Unit 4 review: Engine and Systems

A mixed check of all 4 lessons in this unit. Mixing topics is harder than one lesson at a time, and that's the point: it's how the written test and the oral exam ask.

The unit in one minute

How the engine worksFour strokes: intake, compression, power, exhaust; only the power stroke makes power.
Ignition, fuel and carburetor iceTwo magnetos make their own electricity; the engine runs without the electrical system.
The electrical systemThe electrical system does not power the engine's ignition.
Propeller, oil and engine coolingFixed-pitch: power = RPM. Constant-speed: power = manifold pressure, RPM set by the prop control.

Mixed check

12 questions pulled from across the unit. Wrong answers explain why and point you back to the lesson.

Check: Why do propeller blades have twist?Answer: To keep an efficient angle of attack along the blade. Blade speed increases toward the tip, so the twist keeps the angle of attack efficient.

Check: An ammeter showing a negative (discharge) reading in flight likely means:Answer: The alternator isn't supplying enough current. A discharge means the battery is supplying the load: the alternator isn't keeping up.

Check: What's a common way to correct detonation?Answer: Enrich the mixture and reduce power. Enriching the mixture, reducing power and cooling the engine help stop detonation.

Check: If the airplane's alternator and battery both fail, what happens to the engine?Answer: It keeps running, because the magnetos make their own electricity. Magnetos are self-contained, so ignition doesn't depend on the electrical system.

Check: Why are most trainer engines air-cooled?Answer: It saves the weight and complexity of a liquid cooling system. Air cooling avoids the weight of radiators, pumps and coolant.

Check: After an alternator failure, what should you do with electrical equipment?Answer: Turn off nonessential equipment to save the battery. Load shedding stretches the battery so you have radios and essentials to land.

Check: In an airplane with a constant-speed propeller, what does the propeller control set?Answer: RPM. The prop control sets RPM through the governor; the throttle sets manifold pressure.

Check: If a magneto ground wire breaks, what happens?Answer: The magneto stays 'hot' even with the switch off. A broken P-lead means the magneto can fire even with the key off: treat every prop as live.

Explain it to your CFI

Say each one out loud in your own words, in under a minute. If you stall, reread that lesson. This is exactly what an examiner looks for.

How the engine works. Describe the four strokes of a piston engine
Ignition, fuel and carburetor ice. Explain how magnetos work and why there are two
The electrical system. Describe the main parts of the electrical system
Propeller, oil and engine cooling. Compare fixed-pitch and constant-speed propellers

What the examiner may ask

What does high oil temperature with low oil pressure suggest?

A serious problem like low oil or an impending engine failure; land as soon as possible.

Review: Propeller, oil and engine cooling →

What happens if the alternator fails?

The battery powers the system until it's depleted; shed load and land as soon as practical.

Review: The electrical system →

Describe your airplane's engine.

Know the POH description: for example, four-cylinder, horizontally opposed, air-cooled, normally aspirated, carbureted, and its horsepower.

Review: How the engine works →

What's the voltage of your airplane's electrical system?

Know it from the POH: usually 14 or 28 volts.

Review: The electrical system →