GETTING INTO GAS ENGINES

Expert installation & setup tips

GERRY YARRISH

There are lots of good reasons to use gasoline engines to power your model airplanes. When you fly giant-scale airplanes, reliable engine performance is of upmost importance. Generally speaking, gas engines are also very easy to start and run very consistently while producing their peak power at lower rpm settings than glow engines of similar displacement. These lower rpm tend to produce lower noise levels while also burning less fuel per minute as compared to nitro burning 2-strokes. And there’s the added benefit that gasoline is a lot cheaper than nitro glow fuel.

But as with all things RC, to operate properly, your gas-fed engine needs to be installed and set up correctly. Let’s take a closer look.

MOUNTING

Installations start with properly centering and attaching your engine to the model. This can be done with soft or hard-mounting points. Hard point mounting can be as simple as drilling holes in the firewall and bolting your engine directly into place. For engines with rear mounted carburetors, this will often require using long metal standoffs. In both cases, the mounting hardware (nuts and bolts), need to be secure and tight. For lightly built airframes, soft mounts are often used. These include rubber isolators that separate the mounting bolts from the firewall. They also minimize the amount of engine vibration that finds its way to the rest of the fuselage structure. Be sure to follow the airplane’s instructions for side and down engine thrust angles.

It is preferred to have all your hardware, engine, muffler and fuel system before you begin building your model. This way you can make changes to items like firewall placement, to avoid excessive modifications after the model is assemble to fit your engine and fuel system. A little pre-planning will save a lot of effort afterwards.

LINKAGES

After you’ve installed your engine properly, the next step is to work out and install your throttle and choke linkages. Start by installing your throttle servo. I prefer to use 4-40 music wire with a threaded on heavy-duty ball-link at the carburetor and a soldered-on metal clevis at the servo. You can determine the length of your throttle pushrod by using your transmitter to position the throttle arm all the way to the idle position with full down throttle trim setting. Here too you should visually confirm in which direction the servo needs to move to open and closed the throttle. Since one end of the linkage is threaded you can fine-tune the length mechanically after you solder the clevis into place. The overall throttle travel endpoints can be fine-tuned by programming the travel volume or endpoint adjustments. I personally like to remove the return spring from the carburetor throttle arm to minimize the throttle servo drain on the receiver battery pack. Once this is all done, be sure to remove your throttle linkage and use a solvent to remove all the solder flux to prevent corrosion later one. For the choke you have the option of using servo control or a simple mechanical linkage operated by hand. Using a servo also provides an emergency engine shutoff during flight.