Glow Plugs for Tethered and Radio Controlled Model Engines

   The invention of the Glow Plug, by Ray Arden in 1948, created nothing less than a revolution in model engineering. From that point on, Control Line and RC was transformed, and with the new "Glow Plugs" having the same thread as the old Spark Plugs, old Ignition Engines could be instantly converted into Glow Engines.

   Fuelled by a mixture of nitromethane and methanol, the modern Nitro Engine Glow Plug has a platinum-iridium coil, that is initially heated using an electric current from a "Starter" to ignite the fuel and start the process. From this point, the heat produced from compression and combustion keeps the engine running until the flow of fuel is cut off or simply runs out.

Glow Plugs for Nitro Engines

   Nitro Engines for RC Models, use a system to ignite the fuel mixture, that simply employs a wire coil in a small housing called a Glow Plug. To start the engine, a battery powered Starter, or Glow Igniter is connected to the Glow Plug, and electric current heats the coil to white hot, so that when you pull start your engine, the air - fuel mixture in the cylinder is ignited. With the engine now running, the starter is no longer required. Heat generated under compression is enough to keep the coil element hot enough to keep the engine running.

How to Test for a Burnt Out Glow-Plug

   At some point, the Glow Plug originally supplied with your Engine will invariably burn out. To test your Glow Plug, remove it from the cylinder head and place it in the igniter. If the coil instantly glows bright orange, the plug is healthy, a weak or no glow at all, indicates probable burn out.

Finding a Replacement

   If your engine isn't too old you should be able to obtain a replacement, but if the manufacturer is no longer in business you may have a problem.

   If you still have the instruction book that came with your engine you may find there are a number of optional plugs available. Most Plugs generally have a code, indicating the plug elements effective operating temperature. These codes vary from manufacturer to manufacturer so be wary if you need to consider a plug from a different Manufacturer than that of your engine.

What is the Best Glow-Plug for Your Engine?

   Basically, Smaller engines run better with Hot Plugs, and Larger engines prefer Cold.

   Nitro fuels for RC engines normally have between 10 to 40 percent Nitromethane (CH3NO2). If you use fuel with a high proportion of Nitro, err towards Cold Plugs. Less Nitro, Hot.

   For example, For a .12ci (2.1cc) Nitro Engine, burning High percentage nitro fuel, a mid range plug would be best for performance.

   While a .21ci (3.5cc) Engine, with Low percentage nitro fuel, would prefer a Hot Plug.

   One more thing you may at some point consider when determining the right plug, is the compression ratio of your engine.

   By removing one of the Head shims you can Increase the compression. More shims, Lower compression. This option is not something I would recommend to those with little knowledge, so if you want to try this please be sure to ask someone with more experience before risking your expensive engine.

   High compression ratio engines run better with Cold Plugs. Conversely, Low compression ratio engines need Hot Plugs.

How to tell if you got it Wrong

   If for some reason you use the wrong plug, you will soon know by how the engine runs. With too Hot a Plug, the engine will overheat and could damage your engine. If you hear the engine miss fire at high revs, and you see pit marks on the cylinder head and piston, try either a cooler plug, add a shim to the head, or lower percentage Nitro fuel.

   If your Plug is too cold, your engine will idle poorly, lose acceleration and top speed. You will also notice the smell of fuel from the tail pipe. However, be wary, this could also be because of a rich fuel mixture.

More Hints and Tips

   For more Radio Controlled Model Hints, Tips and Information, check out the list on the RCScrapyard Homepage. ▶ ▶