The Design

I'll save the discussion for “Why a Rotary?” for others. The world doesn't need another preacher on a podium - there are plenty of others already doing enough preaching. I wrote this for readers who have already made up their minds to install a rotary. It is, however, worth some discussion of the particular choices I made during my installation. The first whiff of “This is not your father's Lyc-oldsmobile” comes when you start choosing major components like engine models, turbos, and so on.

The sheer magnitude of the choices you have to make is both a pro and a con. On the one hand, you can choose the best combination for YOU. On the other hand, you MUST choose, and sometimes the differences between the choices can be confusing (or even irrelevant, but not obviously enough that you realize it before you spend 20 hours researching the answer).

Engine installations are like recipes: one brownie has nuts, one doesn't. (Mine definitely has nuts.) Some people put all sorts of weird stuff in their brownies. At a very high level, here's the “recipe” this site describes:

1. Mazda 13BTT engine (aka “3rd-gen”, “FD3s”, or “13B-REW”)
2. NO porting work
3. Conversion to single Turbonetics T04E-50 turbo setup
4. Custom intake manifold
5. CozyGirrrl's engine mount
6. Rotary Aviation PSRU and engine controller (EC3)
7. NACA scoop for water radiator cooling, small armpit scoops for oil and intercoolers.

This page provides only a summary of each high-level design choice. For details on a particular subsystem, visit the appropriate pages using the menu on your left.

I was searching for “13b models” and the first photo came up on Page 1 of the results. It's amusing, and also the best-looking thing you'll see on this entire site (you DEFINITELY don't want a photo of me!) so enjoy it while it lasts.

The second photo is our engine, all… Wow, that's a lot of stuff isn't it? Don't worry, over half of it will disappear during our install.

Wikipedia has an excellent article describing the various engine models Mazda has produced. I won't repeat everything said there, but allow me to summarize a few critical points:

As you can see, the 3rd-gen engine continues a long trend of increasing horsepower and general engine sophistication. Despite the power increase, overall weight was decreased Also, many problems with earlier engines, such as with the sealing and lubrication systems, were addressed with design changes in this version. It is the latest engine of the series that I believe is usable for our purposes.

So why not the Renesis? Don't get me wrong, this is an excellent engine. It somewhat lighter than the FD3S, and produces significant horsepower without even requiring a turbo!

But that's the problem. I wanted a turbo in my setup - not just for more power during takeoff, but because we're doing something Mazda's engineers didn't have to think much about: flying high, in thin air. Even a small amount of boost can have a huge impact on performance at altitude. Although the Renesis could be modified to accept a turbo, you're largely regressing to a FD3S. The Renesis is (typically) more expensive. Why spend the money on something you'll need to retrofit anyway?

That means the FD3S is a perfect starting point. Because it comes with twin turbos installed, it ALSO comes with oil and water cooling fittings on the block. And it has lower-compression rotors, ideally suited to a turbo. Although some builders have used higher-compression rotors WITH a turbo, I wasn't as comfortable with this risk - and besides, I already had two perfectly good rotors in my engine!

While we're on the topic of turbos, I installed a Turbonetics T04E-50, essentially the same turbo John Slade used. For the third time. John has proven that aircraft use is hard on a turbo. We rarely spool up and down - we spend most of our time at constant power levels, where the turbo is working hard and not getting a break. If you spend money NOWHERE else, pay to get a good turbo. It's worth it.

I chose not to port my engine. “Porting” refers to the commonly-performed operation wherein the intake (and sometimes the exhaust) ports are made larger, allowing more air to flow into each intake cycle, and thus producing more power. It's a pretty cheap power boost, too - some builders claim as much as 10-40hp from what amounts to a few hours with a cheap die grinder and a porting template ($30-$60, from a variety of vendors).

However, I felt that porting was the wrong choice for me for three reasons:

1. Porting is most effective in naturally-aspirated engines, where modest reductions in flow restrictions can measurable increase intake charge quantity. Once you slap on a turbo, porting is much less noticeable. The turbo will stuff all the air in that it can, up to its pressure setting. Horsepower gains are still possible, they just aren't as significant.
2. Porting produces a large quantity of metal chips and dust. It's IMPERATIVE that the components be perfectly cleaned before being used. In a race car, seizing your engine because your bearings chewed up some metal shavings or they blocked an oil port is no fun, and a recipe for a time-consuming teardown and rebuild. In an aircraft it's somewhat more problematic!
3. There are plenty of other tasks to address. If my engine produces insufficient power, the next time I have an excuse to tear it down I can make the decision to port it then. In the meantime, I chose to focus on more critical-path issues.

The second comment, about safety, is not an idle point for me. This design is very deliberately built upon the following principle:

Replicate John Slade's design, incorporating design changes he would make if he
started over, plus derating the engine power 5%-10% where 'safer' choices lead to
only most power reductions.

To clarify: John Slade has a proven, flying “Cozy 13BT” configuration. He has excellent power output (almost too much), adequate cooling (by a whisker), and many hours of flight time proving that it works. I've even had the pleasure of flying in it several times. If I could replicate his setup, making enhancements where appropriate, I knew I would be happy with my final result.