Inside Thielert

With automotive diesel technology and economy of scale, Thielert is reaching for a serious share of the GA engine market. Just don't call them car engines.

by Paul Bertorelli

If general aviation has had a piston engine success story recently, Thielert Aircraft Engines, based in the former East Germany, owns it. Four years ago, no one had heard of this upstart and now, thanks to Diamonds edgy decision to use Thielerts diesels in both the DA40 Star and its new Twin Star, Thielert is poised to dominate the world of Jet-A burning piston engines. Given the geological pace of engine evolution and the intractable hideboundedness of buyers, this is no small feat.

In June 2005, as part of our research on Diamonds Twin Star, we spent a day at the Thielert Aircraft Engine factory in Lichtenstein, a small industrial town about 80 kilometers southwest of Dresden . After touring the plant, we later interviewed Frank Thielert, the prime mover in what appears to be a company bent on serious competition with Lycoming and Continental in the OEM engine market.

If Thielert was an unknown upstart three years ago, it is anything but now. We were astonished to learn that the company has some 400 diesel engines flying and is on track to make 1000 certified engines in 2005. Half of those will go to Diamond for new airplanes-singles and twins-and the rest are a mix of aftermarket conversions, with some military work thrown in. Thielert has recently developed a 350-HP V-8 diesel with fuel specifics similar to the smaller Centurion 1.7 Diamond is using for its aircraft; this engine is flying on a test basis.

Although Thielert has a growing profile in the U.S., the nature of the company and its business strategy remains relatively unknown. The purpose of our visit was to fill in the blanks and to see what the companys plans are for future North American market development.

Automotive Background
Part of Thielerts come-from-nowhere prominence is due to a history rooted in the automotive business. Before it launched its aviation engine program-due in part to inspiration from one of Thielerts customers-the company was primarily a builder and developer of high criticality parts for the automotive racing industry, including crankshafts, cams and other machined parts.

Its also we’ll known in the European auto industry for its expertise in manufacturing process control development and prototyping, a fundamental building block of quality control in the production car business. Thielert is clearly applying those techniques to the manufacture of diesel aircraft engines.

During our factory tour, we saw pallets of obviously low-volume crankshaft runs for the likes of NASCAR teams alongside racks filled with aircraft cylinders being machined for Superior Air Parts. (Thielert recently took over final machining of Superiors line of cylinders, a development we’ll report on later.)

Swimming against the current popular tide of outsourcing, Thielert is intensely vertically integrated or, more accurately, self-contained. We were surprised to see practically every part and piece of the diesel engines-including sophisticated electronics that are often outsourced to Asia-designed, built and inspected under the same roof. Thielert does rely on some outside suppliers but it seems to land on those suppliers with both feet when it comes to quality control. For instance, engineer Niels Mundt showed us piston forgings with domes nicked by three tiny burn marks. He explained that piston forgings are 100 percent inspected for material compliance by an in-house spectroscopic lab and throughout the factory, we saw similar examples of QC inspections. We cant say we havent seen the same at Continental and Lycoming, but our impression is that inspections were more pervasive at Thielert.

Frank Thielert later told us that the factorys integration is one reason why the engines have been designed and brought to market so quickly, far more quickly than were used to in the U.S.

Two Engines
Thielert currently manufactures two engines, the 135-HP Centurion 1.7 used in the Diamond airplanes and the 310/350-HP Centurion 4.0, a V-8 design certified in Europe last fall. The 4.0 is known to be flying in a German-developed twin called the TT62, an odd design in which the two engines are inside the aft portion of the fuselage driving a pair of five-blade props mounted on pylons. We believe the 4.0 has flown in U.S.-built aircraft as well, but Thielert declined to provide details.

Both engines represent cutting-edge European diesel technology, with common rail direct injection, intercooled turbocharging and FADEC controls, which, in aircraft, plays out in a single-lever power control that actually works.

When asked to explain the origins of its engines, Thielert staffers tend to squirm and dance around the subject or to change it entirely. Although its common knowledge that the basis of the engines are automotive diesels from Daimler-Chrysler, by agreement, Thielert cant say that, so the details are usually skirted.

Frank Thielert is forthright about where the engines come from, but hes also adamant that these are not converted car engines of the sort found in many Experimental aircraft. For one thing, about half the parts on the Thielert diesels are purpose-made for the aircraft version-the 1.69-to-1 reduction gearbox being the most conspicuous-and second, production and manufacturing controls are far more stringent on certified diesels than on converted automotive engines, almost to the point of obsessiveness, in our estimation.

While critics of the diesels have bad-mouthed the automotive connection, it is fundamental to Thielerts business strategy. During our interviews, we heard the number E400 million mentioned repeatedly as the amount of money Daimler-Chrysler has spent on diesel engine development, a sum that easily outstrips Continental and Lycoming combined R&D many times over.

In Europe, automotive diesels have improved by leaps and bounds, delivering more power and better economy in lighter, quieter packages.Thielert plans to simply coattail its aviation engines on this trend, integrating improvements into the aviation engines as they become available in the automotive market.

For state-of-the-art engines, Thielerts diesels are already price competitive with traditional aircraft engines, although they lag in one important element: power density. For equivalent horsepower, the diesels are about 20 percent heavier than gasoline engines. But again, thanks to high-dollar automotive R&D, Thielert may be able to squeeze the curve from both ends, reducing weight as power is increased. In any case, one source at Diamond aircraft told us the automotive economy of scale puts staggering downward pressure on engine costs. You cant believe what Thielert is paying for those engine blocks, one executive told us.

Still, Thielert faces challenges. With only 65,000 total fleet hours as of July 2005, the engines are still largely unproven compared to traditional gasoline designs. Of more concern is a U.S. service network, which doesnt now exist. Thielert hopes that Diamond will provide this when it introduces diesels in the U.S., but Diamond would like Thielert to set up the service network before the diesels arrive in North America. Heres how Thielert plans to meet these challenges.


Aviation Consumer: Lets start with the diesel engine service issue. Where are you with plans to build a service network?

Frank Thielert: We have more than 70 service centers in Europe. And we plan in the U.S., once Diamond has its airplanes there, to build up a U.S. service network. We have already invited all Diamond service centers to come for training in Europe to allow them to work on both engines. We will offer training on short notice in the U.S., once the aircraft is certified.


Will service centers be like regular FBOs or dedicated only to maintaining Thielert engines?

These 70 training centers have done the training process here, with the computer interface, and they have the special tools to work on those engines.They service all other airplanes, Cessna, Piper or Diamond. They arent dedicated only to Thielert. In the U.S. we want definitely to start with an OEM. If Diamond wants to be first in the U.S., we will start to train Diamond service centers.

Diamond centers would become Thielert service centers if they want to and would be responsible for maintaining engines. This makes sense to us because if the customer buys an airplane for $400,000, he should have one key address or one account he can go to to get the aircraft maintained. The service centers will get all of the training from us and all of the support from us.Diamond thinks we should also have additionally our own Thielert service centers, but we would choose to have Diamond service centers as our first in the U.S. We are dedicated to give Diamond all the support they need from us.

We have so many applications for service centers in the U.S. that we will have to refer to a map so we can see how we can achieve the coverage. We have received about 180 applicants for service centers in the U.S. From our end, we have done nothing; they have just approached us.


As far as the engine itself is concerned, how many fleet hours are there and have you found evidence of any premature wear thats of concern?

We have about 65,000 total hours. The fleet leading airplane, a Cessna 172, has above 1000 hours. Wear has been absolutely as we expected. We have disassembled a 1.7 with 1000 hours and we have found 95 percent of the parts are still to new-part tolerances. We have found no problem parts with the base engine.


How about the gearbox? Geared aircraft engines have traditionally proved troublesome.

We have not seen problems with the gearbox, but it is also under a lifetime extension program. We want to be very conservative in our approach. We have a factory inspection program for the gearboxes.

We are now inspecting them at 300 hours and then returning them to service just to learn more about the gearbox and to make sure we don’t have any issues with the gearbox. All engines get a factory inspected gearbox, at 300 hours, free of cost to the customer. That is for us to learn more about the gearbox for our lifetime extension program. About 1100 have been inspected and we have seen no problems with them.


Speaking of the lifetime extension, TBR is now 1000 hours, with an extension to 1600 hours planned for later this year. When will 2400 hours be reached?

Definitely in 2006. We will have 1600 hours later this year.


Given the longevity of road diesel engines, will TBR go beyond 2400 hours?

We don’t want to, because of liability. It is true that diesel engines have more longevity than gasoline engines. But we don’t want to have risks which are not necessary.


When the engine reaches TBR, the customer will receive an entirely new engine. Will any parts be re-used or overhauled? And what is the cost?

Nothing will be reused. All engine parts will be replaced; installation parts like mounts and radiators can stay with the aircraft. For the 1.7, the current cost is !20,319 ($25,400).


Its understood that the Centurions are adapted automotive engines but youre quite careful to distance the engines from that idea. Why?

No, we cannot consider it an automotive-derived engine because we could not certify it. We have to have design control and we have to have manufacturing control.

If you are converting an automotive engine, it is much easier because you do not have to do that. You do not have to certify it. These engines have nothing to do with the automotive engines used in kit planes, for example.


The basis of the 1.7 is the engine found in the Mercedes A-class, a 97-HP turbocharged diesel. How many of the parts are the same on both the aircraft and the automotive engine?

Very few of the parts for the engine are not from the automotive supply chain. What we have seen is that the automotive suppliers normally have a better quality and a better process capability than the typical general aviation supplier. Around 50 percent of the parts for the engine are manufactured by us. We do this for control, flexibility and efficiency.


Can you give an example?

We manufacture all parts with a high criticality, like the crankshaft, on our own. We have to meet the design requirements for FAR 33 or JAR E. Yes, they are much lower standards than the current automotive standards are.

In general, the requirements regarding process capability and process control are higher in the automotive industry than they are in the general aviation industry.

However, for a crankshaft, the safety factor is higher in aviation than in automotive. Automotive is happy with a safety factor of, let us say, 1.4, but in aviation we want 1.5 to 2. But the process control to achieve 1.4 in automotive is much more complex than the requirements to achieve 1.5 in aviation. Also, the acceptance trial for a crankshaft is much more difficult to pass in automotive than it is for aviation.


Is the core engine block the same for both the automotive and aircraft engines?

Its not manufactured exactly like the automotive part; it is slightly different. It also has a separate quality control process.


If you benefit from the economy of scale of the automotive supply chain, how can that work if so many parts for the aircraft engine are custom-made in low volume?

It absolutely works. Let us take the example of the crankshaft. We use their die and the forging company runs one extra shift and they make for us 1600 crankshafts in one day. There is a tremendous economic advantage in making 1600 crankshafts in a day instead of making 1600 in a year.

That is how we benefit from the automotive economies and this is a huge difference. We normally try to use their tools, all of their experience and their set-up. We may change materials and other small things in the design, but the scaling factor from the large volume is a key issue.


Obviously, cars evolve, sometimes radically, from year to year. What happens if Daimler-Chrysler decides to discontinue this engine?

This will happen. It will happen within the next two years. And then we will start upward compatibility with the next engine generation from them, and the next generation and so on. The engine will evolve.

When you buy a Cessna 172 with our engine today, you will need, say in five years, a new engine. Then you will get in your firewall forward kit a newer engine with all of the latest design changes, but compatible with your old engine.

It will be in your TC datasheet and it will be a dash-2 engine. This is very important for the concept. Today, we have state-of-the-art parts for the 1.7 engine, but 20 years from now, we wont have benefit from the scale of economics. Those parts will be out of production. We will move to a new generation of engine every six to 10 years, which will benefit the customer as long as the engine is upwards compatible. Automotive engines have always gotten stronger and lighter. This will continue.


What if the engine is dropped entirely from the automotive market?

Thats impossible. This type of engine design, an inline four-cylinder, in this category, will be important always. They will continue making parts to service engines that exist. [Editor: About 1.1 million Mercedes A-Class cars have been built; many are diesel.]


Lets talk about weight versus power. One shortcoming of diesels is power density; they weigh more than gas engines for equivalent horsepower. Will diesels continue to become lighter? Can they be as light as gas engines?

Over the long run, yes. But not in the next 10 or 15 years. Because of the higher cylinder pressures, they will stay for some time somewhat heavier than normal aircraft engines.


But how can they be as light as gas engines?

Better materials, mostly. But also manufacturing processes, which also get better. These materials are strongger and lighter than what was used before.

For example, connecting rods … a state-of-the-art automotive connecting rod is much lighter [for equivalent displacement] than an aviation connecting rod is and it has a stronger design. And when the rod is lighter, you have a power advantage because you can use a lighter piston and so on and so on.


Speaking of power, do you think the 1.7 Centurion has more horsepower in it?

Not in the next two years, no. But beyond that, it depends on market acceptance of the 135 horsepower. If we say 2008, for example, it will be between 155 and 160 horsepower. In 10 years, it can be more. The basic structure of the engine will support that horsepower. This current base engine is not capable of larger volume, but the newer one, which we will use for the upward-compatible engine, has higher volume in the same physical size.


One thing weve noticed is that the diesel engines don’t maintain power at higher altitudes as we’ll as gas engines do. How can that be improved?

To have more power and speed at altitude would cost a lot of money, because then you have to have a high-compression ratio turbocharger. It would be physically larger, also. Our engine boosts the pressure, at sea level, to about 62 inches of mercury.

If you want to produce at 18,000 feet 62 inches of mercury, you would need a compression ratio of the turbocharger of more than 4 to 1. It is possible, but it is an expensive part. Our turbocharger has a compression ratio of 3.2 to 1 and this is a good compromise with regard to the top of the power envelope.


You recently introduced a new 350-HP turbocharged diesel. How was this power achieved?

We benefited purely from the automotive improvements. This is the first example that the whole engine design will be upwards compatible. It is a new generation base engine. It allows higher cylinder pressures because of stronger materials and design. It also uses higher injection pressures. We have increased it from 19,500 PSI to 23,500 PSI and we are using piezo electric injection.

This gives a shorter opening and closing period for the fuel injection and therefore you can pump more fuel over the same duration of time. You can also open it for a shorter period so you have multi-phase injection. The better the injection valve is, the shorter you can have the first injection phase and this improves fuel consumption. This gives you more peak power without sacrificing fuel consumption and also better comfort. The engine is both smoother and quieter.

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