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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 20, 2005Highlights of dialogue exchanged on our Forum:The initial question comes from Randy, one of the DieselAir Newsletter Staff. Diesel engines have the reputation of being heavy per HP. So far this has been moderately true for recent engines, and future 2-stroke engines promise a better performance. In any case, being more fuel efficient means that a diesel aircraft can carry less fuel therefore more payload; but this advantage becomes questionable if the useful load ratio of the plane is poor. This ratio is measured by: Total useful load (fuel passenger and cargo)/Empty load. Ex: A Cessna 182 achieves around 0.67; an old Piper Cherokee 6 with the 260HP engine achieves an excellent 1.0 (the plane carries its own weight); Most small twin engines achieve only 0.45 and lower because the extra engine is always a partial dead weight. In that context, information on the power/weight ratio of any diesel engine, weight including all ancillaries (heat exchangers) is welcome. Pete, from Australia, answers: You have made a very good point. The ratios is something that I've never tried to figure out, rather than just using current operating handbook figures and viewing comparisons as need. As I work with SMA Jet-A engines in the Australian region, I know that they have carried out studies on many aircraft parameters as you have just noted. The design and certification team no doubt carried out your findings very early on in the piece. SMA chose the C182 for the STC as seen fit, whether for public demand, or most useful aircraft that could benefit from Jet-A power in the general broad market of General Aviation. Many reasons are evident. Now.... I'm carrying out some of your calculations on some of my favourite singles Wylbur: Because of the need for 100LL in GA, there needs to be a way to replace the TEL (TetraEthyl Lead). I think the diesel engine is the answer for two reasons: 1) Turbo charging - 500 FPM climb is attainable beyond 6000' MSL, plus good cruise speed at higher altitudes; 2) Less fuel needed to make same trip at same speed. As was pointed out in other places, JET-A or diesel is more dense than AvGas. Therefore it weighs more per gal/litre. Full fuel will cause lower "useful" load (I consider passenger and/or baggage to be useful). But for the bigger aircraft (those having > 200HP) this might make economic sense. However, changing over to diesel for most of GA will be incredibly costly. Example: C150-152s are no longer made. They are great trainers, but would it be cost effective to replace the AvGas engine with a Diesel? How about the Piper Cherokee line (which matches the problems of other low wing aircraft)? Is it worth $30,000 (per engine?) to change to diesel? If not, what will an engine overhaul cost should AvGas just go NO LEAD? And will TBOs be reduced? Will a catalytic converted be necessary and where would you put it? For the HI-PERF top end horsepower aircraft, diesel may be the only way out if TEL goes away. And think about it: if AvGAS goes NOLEAD, the cost of production would be reduced. The cost of AvGAS would possibly fall in line with MoGAS (finally!). Chris: I am not sure if I follow this thread. I fly a straight-tail Lance (Lyc. IO-540-K1A5D 300 HP @ 2,700 RPM). Do SMA and Thielert both have equivalent Jet-A burning diesel engines available? What Torque / RPM would the equivalent engine achieve? What is the approximate wet weight comparison of the two? Randy to Chris: Right now, there is no certified conversion available for these Pipers. Some Cherokees fly with the Thielert 135HP, and at least one Dakota with the SMA 230HP with very interesting performance. The Thielert V8 310-350HP is available, but hasn't been tried or even less certified on a single engine plane. The SMA 300HP exists, but isn't yet available. We don't know what will be the final empty weight of any of these conversions since a lot depends of designing, positioning and testing the heat exchangers. One encouraging sign is that the Beech Duke being converted in Germany from O-540 to Thielert is reporting a 360 Lbs. weight GAIN! With any of these diesels you can expect 0.32Lbs/HP-hour and SFC is remarkably constant with a diesel (not with a gasoline engine). Since Jetfuel is 14% denser, you can easily compute your future fuel consumption and range with reserves; you will see that what increases the most is range with IFR reserves. Also, expect a higher torque/rpm with diesel. Randy to Wylbur: I am skeptical about a coming of MoGas on airfields. It has been tried and tried again... The basic Lycoming/Continental design which originated in the thirties was a very simple design, easy to disassemble, tune up and maintain, very rugged, remarkably well adapted to high Octane gasoline. This is why it lasted so long. Converting these engines to MoGas has proven tricky and never was convincing enough to make a success. Converting automobile engines to aircraft has proven either vicious, or expensive, and in any case complex (geared engines...) with the exception of the Volkswagen Beetle engine which happens to be a flat-four air cooled in the first place. I am even more skeptical about a general concerted effort to bring MoGas on the airfields, while Jetfuel is already here in the first place. To read more and express your opinion, join our forum… posted at 6:43 AM |
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