There was a Deltahawk SR20 testbed at one point.

Regarding diesels, an excellent current A/B comparison is the Austro AE300 DA40 NG (link) vs. the Lycoming IO-360 DA40 XLT (link). IMO the value proposition for the diesel version in North America is quite limited, but in areas with limited or expensive access to 100LL makes a lot more sense. Part of the "problem" is that the 180 HP Lycoming IO-360 is an extremely reliable engine and routinely exceeds TBO.

Note that with minimal aerodynamic changes (notably the addition of large winglets), the DA40 NG gross increased 240 lbs (9%) to accommodate the extra weight of the diesel engine. The trade-off was a significant increase in Vso (60 vs. 52 kts).

Chris

Something doesn't add up here.

A 9% increase in weight should net only a 4% increase in stall speed, not the 15% increase you indicated (which would support a weight increase of 33%).

The advantage of diesel is that it can burn Jet-A. 100LL is expensive and rare in many parts of the world. Jet-A is plentiful and cheap. In Europe, it can be a 4 to 1 price difference making a TBM and a Bonanza the same fuel cost per hour.

Another advantage is that it has better fuel specifics, more output per pound of fuel.

At some point, a heavier engine is made up for by having to carry less fuel for the same mission.

Diesels are also somewhat tolerant of misfueling, somewhat like a turbine.

Diesel fuel has no lead in it.

The disadvantages are diesel engines are hard to make light and strong enough, have high torque pulses, are hard to start, and don't like to start in thin air which makes airstarts a problem. History so far is that diesels have been problematic and unreliable.

Diesels also have some unique failure modes. For example, if a turbocharger seal blows, engine oil can dump into the intake and be burned in the engine. This could lead to a runaway engine developing lots of power that the pilot can't control. He can't shut off air, or turn off spark, and the engine will run on no fuel, just on the intake oil alone. My understanding is that some aircraft installations have an emergency air throttle for this purpose, to choke the engine if it won't stop.

The Thielert debacle isn't helping diesel adoption, either.

Mike C.

The power pulse issue is mostly being addressed through the use of direct injection. This gives a more even power stroke, better burn and a few other things I could not follow. Something about vibration/frequency management and thermal barrier on the sidewalls.

Anyway, this is all fairly recent technology (as in the last couple of decades, versus the last century) and is only now becoming more affordable for the automotive world. So this price point, is a factor for the low production aviation engines.

Tim

Not making news, just reporting numbers from the respective AFMs by the same manufacturer (PDF link & link).

I've been quite skeptical of diesels (600 hr transmission TBR ), but Diamond seems to be making progress with engine and (especially) transmission reliability. TBO for both engine and transmission is now 1800 hrs, though the higher-boost DA62 engines are initially 1000 hrs until supported by field data.

If manufacturers can address diesel reliability issues, the benefits of Jet-A are compelling, especially outside North America.

Chris

I dont believe it is the transmission that has that short of a TBO but rather the 'clutch' (a part equivalent to the dual mass flywheel in a diesel car).

Some of the current generation automotive engines use multi pulse injection to reduce the torque pulses inherent in compression ignition engines. If adopted for aircraft engines, it may eliminate the need for the clutch.



The Thielert and Austro are both derived from the same automotive engine which has been extremely reliable in automotive use. It is just not made to be run at 90% power and as a result started shucking cooling nozzles and cracking heads. An engine developed to run at that output level shouldn't have any longevity issues.

The big question is, say you have an engine and transmission at 1800hrs. The price to overhaul those components cant be outrageous to work. To get it mainstream I think the overhaul needs to be under 50K for both.

Never seen this in 40 years of using turbo diesel engines in the oilfield and we have had many turbo seal failures. The engines would produce a tremendous amount of smoke, but shutting off the fuel immediately killed the engine. I have seen an engine run away due to natural gas intake during a blowout, but that is a totally different scenario.
The old Detroit 671 and 871 series engines were supercharged and had an intake shutoff to kill the engine in the event of a runaway ( never saw it happen).
I guess anything is possible, and a simple air shutoff such as you mentioned above would do the trick.

According to this site (link with detailed values current as of April 2015) the total hourly reserve for both AE300 engines in the DA42 is less than $50/hr. 1800 hr overhaul (only) for both is approximately $50k.

BTW, I had forgotten that the TBR on the old gearboxes with Thielert engines was only 300 hrs!

Chris