Propellers practice questions

Answer: A) Each blade tip follows the same plane of rotation within tolerance

A track check measures the path of each blade tip against a fixed reference to confirm that all tips rotate in the same plane within tolerance. Blade angle, balance and diameter are separate checks.

• ACorrect. Blade track is the path each blade tip follows as it passes a fixed point. The track check confirms that no blade tip is outside the allowed tolerance from the plane of rotation.
• BIncorrect. This is a blade angle check, done with a protractor at the blade reference station. It is a separate check from tracking.
• CIncorrect. This describes a static balance check, which finds uneven weight distribution, not where the blade tips travel.
• DIncorrect. This is a diameter check, done after tip damage is dressed out. It does not show whether the blade tips follow the same path.

Answer: B) To avoid shock waves near Mach 1 that reduce efficiency and raise noise

Tip speed is the fastest airflow over the propeller. Near Mach 1, compressibility and shock waves cause large efficiency losses and much more noise, so diameter and rpm are chosen to keep tip speed below that range.

• AIncorrect. Governor flyweights sense engine speed, not blade tip speed. Tip speed limits come from blade aerodynamics, not governor capability.
• BCorrect. When tips approach the speed of sound, compressibility effects and shock waves sharply reduce thrust and efficiency and greatly increase noise.
• CIncorrect. Aerodynamic twisting moment tends to turn blades toward high pitch, not low pitch. It is also not the main reason tip speed is limited.
• DIncorrect. Blade stall depends on angle of attack, which is set by blade angle and airspeed. It is not the reason for a tip-speed limit.

Answer: B) 1/16 inch

• AIncorrect. That's far too much.
• BCorrect. Check the manufacturer's data for exact values.
• CIncorrect. That's too much.
• DIncorrect. A small tolerance is allowed.

Answer: C) Visibility when turning

• AIncorrect. Paint can unbalance blades.
• BIncorrect. This is not the main purpose.
• CCorrect. Tip markings make a turning propeller easier to see.
• DIncorrect. This is not the purpose.

Answer: B) On a knife-edge stand

• AIncorrect. That's dynamic balancing.
• BCorrect. The prop should stay in any position.
• CIncorrect. That isn't balancing.
• DIncorrect. The whole prop is balanced.

Answer: D) A slinger ring

• AIncorrect. That isn't typical.
• BIncorrect. That isn't the system.
• CIncorrect. That's de-icing.
• DCorrect. Centrifugal force spreads the fluid along the blades.

Answer: A) The hub center

• ACorrect. Blade stations are measured outward from the center of the hub.
• BIncorrect. They start at the hub center.
• CIncorrect. This is not the reference.
• DIncorrect. This is not the reference.

Answer: A) Through brushes in a fixed brush block that ride on rotating slip rings

Electric propeller deice heaters get power from the aircraft electrical system. A fixed brush block feeds current through slip rings that turn with the propeller.

• ACorrect. The brush block stays fixed on the engine side. Its brushes ride on slip rings that turn with the propeller, carrying current from the aircraft electrical system to the blade heaters.
• BIncorrect. A wire cannot pass continuously from a stationary part to a rotating one. A sliding contact is needed, and that is what the slip rings and brushes provide.
• CIncorrect. The timer controls when the heaters cycle, and it is mounted on the airframe side. Power still reaches the hub through the brushes and slip rings.
• DIncorrect. The magneto belongs to the ignition system and cannot supply heater power. Deice heaters run on the aircraft electrical system.

Answer: B) Increase

• AIncorrect. Load falls as airspeed rises.
• BCorrect. The blade's angle of attack drops, reducing load.
• CIncorrect. That's a constant-speed prop.
• DIncorrect. The engine keeps running.

Answer: B) Horizontally, with both blades level

Store wood propellers horizontally. If a blade points down, moisture collects in that blade and throws the propeller out of balance.

• AIncorrect. Moisture in the wood moves toward the lower blade. That blade gets heavier and the propeller goes out of balance.
• BCorrect. Storing the propeller horizontally keeps moisture spread evenly through the wood, so it does not collect in one blade and unbalance the propeller.
• CIncorrect. Hanging it this way still leaves one blade lower than the other. Moisture moves into the lower blade and causes imbalance.
• DIncorrect. The finish protects the wood but does not stop moisture from moving inside it. Storage position still matters.