I’m at a point in my build where I need to pick an engine.
The Viking guys love theirs, the rotax guys love theirs, the UL guys etc.
Everyone tells me 130 hp.
Any advice? I have a hard time believing the 750 wont perform well with 100 hp.
Feel free to give your opinion.
Rotax is just costly but they are really light compared to anything else.
It just seems to me that adding weight in the nose would make power off flair challenging.
Any thoughts?
Without knowing your priorities, it can be tough to make a recommendation. So this is more my thoughts based on my priorities.
Based on the performance of the factory built planes at LSA weights, an O-200 offers impressive performance so unless I plan on doing something that requires better than the O-200 performance, 100hp is a reasonable floor.
If money is tight, and I am looking to fly quickly, I would likely be shopping for a used O-200 (there is a 1500 hr O-200A listed on Barnstormers right now, at a price that is in line with the 90hp Viking, is better documented, and will be easier to get A&P support on if you need to farm out maintenance and inspections once its flying. But personally that would not be my first choice.
Once we accept that performance is covered by most options, I would focus on 3 realities: 1) Most EAB aircraft are flown less than 100 hours per year (so that high time O-200, is likely looking at 3+ years before it hits TBO, if you plan to rebuild at that point), 2) If I am building a STOL plane, its because I want to go anywhere, and the last (often overlooked) concern 3)Anywhere includes airports.
Based on those realities (assuming any major engine choice will be reliable), I would look for something well documented, easy to work on, has the fewest calendar time based services, and (because I want to go anywhere) can run on the widest variety of fuel. Personally, I would not build a plane right now that cannot run on 100LL, because even though I hate the stuff, I don't want to be stuck at an airport wondering what impact the fuel will have on my engine. For that reason I would not choose a Viking and would shy away from Aeromomentum (I don't find any info on how well they handle 100LL). This is a bit of an annoying requirement for auto conversions, because many pilots take for granted that the engine can run on 100LL, but modern car engines are not designed to handle it. I'm guessing landing at airports was not the plan when you chose the STOL version of the 750 and for that reason running E15 would also be a requirement. Being able to land at a backcountry strip (or rural road in places its legal) and refuel at the nearest gas station fits my dreams of a STOL plane. That requirement would eliminate all older aircraft engines, most Corvair conversions and most VW (due to limited documentation that I have seen on long term ethanol exposure in these aircraft conversions).
Personally, my first choice would be a mid-time Rotax, its the most cost effective option that addresses my concerns. If I am buying new, especially with backcountry flying, I like the simplicity of a direct-drive, air-cooled engine. Time spent in the shop for work like Rotax's 5 year rubber replacement, maintaining/bleeding the cooling system and inspecting the gearbox is time that isn't spent flying. So, unlimited funds, I would go with a UL power engine.
Last, I want to address why I would go used, I think in 5-10 years the fuel situation in the US will be very different, I personally fear that the 100LL phase out will go really slowly then all at once, but I don't know what the timeline will actually look like. Both the Rotax and the O-200 can handle 100LL and Unleaded alternatives, but if 100LL was phased out tomorrow, I would look at using a modern auto conversion (I personally like what I have seen of the Aeromomentum, but I have no hands on experience with any of them.)
A final note, this is based on what I have read and I am generally unqualified to have an opinion. I am just some dude at his computer.
