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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.News of January 18, 2008What Happened to the Piston Twin? Asks Richard Collins (Flying Magazine, 2/08)We recommend this paper which explains very well why, in 1979, US sales of twins reached an all-time high of 3,000 throughout 31 different models, and a single engine airplane owner considered as a natural, if expensive, step up trading his plane for a twin; whereas today Piper (Seneca, Seminole) and Beech (Baron) are selling a few twins a year practically on special order. Reasons: Natural upgrade from a piston single now is a single turboprop, whereas a Cirrus SR22 or a Lancair fly almost as fast as a conventional twin and has a fixed landing gear; insurance rates were favorable to twins in the past because of perceived safety, and the opposite is true today because singles are much safer than they were. So, is this the end of the twin? We think that, on the contrary, aero diesel engines will open a new market niche for twins supplementing the classy single turboprops; and that the niche will become a big market within 20 years. Collins does notice that the Diamond DA42 diesel is hitting the market. It is the thin end of the wedge. You probably noticed that the most popular single turboprops are big planes such as the TBM 700-850 and the Pilatus PC-12. The Piper Meridian is smaller, but still offers 1,000HP+. And the price tag is very high too, beginning just under $ 2 million. This is because a really small turboprop, such as the Maule MX7-420HP, so powerful that it can almost hang on its propeller like a helicopter (now wait! I said ‘almost’…), is such a gas guzzler that its range at any speed with full reserves is very limited. All these planes suffer of a very high fuel flow at all speeds, meaning a strict flight plan and a swift change to alternates if the weather goes wrong. Which is no problem for a Pilatus, big enough to carry extra fuel; and for its owner, with a pocket deep enough to cover fuel, maintenance and depreciation costs. Turbines have two faults: Because they operate at very high RPM, very high pressures and temperatures, they are inherently costly to manufacture (precision forgings or investment casting with complex alloys, ceramics coatings, composites, ultra-high precision machining, the works.). Look at the Maule turboprop, priced about three times its equivalent with an O-540. Because their combustion is optimized at one airflow speed and power, any divergence from that speed means that the specific fuel consumption goes through the ceiling. What is wonderful with a piston engine is that the piston in high position ‘waits’ for the combustion to complete. With a diesel, even better: injected fuel is always proportional to actual power needed, so the specific consumption is close to constant. Assessing costs in 2008 dollars, but with turbo-diesel engines produced in quantities and in optimal cost conditions, we envision twins with 300-500HP engines, 6 or 8 cylinders, flying at 240 to 280 knots at FL 220-250; priced around $1 to 1.5 million depending on power and weight. They would offer as much room as a single turboprop, much lower fuel costs, and a much, much longer range. posted by Deena at 4:47 AM |
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