AC Aero - Experimental Diesel Engine

[OhioLSA]

Ever since I was a teenager, and that was decades ago, there have been SO many promising new engine projects, that were going to "revolutionize" propulsion for lightplanes. They were always "just one step away" from swarming onto the market. But it takes so much money to develop that they just don't survive long enough to produce anything beyond a prototype.

I'd love to see some of these smart new designs succeed, but in the meantime I'm going to have an airframe needing an engine that's available NOW. Sure, Lycomings and Continentals are old designs, using primitive technology, they're not fuel efficient, etc., ... but they work, and they're pretty reliable.

Best of luck to AC Aero and the others. Hopefully someday they'll be hanging on the noses of newly built airplanes. It just won't happen in time for me.

[noema]

Diamond aircraft with diesel engines are big where I fly (all CD-155s). They work well within the parameters of flight schools and clubs. My local flight club has both DA40s and a DA42 and they usually replace the engines every 4 years after TBO. They probable have a combined flight experience of 40000 diesel engine hours.

There are some observations I made over the years. People generally like the idea of advanced engines but long-term pilots who have flown both Lycomings and Continental Diesel (formerly Thielert) CD-155s generally prefer Lycomings. It's a very common repeating pattern. The Thielert engines are super complex and fail often by FADEC. They are loaded with sensors and the FADEC throws a lot of errors at you over the years. In a way they are both fragile divas yet safe. Many of these errors mean you have to abort your flight. After a while the old-tech Lycoming does not look so bad anymore.

The Thielert engine is a benchmark in power-to-weight. The CD-155 weights about as much as an IO-360 (155 turbo-hp at 295lbs). Alternative diesel engines tend to be much heavier. The newly developed AustroEngine to replace the CD-155 came in at almost 90 lbs heavier. Most competing diesel engines are heavier.

Personally my taste in airplanes moved from fancy to simple and reliable. I don't think this is uncommon. The more you know ...

[zkelley2]

Lycomings are not reliable in any modern context. They're reliable versus all the other complete crap piles that are piston aviation engines.

If I had to put 1/10th the maintenance into the engine in my truck that I do my lycoming I (and anyone else owning one) would consider it the biggest piece of crap ever put in a vehicle in history.
2000 hours is roughly 60,000 miles on a car engine. Could you imagine overhauling your car's engine every 60,000? Or, lets be honest doing it closer to every 30,000 miles because top ends never go 2000. And it's not just the overhauls. The constant failing of accessories.(Magnetos, the most unreliable thing on an airplane), sensors, brackets and other little things that fail and you catch every annual.

Reliable? Not even close. Best we have because of over burdensome regulation? Yes, probably.

A PT6 is reliable. A CF6 is insanely reliable. I wish my truck could go that long.

[jaredyates]

With homebuilts being such a big slice of the light single piston pie, and the turbines being so successful, can we really blame regulation? I think low production volume bears more blame, because the numbers aren't there to justify intense r&d.

[BradW1062]

zkelley2 and jaredyates - I agree with both of you for the most part; the regulation is obviously there to, at least theoretically, ensure public safety and adherence to standards in aviation, but at the same time any innovation is very effectively dampened out due to the regulatory requirements of demonstrating compliance. Add general aviation's very small sales numbers to the mix, just as Jared is saying, and what you have is basically very little advancement, and very few new innovative products. It's a sad situation in many ways. But, that's where our experimental world comes in; Want to innovate? Then knock yourself out. Want to sell your idea? Now you will find out why it doesn't seem that anyone is getting anywhere - it's simply cost-prohibitive.

And, zkelley2, I agree with exactly what you said about reliability. I've said exactly the same ever since I first started flying and learned about these engines. Lycoming piston engines are not even close to being "reliable" in the normal sense of the word. There are so many things wrong with them, that I could do another 10,000 word essay on that with not much thought. Whatever you do, don't ask a pilot about it - you will only get misleading and misinformed mysticism. But, since those engines are what is available, and "proven" in GA, that's what we'll get for our airplane. Or, in my case at the moment, a Continental.

In the general aviation world, in my opinion, "reliability" is highly relative. Compared to what? For example, pilots will tell you that two magnetos (driving two spark plugs in a cylinder) are there to make the engine run better than one like in an automotive engine. Well, two sparks is just and added benefit, it's not the reason - there are two magnetos for one simple reason - magnetos fail. And, the blame is placed on the name "magneto", when it should be more appropriately placed on the breaker points, capacitor and especially the impulse coupling (or at least its spring) that allow the energy to get out of the infernal device. The single-pole permanent-magnet electric generator that is the actual magneto is highly reliable - unless you damage it, as long as it is turning it is generating electricity for your spark plug. The biggest limitation to that output is the slow speed, due to the low direct-drive propeller engine speed. Talk to most any pilot, and some mechanics, and you will get all sorts of mysterious knowledge about how magnetos work and what they do, and how they are so much better than battery ignition systems on cars. The reality is that most of these guys have really no idea what the deal is these things. What you really have are two (as in redundant) electrical generators producing pulses of electrical energy in a highly reliable way, and that is then controlled by a mechanical switch that is highly prone to wear and failure. So, hopefully, at least one of the "mags" will keep working.

My last pickup truck, had 125000 miles and 17 years on it, which translates to between 2000 and 4000 hours since it was a mix of city and highway driving. And towing heavy loads for miles, up and down hills. Brutal daily stop and go in 25-100 degree weather. I replaced the spark plugs at 100,000 miles because it was time - I never had one ignition-related event in the entire time. And I never added any oil between routine changes. That, my friends, is what you call reliability.

[Sir Newton]

Nicely put. Brad you and can be friends! Your understanding of the subject matter is definitely in the advanced category. I to am a real true blue motor head with vast engine experience working in the petrol chemical processing industry. 26yrs. There is a reason I use the nick name fuel to cool! Simply because it is 100% accurate. Mark

[svyolo]

The FAA regulated stuff that made sense in the 1930's and 40's. It, and product liability, destroyed GA in the 80's and beyond. Once a "safety" regulation is in place, it is rarely if ever removed as no bureaucrat wants to accept that responsibility. So we can only hope for more regulation like Light Sport, and hopefully have that category expanded.

There are a bunch of successful businesses, like the company that sold me my EI/EFI, that have no plans to even try to certify their products. The investment to certify stuff is usually not justified by the numbers they can sell after millions have been spent testing.

[zkelley2]

zkelley2 and jaredyates - I agree with both of you for the most part; the regulation is obviously there to, at least theoretically, ensure public safety and adherence to standards in aviation, but at the same time any innovation is very effectively dampened out due to the regulatory requirements of demonstrating compliance. Add general aviation's very small sales numbers to the mix, just as Jared is saying, and what you have is basically very little advancement, and very few new innovative products. It's a sad situation in many ways. But, that's where our experimental world comes in; Want to innovate? Then knock yourself out. Want to sell your idea? Now you will find out why it doesn't seem that anyone is getting anywhere - it's simply cost-prohibitive.

And, zkelley2, I agree with exactly what you said about reliability. I've said exactly the same ever since I first started flying and learned about these engines. Lycoming piston engines are not even close to being "reliable" in the normal sense of the word. There are so many things wrong with them, that I could do another 10,000 word essay on that with not much thought. Whatever you do, don't ask a pilot about it - you will only get misleading and misinformed mysticism. But, since those engines are what is available, and "proven" in GA, that's what we'll get for our airplane. Or, in my case at the moment, a Continental.

In the general aviation world, in my opinion, "reliability" is highly relative. Compared to what? For example, pilots will tell you that two magnetos (driving two spark plugs in a cylinder) are there to make the engine run better than one like in an automotive engine. Well, two sparks is just and added benefit, it's not the reason - there are two magnetos for one simple reason - magnetos fail. And, the blame is placed on the name "magneto", when it should be more appropriately placed on the breaker points, capacitor and especially the impulse coupling (or at least its spring) that allow the energy to get out of the infernal device. The single-pole permanent-magnet electric generator that is the actual magneto is highly reliable - unless you damage it, as long as it is turning it is generating electricity for your spark plug. The biggest limitation to that output is the slow speed, due to the low direct-drive propeller engine speed. Talk to most any pilot, and some mechanics, and you will get all sorts of mysterious knowledge about how magnetos work and what they do, and how they are so much better than battery ignition systems on cars. The reality is that most of these guys have really no idea what the deal is these things. What you really have are two (as in redundant) electrical generators producing pulses of electrical energy in a highly reliable way, and that is then controlled by a mechanical switch that is highly prone to wear and failure. So, hopefully, at least one of the "mags" will keep working.

My last pickup truck, had 125000 miles and 17 years on it, which translates to between 2000 and 4000 hours since it was a mix of city and highway driving. And towing heavy loads for miles, up and down hills. Brutal daily stop and go in 25-100 degree weather. I replaced the spark plugs at 100,000 miles because it was time - I never had one ignition-related event in the entire time. And I never added any oil between routine changes. That, my friends, is what you call reliability.

What's interesting is with electronic ignition, you're taking that highly unreliable switch in the magneto and making it solid state with a MTBF of millions of hours. You're still using an alternator or generator to give it power same as in the magneto, and those pretty rarely fail. Voltage regulators, especially the non digital ones fail pretty often, but with 2 of each, you've essentially rebuilt the magneto, taking the crap parts out.

The only in flight piston engine mechanical failures I've ever had has been magnetos. I cannot count the amount of trips a dead mag on the ground has caused to be canceled. They truly are a giant POS. In my experience they rarely make 500 hours without issues.

[svyolo]

I am using EFI so I need the trons to keep flowing. At first I thought I would have two alternators, but looking into alternator reliability, I went with two, switched, VR's to operate 1 alternator.

[chuckkemp]

What's interesting is with electronic ignition, you're taking that highly unreliable switch in the magneto and making it solid state with a MTBF of millions of hours. You're still using an alternator or generator to give it power same as in the magneto, and those pretty rarely fail. Voltage regulators, especially the non digital ones fail pretty often, but with 2 of each, you've essentially rebuilt the magneto, taking the crap parts out.

While I'll agree with most of your observation regarding mag's they do offer double redundancy failure rejection with two isolated power sources along with a simple installation. Simply using a generator/battery as the single point failure mode is asking for trouble. Ask Elliot Seguin when the Titan P51 with a Chevy LS1 engine he was test flying landed gear up and engine out due to the fact the electronic ignition had no power input redundancy. The ignition failed due to the hyd pump running continuously along with the fuel boost pump which overwhelmed the main bus circuit breaker thus causing a complete DC bus failure and subsequent engine failure.

I think these new electronic ignitions are awesome, offer more power and economy, but before installing one or two, you should do some serious fault analysis to ensure you have all the bases covered (read not just a simple bolt on and forget installation). One question I have is how many of these auto-derivative electronic ignitions are flown regularly for 500 hours or more? We know that the average mag will usually make 500 hours and a huge share of mag failures are usually attributed to lead fouling of the plugs or harness issues due to improper or careless installation.

I must also point out that I'm generally speaking of auto-derivative electronic ignition and fuel injection and not the P-Mag or those with built in power supplies. The other mag replacements like SureFly, Electro Air etc also need redundant input power if you were to use two in an installation the same as the auto-derivative.

On the Rolls Royse 250 series turboshaft engine used in a lot of helicopters with FADEC engine controls they add a separate redundant permanent magnetic generator driven off the accessory drive to ensure uninterrupted power in case of a full electrical failure.

Auto engines are cool and much more modern, but the landscape is littered with many that tried to break into the aircraft world, why wasn't the Orenda V8 engine that made it thru certification not successful? There's a boat load of people jumping on the bandwagon to install snowmobile engines, yet I don't think many are installing them for cross country cruisers either.

One last comment on the AC Aero engines, I too visited them at OSH and thought their hardware looked really solid and the same holds true for me is I can't afford them either. My only negative comment other than price on the Gladiator/Centurion installation is the fact you have to remove the whole bank when dealing with a single cylinder issue. So stocking spares may be costly too as you have to keep half the engine as a backup. I'm assuming the left can go on the right and vice versa and if not then the stocking cost rises even more! Hopefully they will be extremely reliable and this won't be a concern, but one doesn't know until they get a boatload out in the market.

[zkelley2]

While I'll agree with most of your observation regarding mag's they do offer double redundancy failure rejection with two isolated power sources along with a simple installation. Simply using a generator/battery as the single point failure mode is asking for trouble. Ask Elliot Seguin when the Titan P51 with a Chevy LS1 engine he was test flying landed gear up and engine out due to the fact the electronic ignition had no power input redundancy. The ignition failed due to the hyd pump running continuously along with the fuel boost pump which overwhelmed the main bus circuit breaker thus causing a complete DC bus failure and subsequent engine failure.

Then the ignition(or EFI) was wired incorrectly for aircraft. You absolutely must be able to isolate and power at least 1 ignition(or ecu/what have you) by itself from an independent source.
For example on my dual SDS ignition, the main alternator powers everything, but I can isolate 1 ignition from the rest of the electrical system and run it on the vacuum pad driven alternator. More or less an essential bus with just 1 thing on it.
By doing this, you have 2 independent redundant power sources to the parts that keep the engine running.
As you said, that's not different then what we do with turbine FADECs. Main generator(s) on the engine(s) and the fadec has it's own generator. We can get electrons there at least 2 ways and a failure elsewhere cannot effect the essential components.

Every modern jet from Boeing/Airbus/Embraer is an electrically dependent aircraft. Not only is it common, but it's not even that hard to do safely. It's not like we're talking resonance testing that no auto manufacturer will do, it's simple electrical logic.