gallon” means that it is “the fuel efficiency divided by the number of passengers.” Far from it - fuel efficiency is measured in miles per gallon, so passenger miles per gallon would be fuel efficiency multiplied by the number of passengers. Ya don’t even need 12th grade math to understand that…

3) the article furthermore describes the use of electric engines as a possible alternative to using the jets to provide the propulsion for taxiing while on the ground. A comparison is made between a jet airliner using “5 megawatts of energy” as compared to an electric drive system that only uses 2 (yep - TWO!) kilowatts.

Folks, my minivan needs 85kW to accelerate its 3,000+ lbs halfway decently (faster than a tractor)… you’re trying to tell me that a 2 kW motor would be able to move an Airbus 320 at ANY speed down the taxiway? An Airbus A320 weighs in at a peak start weight of 78 metric tons!

Its beside the fact that fitting any sort of drive system to wheels that spend their time either supporting those 78 tons or residing in an unheated compartment at up to -50°C, with occasional blasts of fun while taking massive impact force during landing. Probably not an environment you want to be installing somewhat sensitive drivetrain components in.

Also, to take the same A320 as a reference: it burns 2,700kg of fuel per hour at full blast. The fuel, Jet-A, is nearly identical to Diesel fuel, so we can take that to calculate energy content. Diesel contains about 43 MJ of usable energy per kg. One kW-hour = 3,6 · 106 Joule, so per kg, Diesel would then contain about 12 kW-hours per kg.
The burn rate is then 32.400 kW during full travel speed (probably 80% of full thrust?).

Where on earth did the 5 Megawatts come from? That is the power generated by the first civil-use nuclear power plant in Obinsk (1954) at peak output!

Unfortunately, one has to be a registered member of ScientificAmerican.com to leave a comment (which is probably the reason there are - to date - only two comments, and both completely irrelevant to the article).

Subsequently, I’ve been forced to put this in my blog and tweet it to the world.
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