THIS BIG GAS BURNER IS FOR SERIOUS RC POWER

In the world of giant-scale RC model aircraft, the gasoline 2-stroke engine in the 60cc displacement class has reigned supreme over all other engine sizes and varieties. Historically, this class of engine has powered warbirds weighing up to 35 pounds and acrobatic aircraft up to 96 inches in span (give or take an inch). Why the popularity? I think that price creates the line between those who want to grow only as far as their budgets (and nerves) will allow and those for whom money (and aircraft size and complexity) isn't a consideration. I'm the former kind of modeler; I've found that 60cc gas engines are an extraordinarily good value and highly versatile. It's no accident that there's a plethora of aircraft kits, ARFs and plans for aircraft that match these engines.

The Fuji BT-64A spans the divide between the two types of modeler I describe. As I discovered when I tested it for this review, it's potent, affordable, well-built and easy to operate.

ABOUT THE ENGINE

The BT-64A was designed by entrepreneur/engineer and avid RC modeler Seiji Tanabe specifically for model aircraft. The entire Fuji gasoline engine line benefits from the same state-of-the-art technology and has a few value-added features that I'll get into shortly. If you aren't familiar with the brand name Fuji as a gas-engine manufacturer, just think back to the Byron Originals' Mustang 50 gas engine; yes, that was a Fuji! I have several RC buddies who still own these engines and report that they run as well now as on the day they bought them.

While the BT-64A comes with an exhaust for right-side-up or inverted use, Bisson Custom Mufflers offers excellent, high-quality alternatives for the Fuji line, and the BT-64A is no exception. For my performance tests, I used the standard Fuji exhaust and the Bisson inverted Pitts-style (note that Bisson also offers a vertical exhaust for installation in narrow cowls). Last, Great Planes offers a modestly priced engine kill switch that has both toggle and microswitches in a single wiring harness for external or servo-activated engine kill. The manual recommends the use of an external switch for additional safety, regardless of whether you use the servo-activated microswitch inside the aircraft.

AUTOMATIC TIMING MODULE

Key to the Fuji engine line is the Automatic Timing Module (ATM)-a brilliant solution to the starting difficulties that often plague capacitor-discharge-ignition (CDI), or "magneto," engines. To illustrate: a magneto engine typically has its timing permanently set at the top of the rpm power range for optimum performance; this leaves the low end with significant spark advance. For many modelers, hand-flipping the prop proves to be a lesson in frustration and occasionally involves prop kick (that hurts!). The brilliance of Fuji's ATM ignition lies in its module's timing-advance control; it eliminates the traditional low-end early spark advance. When they're being started, Fuji gassers behave like electronic-ignition engines: the spark advance is reduced to allow safe, injury-free hand-starting. From idle to top end, the timing advances linearly as rpm increase, and this ensures optimum timing through the entire powerband.

SOME ASSEMBLY REQUIRED

You have to attach the exhaust, the prop hub, the throttle linkage and the kill switch (you supply your own linkage and switch). A metric hex wrench is provided. The throttle linkage is your choice; I like ball-end components and used Du-Bro 4-40 ball-link hardware. The carburetor's throttle arm has a hole that is large enough to accommodate most other linkage options, so you can use your favorite setup; as with any ignition engine, use a non-metal pushrod for throttle activation.

THE MANUAL

The Fuji manual is the best I've yet encountered! While other manufacturers fail to inform users about throttle-pushrod material, the distance between the receiver switch and the kill switch, and how to install the kill switch, the BT-64A's manual covers all these very nicely. It also has a great simple guide to tuning adjustments and troubleshooting-even instructions for easier starting. The BT-64A offers three choices for starting: hand-flip, spring-start and electric starter; the manual discusses all of them clearly.

Diagrams for the correct prop/flywheel magnet orientation are clear and well detailed, so no one should misunderstand this important relationship. The Fuji manual also covers safety precautions-always crucial aspects of our hobby.

PROPS AND LUBES

The manual recommends the use of a 22x10 wooden or carbon or 22x12 carbon prop. To obtain a clear picture of the Fuji's torque curve, I selected wooden props ranging from 22x10 through 24x10 in a variety of blade styles. I balanced all the test props-absolutely mandatory! I give the weight of every prop I used.

The manual recommends that you use a high-grade synthetic 2-cycle oil, mixed at a fuel/oil ratio of 25:1, for a one-hour break-in; then you should decrease the oil content to a ratio of 40:1.

RUNNING THE ENGINE

I followed the steps given for priming and choking the Fuji 64, and it started easily, without a glitch. With the kill switch in the off position, flip the prop over-perhaps 10 to 20 times-until you see gas fill the line. Close the choke, move the kill switch to the "on" position and flip the prop until the engine pops. Then open the choke and set the throttle to just above idle, and flip the prop again until the engine starts. The test engine fired on the third flip right out of the box-pretty darn encouraging.

For break-in, I used a Top Flite PowerPoint 22x10 prop and a 25:1 ratio of Amsoil and high-octane gasoline fuel mix. Early tachometer readings were around 5,600rpm, but they increased steadily until leveling out at 5,700 by the end of the first gallon of fuel. This rpm number may seem a bit low, and I'll explain it just ahead.

The Fuji BT-64A is "factory-tuned" and ready to run; the manual includes the factory default settings in case you get lost when you tune the needle valves. The high-speed needle is very responsive; 1/8 turn made a noticeable difference to engine speed. The factory settings worked well for me. Throttle transition was crisp, and the torque curve between 6,100 and 7,000rpm was pretty flat when turning a variety of props. Even turning the 10-ounce APC 24x10 prop, throttle transition was very good.

The performance tables show the readings obtained with each of the props I used. Remember that an engine responds differently to variations in prop pitch and diameter and particularly to prop profiles, i.e., the surface areas that do the work. APC props' profiles are significantly smaller than those of a standard Zinger or Top Flite PowerPoint prop. As a result, the APCs run faster than they do, and in this case, they delivered more thrust as well. Some engines develop more torque at lower rpm; others require higher rpm for better performance. All of these props are great performers; it's just a matter of finding the right one for your particular application. That's why I test to find out which ones offer the highest thrust at the most acceptable decibel readings. Comparing rpm figures is not the only way to evaluate performance; they are a byproduct and will always increase engine noise levels as they increase.

With regard to decibel (dB) readings, the FAI (Federation Aeronautique Internationale) assesses dB levels at 3 meters from the prop with the powerplant running at full throttle. Decibel readings encompass all the noise generated by the engine, including exhaust note, prop noise, carburetor induction and airframe resonance. To lessen the overall influence of these factors, a number of steps can be taken, although the most effective is to use a quieter exhaust (which also tends to suppress performance). Reducing prop noise, some of which is generated by excessive tip speed, is most often accomplished by using a prop with a smaller diameter and a higher pitch; this may reduce your engine's optimum thrust. There isn't much you can do about induction noise, though popular opinion is that rear-induction engines arc less noisy. Often overlooked is airframe noise. Engine vibration is transferred to the airframe, which, depending on its weight and construction, may actually amplify that vibration. Use soft, vibration-damping engine mounts or isolation mounts to reduce airframe noise.