Powered Parachute Flying Handbook

Chapter 4 — Powerplants

Ignition System

The ignition system provides the spark that ignites the fuel-air mixture in the cylinders. Components include a magneto generator, an electronic control box that replaces mechanical points, spark plugs, high-voltage leads and the ignition switch(es). Individual manufacturer designs will vary and pilots must be familiar with the aircraft operating procedures for the PPC being flown.

A magneto uses a permanent magnet to generate an electrical current independent of the aircraft’s electrical system which might include a battery. The aircraft electrical system can fail—the battery can go dead—however, this has no effect on the ignition system which uses a separate generator in the magneto. The electricity from the separate ignition coil on the magneto generator goes into the ignition control box where the correct voltage is produced and timed to fire the spark plugs at the proper time. The magneto also sends a signal to the electric control box to provide the timing signal to fire the spark plugs.

Most modern PPCs use an electronic timing system instead of the mechanical points inside the old magnetos which also housed the points. Capacitor discharge ignition (CDI) systems are a common example of an electronic ignition system. Electronic ignition systems operate without any moving parts to increase reliability and efficiency. A CDI system begins to fire when the starter is engaged and the crankshaft begins to turn. It continues to operate whenever the crankshaft is rotating.

Most powered parachutes incorporate a dual ignition system with two individual coil systems in the magneto, two individual electronic ignition timing systems (electric box), two separate sets of wires, and two spark plugs per cylinder. Dual ignition systems increase overall reliability of the engine. Each ignition system operates independently to fire one of the two spark plugs. If one ignition system fails, the other is unaffected. The engine will continue to operate normally, although you can expect a slight decrease in engine power.

The operation of the ignition system is controlled in the cockpit by the ignition switch(es). Since there are two individual ignition systems, there are normally two separate ignition toggle switches.

You can identify a malfunctioning ignition system during the pretakeoff check by observing the decrease in RPM that occurs when you first turn off one ignition switch, turn it back on, and then turn off the other. A noticeable decrease in engine RPM is normal during this check. If the engine stops running when you switch to one ignition system or if the RPM drop exceeds the allowable limit, do not fly the powered parachute until the problem is corrected. The cause could be fouled plugs, broken or shorted wires between the magneto and the plugs, or improperly timed firing of the plugs because of the control box.

It should be noted that “no drop” in RPM is not normal, and in that instance, the powered parachute should not be flown. Following engine shutdown, keep the ignition switches in the OFF position. Even with the battery and master switches OFF, the engine can fire and turn over if you leave an ignition switch ON and the propeller is moved because the ignition system requires no outside source of electrical power. The potential for serious injury in this situation is obvious.


During normal combustion, the fuel-air mixture burns in a very controlled and predictable manner. Although the process occurs in a fraction of a second, the mixture actually begins to burn at the point where it is ignited by the spark plugs, then burns away from the plugs until it is consumed completely. This type of combustion causes a smooth buildup of temperature and pressure and ensures that the expanding gases deliver the maximum force to the piston at exactly the right time in the power stroke.

Detonation is an uncontrolled, explosive ignition of the fuel-air mixture within the cylinder’s combustion chamber. It causes excessive temperatures and pressures which, if not corrected, can quickly lead to failure of the piston, cylinder, or valves. In less severe cases, detonation causes engine overheating, roughness, or loss of power.

Detonation is characterized by high cylinder head temperatures, and is most likely to occur when operating at high power settings. Some common operational causes of detonation include:

• Using a lower fuel grade than that specified by the aircraft manufacturer or operating the engine after it has been sitting for an extended period; after 3 weeks or as indicated by your POH you should drain old fuel out and replenish with fresh fuel.
• Operating the engine at high power settings with an excessively lean mixture.
• Detonation also can be caused by extended ground operations.

Detonation may be avoided by following these basic guidelines during the various phases of ground and flight operations:

• Make sure the proper grade of fuel is being used. Drain and refuel if the fuel is old.
• Develop a habit of monitoring the engine instruments to verify proper operation according to procedures established by the manufacturer.

Preignition occurs when the fuel-air mixture ignites prior to the engine’s normal ignition event. Premature burning is usually caused by a residual hot spot in the combustion chamber, often created by a small carbon deposit on a spark plug, a cracked spark plug insulator, or other damage in the cylinder that causes a part to heat sufficiently to ignite the fuel-air charge. Preignition causes the engine to lose power, and produces high operating temperature. As with detonation, preignition may also cause severe engine damage, because the expanding gases exert excessive pressure on the piston while still on its compression stroke.

Detonation and preignition often occur simultaneously and one may cause the other. Since either condition causes high engine temperature accompanied by a decrease in engine performance, it is often difficult to distinguish between the two. Using the recommended grade of fuel and operating the engine within its proper temperature and RPM ranges reduce the chance of detonation or preignition.

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