Here I go again
I say that because I voiced similar concerns in the Jabiru engine thread a while back. A response back was ?don't worry, we do this for a living and we know what we are doing and we won't do something that won't work.? OK, I am fine with that, nothing more said.
Now here I am again about to say what some don't want to hear. I am taking deep breaths contemplating submitting this post.
My main points:
Rudi has it right (in a different thread) when he says the 12 is a sweet spot regarding payload and performance within the LSA envelope. Van's says the design works because it is an integrated package and everything is sized and specifically designed as light as possible. I sure hear that, having built one and massaged every part in the plane.
Weight & Balance
When moded out with most of the alternate engine choices the sweet spot appears to go away, my opinion. An additional 20 pounds on the nose-wheel may result in forward CG issues with typical passenger loads when the fuel is burned off. Remember the pilot and passenger sit forward of the spars and the CG in this design. What is going to happen to the happy control harmony?
Structural integrity
Look at the firewall. The structure and motor mount hard points sure appear to be specifically designed for the Rotax circular engine mount. The Rotax is an 87 cubic inch power plant. It makes it's horsepower through RPMs not a lot of torque. An engine with twice the displacement is going to have heavier reciprocating parts and potentially more vibration issues. Look at the top motor mount hard points (picture below). They are unlike all of the other heavier built RVs which have the top and bottom motor mount brackets widely spaced with the top brackets tied directly into the longerons. Those firewalls are designed for a variety of engines.
Here is a picture of one of the RV-12 top motor mount brackets.
These brackets are just pop riveted onto the instrument shelf. Now I am not an aeronautical or structural engineer but the design looks minimal and optimized for the Rotax power-plant to me. To cantilever a heavier and more powerful engine off these mounts an additional 12? or so forward of the Rotax position seems cavalier to say the least.
I agree the UL engines (and others) are a work of mechanical art. They are simple, traditional but modern and not too expensive. They would be great perhaps on a redesigned and more robust firewall with careful consideration of weight & balance, or an RV-9.
The argument for choice in engines with the ability to chose price, air or water cooling, manufacturer, USA or import, etc. is a strong one. The question: Is the 12 compatible? Doubts exist in my mind.
My only reason for posting is safe RV-12s and happy pilots. Do I sound too much like a Van's Fan Boy? I guess I am.
Tony