HOW TO WIRE AN IGNITION ENGINE FOR FREE FLIGHT
Bill Schmidt of Bel Aire, KS, inventor of the transistorized ignition known as the "Schmidt Trigger", sent us this drawing on how he hooks up his Free Flight planes. For those not familiar with transistorized ignition, it is very commonly used and the main purpose is to take the large coil current off the engine points to eliminate point wear and to provide a hotter spark to the spark plug. The timer and the engine points then only carry a very small current that is used to drive the base of the transistor, which switches the larger current to the coil.
Bill in particular wants to call attention to the 16 gauge wire used in that part of the circuit used to feed the primary side of the coil. This is the loop including the Collector and Emitter of the transistor, the Battery, and the two primary connections to the coil. This is where current flow is largest and any voltage loss due to resistance is detrimental to the performance of the ignition system. The actual size of the wire you use needs to take into account how long the wiring is in this circuit. A very short loop length can use smaller wire. All connections must be soldered or be very solid. Just twisting wires will not pass muster.
Bill uses the #123 Lithium battery and says he gets several years use from it before replacement.
Bill also says use of the on/off toggle switch is very important. Keep the switch off when not actually running the engine. This will prevent a constant and heavy current flow from depleting the battery while just sitting there should the engine points be closed.