Reciprocating Engine Induction and Cooling Systems practice questions

Answer: A) Moisture hits cold inlet surfaces

• ACorrect. It forms below freezing and can block air filters and scoops.
• BIncorrect. Ice needs moisture.
• CIncorrect. There's no airflow.
• DIncorrect. Heat prevents ice.

Answer: B) Exhaust valve and port

• AIncorrect. Fresh charge cools it.
• BCorrect. Hot exhaust passes there.
• CIncorrect. That's cooler.
• DIncorrect. That's cooler.

Answer: C) Without ram airflow from forward speed, cylinder temperatures can exceed limits

Air-cooled engines need airflow across the cylinder fins. On the ground there is no ram air, so long high-power runs can push cylinder temperatures past their limits.

• AIncorrect. A propeller turning with no forward speed actually carries a high aerodynamic load. Overspeed is not why ground runs at high power are limited.
• BIncorrect. Carburetors and fuel injection systems run richer at high power to help cooling. Plug fouling is mainly a problem during long idling at low power.
• CCorrect. Air-cooled engines are cooled by air moving across the cylinder fins. On the ground there is only propeller slipstream, so at high power cylinder head temperatures can quickly go past the manufacturer's limits.
• DIncorrect. The engine-driven fuel pump is sized to meet full-power fuel demand whether or not the aircraft is moving. Ram air has nothing to do with its output.

Answer: A) A self-sustaining drift in manifold pressure caused by exhaust-energy feedback

Bootstrapping is a self-sustaining turbocharger feedback loop: changes in exhaust energy change turbo speed, which changes power again. The result is unstable, drifting manifold pressure.

• ACorrect. A small change in power changes exhaust energy, which changes turbocharger speed, which changes power again. The result is unstable manifold pressure that keeps drifting instead of settling.
• BIncorrect. That's overboost. It is a separate malfunction, usually caused by a wastegate or controller failure, not the feedback-driven drift that defines bootstrapping.
• CIncorrect. That's turbocharger lag, the time the rotating assembly needs to speed up. It isn't the self-sustaining drift called bootstrapping.
• DIncorrect. That describes operating above critical altitude, where the turbocharger can no longer maintain rated manifold pressure. It isn't bootstrapping.

Answer: B) Reduces cooling drag

• AIncorrect. Closed flaps reduce airflow.
• BCorrect. Less cooling air is needed in cruise.
• CIncorrect. That's carburetor heat.
• DIncorrect. That isn't the effect.

Answer: B) The idle mixture

• AIncorrect. This is unrelated.
• BCorrect. Unmetered air leans the mixture most noticeably at idle.
• CIncorrect. This is unrelated.
• DIncorrect. This is unrelated.

Answer: A) A mixture of water and ethylene glycol

Liquid-cooled aircraft engines use a water and ethylene glycol coolant. The glycol raises the boiling point and lowers the freezing point compared with water alone.

• ACorrect. Ethylene glycol mixed with water is the standard coolant for liquid-cooled aircraft engines. Compared with water alone, it raises the boiling point and lowers the freezing point.
• BIncorrect. Plain water freezes at low temperatures and boils too easily for aircraft use. That is why glycol is added.
• CIncorrect. Water and methanol is anti-detonation injection (ADI) fluid. It is injected into the induction air for power augmentation and is not circulated as jacket coolant.
• DIncorrect. Engine oil carries away some heat as it lubricates, but liquid-cooled engines use a separate glycol-based coolant in the cylinder jackets.

Answer: C) Reduced manifold pressure and power

• AIncorrect. That isn't the effect.
• BIncorrect. It restricts airflow.
• CCorrect. Less air reaches the cylinders.
• DIncorrect. Power drops instead.

Answer: D) Hold sea-level manifold pressure

• AIncorrect. It still has a throttle.
• BIncorrect. That's turbosupercharging.
• CIncorrect. It needs intake air.
• DCorrect. It does so up to its critical altitude but doesn't boost above sea-level pressure.

Answer: A) An exhaust shroud heat exchanger

• ACorrect. Air passes around the hot exhaust.
• BIncorrect. That isn't typical.
• CIncorrect. That isn't the common source.
• DIncorrect. The muff supplies carb heat separately.