Source: 2002-Q4 Beartracks, Mike Meador and Bob Barrows
Sometimes it is difficult to put into words (particularly written words) that which you know. To transfer knowledge that has taken many years to acquire in a few short paragraphs is not a skill that I have mastered very well. I marvel at other writers’ ability to take a difficult subject and make it understandable to me. It would be easy to give yourself a list of part numbers and say “Here you go! Assemble it according to the manual and you should be OK.” Stuff made today is almost idiot-proof, but, I am an example that they are making better idiots every day. I thought that this series of articles would serve to show you how easy it is to put together your own engine. Instead it has served to be a list of generalizations that can only steer you in the right direction to a destination- mainly the perfect Bearhawk engine.

In this final installment, let’s discuss fuel delivery systems and various ways to light your fire.

As you already know, the Bearhawk will operate via gravity flow for a carburetor, so no fuel pump is needed. If a fuel injection (FI) system is desired you will need not one pump, but two: the mechanical pump attached to the engine, and an electrical boost pump for backup. FI systems are more expensive, and as a result of needed fuel pumps, weigh more than a carburetor. The main advantage of FI over carburetor (for the Bearhawk application) is the difficulty in developing intake, or carb ice. FI is expensive, and can run as much as $1000 more than a comparable carburetor, and that does not include the extra fuel pumps!

There is a middle ground between the two systems called a pressure carburetor. It requires a fuel pump but has a lot of the advantages of FI system that are not really needed on a Bearhawk. The ability to fly inverted is not something that I think you will need to be doing very much of anyway.

The ideal Bearhawk engine will take advantage of the “free” gravity flow and use a carburetor. The limitation of carb ice is something that you should have been trained to deal with in your flying lessons. There are devices that can warn you when ice is building up, or you can keep your manifold pressure gauge (if so equipped) in your instrument scan. A slow drop in manifold pressure during cruise indicates a building restriction due to possible carb ice. Most carburetors are shop rebuildable, where as the FI system needs very specialized tools and training to work on. Finally, the carburetor is the most cost-effective way to deliver the fuel/air mixture to the cylinders. We are in the business of keeping it simple, and carburetors do just that.

The final systems to consider are the ignition systems. Up until recently you really only had the choice as to what brand of magneto you wanted to install. There are now several different types of electronic and mechanical systems that you can choose from. There is a reason that the magneto has reigned supreme for nearly 100 years- it works. Any electronic ignition system (EIS) that you choose must have a built-in redundancy to prevent engine failure. The main disadvantage of the magneto is that once you have set your timing it is set for good regardless of power setting. With the exception of startup (due to impulse coupling) you are locked into the advance you set the mag at. This is where the EIS really prove their worth- variable timing. Another advantage of the EIS is a much hotter spark that results in an improved flame front and better fuel burn. Currently Unison Industries (Slick) is considered to have the most advanced EIS on the market.

The Slick system is actually two magnetos with a piggy-backed electronic ignition built in. In effect you have four ignition sources- sounds like a lot of sparks. The Slick system is certified and is available to home builders. There are at least two other non-certified EIS available. So far the results have been generally good, and that is promising. Most of the engines that we ship out of our shop that have an EIS also have one old-fashioned magneto for backup.

Another system that looks intriguing uses miniature catalytic converters to light off the fuel/air mixture; it has no moving parts. I’ll take a wait and see approach- in other words, you go first.

That about wraps up your Bearhawk engine. As you can see you have a bewildering number of choices. So I would like to present you with what I consider to be the perfect Bearhawk engine. The following listing has been worked up with the Bearhawk in mind:

• Lycoming O-360 set up to burn auto fuel
• Narrow Deck
• Angle Valve Cylinders
• Conical Mount
• Rear Entry Oil Sump (with adapter)
• Constant-Speed Prop Setup (need governor drive)
• Rebuilt Bendix Magnetos
• Rebuilt Carburetor
• Maybe a Vac. Drive for a Mini Alternator
• Aluminum-Steel Gear One Piece Oil Pump

This is nearly the exact engine on the prototype Bearhawk. It is relatively inexpensive to build and a brute of an engine. The angle-valve head keeps things cool during those long climb outs and the large valves let it breathe a lot easier.