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Available aircraft engines: What's out there in diesels?

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Twodeaddogs

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probably the day after the formal retirement of them; I suspect the stores system will be told to dump the stock of MQ parts and they will be sold/given to friendly nations or simply surplused. I recall seeing a particular helicopter model being formally retired and it's entire stores holding was immediately quarantined and nothing could be drawn from it; the computer system was altered to effectively remove it from the record and the entire (small ) fleet was sold off by auction.
 

pictsidhe

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The aviation world has been clamoring for new engines for a long time. Owners want EFI and EI, or they want diesel. But they think that since General Motors can develop this stuff and sell it in a new car for $30K or whatever that Lycoming and Continental can build it for the same price as the legacy gasoline engines.

But it doesn't work. New technology (in aviation, almost anything is new) has to be designed to be safe and reliable, and it has to be tested for thousands of hours, and then it has to be certified, which is when the lawyers and the FAA and insurance companies get involved and costs really go up. Lycoming built the iE2, an EFI/EI engine, but it cost more than owners would pay. SMA and Thielert built diesels, but they weren't cheap either and they had considerable teething problems. I worked on an SMA about eight years ago, fixing some of those issues, and SMA told us that they had spent a billion (with a "b") dollars so far and had, at that time, 50 engines flying. Total. Worldwide. Things like that make a lot of CEOs say "no way" to new developments.

Aviation is expensive. Aviation with neat new technologies is prohibitively expensive. Even in the uncertified homebuilt world that new stuff isn't cheap. If someone is selling it they have to cover themselves against litigation when some guy flies into a mountain in the clouds and the jury blames the ignition system or something.

Diesel? Noisy. Smoky. Smelly. Oily. I'd rather smell avgas. The old 80/87 has a lot of nostalgia to it. Old airplanes smell like it. And diesels are hard to start in the cold. IIRC, SMA had a lower starting temp limit of about -10°C. Works in Africa. Not so good here.
GM et al are possibly the best source for new engine tech. Stuff that's been proven for 10 years in millions of cars should have a head start to migrate skywards. Althoug aviation is stuck in the dark ages as it likes using proven tech, car tech seems to me to be more reliable now...
Car diesels start at way less than -10C. I struggled once at -16C. I soon found that I had lost 3 out of 4 glowplugs. The fact that it had to get that cold for me to have an issue with only one working glow plug should give a clue about cold starting.
I owned 5 different diesel cars in the UK. I can assure you that they are highly addictive. Modern diesels aren't noisy, smelly, smoky or oily. But they are about as common as rocking horse droppings in the USA. The most recent diesel I drove was my sister's Jaguar XF. 275hp and 45mpg. Yes, it's really quiet and smooth as a Jag should be, though it does growl pleasantly when you press the fun pedal. That engine could make a good aero conversion, if you can find a way to legally import one...
Somehow, despite the EPA being one of the worlds strictest emissions bodies, US diesel vehicles lag way, way behind the rest of the first world in most areas, other than spewing out noxious stuff where they seem to be leaders.
 

Twodeaddogs

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Dead right. You look at some of the small turbodiesels coming out of Japan and Korea, as well as Europe, in the last twenty years. They are getting smaller, lighter, more efficient and are made in their millions. I don't know what aviation certification thinks it is trying to achieve, but it appears to be more concerned with ass-covering than delivering efficiency.
 

TFF

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It is about ass covering. Because it is tightly regulated by governments, easier for a lawyer to find a fault. By government standards airplanes are perfect or they are not safe. Autos don't have the same scrutiny. Aviation companies are having to cover their butts for the inevitable. Malpractice insurance in one way. It's not what they want but the only way they can not go bankrupt. The technical challenge definition is simple, weight. Unless they come up with a super material, the diesel is always heavier per horsepower. When that is how you measure this, you have to be willing to give up performance. Does not work commercially. As a hobby is one thing.
 

BJC

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GM et al are possibly the best source for new engine tech. Stuff that's been proven for 10 years in millions of cars should have a head start to migrate skywards.
Agree, but must note that GM’s early efforts, with lousy results, to use diesels in passenger cars probably contributed to today skepticism of diesel cars.
Car diesels start at way less than -10C. I struggled once at -16C. I soon found that I had lost 3 out of 4 glowplugs. The fact that it had to get that cold for me to have an issue with only one working glow plug should give a clue about cold starting.
I drove a VW diesel over 200,000 miles in the early 1980’s. The only needed repair was the replacement of one glow plug. I added gasoline to the diesel in cold weather, and, like you, never had starting problems in cold (5 to 10 degree F) weather.

Somehow, despite the EPA being one of the worlds strictest emissions bodies, US diesel vehicles lag way, way behind the rest of the first world in most areas, other than spewing out noxious stuff where they seem to be leaders.
I wonder if VW’s faking of their diesel emissions is a factor. Also, there is no fuel cost savings in most places. When we were driving diesels, the cost of diesel energy was considerably less than the cost of regular gasoline energy.


BJC
 

Twodeaddogs

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Modern diesels will endure tougher conditions than petrol engines. Diesel engines in cars will routinely reach a half million miles before overhaul. Diesels, like gas turbines, love nothing better than to sit at one RPM, drink clean fuel and air, run on clean oil and get checked once a year. A diesel engine in an aircraft, operating at cruise RPM, would run for ever and be so much cheaper to run than a piston engine....... Fuel is so expensive at the retail pump because of taxes. The actual cost per litre, to refine petrol or road diesel is mere pennies because of the sheer volume of the stuff. Fuel like marine diesel gets even less refining and heavy oil for ships engines gets virtually none compared to road fuel. Avtur, despite the claims of the airlines that aviation fuel is hideously expensive, is cheap compared to domestic car fuel..........we should have a lot more diesels in the training fleet, coupled to grant aid to industry to improve the engine. meanwhile, the amateurs will just have to continue to experiment...
 

Dan Thomas

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Thielert based their certified Centurion diesel on the Mercedes four-banger. It had plenty of problems, some due to the FADEC and some due to the redrive. Then there was an embezzlement scandal at the plant that finally sank it and left the owners of some airplanes out of luck until Diamond came up with their Austro, which was, I think, basically the same thing.

The FADEC needed a certain minimum voltage to keep it on. If the generating system failed, or some big load was applied to the system, the voltage could fall and the engine would die. There are 23 ADs associated with that engine, a horrible record for an engine that barely entered service.

The SMA was a clean-sheet affair. It made 230 HP at 2400 RPM out of four big cylinders at 15:1 compressions. That's guaranteed to produce strong vibration, and there were items that cracked due to it. We even found a cracked composite propeller blade. Various mounting brackets were cracked. The engine had about 150 hours on it. The heads were both oil- and air-cooled, and oil would leak from the head gasket. Yes, it had heads separate from the cylinders, and there were oil passages from the case through tubes in the cylinders to the head. There was a huge oil cooler as well as a big intercooler. The problems of starting in the cold may have been partly due to trying to crank a big cylinder at higher compression. The engine had turbos to keep the induction pressures high enough to get compression ignition at altitude. The engine was certified to use only Jet-A, not diesel. Something to do with the lubricity of Jet for the pump, IIRC, and probably the quality control of Jet contrasted sharply with highway diesel.

When I was young, diesel fuel was half the price of gasoline. And the mileage was nearly twice that of gas. The price shot up when diesel cars became popular. Just like propane did once a bunch of folks converted their autos to it.
 

tspear

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The technical challenge definition is simple, weight. Unless they come up with a super material, the diesel is always heavier per horsepower. When that is how you measure this, you have to be willing to give up performance. Does not work commercially. As a hobby is one thing.
Not really. Total mission weight is the critical aspect. Fuel, plus power train. Once you look at burning the extra fuel avgas requires; any flight time over roughly three hours a diesel makes more sense.

Thielert based their certified Centurion diesel on the Mercedes four-banger. It had plenty of problems, some due to the FADEC and some due to the redrive. Then there was an embezzlement scandal at the plant that finally sank it and left the owners of some airplanes out of luck until Diamond came up with their Austro, which was, I think, basically the same thing.
A lot of differences. Austro kept the Benz iron block instead of making an aluminum. They replace the ignition, rails, and all accessories components.
Big difference in how vibrations are handled. Thierlert went with a clutch, and eventually a double clutch system under Continental. AE-300 uses a rubber torsion disk.

The FADEC needed a certain minimum voltage to keep it on. If the generating system failed, or some big load was applied to the system, the voltage could fall and the engine would die. There are 23 ADs associated with that engine, a horrible record for an engine that barely entered service.
Not really, pretty much any clean sheet avgas engine has the same horrible track record for the first decade or so. The power drop example you gave was caused by a pilot taking off with bad batteries and using a GPU to start the plane, which is expressly prohibited in the POH. The solution was to require additional batteries on the engine which must be replaced every year, and that pilots cannot override.

The SMA was a clean-sheet affair. It made 230 HP at 2400 RPM out of four big cylinders at 15:1 compressions. That's guaranteed to produce strong vibration, and there were items that cracked due to it. We even found a cracked composite propeller blade. Various mounting brackets were cracked. The engine had about 150 hours on it. The heads were both oil- and air-cooled, and oil would leak from the head gasket. Yes, it had heads separate from the cylinders, and there were oil passages from the case through tubes in the cylinders to the head. There was a huge oil cooler as well as a big intercooler. The problems of starting in the cold may have been partly due to trying to crank a big cylinder at higher compression. The engine had turbos to keep the induction pressures high enough to get compression ignition at altitude. The engine was certified to use only Jet-A, not diesel. Something to do with the lubricity of Jet for the pump, IIRC, and probably the quality control of Jet contrasted sharply with highway diesel.
I never did think a diesel direct drive makes sense based on the reasons above. You really need to gear it down some, not a lot but enough that you can run the engine at a descent speed.

Tim
 

Twodeaddogs

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Not really. Total mission weight is the critical aspect. Fuel, plus power train. Once you look at burning the extra fuel avgas requires; any flight time over roughly three hours a diesel makes more sense.



A lot of differences. Austro kept the Benz iron block instead of making an aluminum. They replace the ignition, rails, and all accessories components.
Big difference in how vibrations are handled. Thierlert went with a clutch, and eventually a double clutch system under Continental. AE-300 uses a rubber torsion disk.



Not really, pretty much any clean sheet avgas engine has the same horrible track record for the first decade or so. The power drop example you gave was caused by a pilot taking off with bad batteries and using a GPU to start the plane, which is expressly prohibited in the POH. The solution was to require additional batteries on the engine which must be replaced every year, and that pilots cannot override.



I never did think a diesel direct drive makes sense based on the reasons above. You really need to gear it down some, not a lot but enough that you can run the engine at a descent speed.

Tim
that has to be the dumbest thing I've heard in a long time. An aircraft that is not allowed to use a GPU for starting?!
 

gtae07

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that has to be the dumbest thing I've heard in a long time. An aircraft that is not allowed to use a GPU for starting?!
Electrically-dependent engines (like this aircraft had) shouldn't be jump-started--they need healthy batteries to keep the big fan turning. You can't just prop it off and figure the alternator will handle things for you like you can on a traditional engine.

If they're dead to the point of needing a jump start, then the proper course of action is to fully charge or replace the batteries before flying.
 

Swampyankee

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Since most countries in Europe have to import all petroleum products, their governments tax fuel heavily. Some countries has lower taxes on road diesel — an indirect subsidy on diesel vehicles — diesel cars started being produced to fill a market. That need never really arose in the US, because fuel is cheap and fuel economy for cars is deprecated.
 

Dan Thomas

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Electrically-dependent engines (like this aircraft had) shouldn't be jump-started--they need healthy batteries to keep the big fan turning. You can't just prop it off and figure the alternator will handle things for you like you can on a traditional engine.

If they're dead to the point of needing a jump start, then the proper course of action is to fully charge or replace the batteries before flying.
We will soon have airplanes that can't be used without a mechanic and a bunch of tools on board, just like the 1920s. We old guys will miss the days of hand-propping the engine and flying home NORDO. The magnetos feed themselves.
 
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tspear

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that has to be the dumbest thing I've heard in a long time. An aircraft that is not allowed to use a GPU for starting?!
As gtae07 noted, it is stated that way expressly to determine battery health. Checking volts is not enough, you really need to check volts under load.
Only practical way to do that is when the starter pulls power to turn the engine. If you use a GPU, you eliminate that test.

Tim
 

lr27

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I think if there was a significant demand for long range, slow light aircraft, we'd see more diesels developed. Wonder if it's possible to have some kind of mechanical backup for FADEC, or a system that really doesn't need much of a battery when the alternator is working.
 
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