Getting down to earth

(NB:  This post was almost titled "On Bullshit", but I thought the better of it.)

Over at Futurepundit, a commenter quotes a 1979 Mother Earth News article about a home-built hybrid car.  This article is, unfortunately, typical for the publication:  short on firm data and long on claims, some of them dubious.

The blogosphere and society in general are full of people making unsupported claims and questionable statements.  Picking them apart is a good hobby; it dulls the superficial attractiveness of the nonsense and sharpens the mind.  A few examples will suffice to illustrate.

According to David, the Opel has not only a virtually unlimited range (when driven prudently), but also a top speed of 90 miles per hour . . . and emits a minimum of pollutants as it tools along the highway.[Emphasis added.]

It did?  How did they know that it was so clean?  Did they measure it?  Put it on a chassis dynamometer with an exhaust analyzer?  What are the chances of that?

Lawnmower engines of the day were bad polluters even by old standards.  They were air-cooled (with consequent loose tolerances), had no pollution controls and often ran well rich.  A 1979 car would have had an early catalytic converter system, perhaps with air injection; the lawnmower engine had none of these things.  By 1982, cars were running closed-loop mixture controls to make the catalysts work better.  The one advantage the lawnmower engine would have is that it could run at constant speed.

... the engineer installed four 12-volt, heavy-duty automobile batteries-in series-which are "fed" by a 100-amp generator that's run off a 5-horsepower lawn-mower engine.

He's certainly not producing 100 A @ 48 volts (4.8 kW) with a 5 HP (3730 W) engine.

Nor was the builder cruising at even a continuous 55 MPH on a mere 5 HP.  I'd believe that "prudently" meant 40-45, not the 50 claimed.  If a typical car requires ~20 HP to cruise at 60 MPH and drag scales as speed squared (meaning power scales as speed cubed), the ~4 HP available through the engine, generator and motor would deliver enough power for about 35 MPH; a small car like an Opel would get a bit more out of it.  That's plenty for around town, but forget cruising the Interstates.

Hot or traveling in a very mountainous area-could, however, tax the car's charging system . . . but even these demands don't pose much of a problem, because the batteries can be brought from a 1/4 charge (the effective "dead" state, with a built-in safety factor) to a full charge in only 15 minutes.

The author states that battery can be charged from 25% to 100% in 15 minutes using less than 4 kW.  This means the storage is 1.3 kWh at most, which is quite a bit less than the Prius carries.  You're not going to get much range on that; any driving on Interstates better be between closely-spaced exits.  (An alternate explanation is that the claim was erroneous or the builder was mis-quoted.)

How many people bought the plans for the hybrid conversion and expected "miracle carburetor" results?  How many built it and were disappointed?  I don't know, but my money is on the square marked "most".

My point here is to show that the Mother Earth News is not a technical journal, and its breathless praise should not be mistaken for honest and critical analysis.  Neither should most of what's found on the blogosphere or the media at large, unless you can confirm the claims and repeat the calculations... and that goes for The Ergosphere as well.  ¶ 5/24/2005 11:19:00 PM