AN ON-BOARD IGNITION SYSTEM
…………………………....that works!
by Jim Taylor - Mar. 4, 2007

Did you ever wonder why your glow engine idles so much better when the glow starter is still attached? It is even harder to maintain a good smooth, reliable idle when the engine is mounted at an angle below horizontal which allows for the possibility of accumulation of unburned fuel or oil around the glow plug. An on-board ignition system is likely the answer.
The on-board ignition system is turned on when the throttle setting is reduced below about 20% and turned off again when the throttle is advanced above 20% to conserve the on-board battery and save the glow plug from over-heating.
This easily assembled system also provides additional security during critical maneuvers like approach and landing when the engine is at or near idle speed. A micro switch on the throttle servo connects a 1.2 Ni Cad cell to the glow plug in the “RUN” position to keep the plug hot during idle periods and turns it off at normal engine speeds.
This is a system you can build yourself at a considerable savings in cost over commercially available systems. If you aren’t handy with a soldering gun, then simply ask one of your hobby club buddies to give you a hand. Parts are obtainable at your nearest Radio Shack, and you’ll need the following:

1– Miniature micro switch
1– miniature earphone jack
1– miniature earphone plug to match
1– Ni Cad cell, ax. 2000 Mah capacity
1– Miniature double-pole, double-throw switch
(DPDT)
1– Remote glow starter lead with clip and jack
Some 18 ga. hookup wire in several colors.

You’ll also need to find a simple D.C. charger that delivers at least 200 milliamps at about 2.0 volts. Solder the earphone plug to the output cord on the charger using the center post as the positive connector, and the outside connection as the negative connector. Be sure to wire the earphone jack with the same polarity on the Ni Cad in the airplane.
Most of the wiring can be done outside the airplane and then installed in convenient locations inside. Be sure to make the wires long enough to allow some adjustment of placement within the airplane.
A simple mounting bracket for the micro switch at the throttle servo and an actuator for the micro switch from the throttle arm are things you’ll need to innovate to suit your individual arrangement. A small machine screw serves well for the latter. The picture below might help. Be sure to allow some adjustment of the positioning of the micro switch to permit some calibration of the actuating point, and wire the switch so that it closes when the throttle setting is lowered. There are usually three terminals on a micro switch, so you will use the center one and either end to accomplish this. Adjust the position of the micro switch so that the contacts close at about 20% of throttle travel as you reduce the throttle position.
Good luck!