PSRU are easy to make, hard to master. For 200HP belt drive should be fine. No need to go all double helical. There are quite a few high end PRSUs and also lower end. A smart designer would stick to off the shelf bearings/belts/gears so a breakdown is little more than a call to mcmaster/carr or somesuch.
The Subie company (Eggenfelner) folded and left a lot of people hanging. And the owner almost immediately started the Viking engine company. I wouldn't touch 'em with a 10 foot pole, even though they have seemingly had some success, at least in selling engines. That said, I don't see many flying engines in the field except for a handful of RV-12's. One of those was built by an acquaintance of mine who was "very happy with it" but if you pressed for weight and performance details vs Rotax powered examples, he clammed up like Michigan T. Frog (look it up).
Rotax happily supplied the ultralight market with new engines, and even developed the gearboxes to drive the props. They did not "get pulled" into aviation. Nobody forced them to develop of build anything for airplanes. Where do you get this stuff?
I installed an RAF Subaru conversion in a Glastar and flew it. The airplane owner wanted an engine cheap to buy and cheap to operate and cheap to overhaul. He got none of those things. When he sold it he got only half the value of an equivalent Glastar with a Lycoming in it.
That screams "CERTIFICATION/REGULATION OBSTACLE" in all caps. In a rational world, incremantal changes learned through experience to reduce manufacturing costs wouldn't need or require a ground-up re-certification gauntlet.
Oohhh, what a sure path to potential disaster. Beancounter asks for a cost reduction, small manufacturing detail changed to reduce cost, blocks/cranks/pistons start failing 500 hours later.
No at all. Mercedes, as with most auto OEMs, would tweak their engine and vehicle designs on a semi-regular cycle. For Austro, each of those tweaks also required minor alternations to the approved type design for their TC’d engine, just as any TC holder must do. It had nothing to do with reducing mfr. costs. But also, it was hardly a ground up re-certification.
High revving four bangers is indeed the solution. Ask Rotax.
Exactly - they're already designed to run at constant high power settings and drive a reduction gearbox.
In a waverunner it would direct-drive a pump. Even if it drove a marine prop via a gearbox, it would not have to deal with the massive TV presented by aircraft props.
A good aircraft conversion design could and should decouple the engine from the prop's thrust/gyroscopic loads.
I believe he is referring to torsional vibrations vs any "loads" which while they can be reduced through various methods cannot be eliminated. So simply replacing a boat prop with an aircraft prop would typically require a redesign to handle those vibrations.
Yes. Torsional vibration. That heavy propeller wants to turn at a steady rate, like the flywheel that it is. The engine's crankshaft does not turn at a steady rate; every time a cylinder fires it accelerates, and on every compression stroke it decelerates. This makes the gears or chain chatter, especially at resonant frequencies related to RPM, and the loads thus placed on the PSRU can be many times the load of the engine driving the prop. Belts can absorb a little more of the TV, but they can still fail. So the PSRU has to be designed to be either really stout (meaning heavy) or with enough damping and flex to absorb the TV.
For aviation use, this engine would require a PSRU, which would have to support the propeller loads.
Not true. Rotax was in airplanes before snowmobiles, IIRC. They sell a lot of snowmobiles, sure, but that's never been their only game
In 1962, Rotax started supplying engines to in Ski-Doo snowmobile. Ski-Doo was part of Bombardier. In 1970 Bombardier acquired Rotax. Then in 1975 Rotax developed their first aircraft engine, the Rotax 642.
They were founded 1913, built aircraft components as early as 1917.
Different Rotax. That's a UK company, the Rotax that we're talking about is Austrian. Here's part of the history from their website;
On the SMA diesel I worked on, we found a cracked blade on the MT composite prop. I believex it was from the vibration, which was rather extreme at idle, and the FADEC would not let you change anything, not even idle speed, until the engine was warm enough to satisfy the computer. For big cylinders at 15:1 compression (even at idle, of course, in a diesel) to make it a 230 HP engine, means lots of vibration. These engines did not have the fancy multi-pulsed injection we find in modern autmotive diesels; it was all at once on each firing, making a sharp acceleration pulse every time.
Rotax service was garbage. They had no service centers in the US until it affected sales.
PREACH IT BROTHER.
And you totally didn't read the two (of many dozens) posts I gave regarding lack of support/parts? Rotax's early ventures (the 2 strokes) had TBOs in the low 100s of hours. Its only later did things improve (most likely due to changes in ownership) did things improve.
Certified? Until recently* (as defined in aviation circles), all the Rotax powered stuff was experimental and didn't need a certified shop. Certainly my friends who flew/fly behind Rotaxes didn't have any problems getting parts or service.
Bombardier, a Canadian company, bought Rotax in 1970 and we have had Rotax distributors here for a long time. I will remind you that ultralights did not exist in 1970. When they came along, Rotax was already here supplying engines for other applications.
Would also be nice to know what his hands-on experience is, in both maintenance and flying, with the various aircraft engines he so often condemns.
A data pool of 'a couple of people' is not indicative of anything. I posted 'a couple of people' having poor service as late as a few years ago.
I snagged a run out IO-470. Working on lengthening the BD's fuselage for W&B (common mod), that's gonna require redoing all the controls to the rudder/elevator. Hangar is brutal in summer so I'm kinda stuck in my conditioned garage overhauling the -470 and Pentastar.
Comparing an engine designed in the 50's to one several decades later and then saying 'gee, look how much better it is' is not making the point you think it is.
