CHARTER 4 ENGINE AND FUEL TANK INSTALLATION

When it comes time to choose an engine, by all means stay within the engine range recommended for the model. Installing a larger engine can cause weight and balance problems and could possibly overstress the airframe.

THE PROS AND CONS OF VARIOUS ENGINE MOUNTING POSITIONS: At the R/C field you will see models with the engines mounted at many different angles. Some will have the engine mounted upright, some will be inverted, and others will be sidemounted. There are many things to consider when deciding which way to mount the engine in your model - running characteristics, fuel tank installation, and muffler installation are all affected.

An upright engine (cylinder head up) generally makes for easy starting, simple muffler installation, and good access to the engine's carburetor for adjustments. Most sport models will show an upright engine installation, and beginners are encouraged to use this approach. Inverted engines (cylinder head down) tend to be more difficult to start and idle less reliably. An inverted engine should only be used if absolutely necessary to conceal an engine on a scale model or where appearance is the highest priority. Side mounted engines (cylinder head horizontal) are a good choice for aerobatics and advanced sport ships. Side mounting avoids the starting problems of an inverted engine and can sometimes make it easier to line up the fuel tank in the airplane since the needle valve sits lower than it would in an upright installation (see section on fuel tanks for specifics on ideal tank location). Sometimes it is necessary to mount an engine canted somewhere between upright and sidemounted in order to get the muffler to clear the fuselage side. If your airplane has a cowling, be certain to make provisions for access to the needle valve and glow plug.

No matter how you decide to position the engine, it must be firmly bolted to a strong mount. The vibration of a loose engine can cause radio problems as well as serious structural damage. If you can see the head of the engine jumping or blurring at idle speed, the mount is not solid enough.

HARDWOOD MOUNTS: Some kits are designed to mount the engine directly to hardwood or plywood motor mounts that are built right into the model's structure. This type of engine mounting is quick, easy, and relatively inexpensive. The drawbacks are that they are difficult to repair after a mishap and can become weak and oil soaked with age.

FIREWALL MOUNTS: Another popular method is to use a thick plywood firewall built into the model, and a separate glass-filled or aluminum engine mount. Firewall mounting is considered to be the best in terms of toughness and vibration elimination. It also offers a lot of versatility since the mounts are removable and interchangeable if you ever want to switch engines. Almost all of Sig's R/C models are designed for firewall mounting and have two-piece, glass-filled engine mounts included in the kit. The split design of these Sig mounts allows them to be adapted to a variety of engine sizes and widths. (See page 15 for a photo of the engine mounts.) A few Sig kits have aluminum engine mounts which must be drilled and tapped for the engine mounting bolts (see below for instructions). If you want a one-piece firewall mount, there are many good brands on the market to choose from, as an optional accessory.

The .60-sized Sig King Kobra is a smooth-flying sport aerobatic ship. The side mounted engine performs well in an aircraft like this and is still easy to start.

ABOVE: The Sig Komander features a shoulder-mounted foam wing and gentle flight performance. This one also features a canted engine installation. BELOW: The Sig Kadet Mkll has taught more pilots to fly R/C than any other trainer in history. The upright engine installation makes for easy access, and is recommended for beginners.

LEFT: Scale models like this Sig P-51 Mustang often use inverted engine installations to conceal the engine. Only the front edge of the cylinder head and the glow plug can be seen on this model.

TAPPING ALUMINUM ENGINE MOUNTS Clamp the engine mount securely in a vise and center punch the motor mounting holes. Drill the holes with a sharp twist drill bit in a variable-speed electric drill. If possible, use a drill press instead of a hand held drill. Lubricate the drill bit with machinist's cutting oil, special aluminum tapping fluid, or other light household oil such as Marvel or 3-in-1. Run the drill at a moderate speed with moderate pressure. Let the bit cut its way through the aluminum at its own rate. Don't try to force it with excess pressure or high bit speed. Aluminum galls easily and may jam and break the drill bit if forced. If resistance builds up, back it out of the hole frequently and clean off the metal fragments. Relubricate the bit and hole with more oil and continue drilling. Tapping the drilled holes is easy if the same precautions are taken. Lubricate the tap liberally with cutting oil. Use moderate constant pressure when turning the tap into the hole. If resistance builds up, back the tap back out frequently and clean the fragments out of the threads. Use plenty of oil and work slowly.