Gary Burdett, 2,850cc Zenith 750, now flying. (engine selection)

Builders,

A few days ago, I spoke with Gary Burdett of Lincoln Illinois and covered some notes on his upcoming first flight of his Zenith 750. The conversation was fairly short because Gary had done all his homework, he knew what he was planning on doing and all his bases were covered. Near the end of today, (Sunday) Gary called to say he had done a 30 minute first flight, and all went well, absolutely no surprises. Again the conversation was fairly short. He is planning on going up again as soon as his local weather improves. We didn’t have to speak about any corrections nor issues, he didn’t have any to speak of.

Above, Gary Burdett with the 2,850cc Dan bearing engine we built for his 750. It is rated at 110HP. He picked it up at the 2012 Zenith open house.  His firewall forward is made of our standard off the shelf components for Zenith installations. Gary decided that he was going to take full advantage of our 9 years of successful Corvair installations on Zeniths by sticking directly to our the step by step notes in our Zenith installation manual. This is the best way to insure an uneventful first flight just like Gary’s. On his first flight, Gary stayed aloft for 30 minutes. He said the OAT was a cool 60F, but the CHT on the engine never exceeded 300F. Not bad for a brand new motor, on a design with a factory 575F limit. In hot summer weather with a fully broken in engine Gary’s instalation should run 350F in climb and 325F in cruise, a very large cooling reserve on the 750. 

One of the reasons why Zenith aircraft are so popular is the amount of engine choices available to builders. Compare two well-known LSA aircraft the Van’s RV-12 and the Zenith 601/650 series. The only engine allowed on the RV-12 is the Rotax 912.  The Zenith can use a 912 also, but there are also seven other popular engines commonly installed. Zenith believes that if you are smart enough to build and fly a plane, you can probably select an engine that matches your needs. Sebastien Heintz, Zenith’s president, has demonstrated his commitment to this path by inviting many engine companies to his open houses and having a day at Oshkosh were there companies simultaneously met builders in the Zenith booth. To me, this fits with my perspective that homebuilding is about making educated decisions for yourself. The concept that a Homebuilder would be restricted to a single engine suggests both an inflexible airframe design and philosophy of post-sale control, neither of which are particularly appealing. Even the owners of certificated aircraft can select different engines through STC’s, homebuilts should have at least as much freedom.

At Sun N Fun this year, I had at least 100 people a day walk into our Flycorvair booth and ask the same two questions: What does it weigh? and How much does it cost? Any builder who has these as the primary two questions is not ready to choose an engine, period. Notice above, I said I am in favor of builders making educated choices. I told every one of the people with the two standard questions that they needed to do more homework, specifically evaluating what they wanted out of an engine, and which characteristics were important. To open their mind a bit, I pointed out that even if an engine weighed only 100 pounds and cost just $1000, it would do you no good if it wasn’t reliable. The first thing you need to know about any aircraft power plant is simply it’s reliability.

Many people think that this can be evaluated by simply asking the sales rep. What is the TBO? First, in the experimental world, companies often make up any number they like for TBO, particularly auto conversion companies. I have seen companies claim a 3,000 hour TBO on engines that had yet to have a single example fly more than 100 hours. If the engine made 100hp at 5000 rpm in a compact car, then the car would have done about 120mph at the power output that is used to fly a draggy plane. A 3,000 hr TBO says that you could take the same compact car and drive it at 120 mph for 360,000 miles without wearing it out or expecting it to break. Does that sound realistic? Think you could get a car to do 25 coast to coast trips at 120 mph /5,000 rpm? That is a pretty big goal, and it is only 500 hours.

Real reliability is a much more complex issue than a TBO number. First, reliability is about how long between a power plant breaking, not how long it is before it wears out. In WWII, a Rolls Royce Merlin was considered a very reliable engine, but the TBO was only about 250 hours. It was not an issue of how long it lasted, the vital question was would it break without warning? An engine getting tired over time is acceptable, and engine breaking is not. My perspective on how to achieve reliability is to lower the stress on the engine by running it at a fraction of the automotive rpm and HP, increase the strength of internal components by using parts like forged pistons, make the fuel and ignition systems as simple as possible, and then train the operators to really care for the engine by allowing each of them to become his own mechanic/engine expert. I would love to take credit for this as an original idea, but two other engine companies thought of it first. You may have heard of them, they had some pretty good success with the concept. Their names are Lycoming and Continental.

Beyond the basic engine, we offer several things for Zenith builders:

1) Conversion, installation and flight ops manuals.

2) The availability of every single installation component, flight proven over nine years and 70 flying aircraft.

3) We have a separate on-line peer-to-peer discussion group just for Corvair/Zenith flyers to directly and freely share information and data with each other in a civilized productive format.

4) We have free Colleges and I still make free house calls.

5) the Corvair is fully insurable from hour number one, at the best rates.

With all of the above and the Corvair’s 53 year flight history, you might think that the majority of Zeniths would be Corvair powered. In reality, the portion of  Zenith builders we are working with is about 20%. The Corvair isn’t for everyone. If I said it was, I would be no different from an airframe guy who told you there was just one engine for his design. Over the years the 20% number has largely remain unchanged. A business man would be focused on “market share”, but I am first and foremost a Homebuilder, and I recognize that the Corvairs greatest appeal is to ‘traditional’ homebuilders, the people who are in it to learn new skills and be the master of their creation, not just it owner. That attitude was once 100% of the EAA, but today, all kinds of people are attracted to homebuilding. Most of them don’t think like I do, (some are hardly thinking at all) but nor are they required to. I am just here to work with the builders who have carefully thought out and evaluated their needs, and have made a selection at a much higher level than What does it weigh? and How much does it cost? -ww

About William Wynne
I have been continuously building, testing and flying Corvair engines since 1989. Information, parts and components that we developed and tested are now flying on several hundred Corvair powered aircraft. I earned a Bachelor of Science in Professional Aeronautics and an A&P license from Embry-Riddle Aeronautical University, and have a proven 20 year track record of effectively teaching homebuilders how to create and fly their own Corvair powered planes. Much of this is chronicled at www.FlyCorvair.com and in more than 50 magazine articles.

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