Something a little debatable for the Christmas round table, and Merry Christmas all. Have a quiet moment with the kids playing with their toys where I get to ponder.

I’ve flown a couple thousand hours suspended by Lycoming four and six cylinders, and have profound respect for the 320, 360, and 540 in particular. They are however, extremely antiquated (with which comes the reliability, to be sure).

I can’t help but keep getting itchy looking at newer offerings, in particular for my little runabout, a Murphy Rebel on amphibs that’s motivated by a 150hp 320.

If I had to pick downsides to my beloved Lycomings, they would be,

1) High altitude performance, which is equally applicable to all naturally aspirated engines.

2) Weight, these engines are solid, and by no means the lightest power available per HP when considering uncertified power.

3) Fuel economy, I believe the inherent limitations of the Lycoming induction system, the passage ways and valves, limit efficiency being tuned to the utter maximum.

The most interesting engine to me at this moment is the Rotax 915is. Performance is maintained to altitudes I’ll never fly at, about 60-70lbs would be removed from the nose of my plane near as I can discern which is huge in this weight class, and while not cheap it’s very comparable to a new Lycoming. It also appears at cruise that fuel economy would be improved, and therefore range and payload, due to either being able to go further on the same fuel, or carrying less fuel for the same.

Performance at sea level would likely improve over the 320 due to the weight reduction, and only giving up single digits in HP.

Food for thought, what would you run if cost wasn’t a factor, and efficiency, weight, altitude performances and quiet running were the mains?

Personally, I would be looking hard at a Edge 300 built off the yamaha motor. I plan to build a homebuilt Scout powered by the same motor.
Jason is the dealer over here in Alberta and is running one on his S6. I believe Steve Henry is running one as well. I like rhe extra power. https://badasspowersports.com/badass-sh ... x-engines/

That’s wild, full respect for the engineering that’s taken place there, especially in regards to the gearbox. Also like to see Canadians doing stuff like this, I’d wondered about some of the higher strung motorcycle power plants, in particular the Hayabusa based V8s being put in race cars.

That said, the stuff’s too wild for me. I’ve had one engine failure in the act of aviating (courtesy of Rolls Royce) and they’re rarely convenient where I like to fly. Often it could mean the story. I’ll pay the money to have a certified engine or variant of, but I agree with what you didn’t have to say, this limits the innovation in the available engines a great deal.

That little 915is seems to hit a sweet spot for my little plane.

A very thought provoking subject. The GA community is screaming for an advancement under the hood but equally values reliability. The experience's I've had with engine issues, three do date stemmed around the accessories, not the engine itself. I know potatoes, potatoes a failure is a failure regardless of the how. With advancements in accessories like FEDEC, solid state ignition etc. have we mitigated those risks other than an all out catastrophic event.

The 915is raised my eyebrow as it’s a thoroughly modern engine, and certified to boot. Would be a significant drop in weight and a leg up in efficiency, plus making rated power to 15,000’.

As mentioned I have huge respect for the Lycomings and Continentals. There’s a reason Burt Rutan chose Continentals for his Voyager 76. This said, that was forty ago, and I could see the same plane with a 915s today.

I love the idea of a lightweight, modern motorcycle / auto conversion. And especially a lightweight jet fuel burning turbo diesel, but for now I’m a definite certified engine close minded sort. There’s just too much at stake true bush or mountain flying something more adventurous, for me.

I TBOed only three and a third 0-320s, at 3,000 hours average TBO, in ten years flying pipeline. The problem with data on your newer engines is getting that kind of TBO data outside pipeline patrol, which is going to stay with the proven engine until the newer one gains years of recognition. You young guys maybe should fly a few of the newer models around the world non-stop.

Jim nailed it. Even that “certificated” Rotax engine you like has very little operational history....yet. That, of course, doesn’t imply it’s not reliable. And, Rotax engines in general have proven themselves worthy.

I for one, like the idea that Rotax is actually developing and building engines for aircraft use. Unlike Yamaha and others, which are being “adapted” by some smart folks. Those may work, and may prove to be reliable......or not. But they’re not purpose built aircraft engines.

MTV

The Rotax 91X series is awesome. I've really enjoyed the hours I've spent behind the 912. Add turbo and efi and it's even better. I would likely choose this option if the engine balanced out on the airframe.

One thing that takes getting used to is the higher auditory note of 5700 RPM vs 2700 RPM. The direct drive engine note is a little more pleasing IMO.

Rotax parts are not cheap. And I think they have some mandatory service items at TBO that are pretty costly. That's just aviation.

The props available are lightweight and cool. Airmaster hub for electric in-flight control? Yes please.

The O-320 is a sweetie but I'm guessing this is going in a cub type airplane and they are heavier powerplant. Saving weight on the engine is great but it has to balance.

contactflying wrote:I TBOed only three and a third 0-320s, at 3,000 hours average TBO, in ten years flying pipeline. The problem with data on your newer engines is getting that kind of TBO data outside pipeline patrol, which is going to stay with the proven engine until the newer one gains years of recognition. You young guys maybe should fly a few of the newer models around the world non-stop.

And that's exactly how this 2700 hour Rotax 912S pilot feels about the Yamaha engine. Looks cool, following it's development, but waiting for fleet hours to build, ain't there yet. Kinda like the legacy engine pilot's talked about the 912 15 years ago!

My last total and unexpected in flight engine stoppage was with a Lyc 320, in an Avid Magnum I was flying the 40 hours off on. Turns out the issue was too much air in the fuel tanks, yeah I ran it dry! My eyeballs weren't calibrated to the sight gauges...what looked like a good hour+ plus of flight time to eyes set to 3-4 GPH, turned out to be "less" time remaining then that , that and a little distraction lead to a no damage landing in a farm field. Some would call that operator error, and not blame the engine, and they'd be right, but really, the fuel flow turned me off. Ha ha.

The Rotax line of engines are developing very nicely and they have a serious competitor in the ULPower models as well, maybe the times are slowly changing.

All fair points, and appreciated. In gentlemanly debate I’d argue the Rotax 915 / 912 has reached legacy engine status. The 915 is same displacement and architecture as the 912 line, which has flown 60 million hours. It’s just the most modern of the line in terms of refinement, and is best thought of as a 2018’d Rotax 914.

Which I’d argue is well proven, the fleet currently does 5 million flight hours a year and climbing fast as the engine family finds numerous new factory installations every year. I first flew one as a student pilot 20 years ago, and it wasn’t close to new then. First solo and pilot permit was behind the Rotax as well. The certified turbo variant has been in production and flying for 25 years.

I just hope to see small Jet-A fuelled aircraft diesels come from Rotax in the next 10 years. That, especially opposed piston or rotary diesels, is the future of light aviation in my eyes. I’d like to see a single fuel aircraft industry, but this is another discussion.

On the sound of the 912 family, I agree it’s not a “relaxing” note, but installed right it’s quieter to my ear than the Lycoming db wise overall. I ride race motorcycles on road courses as entertainment, so I’m fairly well seasoned to rpm noise.

I’d happily “put up” with it for the efficiency and weight savings. On balance, it would be simple as Murphy builds the Rotax mount and cowling factory, it’s installation is in the build manual, and their factory is an hour from my house. I’d just go buy the installation hardware and make the change as the Murphy is a homebuilt.

The only question left my end is am I keeping the Murphy for the long haul, my O-320 is at 2150hrs on the bottom end. While there’s good life there I’d be loathe to make a major investment in it when I could be upgrading to a far more modern engine, that would perform better in just about every metric on my little plane.

Personally, I would switch to the Rotax if it were me in that position. Yes the legacy engines are great, but I think these newer engines just have to much to offer to not take advantage of them. I would agree with you that the Rotax has a proven track record.

To me a motor is a motor. Block, crank, pistons, etc,etc. and the quality of the engine is based the quality of those parts. Both the Rotax and the legacy engines have pretty well established themselves as being reliable unless poor quality parts are installed or the motors are abused. The Rotax is using electronic fuel injection and full electronic ignition control and it automatically adjusts those based on temperature and altitude and many other things. I believe an O-320 set up the same way with something like the SDS kit would give the Rotax a good run for its money horsepower for horsepower. What I find funny or strange is that people have no problem accepting that kind of engine control on a Rotax or UI motor but if you talk about doing that to a legacy motor every body looks at you like you are crazy. To me there is a huge boat being missed in the armature built scene to bring those legacy motors into todays world at reasonable costs. Granted the Rorax may be lighter hp per hp than a legacy engine but I am not so sure when you get rid of all the junk on a legacy engine and you weigh a fully dressed turbo Rotax.

Rotax might benefit by running some patrols with Rotax powered airplanes. They would have to duplicate official patrols because they would not be able to be insured for the contract. Anyway they would be able to demonstrate, or not, that they could go average 3,000 hours at 200' AGL in the heat of day.

Why wouldn’t the Rotax be allowed to fly pipeline patrol by insurance contact? They’re certified here and there, and available in certified aircraft both sides of the border.

We ran a lotta pipeline at Airborne both in Canada and stateside with turbines that don’t allow any sort of on condition run time past TBO, and the overhauls are in another dimension of cost. If it wasn’t a helicopter patrol, the cheapest fixed wing they could get their hands on was used, usually a very old Cessna.

The acquisition cost of new Rotax powered certified aircraft is the reason we don’t see them doing a ton of this, when a $30,000 Cessna will do it which is less than just the 915is costs without the plane around it. This said, that’s not a knock on the Rotax, we all know where the price of a new Cessna has gone!

There would be no issue insuring the aircraft, as we’ve run a huge spread of types and engines in pipeline, both here and in the US.

175 Magnum good points,

On the specifics of engine design it’s a good point that the Lycomings and Continentals are artificially held in the before times. Unfortunately however, they do have design limitations that cannot be overcome with more modern accessories and controls. A major one when I compare my O-320 to a 915 is the lack of turbo charging and as a result turbo-normalizing.

I fly at altitude frequently here in B.C., and have had many, many hours of wishing for sea level performance above 5000’. Adding turbo-normalizing to the 320 will increase its already high weight even further, and decrease its life span. There reaches a point where the design has been pushed simply too far. I want to shed a lot of weight, gain turbo-normalized power, as well as decrease fuel burn. The 320 just isn’t going to get there unfortunately.

Probably better to compare a custom turbo O-200, but that too is going to struggle compared to the 915is in my opinion, and likely not save me anything and give up the reliability of the package.

Contract with the oil companies requirements in US. Shell and many other pipeline owners sold their lines with the stipulation that they have first option on putting products through them. Limits their liability, which is a huge issue here. New owners fly every two weeks when old owners flew every week. Every two week will cause 21 day not flown shut down in the east and midwest because of stationary fronts. All of that may have changed. Last I flew pipeline was 06.

I think a Rotax sounds like a fine idea if it fits your desire. Z mentioned it already but I think the biggest consideration is can you handle the weight loss on the nose? Because of the significant difference in weight between a 915 and a 320 your empty CH is going to move aft a bunch. Will you have a useable airplane with that aft CG move?

I do have to agree with 175 magnum; they are made of the same basic mechanical parts so just add whatever you want to whichever engine you want. A turbo normalized 320 isn’t any more stressed than a NA 320 at sea level...their both operating at the same DA.

Back when I flew my Luscombe I like to razz courierguy when he would post about the efficiency of his rotax/S7. My Luscombe/C85 could fly at the same fuel flow and the same speed as him...maybe even a touch faster

The Continental in my Bearhawk has electronic ignition but I kept the Continental fuel injection because it simple, reliable, and I like it. I really wanted to put a more modern engine in it but there is nothing. The few options have no real engineering to back their psru installations and I’m too chicken to experiment with that.

I guess what I’m saying is all engines are pretty easy to modernize. But if the 915 meets your specs it’s easier to just write a check.

Unfortunately, the 320 turbo normalized will likely weigh 100lbs more than the 915, which is massive in a small plane. Also, turbo normalizing still requires increased cooling, and reduces engine life. You’re removing the altitude derating the engine enjoys in cruise, and essentially operating it at takeoff power, all the time. Combine that with the extra heat, and we won’t be flying that 320 to 3000hrs.

The biggest concern would the the weight of the package, you could easily be looking at 100lbs more than the 915. Finally, the Murphy Rebel was pretty well designed around the 912, so it fits and balances perfectly, the 320 was an afterthought in the Rebel as a higher output Rotax didn’t exist at the time. It does now.

My small change.

Back when I flew my Luscombe I like to razz courierguy when he would post about the efficiency of his rotax/S7. My Luscombe/C85 could fly at the same fuel flow and the same speed as him...maybe even a touch faster

Probably faster! Luscombes haul ass for sure! One lift strut, clean metal wing/no flaps, small tires....but I'd bet if my tweaked Rotax was in one (or a T-Craft) it'd really make a different airplane out of it! I'm swinging a 78" prop, try that with a C-85. 3.25 to 3.5 GPH on average, tilted towards the lower number. Mogas of course. Living at 5640' , I feel no need for the weight, complexity, and heat issues of a turbo, go figure.Last time I was at 13K I was climbing 300 FPM, that's good enough. Noise? here's a short clip a neighbor shot, seems pretty quiet to me. https://www.youtube.com/watch?v=mfOJi-TU-og

I’m a Rotax fan as well, they build an excellent motor and the power to weight is hard to beat.

Unfortunately (well, fortunately!) I run an amphib off high alpine lakes in the mountains here, there’s no way at all she would depart naturally aspirated. Even the 300hp Wilga struggles.

After a high efficiency engine of 140-160hp that will put out at 10,000’ what it does at sea level, that throttles back to less than 5g/hr cruise, with certified reliability. And being an amphib and therefore very heavy with limited useful load, I’d like to get a bunch of weight out the plane. Even 50lbs would be a game changer, that’s 2hrs more range of fuel to feed a 915. Combine that with the 915’s better cruise fuel efficiency, and I’m looking at double the hang time and range. (4.5g/hr for the 915 and 44 gallons on board, vs 7.2g/hr for the 320 and 35 gallons on). I frequently do 800nm trips across our province here headed to work, and eliminating a fuel stop sounds really good.

That makes a mighty short list, and gets me scribing posts like this trying to talk myself into one.