News, facts, and comments on the coming revolution for piston-engine aircraft.
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News of October 03, 2011
More automobile diesel engines converted to LSA applications open new lines of thought.
Two of our subscribers, Paul Lucas in Europe and Chas Kenny in New Zealand, sent me reports on interesting conversions of an LSA with an automobile diesel.
The Isuzu 1.5 liter, 67HP, indirect injection, is the engine of the Opel Corsa among other cars. Lucas reports a 700 h flying experience from 1988 to 2000 on the Dieselis, see http://membres.multimania.fr/dieselis/, an LSA equipped with this engine. At take off the engine delivers 67HP at 3,600 rpm. At cruise, it needs only 26 HP at 2,800 rpm and consumes then 6liters/h, or 1.6 USG, while flying at 90 Kts. Of course as with all diesels the sole control is the throttle. Lucas says the engine has a very high torque. Because of the high compression ratio, the propeller becomes a strong air brake at low settings and the throttle then also acts as a simple control of the sink rate during approaches. I recently wrote that an engine of less than 100HP seemed of limited interest for an LSA. Lucas contradicts me, rightly it seems, saying such an engine is very suitable. He says: ‘You can purchase it at your local automotive dealer, new or second hand. It is a well proven engine, with millions of units produced, and spare parts everywhere. Water cooling is a standard and efficient device: every automotive engine builder has dropped the air cooling. A diesel needs a very efficient cooling and constant temperature. With an air cooling, you restrict the flight domain: impossible to climb at high angle (too hot), impossible to descend at high angle (too cold), especially with a clean machine, gliding at an L/D of 15. We installed a cogbelt (timing belt) reduction drive, and it worked.’ Is it too heavy? Lucas says: ‘Every one said that before the first flight. In fact the propeller efficiency (thanks to large torque, large prop diameter, slim engine cowling) is quite better than usual. We got 1000 ft/min with two aboard, on a plane which weighs 800Lbs empty. And this was with a heavy engine (cast iron block) and a wood and fabric wing. Conclusion: 60 to 80 hp is quite sufficient for a good LSA.’ I would add: Yes, if it is a diesel…
Lucas then raises an interesting point regarding weight and cooling: the water cooling airframe integration. In the Thielert approach, he says, the radiator is under the engine cowling, which leads to low cooling efficiency and more drag, because of too small a radiator and poor ducting. For better efficiency, one needs a large radiator located aft, and long inlet and outlet ductings, same as on the P51 Mustang. Advantage: the aft cooling weight helps balancing the heavier engine. But this layout needs too much room to be installed in front of the firewall. Lucas concludes: ‘We have to design new aircrafts to cope with those new diesel engines.’
Chas Kenny reports from down under: ‘I flew a Jodel D9 for many years. When Jean Delemontez drew the D18, it sparked my interest in building a homebuilt again. The only other Jodels in New Zealand were the popular D11. But having a farming background I always appreciated a good diesel engine and wanted to fly one. The Peugeot 1.9 liter diesel was new in NZ around that time. I worked my own Peugeot conversion design out of a Jodel D150 airframe design. After much of the airframe was built I discovered Delvion, A diesel Jodel using the same engine with a direct drive, no gear, by Jean Delemontez and Jacques Vion in France. While based on a bigger airframe the good news was that it worked. The radiator is in the wing like the DH Mosquito, and the Oddessy battery is in the left wing. They are mounted in what would have been cuff fuel tanks in the D150. The 43013 wing section gives plenty of room. This section as used on later Jodel / Robin aircraft will help me get off the ground earlier. The engine is in a bed mount and has had the injection pump overhauled and the fueling set for max fueling at 2000 / 3300 RPM. A short exhaust allows the turbo to spool up quicker. Being direct drive the drive axle is driven through a Centaflex LF22 coupling. All has worked out to an engine system weighing around 300 Lbs. The inlet manifold and intercooler will be placed below the cowl line. During the next weekend it will taxi for the first time. While all seems good my conversion is not yet proven. If it goes as well as Delvion D103, or even as well as my old D9 I will be happy.’
Meanwhile the Delvion is flying in Europe. I got messages that Diesel Jet Srl in Italy is demonstrating a Fiat-based aero diesel which just got EASA certified. It is a 4-cyl., 1.9 lit. liquid cooled engine, 8 valves, with turbocharger, FADEC and Common Rail injection.
Remarks and Questions: All these engines weigh around 300 Lbs for powers of 80 to 100HP, which is very heavy. The Thielert-Centurion has the same weight, but delivers 155HP because so much more development work has been done that the engine has nothing in common with its Mercedes-Benz ancestor besides the engine block arrangement. Incidentally the Finch Aircraft Ecoflyer, also designed on the proven DR400 design ex from Jodel, sells with a Thielert 155HP and seems to give a lot of satisfaction. This is an occasion to remind all that what matters when comparing performance of diesel versus gasoline engine is not the sole engine weight, but the weight of engine plus maximal fuel. An LSA doesn’t need a long range since it is limited by regulations to local flying. Neither does a 2-seat trainer for flight academies. So they can fly with a tank all the smaller that fuel consumption is low. Also room becomes available in the wings for batteries and cooling system as the Delvion illustrates. On bigger planes, the weight handicap of diesel diminishes with power: Thus the SMA diesel 4-cylinder of 230HP, installed on a 182, weighs slightly more than the original O-470 and the same as an O-540. Only 4 samples of the Thielert V8-300 HP became operational (on Cessna 206s) until Thielert’s bankruptcy compelled the firm to suspend development, but one could observe that the engine weight was close to the weight of the airplanes’ original 300HP 6-cylinders. Forecasting work we undertake at DieselAir with our panelists show that aero diesels of powers in the 300-500 HPOur subscribers who have experiences with flying a Delvion, or similar conversions of an automobile diesel of any power above 65 HP and available for Experimentals, are welcome to send me a report, with photographs. As one could expect, automobile diesels are heavy for aviation use, especially with powers of less then 250HP. But if the airframe design can accommodate the engine and two passengers, and if the engine has a torque good enough at low rpms to dispense with a gear, considering that a long range is not requested and the fuel tank can be small, the main advantages remain: A plane that uses Jet A and is not dependent on 100LL (or VLL which has only 19% less lead therefore doesn’t have a long term future), which is highly economical, and very safe. And then, availability of some cheap spare parts from a mass-produced auto engine, plus doing away with an expensive gear transmission makes a lot of sense for LSAs. As for using a timing belt gear, this is very economical and feasible if you respect a short TBR… and do not plan to cross 500 miles of sea.
posted at 2:16 PM
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Every month: news, facts, and comments on the coming revolution for piston-engines aircrafts between 130 and 400 HP: Retrofitting a diesel engine to run on Jetfuel or Kerosene, reduce Gallons/Hour by some 30%, eliminate ignition systems (magnetos, spark plugs) and their problems, eliminate mixture control, increase TBO to 2,400-3,000 hours, increase performance between 6,000 and 12,500 ft., and drastically reduce Operating Costs.
The letter is intended for piston engines aircraft owners, manufacturers, fleet operators and FBOs, re-manufacturers of engines for these aircrafts, manufacturers of engine components and ancillaries, and all professionals acting in decisions of engine exchange or refitting at TBO, in North and South America, Pacific Rim, African continent, and all parts of the world were Avgas, Mogas, Kerosene and Jetfuel are available.
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