The quiet rise of Rotax: 160 HP for 90 Kg ???

Flyingfish wrote:

the 12% weight advantage of Mogas vs JetA

Yes, but diesel engines generally have higher efficiency compared to petrol engines, so it not clear if there actually is a weight advantage in the amount of fuel you actually have to carry.

(I was also going to write that jet fuel has higher energy density than MOGAS which would offset the weight advantage, but fortunately I checked, and to my surprise it is the same within 1-2% ! OTOH AVGAS has lower energy density.)

@Flyingfish, the high rpm of the UL Power engine is not a problem if you accept that it’s just a way to boost the rated power. Many applications of the engine operate it at lower rpm for a good propeller design, and accept lower power in doing so. Recalculate the power to weight ratio on that basis, and you might find it still works for you.

I think the turbo Rotax engines are an evolutionary dead end for the 912-derived family. For the reasons @Dan and others explain (cost and complexity) they don’t and won’t attract a huge number of buyers. After 35 years of development they are where they are, and apparently those at BRP and Bain Capital (who hold the purse strings) don’t want to do a 150 HP normally aspirated 6 cylinder version.

A new 200 HP lightweight diesel flew recently, we’ll see if that one ever makes it to GA applications. I don’t think it would sell well either but on the other hand the R&D is already paid for, and it would have many thousands of fielded operational hours before civilian certification.

Silvaire wrote:

@Flyingfish, the high rpm of the UL Power engine is not a problem if you accept that it’s just a way to boost the rated power. Many applications of the engine operate it at the lower rpm the propeller wants, and accept lower power in doing so. Recalculate the power to weight ratio on that basis, and you might find it’s still works for you.

I think the turbo Rotax engines are a desperate evolutionary dead end for the 912-derived family. For the reasons @Dan explains (cost and complexity) they won’t attract a huge number of buyers.

Silvaire, I’m not sure if 915/916 cost in Europe is much higher comparing to LyConti in Europe.
A Rotax with an injection would typically have better SFC, so the TCO could be lower.

For the challenge with 915/916 is in it’s ceiling – it is limited to FL230 in the manual, so there is no way to build an IFR tourer (SEP or MEP) that could fly FL250, which opens many shortcuts.

The Norwegian Rotax derivatives are also nice..
ep917ti-180hp

One benefit for Rotax might be the fact that they are really mass produced (incl the drone market). I don’t know how many new engines Lyco/Conti makes today, but probably not in thousands per year..

Flyingfish wrote:

I love the UL Power engines and their very smart engineering and build quality. Didn’t know about their turbo engine, will take a look, thx.
I hope they go certified one day and wish them the best of success. They certainly deserve it.
The one thing that disturbs me about them is the high prop RPM they impose, resulting in shorter blades to prevent tips going into excessive speeds. This in turn means reduced prop efficiency due to smaller prop disc.

I don’t think ULPower ever will be certified. There’s no market in that power range. The market is UL and experimental. If they would go to certification, I don’t see how they would do it except someone specifically built an airplane for one of their engines. And the only sort of airplane that would be, is a dedicated trainer for commercial flight schools, and that market is already well served with Cessna, Diamond and Piper. If they were to certify something, I think it would be for helicopter (not that I think they will, but who knows). The Rotax 916 will end up with the same problem, even when certified. What kind of certified aircraft would be in need for such an engine? The only option would be a UL derived one than would work just as well uncertified. Experimentals is another story, but IMO nothing that an UL520 wouldn’t do with much more ease. Replacing a (I)O320/360 with Rotax 916 is a bit over the edge, for literally no added benefit for 95% of homebuilders.

They don’t really impose high RPM. They can handle high rpm, and they also have a limiter that prevents them from over revving. Let’s look at the UL520i (lower compression version that can run very low octane fuel). It has 180 hp at 3200 rpm. If you reduce that to 2800 rpm, you still have 170 hp. Or you can reduce the prop diameter a tiny bit, increase cord a tiny bit and run up to 3200 rpm for 180 hp. The loss of efficiency is nowhere near that 10 hp. Most people would probably just settle for 2800 max rpm and 170 hp, just for good measure. What you get is an engine that runs well below it’s max potential, but still beats the whole bunch in terms of hp per weight. And it can run on 91 RON, well below standard mogas (95 RON). If you want even more hp, then there is the UL520iS (min 97 RON). You will then get about 185 hp at 2800 rpm.

A 912 ULS/S and in particular the 912 UL/A/F are true and trusted engines. The 915 and 916 are pushing it a bit far IMO. Certainly cool, and they will probably sell a whole bunch.

Flyingfish wrote:

Actually the STC for the 155HP DA42 was very difficult to obtain. I recall issues with Vmc resolved with vortex generators on the rudder.

But precisely this STC would provide a good starting point, simplifying the R916 STC

There are two great reasons of having liquid cooled diesel engines in DA42:
1. Jet-A1 availability – practically everywhere.
2. Practically no possibility to shock-cool the engine.

I’m sure Rotax produce great engines but somehow I don’t see them in DA42.

Dan wrote:

The dry weight of le O-320 is 122 kg

@Dan, as there are so many O-320 versions, I thought it could be valuable to give a specific example:
the O-320-D1A, direct 160 HP @ 2700 RPM carburetor parallel valve
comes at 255 lbs (115,5kg) w/ mags, fuel system and starter
that’s according to type certifficate date sheet

By using dual self powering pmags in lieu of mags one can save at least 1,5 kg at the same time gaining variable ignition timing
all in all it’s 114kg for an engine which when cared for properly and operated within factory limits would outlive our kids