February 3, 2021
I wonder what would happen if I hit this hornet's nest with this stick? This one is likely to get me into a lot of trouble. I never liked the idea of putting an automobile engine in an airplane. My reasoning is that as an engineer I think that you should use the right tool for the job and not try to shoehorn something into a role that it was not designed for. Automobile engines were not designed to power aircraft (Subaru apparently had some aircraft intentions within it's boxer engine design). After doing some research I realized that it would be very difficult to put an auto engine in a plane for much less the cost of a new airplane engine. After you are done redesigning everything to fit in the cowling and make the prop turn slower you have spent a lot of time, energy and money and in my opinion have not gained much.
There are those that say airplane engines are antiquated and based on ancient technology. I don't buy this argument. Last time I looked inside a car engine it had pistons attached to a crankshaft going up and down inside a cylinder. Yes there are lots of enhancements in engine management systems, ignition control and fuel injection that may not have found it's way into aircraft engines yet but the engine is the same, and I am building an experimental airplane so I can put an EI and fuel injetion on my plane if I like. I've heard the argument that airplane engines use big bore and long stroke and that this is old and or bad for some reason. This is not old or bad it is how you get 180 HP out of a 360 cu-in engine at 2800 RPM. A 360 cu-in car engine has double the moving parts and has to spin 5000 RPM to achieve the same power. Cars will always have a reduction drive so achieving the designed power/torque/reliability from differing engine speeds is acceptable because you can adjust the gear ratio to be what you want. A direct drive aircraft engine to me is a better alternative, but you are fixed on what speeds you can run the crank.
Now that I have made all the car engine guys mad let me say this. There are some real advantages to automobile conversions. I did look at a couple of them and I seriously considered the Eggenfellner Subaru package. I think that he is heading in the right direction and if he were a little bit furthur along with the Supercharged version I might consider it. The two things that I like the best on auto engines are water cooling and free overhauls (I know they are not free but compared to airplane engies they sure feel like they are free). I like the idea of being able to pull the throttle at 10,000 ft and dive for the runway at 200 mph if the notion strikes me without having to worry about shock cooling the mill. I won't ever be able to do that with an air cooled airplane engine. I also found that there is some difficulty in getting insurance with the auto engines and this cost seems to completely offset the free overhaul. Not to mention that it will likely be 15-20 years before I need an overhaul anyway.
Now that I have said all that and made everybody mad let me tell you what my current plans are for an engine. I never was able to find a used engine that really lit my fire so I decided that I would go with a Superior Air Parts XP-360 Lycoming look-alike. This engine is built from all PMA'd Lycoming parts. I am going with one Lightspeed EI on the left side and an Air Flow Performance fuel injection system.
I have at least one more concern on the aircraft engines that I don't see discussed on the web much and that is one of break in. If I understand Lycoming break in procedures correctly they involve running the engine at high RPM and high power for an hour or two to get the rings seated. I don't really want to have to think about this during the first 10-15 hours of "engine running on the airplane" time. I would much rather deal with break in on the ground and leave my mind clear to doing other things while flight testing. I would also like to get a few hours of running the thing up and down the runway before I ever try to commit aviation. So I am trying to find out what it would take to get the engine run in on the ground so I don't have to worry about it during my initial flight testing.
As far as the big pilot cooling fan that goes on the front. I imagine that I will go with a Hartzel CS prop. This plane stalls at 58 and will go 200+ so being able to switch gears is a must in my opinion. I have considered saving lots of $$$$ and going after one of the many mid time 160 HP O-320s that are out there but the problem that I have found in the used engine market is that the 0-360s are impossible to find and there seems to be very few O-320s that can accept a hydraulic CS prop.
Well there is the long answer to a short question. This answer has changed many times since I started the project. At first I really wanted a diesel but that has proven to be impossible. The technology just never came of age during my project. I suspect that I will eventually have that diesel engine. Maybe in the RV-10 :-) For now I am anxious to get this thing finished and go flying. There will be plenty of time to experiment with different engines on the next plane.
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