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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 September 04, 2008In 2008, four major events are causing a shock in the aero diesel market – DieselAir special review, Chapter 2: The Engineering Arena.
 Scroll down and see Chapter 1 dated July 9. Aero-News says (7/28/08): The 170 hp AE 300 engine incorporates a number of key advancements over the Thielert engine, including an improved gearbox with a torsional vibration damper instead of a friction clutch, designed to offer gearbox life of 2,400 hours. A new, four-point engine mount is also featured, as is an improved turbocharger and a FADEC-controlled, but otherwise conventional engine governor. The Austro engine also sports an integral oil/ coolant heat exchanger, eliminating external oil lines and the need for an external oil cooler. This leaves open some questions: One is we still do not know the weight incidence on a DA 42 of replacing the Thielert 2 Liter by the Austro. But more generally how will an engine rated at 85HP per Liter of Cubic Capacity behave in terms of wear and tear? Keep in mind that a conventional Avgas engine such as Lycoming or Continental is rated around 30-35HP per Liter, and an SMA diesel, at 50HP per Liter. Now, a power close to 100HP per Liter is nothing exceptional in itself. In the fifties, for instance, an Alfa-Romeo Alfetta Formula One 1.5 Liter, supercharged, was delivering 300HP per Liter! But it was expected to last only a few hours. Today, many European and Japanese automobiles have diesel engines rated between 70 and 90 HP/Liter, and they easily exceed 100,000 miles, corresponding to a TBR of well over 3,000 hours. But they do not drive at a constant speed of 125 mph, at which their full power is needed. The two key differences between an airplane engine and an automobile engine are: First, when you are flying in IMC on your way to an alternate, you cannot stop on the safety lane to open the hood and check what is wrong with your engine and then wait for Triple-A service. Second, an aero engine must be light. To make it lighter, you remove metal volume, and refrigerant volume meaning accordingly circulating oil or water. The lighter it is, the more vulnerable it becomes to thermal shocks, and each of these shocks increases the wear and tear. Adding fifty pounds of weight to an auto engine is not that bad, even though it comes to sense that the life expectancy of a 5 Liter V8 is higher than the one of a 4 cylinder 750cc engine. But to an aero engine, less weight is critical. So far, the Thielert saga has proven the point of the old timers saying that you can’t beat cubic inches when it comes to reliability. Does it mean that they are right? Not necessarily. If your engine is using state of the art technology for alloys and even more for surface treatments, the fact is that the reliability has incredibly increased compared with the 40s and 50s when your Lycoming and Continental were state of the art, and that the experts in these technologies are in Europe. It made sense to expect that the most sophisticated European R&Ds in automobile engine knew how to make a small aero engine that would last longer than expected, whether diesel or gasoline. Thielert comes from the race car engine profession. The SMA team originated with Renault Sports who was designing the famous Renault V10 Formula One engine. Mark Wilksch, founder of Wilksch Airmotive, came from the famous Cosworth team. These three firms, coming from same background, opted for three different solutions: In-line, water cooled, 4 cylinder, 4 stroke, high rpm geared engine, high power per Liter (Thielert, Austro); Opposite piston, air cooled, 4 stroke, no gear, medium power per Liter (SMA); V design, 2 stroke, no gear, medium power (Wilksch). And we can assume they had access to the same know how in terms of alloys, surface treatments, techniques for vibration control, for fuel injection, heat exchange, exhaust design, etc. Why did they disagree on design? And who is right? I have one explanation: Any engineer in automobile engine design owns a car, drives around, maintains it, pays for it, and tinkers with it. Very few of these same engineers own and operate an airplane and live in everyday life how dramatic must be, on any aircraft cruising close to full power, the zero defect, zero incident, trouble-free factor, down to the most modest hose, seal, connector, bearing, and bolt. Therefore these Europeans, lacking that background, began trying different solutions, each one in his neck of the woods. Who is right? Time will tell, but it looks like LSA diesel engines of 100-120HP will be 2 stroke, that so far Thielert has caused a setback to the high rpm in-line geared engine, that Austro has not yet clearly explained why they will do radically better than Thielert, and that SMA, as of now the only FAA certified and world certified engine that seems to run trouble free, does not have yet enough engines actually flying to take advantage of the situation. posted at 9:52 PM |
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