RC Glow Plug and Glow Driver Guide: Ignition for Nitro Engines

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Ask a nitro pilot why a plane will not start and the answer usually lands on fuel. Plug trouble is nearly as common, a lot cheaper to fix, and easy to blame on something else. A plug that glows orange on the bench can still fail once the engine is turning. A driver that lights its LED can still be too weak to keep a cold engine lit. Before any of that, though, it helps to know which kind of ignition your engine uses.

This is a researched buyer's guide. It draws on O.S. Engines documents, Horizon Hobby product pages and manufacturer listings, not on our own bench or field testing. Where we could not confirm something from a maker, we left it out, which means there is no heat-range cross-reference chart here. Those charts disagree with each other, and the engine manual is a better authority.

Glow or spark: know which engine you have

Glow engines burn a methanol-based fuel blended with oil, and usually nitromethane. They have a glow plug, a small heating element that you power briefly at start-up. Gasoline engines are a different animal. They use a spark plug and an electronic ignition module, like a chainsaw.

O.S. lists these as separate product groups. Its gasoline-engine plug page shows CM-6 spark plugs, and its glow plug pages cover standard, long-reach, four-stroke and specific-engine plugs. A DLE-20 gas engine, for example, is listed at retail with a CM6 spark plug gapped to 0.018 to 0.020 inch. Do not order a glow plug for a gas engine, and do not expect a gas engine to fire from a glow driver.

If you fly gas, read the gas engine guide. If you fly nitro, the fuel matters for plug life, so the fuel guide is a natural companion to this page.

How a glow plug works

Per the O.S. FS-95V manual, ignition on a glow engine starts with a 1.5-volt power source applied to the plug. Once the battery is disconnected, the heat retained in the combustion chamber keeps the plug filament glowing, so the engine keeps running. The manual adds that ignition timing is "automatic": under reduced load, with higher rpm, the plug gets hotter and fires the charge earlier. At lower rpm the plug runs cooler and ignition is retarded.

That is why O.S. describes glow plugs as expendable items. The same manual lists what extends plug life:

• install a plug suited to the engine,
• use fuel with a moderate nitromethane percentage unless more is truly needed for racing,
• do not run the engine too lean,
• and do not leave the battery connected while adjusting the needle.

When to replace a plug

The O.S. manual lists the signs that a plug is no longer giving its best, even when it is not burned out:

• the filament surface has roughened and turned white,
• the filament coil has become distorted,
• foreign matter has stuck to the filament, or the plug body has corroded,
• the engine tends to cut out at idle,
• starting qualities deteriorate.

It also says to replace the plug when the element does not glow or is burnt out. When you check an element, hold the plug with pliers or similar tools and keep it away from your face, because fuel left in the filament can burn you.

The practical field-box rule follows from that: carry spare plugs, the same way you carry spare propellers, and do not wait for a no-start to buy them.

Choosing a plug: the manual first

The most reliable instruction is the plug your engine's manual names. O.S. ships the FS-95V four-stroke with a Type F plug, and its parts list gives code 71615009 for that plug. Heat designations also vary between makers, so a number on one brand's box does not carry over to another. Treat any online cross-reference chart with caution.

What O.S. offers

O.S.'s own glow plug pages group its plugs into:

• Standard type plugs (codes 71605300, 71607100, 71608001, 71605100),
• Long-reach plugs (codes 71653000, 71653400), with a note that using a long-reach plug in a standard-reach engine requires one additional plug gasket,
• Plugs for four-stroke engines (71615009),
• Plugs for specific O.S. engines,
• T series plugs (the O.S. Speed line),
• Plugs for gasoline engines.

Horizon Hobby's product titles carry the heat designations for the common aircraft plugs:

Reseller listings add some descriptive text:

• #8 (71608001): a favorite for most two-stroke engines, with a platinum-alloy coil that holds heat without an idle bar. It is described as a medium-heat plug recommended for most current O.S. two-strokes and some other brands.
• #6 (71605300): a hot-range plug, formerly the A3, described as working in two-strokes from .10 size to .60.
• Type F (71615009): a shielded long-reach plug for four-stroke engines. The shield is described as keeping the plug hot for lower idle rpm.

There is one wrinkle. O.S. groups the #8 code with its standard-type plugs, while Horizon and Amazon titles say "Long." Rather than assume, check the reach your engine manual specifies before you buy.

Product links:

• O.S. #8 glow plug (71608001) on Amazon for a general-purpose two-stroke plug, when your manual calls for it.
• O.S. #6 A3 hot plug (71605300) on Amazon for engines whose manual specifies the hot A3 plug.
• O.S. Type F plug (71615009) on Amazon for four-strokes that use it, such as the FS-95V.

A few notes:

• O.S. also sells a "Glow G5 Gas Plug" (GGT15) on Horizon, which O.S. lists for gas engines. Follow the engine maker's documentation for which plug it specifies.
• There is no point trying a plug in a different class of engine just because it threads in. The right plug depends on the engine design.
• Buy from an established dealer rather than the cheapest anonymous listing.

Glow drivers

A glow driver is the handheld battery clip that supplies the starting voltage. O.S. calls this a 1.5-volt source and suggests a commercially available glowplug heater with its own battery and leads. There are three common types.

An AA-powered igniter. The simplest type. The Hobbypark AA glow plug igniter uses standard AA batteries, which are not included. It has no meter or regulation features listed, and its performance depends on the cell you put in. It makes a reasonable backup.

A rechargeable driver with an LED. The Dynamite LiPo Glow Driver (DYNE0201) is described by Horizon as designed to make glow ignition easy, with a USB-style charger and an LED that shows whether the plug is good or the unit needs charging. The Amazon listing adds a 1S 1200 mAh LiPo, a switching power stage with low heat dissipation, and the claim that it fits all glow plugs. Horizon lists it in stock. Dynamite LiPo Glow Driver on Amazon

A metered driver. A meter can show current draw, which tells you more about a plug than an LED does. The Dynamite Metered NiMH Glow Driver (DYNE0200) is described with a 2600 mAh Sub-C NiMH battery, a locking plug clip and a USB-style charger, but Amazon lists it as unavailable, so check for a current equivalent.

Whichever driver you use, remember the O.S. caution: do not leave the battery connected while you adjust the needle. And do not let the driver become a crutch. An engine that only runs with the igniter attached has a tuning or mechanical problem waiting underneath, and our nitro starting guide walks through it.

Onboard glow drivers

A plug in a cowled or inverted engine is hard to reach and hard to keep hot at idle. An onboard driver holds heat in the plug from an onboard battery.

Model Airplane News, describing Sullivan's single- and dual-cylinder drivers, says a driver can be wired in parallel with the throttle servo on a Y harness for automatic operation at low throttle, or switched manually through a spare channel. A flashing green LED on those units indicates a burned-out plug. A Model Aviation article on glow heaters adds that inverted engines and some four-strokes are prone to dying at idle because the plug cools.

Driver models, voltage ranges and wiring vary, so read the maker's instructions before you fit one. The Sullivan M060 may be unavailable, so check the current listing, and other makers offer similar drivers.

An onboard driver does not replace a correctly tuned engine. If it is masking a rich mixture or a wrong plug, the engine will misbehave as soon as you push it.

Remote access

If the plug is simply hard to reach, a remote adapter moves the connection point somewhere accessible. Horizon lists two from Hangar 9, both in stock when this guide was researched: the Hangar 9 Remote Glow Plug Adapter (HAN122), and the Remote Glow Plug Adapter with Starter Adapter (HAN3025). Search for the Hangar 9 Remote Glow Plug Adapter on Amazon

A remote lead fixes accessibility. An onboard driver fixes power and automation. They solve different problems, and you can use both.

Tools and field box

Carry a plug wrench that fits your plug and reaches into a cowled head. Dynamite's Nitro Glow Plug Wrench (DYN2510) showed as out of stock at Horizon when researched, so look for a long socket-style wrench of the right size. Search for a glow plug wrench on Amazon

A sensible nitro field box has:

• two or three spare plugs of the type your manual specifies,
• a charged glow driver and a backup,
• a plug wrench,
• an electric starter or your preferred starting aid, and fuel filters.

Troubleshooting

• The plug glows on the bench but the engine will not run. Bench glow proves very little. Check the O.S. replacement signs listed above and swap in a fresh plug, which is the cheapest test.
• The engine only runs with the igniter on. Work through the driver, the plug, then fuel and mixture. A rich mixture, stale fuel or a cold engine can produce the same symptom. Our no-start guide covers the rest.
• The engine dies at idle. The O.S. manual lists this as one reason to replace a plug.
• Starting has become harder over time. Same answer. Check the filament and replace the plug.

FAQ