Engine choices

Engine

For my mission, I'll be looking at engines in the 90 to 110 horsepower range.  That gives me enough horsepower to carry two people and eventually be on floats.  This will be one of the biggest and arguably important pieces of the build.

In realm of suitable aircraft engines, the choices are many.  My main focus will be on cost, reliability, ease/costs of repair and overhaul.

Although Rotax makes excellent motors that have powered countless aircraft over many decades, I'm concerned about the short time between overhauls, having to run an oil mix fuel (in the case of 2 stroke engines).  The Rotax 912 series is four stroke but even a decent second hand 80HP model is worth more than my airplane will be complete.  Seems a bit steep for my plans.  And overhauls and parts are either very expensive or in the case of 503 to 582 models more and more difficult to obtain.

Another thing I am looking for is an engine that is air cooled.  I live in northern Ontario and I've known guys who have had countless issues with their liquid cooled engines freezing up solid or springing leaks.  I want something simple and the addition of a liquid cooling system adds a level of complexity that I'm not comfortable with.  I'd rather be flying than worrying about springing a leak in the air that could lead to engine failure.  I'd also rather be flying than fussing around trying to make a liquid cooled engine installation work.

Certified engines (Continental and Lycoming) are good, robust and aircooled with decades powering small airplanes.  However, even when out of certification and being used by homebuilders, they are hard to get parts for, those parts are expensive, made in China and extremely hard to work on (specialized tools).

For many years, groups of builders have been trying to adapt automotive engines to airplanes, with varying levels of success.  The thought of a modern car engine with all the advantages of fuel injection, variable valve timing and easy to obtain parts is appealing.  Unfortunately those ones that have been "successful" in the market have now placed themselves out of the reach of my project.  Most are overly complicated, liquid cooled and weigh a lot (my goal is to remain as light as possible).

Another disadvantage typical automotive conversions have is the same as the Rotax series.  These motors develop their best torque (a measure of force around a point, in this case a propeller creating thrust) at high RPMs (as they were designed for cars).  This high RPM is not acceptable for driving a propeller, so these installations require a reduction drive which adds further weight, complexity and maintenance.

So where does that leave us?

For a couple of years now, I've been following the automotive conversions being completed by builders using Chevrolet Corvair engines.

But wait a minute, didn't I just say that automotive conversions were heavy, complicated and very high RPMs?

I did.  But what makes Corvair engines unique is that:

• Chevrolet designed them from the outset to have high horsepower compared to weight
• air cooled (it was a rear mounted engine in cars) 
• very smooth (six cylinders, horizontally opposed, much like a Porsche)
  
• it can be direct drive (no reduction drive required)
• core engines for rebuild are plentiful (Chevrolet made of 1.7 million of them) and the most appropriate cores for conversion are the least desired by automotive restorers (therefore cheap)
• parts are readily available and still being made despite being originally made in the 1960's
• in an aircraft conversion, you are tasking it with producing torque/HP well below the operating range it was designed for in a car on the road so it is reliable
• In conversion, it produces between 90 and 110HP reliably, and is comparable if not better in weight and size of a Continental O-200, Rotax 912 or Subaru EA81.
• There are literally hundreds of converted Corvairs now flying so the community of builders is strong and proven
• A converted Corvair, installed and flying will cost one third of a comparable motor mentioned above.

As one of the guiding principals of this project is to learn new skills, rebuilding a Corvair would be very interesting without blowing my entire build budget.

So a Corvair fits nicely in my plan.  Next step, start looking for one.