Friday, March 25, 2011

Fuelish Comparison

There was an article a while back on the wonderful site Low-Tech Magazine that stated that only recently have jet airliners achieved fuel efficiencies comparable to the highly developed piston engine powered airliners of the 1950s. Examining the evidence this appears to be true,strictly speaking, but there are so many other considerations that any real operational comparisons are essentially meaningless.

The 50s airliner directly compared was the wonderful, and thoroughly beautiful, Lockheed Constellation. This needle-like beauty was the utter apotheosis of gasoline-fueled piston engined passenger aircraft. I'm old enough to have actually flown in one as a child and am grateful for the experience and as a now card-carrying old fart I am ever appreciative of the technology of simpler times. The Constellation was a technological tour de force for its time with a super sleek airframe, a quirky triple-finned tail, and was one of the first to offer non-stop service between the coasts. Its four engines were 18 cylinder Wrights producing over 3200 horsepower each which provided a cruise speed of a bit over 300 mph at 22,000 feet. It carried from 65 to about 100 passengers. It was the height of speed and luxury just before the dawn of the jet age.

The original jetliners in commercial service were huge leaps in performance and carrying capacity albeit at the cost of higher seat-mile fuel usage. Obviously fuel usage was a less important factor 60 years ago due to the much lower costs but there are a number of very important differences to remember. Firstly piston-engined airliners of the age used expensive high octane aviation gasoline as opposed to the far less costly kerosene based fuel used by jet aircraft. Jet fuel has several more advantages to consider. Kerosene based jet fuel contains significantly more energy per gallon compared to gasoline and it has a much higher resistance to vaporization at high altitudes. This both allowed transcontinental ranges, despite the greater amounts needed, for jetliners and abetted their ability to cruise at much higher altitudes. Cruising at such high altitudes greatly enhanced the ability of jetliners to attain ground speeds of some 200 mph greater than piston airliners which shortened trip times dramatically and also conferred the ability to fly over bad weather that piston airliners had to fly around.

Interestingly if jetliners were forced to cruise at altitudes similar to that of 50s era passenger airliners their speeds would not be much greater and their seat/mile fuel usage would be significantly worse. The ability to cruise in the thin air at 35,000 feet and above confers much, if not all, of the jetliners superiority performance-wise. Add to that fact the subsequent 50 plus years of jet turbine technological development and it's hardly a surprise that fuel-efficiency, in any measurable metric, is now the equal of such as the Constellation if not somewhat better. Throw in the same 50 years worth of development in the areas of aerodynamics and lightweight structural design and the jetliner's advantages become completely insurmountable.

Also noteworthy is the fact the huge turbo-compound multi-row radial piston engines of the pre-jet era were exceedingly complex devices requiring significantly more maintenance hours than modern turbofan jetliner powerplants. Modern jet engines are horrifically expensive to manufacture but their maintenance complexity is far less than commonly assumed.

Not to be ignored in the equation is that jetliners routinely carry multiples of the number of possible passengers on 50s airliners thus requiring far less time, and fewer aircraft, to deliver a given number of passengers to their destinations. Many small regional airliners routinely carry as many passengers as could embark on the Constellation and the comparisons become entirely absurd when considering the capacities of such behemoths as the massive Boeing 747 and the even larger Airbus 380. Another not inconsequential factor is that average ticket prices are now lower in actual dollar terms than in the 1950s and of course wildly cheaper when factoring in inflation. Longings for a bygone era of romantic air travel notwithstanding the advantages of the modern jetliner are so overwhelming that no possible prodigies of technological development could remotely result in even the highest tech version of a gasoline fueled piston powered aircraft matching a jet's performance and utility.

Theoretically I suppose it might be possible to design and build a kerosene (diesel) powered propeller driven airliner that could compete favorable with jetliners on seat/mile fuel usage but they would still fall well short in every other performance and utility metric. Plus the chances that any aircraft company would devote the billions in development money needed for such an enterprise are precisely zero. Modern jetliners exhibit such fantastically high levels of cost efficiency now that not even the most fanatical technological retro-grouch, such as me for instance, can deny the immense advantages modern jetliner travel. The sundry annoyances of modern air travel may frustrate millions but the technology of the aircraft themselves is not any sort of issue.


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