So the Patrol is rated for between 115 and 210hp... what's the limiting factor on the 210hp? Just weight? Torque? Something I don't understand (quite likely)? My reason for asking is that I like tinkering, and like hp, and am quite interested in ULPower's work on the Yamaha Apex snowmobile engine. I know how powerful and reliable these engines can be, and 250-300hp is pretty easy and relaxed for that platform. Also, weight is pretty low, right around 200lbs with gearbox, alternator, turbo, etc...
edit: please don't let this drop into a discussion of the viability of this engine platform. I'm just curious what the limiting factor is in the Patrol keeping it to 210hp. If weight were the same, would 225hp be ok? Or what would it do to the flying characteristics? 300hp???
The limiting factor on aircraft engine power is weight, supporting systems, fuel consumption, and Vne. If you have an engine that's too heavy, then your airplane will have odd CG limitations or limited useful load. If the engine puts out way more power than you need to beef up the engine mount and airframe to support it or you might need a much larger prop that would require landing gear changes. If the engine consumes too much fuel then you will have a limited range or too much weight in fuel. If the engine is strong enough to pull the airplane past its Vne in level flight, then you could run into flutter, which very much could kill you.
As for your comment about engines: aircraft engines are not the best place to tinker. Seriously, if you don't know a bit about torsional vibration, propeller harmonics, P factor, gyroscopic forces, and the complexities of gearboxes, then you don't know what you don't know.
Your comment about ULPower's work on the Yamaha engine causes me to wonder how familiar you are, as ULPower makes its own engine and isn't related to Yamaha. You were almost certainly talking about Edge Performance.
I am also quite familiar with the apex engine, and while getting 300hp is pretty easy with boost, calling 100hp per liter "relaxed" is stretching it. Some people say that you would only run at 300hp for a limited duration. I would say, when? Takeoff? That's the worst time to have engine failure.
Everybody is looking at STOL drags and Steve Henery and thinking, I could do that. And you can, but Steve has walked away from a lot of engine failures. He is comfortable gliding off a cliff without any engine at all. Bottom line, if you aren't absolutely comfortable with an engine blowing up 400 feet in the air a 1/2 mile from the runway, then you have no business tinkering to the tune of 300HP per liter.
I know you said you said, "please don't let this drop into a discussion of the viability of this engine platform" so you probably don't want to hear what I just said, but hey, this is the Internet, and the last thing any of us want to see around here is you or your Bearhawk strike the ground in an uncontrolled fashion.
Least you get the impression that I'm against the Yamaha platform or against innovation, here is what I think it would take to get the Yamaha going in a patrol:
1. Figure out a safe tune that doesn't stress the engine too much. The patrol is a lot of airplane on 180HP, 200 is plenty. I'd probably setup for turbo normalized at the 215hp level. That should keep your fuel consumption, range, speed, and prop size all pretty reasonable while at the same time having a very high-performance airplane that won't run the risk of blowing up. Yes, Steve runs it at 300hp, but that is a competition plane where reliability comes second to performance.
2. I would try to figure out exactly what it weighs and do what you must to make a longer nose/engine mount to get the CG where you want it. You might get lucky, or you might have to build a few different mounts and rebuild the nose until you get it right.
3. Figure out how to make the fuel system work. I can't remember what Steve is doing for a fuel system, but in order to have cool fuel up front, you will probably want a return to tank fuel system and dual pumps. This causes new issues such as pumping faster than the engine consumes can cause the pumps to bring air into the system when you are low on fuel. A stock bearhawk fuel system probably won't work for this engine, and fuel system design isn't as simple as it sounds.
4. Figure out cooling. You will need to figure out all of the radiator stuff and how to cool that engine. It's not super hard but will require a bit of experimentation.
5. Figure out the prop. Some airplanes are bigger, some are draggier, some have ground clearance issues. From what I understand you will need to have an electric constant speed prop. The ones I've seen aren't that large, and may not work that well on a patrol. I suppose you could bolt a large fixed pitch to it, or perhaps a ground adjustable, but you will give up some ground roll or cruise speed.
6. Engine mount. This is not as simple as it sounds. A lot of people in this space just weld something together and roll with it, but I don't think that's very safe. Overbuilt can cause problems just as fast as underbuilt. One fellow on the facebook group mocked up a mount and built a rig to stress cycle it. That's a much better way to do it.
I was mainly curious about the flight characteristics issues I may anticipate with a higher HP setup, and you at least touched on them. I probably shouldn't have even mentioned the Yammy power in my post, it just caused digression. And yes, I meant to type Edge Performance, not sure why I said ULPower instead...
