Ah, Bill Brogdon's opinion on the subject! It's an interesting one, and a likeable guy, but it's hard to take too seriously from someone who pissed away one of the few opportunities to design a clean-sheet aero diesel, admits that it failed because of "too much weird" and then proposes yet more weird for his "solution"

What's with his screwed up cylinder barrel design? Head gaskets are doing fine for the gazillions of diesel engines out there. And through-bolting as he proposes is heavy-heavy-heavy! Four valves-per-cylinder is completely unnecessary and arguably an impediment to good combustion, cylinder head structural efficiency and cooling.

As Bill demonstrates admirably, it's easy to design a lot of unnecessary hurdles into your diesel engine...

Have you sat in one? Impressive numbers, but they're sized for dwarf pilots. I guess they were concentrating on keeping the CdA down...

yep i have, and thats why i dont own one. a bit to cosy for my liking..

I would guess the major GA Countries are not the market Piper has in mind for the Archer DX.
Therefore any pros vs cons argument is a bit pointless.
Most of the planet has either little or no Avgas.
The Archer DX will be the ideal (and only) choice to most of the emerging world.

The Dyn'aero Sportster does 150-160 on a 100hp Rotax 912. That is efficiency for you, but it's micro sized.

Diesel / JetA1 is the fossil fuel for the future or at least until the big jets stop using JetA1.

But they're not running at 75% power day in day out and not going to 100% power every time they start moving.

The 1.7 litre Thierlerts were unreliable at 135 HP. That's why they stated fitting 2.0 litre 135 HP variants. The 2.0 litre ones at 155 HP are approaching the same power to cc ratio as the 1.7 litre ones were at 135 HP. I'd say it's reasonable to presume reliability will suffer for the 155 HP 2.0 litre variants. So far as I know the 2.0 litre 155 HP version hasn't been used in any numbers yet.

The gear boxes are another issue. Gearboxes on engines of less than 9 cylinders producing much more than 100 HP have generally never been all that successful/reliable.

No doubt about it diesel or JetA1 is the way to be heading, but no one has yet built a successful diesel GA piston engine, much less one that is based on an automotive engine. By successful I mean one that can compare to the likes of the typical Lycoming or Continental for cost, power to weight and reliability/TBO.

What makes you say the 1.7's were unreliable?

I'm pretty sure they changed to a 2.0L block of their own design because of supply issues with MB - always a problem when using short production lifespan auto parts.

As far as the gearbox reliability issues go, I have heard from an ex-Thielert engineer that the 300hr, now 600hr inspection was a bit of a con and amounted to not much more than a poke around with a borescope through an inspection hole before sealing back up and shipping back to the customer. They also mentioned that the military/UAV derivatives were much more advanced than the GA version because the re-certification issues were a financial burden the product couldn't bear, despite the leaps and bounds made in the military applications of essentially the same engine.

I understand an operator here had more than a few issues with the 1.7 litre engines and has re-engined with the 2.0 litre engine. Admittedly second had info but I think it's correct.

Also I seem to remember reading the reason for the bigger engine was to improve reliability.

At least one large DA42 operator in Australia re-engined their fleet with (L)IO360s after quite a number of IFSDs.

VH-XXX

Just for the record ...
Narrow deck Lycoming IO-540

POWER PLANT

1. ENGINE
a) Manufacturer Lycoming
b) Model IO-540-E1B5
c) Fuel 100/130 Octane (Minimum grade)
d) Oil grade Per Mil-L-22851. See Lycoming Service Instructions
e) Engine Operation Limitations
CONDITION --- --- BHP--- RPM--- TIME
Takeoff -------------290 ---2575---- No Limit
Max cont at SL -----290--- 2575---- No Limit

They must have plenty of margin built in there if they certify to run flat chat 24x7.

The O -320 is also good for FT 2700 max continuous. So it's not unusual in the aircraft world to have unlimited full power operation.

Some IO360 aircraft I've flown have no time limit on full throttle/2700rpm.

As I mentioned in a previous post there being no time limit as far as I am aware regarding basic piston engine power plants & I would imagine that this is because the manufacturers would have no way of controlling any said limits once it left the factory anyway. I mean there would be a lot of pilots out there whom just run the engine anywhere within it's operating range inc full power all day everyday with minimal care.
These power plants would have been tested well beyond their normal operating regime to gain certification anyway.
Bit like the SWL of a crane, it would have been tested to destruction to find it's max limits them probably reduced by half.


Wmk2

I don't think in-flight shut-downs or reliability issues had anything to do with that it was only 1.7L. Most of the rumours I heard were to do with the electrical/FADEC system

Cessna took on the Thielert as a production engine 172TD in 2008, a dozen went to the Iraq Airforce. In the mean time Thielert went broke and the program was abandoned.

http://web.archive.org/web/200803082...d_brochure.pdf

As Cessna now have the 182JT-A and have not re released the 172TD it makes you wonder.

Having flown a 172R with the Centurion I can tell you it's a dog.

STC's to fit the 135 hp Centurion engine in the Warrior have been around since around 2005, Thielert would not offer the 155 hp version into the retrofit market trying to keep it up there sleeve to induce the OEMs with more HP.

Gearbox, clutch and fuel pump require frequent replacement. The 2,400 TBO has been promised since around 2005. This was to be paid pro-rata on the 1,000 hour engines but as Thielert went tits up many owners were left high and dry.

Yes common Rail diesels are very reliable and efficient however to get the power to weight small diesels had to be used and pumped up. The base Thielert in its previous Benz spec is only about 60 kW and will do millions of Kms, nearly double the output and boost and the reliability goes out of the window. In the car it cruises at probably less than 30 kW. Diesel has excellent lubricity so the HP fuel pump survives in the automotive world on Jet A1 the pumps just don't last, these things run nearly 20,000 psi of fuel pressure between the HP pump and the rail and the by product is heat, having flown the Simpson with the fuel temp in the red I can tell you this is also a major concern.

You're right – and the diesel 42s had 2.0s. Still relevant to the discussion of overall reliability.

172TD Brochure link
 

FTAs 6 x DA42's had 1.7 Thielerts, they were removed after lack of confidence due to 13 un-commanded power losses as well as replacements due to head gasket problems. The aircraft sat for 18 months until the Lycoming retrofit was carried out.

Ask anyone that has had one if they would buy another .....