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When will a diesel be available for my aircraft? |
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News, facts, and comments on the coming revolution for piston-engine aircraft.
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News of September 15, 2011A fanjet airplane will never be effective when flying low or slow. Yet, with future energy costs, that is how many future airplanes may have to fly.If a 5,000 HP diesel engine can burn no more than 0.22 Lbs of fuel per HP-h, while weighing no more than 0.18 kg. /HP dry, it will trigger new concepts for air travel and cargo in 2050. Our panelists say it can be done. DieselAir engages research here on a Special Report. Are you working on an innovative diesel concept which could reach such performance? Now read this. What follows here is public information. Conclusions we made are our own. Fact: According to UN, world population will stabilize around 11 - 12 billion people by 2100. Until then, we know that the price per kWh of any kind of energy, whether mineral, renewable, nuclear, syn-organic, or bio-organic, computed in hours of average salary, will go way up, same as the price of virtually all commodities. And I mean way up. Fact: A Boeing, Airbus, Bombardier, or Embraer airliner is based on an aircraft concept originating in the late 40’s: Swept-wing, all-metal jet plane, flying above the weather, fast enough to cross the Atlantic non-stop in a few hours. It was far more productive in terms of passenger-miles per year than a DC7C, the most advanced piston-engined airliner of the fifties. Fuel efficiency was a factor only insofar as it affected range and payload, as always in aircraft technology. Petroleum availability was not an issue. Emissions and noise control were minor issues. Fact: The ancestor of this concept is the Boeing 707, first truly successful jet airliner, origin of a large family of airplane models, of the Airbus family sticking to the same concept, and then some others. In 1954 when the 707 prototype first flew, gold price was $35 an ounce and petroleum was $1 a barrel. Now the figures are $2,000 and $80. Average salaries followed, of course, until the 90’s. That’s over now. And the real crisis is only beginning… By 1960, the turbojet engine was the obvious future: It is very efficient at stabilized, high altitude cruise speed. It is a gas-guzzler in-between, during transitional phases of taxiing, take off, climb, hold, descent and approach, land, which meant one had to use IT, Navaids and good management to minimize these phases in the leg. And the longer the leg, the less they mattered. Since the fifties, IT and Navaids made momentous progress. Hub airports were favored to take advantage of jumbo jets flying legs of up to 15 hours today, packed with low-fare passengers complaining about clogged lavatories after 10 hours… Fact: The efficiency of the turbojet itself also made progress: A 1944 Junkers Jumo 004B turbojet equipping a Messerschmitt 262 fighter jet had a specific fuel consumption when cruising (never for very long) of 1.6 kg per kg of thrust and per hour, with a TBO of 20 hours if the pilot was lucky. Now a CFM turbofan and its state of the art competitors achieve 0.35 kg. And the next generation might do 8 to 12% less. The jet airliner concept triggered, from the sixties onwards, an explosion of air transportation not only for passengers but also for air cargo. Cost per passenger-mile and per tonne-mile has been going regularly down from the Douglas DC3 of 1935 to the Airbus 380 and Boeing 787 of today. It looked as if it might go on for ever… Well, this is not true anymore. The whole industry engaged in designing the airliners for the 2040-2090 era, their engines and components, are questioning the concept because the turbojet cannot be efficient when flying low or slow, whereas absolute energy need per tonne-mile is always lower at low speeds. I say energy need, not fuel consumption. The most effective motor gliders, with glide slopes of 40, cruise around 120-140 Kts. See example at http://www.skykingsoaring.com/motorglider.html. If you seek even lower energy needs, look at the Solar Impulse weighing 1.6 tonne which cruises – very slow - with photovoltaic-generated 40 HP, see http://www.solarimpulse.com/. The most obvious reasons are oil and gas prices and availability; energy costs escalation in general; environment concerns, among others CO2 emissions; and a world crisis affecting the whole world’s purchasing power. But IT and Internet are another, as they make fast business travel less necessary. Changes in life style are another: Why go through the stress and discomfort of commuting to crowded airports, going through 2-hour security checks, being packed for hours in narrow seats, fighting to get your luggage, and again commuting, etc., when on top of that airline fares will go way up? Couldn’t one at least go non-stop to final destination, even if in a smaller, slower but roomier plane, since more and more smaller airports get equipped to host at least the commuters of today? As for air cargo, it uses Boeing 777 and Airbus A330 and the like because they happen to be available. Nobody said that parcels had to fly as fast as 400 knots if it is no more economical? What about the propeller? When the fantastically successful Lockheed C130 Hercules military cargo first took off in 1954 (yes, same as the 707), its design team would never have anticipated that, 60 years later, the new Airbus A400M of similar mission would look like a bigger Hercules, still with 4 propellers, but more efficient ones of course, giving it a top speed of 375 knots. The propeller is alive and kicking. So is it time to consider a new concept? What could it be? There may be one: A diesel-equipped airplane, if the diesel could be at least as efficient as a turbofan at cruise speed, and of comparable weight per power. The obvious advantage of a diesel, if it was efficient enough at cruise speed, results of its constant specific consumption at any speed and during all transitions, which means that when flying slow, therefore using a low power setting, the fuel consumption stays practically in proportion of the actual power consumed, therefore drops to extremely low figures when the plane flies close to best range speed, typically 1.5 times stalling speed. So that minimal energy need does translate into minimal fuel per mile. A cargo plane could be a large, unmanned moto-glider tracking a route negotiated in real time between a GPS and a weather report to get to destination at lowest cost per mile instead of at imposed speed and time of arrival, while taking advantage of best meteo conditions (tail wind, soaring…) It wouldn’t do for a passenger plane, but one could simply imagine larger, roomier but slower planes flying above the weather during cruise, same as a jet, but capable of very economical flights when the same optimizing system would navigate during transitions. Now let’s benchmark: The turbofan of a state of the art 2011 airliner, assuming a cruising speed of 430 knots (800 km/h), is consuming around 120 grams (0.26 Lbs) of fuel per HP-hour. A heavy marine diesel 2-stroke of some 20,000 to 100,000 HP (MAN or Wartsila-Sulzer) also achieves 120 grams. But its very high weight per HP makes it suitable only for stationery or marine applications. An aero diesel piston-engine, such as the ones on the market or close to (Centurion-Thielert, SMA, Austro, DeltaHawk…), achieves around 155-160 grams per HP-hour. But the turbofan hasn’t said its last word. The coming P&W1100G (Geared Fan) or the GEC-Safran Leap X might reach around 105-110 grams… These are abstracts from a more detailed benchmarking spreadsheet prepared by our panel of experts. They estimate that a totally innovative diesel concept of around 5,000 HP, promising a Specific Fuel Consumption (SFC) of 100 grams (0.22 Lbs.) per HP-hour for a dry weight of 0.18kgs/HP, is possible, and would allow a breakthrough in terms of average fuel cost per tonne-mile, for a lower capital cost than the turbofan. Of course advantages would be more obvious on short and midrange applications, beginning with commuters. We do not foresee that the turbofan would disappear, but that it would specialize in long range, mass transportation between hubs, for passengers willing to pay the rate. Do you know of a diesel project promising to meet such specs? Better, are you working on one? If you do, alert me at atc@dieselair.com and expect a quick answer. I will send our panelists’ benchmarking spreadsheet to any subscriber requesting it. And we will publish your story. Andre Teissier-duCros, Publisher posted at 7:01 AM |
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