All about GLOW PLUGS

Written by Brian Gardiner, and Central Coast Model Aero Club Inc.
Submitted by Wayne Beasley

_________

How Does A Glow Plug Work?

Contrary to what many have previously been lead to believe the following is an explanation of how a glow plugfunctions in a motor. The plug is initially heated by applying a voltage (typically 1.5 volts) to it. This is to cause it to glow so as to ignite the fuel at compression and start the internal combustion cycle.

Once the cycle has started, the power source can be disconnected, as with the heat generated at combustion the CATALYTIC Reaction generated between the methanol and platinum in the plug coils becomes sufficient to keep the process going. The catalytic reaction is a reaction whereby platinum will glow in the presence of methyl alcohol vapour. This will happen without any external power source being applied.

How do you select the correct PLUG for your application, and why ?

To do this you need to understand a little more of the theory behind the process. In glow fuel the catalytic reaction is generated between the methanol and platinum only. Castor oil, synthetic oil, nitro methane, etc do not generate a catalytic reaction with the platinum.

Next you need to understand that a certain surface area of platinum is required to generate a sufficient catalytic reaction to keep the internal combustion process going. Also it is necessary to allow extra surface area for the reaction to be great enough when it diminishes with the available methanol dropping as in the case at motor idle. Simply put, cold plugs are manufactured using a thicker wire to give greater surface area to facilitate a greater reaction and thus the required catalytic reaction where less methanol is present in the fuel mixture.

So! More nitro means less methanol which in turn means a greater surface area to platinum will be required to generate a sufficient catalytic reaction. Suddenly it all makes sense! To work out which temperature plug to use, you need to know how much methanol is in your fuel, not how much nitro or oil.

As a rough rule of thumb;

  • 70%-75% use a medium plug.

Idle Bars and Other Stuff

Again, contrary to what many believe, the idle bar on a glow plug is not necessarily what its name would suggest. It is in fact to stop any fuel not vaporized from dousing the platinum coil of the glow plug by dispersing it away from the coil.

Why are plated coils not as good as platinum alloy coils?

Plated coils suffer from very quick degeneration as the plating breaks down under operating conditions. As bits of plating come off, the plug is effectively becoming a hotter and hotter unit until in a comparatively short time it is

no longer able to perform its function. Conversely, a platinum alloy coil will still degenerate, but as it is platinum alloy throughout, the surface remains as platinum alloy and the plug continues giving much the same characteristics for quite a long time.

Plated coils are very poor value when compared to platinum alloy coiled glow plugs.

 

courtesy, Warringah Radio Control Society Incorporated


GLOW PLUG REFERENCE LISTING

Submitted by Brian Cooper
Cooper's Custom Blended Fuels LLC
  -  www.cooperfuels.com

MFG

Number / name

Use

Remarks

Hot Glow Plugs- for low nitro fuels

Mc Coy

MC 55- R/C Long

sport hot

Similar to K&B 1L

Mc Coy

MC 59

sport hot

low nitro

Mc Coy

MC 14

very hot

heli/ inverted 4-stroke

Fireball

Hot 1.2-3.0V

sport hot

red

Fireball

S-20 R/C Long

sport hot

1.5-2.0V

SonicTronics

Glowdevil #300

sport med-hot

 

Rossi

R/C Hot, R-1&R-2

sport hot

low nitro

Sig

R/C Long`

sport hot

 

Enya

#3

Sport hot

low nitro

Thunderbolt

R/C Long`

sport med-hot

 

K&B

1L

sport hot

 

Fox

Miracle

sport hot

low notro or 4-stroke

Fox

Standard

sport hot

 

Fox

R/C Long (2V)

sport hot

 
       

Standard (med) glow plugs-for 10%-15% fuels

MFG

Number / name

Use

Remarks

Fireball

Standard 1.2-2V

standard sport

yellow

Sonic Tronics

Glowdevil standard

standard sport

 

Rossi

Medium and R-3

standard sport

 

Enya

#4

standard sport

med-hot

Enya

#5

standard sport

med-cool

Mc Coy

MC 50

all purpose

sport w/idle bar

Mc Coy

MC 8

sport med-cool

med to high nitro

Hangar 9

Sport Long

standard sport

MC 50 packaged for Hangar 9

Tower

Performance plug

standard sport

w/o idle bar

Fox

R/C Long (1.2-1.5V)

standard sport

med-cool

Fox

Gold

standard sport

med-cool

       

Cold Glow Plugs-High nitro, 25% and over or racing/ fans

MFG

Number / name

Use

Remarks

Mc Coy

MC 9

hi-perf

Ducted Fan / racing / high nitro

Fireball

Cool 1.2-1.5V

hi-perf

Blue

Enya

#6

hi-perf

extremely hot engines/high compression/high nitro

K&B

Long & Short

hi-perf

cold standard plug

K&B

Hi Perf Nitro Plug

hi-perf

high nitro / high perf

Rossi

R/C Cold

hi-perf

R-4 & R-5

Rossi

Extra Cold

hi-perf

R-6 & R-7

Sig

Cool 1.5V

hi-perf

 

OS

R-5

   

Fox

R/C 1.2V

   

Fox

#8

hi-perf

high nitro / high perf

       

Four Stroke plugs- hot

MFG

Number / name

Use

Remarks

Fox

Miracle

4-stroke

2-cyl low nitro or 4-cyl

Mc Coy

MC 14

very hot

heli and inverted 4 strokes

OS

Type F

4-stroke

 

Sig

GP-001

4-stroke

 

Sonic Tronics

Glowdevil St 301/302

4-stroke

 
       

Diagnosis or Symptoms:

High Nitro = Hot Fuel: needs colder plugs

Low Nitro = Cold Fuel: needs hotter plugs

High Nitro + High rpm's: needs colder plug ie:ducted fans

 

If engine sags when the battery is disconnected, the plug is too cold or more nitro is needed

If the engine bites back or backfires when hand cranking, the plug is too hot or less nitro is needed

 

Most HOT plugs can take 2 volts

Most COLD plugs can take 1.2 - 1.5 volts

 

Most 4-strokes need very hot plugs or high nitro

 

Note: Mc Coy 4-cycle plugs (not the MC 14) are "Saito Original Equipment"

Hangar 9 plugs are Original Mc Coy plugs packaged for Horizion

 

The above information was shared by:

Charles Thacker of Fox  manufacturing

Mr. McCoy of his own company

Hank, the owner of SonicTronics

Sig Manufacturing

This spreadsheet is meant to be guidance only, by no means is it the finite answer about glow plugs.

 

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