Reliability and complexity of alternative engines.
 

Forum,

I've been doing a lot of research and reading about using a subaru engine in my project and one thing that I'm struggling with is the complexity of alternative engines. Face it, there is just a lot more to fail when your dealing with EFI controller, Ignition system, electric fuel pumps, alternator, battery, cooling system, turbos, etc.

I do agree that the basic subaru engine is far more reliable than a lycoming, but I'm not sure it is when you include all of the other systems it depends on. A gravity fed carburated lycoming is so simple that there isn't really anything to fail shy of catastrophic failure like dropping a valve or breaking a crank, where the NTSB is riddled with cases where a subaru engine lost power because of wiring or a fuse or some small dependency that doesn't exist in the lycoming.

At this point I'm trying to determine which poison I want:

Lycoming and the noise, vibration, pain in the neck cold weather operation, expense, and risk involved with using a 50 year old case and crank.

or

Subaru and the complexity of the installation and massive amount of dependencies.

I'll summarize my concerns with an example: Bud Warren. An A&P who makes a great gear drive, that has shown to be reliable, and uses a chevy engine which is also shown to be reliable, still lost his plane because of a failure in the system. Granted, the fuel line could have failed on the lycoming too, however, it goes to show you that the installation of the system could compromise it, and generally speaking, the system required to run a lycoming is MUCH simpler.

Anyone have some thoughts on this? I really really want to run a subaru since I live in Alaska and having heat in the cab would be wonderful, but this place isn't at all tolerant of failure and I'm concerned about the complexity of running a subaru engine.

Thanks,
schu

Not as much difference as you think.
 

It all comes down to your comfort level, and how much you are going to make vs. buy on an alternative powerplant.
I went with an Eggenfeller FWF package that was quite simple to install. If you are planning to 'roll your own' then it is a lot more work and complexity in the design and installation.
As far as the 'massive dependencies' for the Subaru, it's really only the externally supplied electrons vs magnetos.
Both engines have alternators, and turbo systems if you're going that route, and even a carburated Lyco needs fuel pumps on our low wing planes, so that's a wash from a dependency viewpoint.
Cooling is different, but the difference is in the installation. Engine failure due to cooling failure doesn't seem to be a big issue. Getting your cooling system to work well is a bigger issue. In Alaska you'll have fewer problems than most :cool:
So you need a robust electrical system. It is a dependency the Lyco doesn't have, so you have to decide if the benefits outweigh the risks. You have to be comfortable that you can design and implement a reliable, failure tolerant system. Don't forget immediate notification of alternator failure! Designs (and support) are available on the AeroElectric Connection.
When you say the NTSB database is 'riddled' with cases where a Subaru lost power due to a dependency that doesn't exist in the Lyco - exactly how many are we talking about? (I've never bothered to look - I hope it's not many :eek:)
Oh, and I doubt your Lyco will have a 50 year old case and crank. The design may be that old, but the parts will probably be a bit newer :rolleyes:

I've got twin batteries and twin alternators on my EG33.

With your gravity feed to the HP pumps (two) you should never have a fuel feed or VL situation.

The controllers are bulletproof if they don't get wet.

Follow current best practices on the cooling system and I would not expect any problems there in your climate.

More unknowns exist with the PSRU as each installation is unique and untested.

All supporting system must be well designed as you correctly point out, this is where most problems have occurred to bring down alternative engined aircraft.

STOP!
 

The Subaru basic engine is not more reliable that a Lycoming. (as stated in the second paragraph of the first post)
Be honest with yourself. You can have your own point of view, but you can't have your own facts.
There are no alternate engines that are demonstrably more reliable in aircraft than 'aircraft engines'.
Now that I have that off my chest......proceed with caution, I am.
I'm having a blast building my power plant, and redoing so many parts is just going to happen. Not only are there very few pre-made parts, most parts you make will be redesigned, refabricated, or repositioned. Plan on it and enjoy it. Once you get the engine running, you must evaluate all the systems you created. On a Lyc system you can pretty well count on the basic systems to integrate with minor problems. Not your combination, they never knew each other before this moment.
Most Lyc parts have been developed to go the distance and the estimated life is already known. The same for the accessories like mags.
All your custom designed brackets, pulleys, hoses, tubes, filters, mounts etc. etc. are one off articles that will require vigilant evaluation over their entire lifespan, which is unknown, because no historical data has been available on your unique arrangement.
If you are up for that, then go for it. Don't fool yourself, go forth with clear mind and eye, build the engine of your dreams.

Here we go - sit back and watch !!!!
 

I think I'll pop up some microwave popcorn for the show to come...gets more interesting and a little bit crazier every time!

Hey Stein, make mine with extra butter:D

Something better
 

Hey Stein,

I'll bet some Kettle Korn would be even better. Shhhh..... Quiet the previews are starting. This is going to be good.

Here we go again.........


The endless engine debate. I think it would be helpful to have 2 tables side by side. The first would have all the parts to a disassembled Lyc the second all the parts to a disassembled Sub. The builder/pilot would peruse pick up and handle the parts from each table. After careful observation the builder pilot would make his/her selection. Nothing written online or in print would have the impact of such an exercise. The lightbulb would come on. The choice would be clear.

I think the original poster was talking about the core engine, not the entire powerplant assembly of which he is well aware is a one off, unproven collection of parts. I've worked on both engines. There is nothing inferior in the Subaru design to the Lycoming. This has been proven in BILLIONS of hours of use, hundreds of thousands of flight hours, millions of engines in service and validation exceeding certified engine requirements.

If you are not mechanically inclined, patient and willing to do a lot of fab work and testing, don't go down this path- bite the bullet and get a well built 540 from Barrett or Aerosport. You will get into the air sooner and likely have less headaches in the long run.