Silvaire wrote:
An engine driving a constant speed propeller tends to increase in efficiency with increasing power because friction losses remain constant at constant rpm.
You seem to presuppose that the rpm is the same at different power settings. They are not on the Diamond diesels at present. Adjusting the power also makes the ECU adjust the RPM. So frictional losses are lower at lower power settings, unlike e.g. the Cirrus arrangement, where the RPM is kept at 2500 RPM over a very wide range of power settings.
I think the “linear” bit is stressed here because the power-to-fuelflow curve is fairly linear on the diesels that Diamond uses. If you look at a Lycoming (even taking into account most effective RPM) you will see that the sfc rises more sharply at higher power settings than the diesels do. In other words, the diesels not only have a low sfc to begin with, also the sfc curve stays low over a wide range of power settings compared to classic piston engines.
Obviously, and as I made clear, the ECU or pilot (in most types) can maximize efficiency by reducing rpm to the greatest extent possible for a given power output. As I further explained diesels can run high torque and low rpm without concerns about fuel detonation, but as I even further explained it doesn’t matter if in real world service the pilot wants to get where he’s going quickly and does not reduce power greatly in cruise. I wasn’t presupposing the engine would be run at constant rpm, only that in the real world most people don’t fly at ultra low power settings (i.e. at much reduced rpm) to achieve maximum engine efficiency, regardless of engine type. I assume this is why Cirrus uses constant rpm control but I’ve never flown a Cirrus, don’t know anybody locally who flies a Cirrus, and don’t have any interest in the type. Or in Diesels either.
I do have a friend who likes to pass me while flying his 180 HP RV8 at some ridiculously low rpm and lower setting (1900 rpm and 5 gph or something like that) but he does it to make the point that his airframe is very efficient 
As he passes my plane might be burning 7.5 gph with a 150 HP engine…
Some interesting news from Diamond today regarding the DA50.
It seems the project is very active and there have been some significant updates.
1. The aircraft will be retractable.
2. The engine is now the certified CD300 (which replaces the previous SMA 280hp engine)
Certification is targeted by next summer.
This is interesting because it’s adds additional power and retractable gear. Diamond previous said they’d reached ~170kts with fixed gear and the SMA engine, one would think the new configuration would get you closer to ~190kts at max cruise and ~180kts in normal cruise.
The DA62 is a remarkable aircraft and very very comfortable, they have a good airframe to work with and it will be a much more spacious cabin than the Cirrus. A very modern, spacious, fast, fuel efficient, jet fuel burning and sub 2000kg tourer seems pretty prefect for Europe and much of the world. I hope they can deliver it at a competitive price to the SR22.
Looking forward to seeing how this develops!
The fatal flaw in both these designs is that they’re not pressurized. They would kill it if that was the option. Now, people that can spend that kind of money and are at that point in their flying, will look at other aircraft. You can get a used TBM, M500 etc for the same money with lots more utility.
What happened to the turboprop version?
Quite a few changes since original plans. It’s been some time since we didn’t hear about DA50 that was looking promising. Probably too close to the SR22, they wanted some added value.
https://www.diamondaircraft.com/en/about-diamond/newsroom/news/article/diamond-aircraft-da50-program-changes-and-new-engine/
Hope that it will have a chute.
In fact, it is getting closer to TB20 concept. The picture shows very different wing shape from DA40 and just 4 places… Front glass looks like chipmunk’s one. And yes, turboprop may be for later…
With a chute it could compete with Cirrus. I’d take a 300 HP single lever diesel over old Avgas designs. 9GPH of cheap diesel for 190kt cruise sounds great. With retractable gear pilots could also look down at SR22 owners (unless they retract it on the ground haha).
Test flight was apparently still with a Fixed Gear configuration, but exciting development! The more competition (Cirrus need some!), the better.
(that red-silver looks waaaaaay better to me than the gold-purple one)
I hope they finally move to a side-stick. You’re not exactly going to be flying aerobatics anyway
We need more competition for the diesel type engine to get the price down. They moved from sma to austro engine finally…
