Rotorcraft Fundamentals practice questions

Answer: C) The hub striking the mast from excessive flapping

• AIncorrect. That is a tail strike.
• BIncorrect. It is a dangerous condition.
• CCorrect. It can cause catastrophic failure.
• DIncorrect. It is a structural contact.

Answer: B) Rise and fall independently

• AIncorrect. The feathering hinge does that.
• BCorrect. Flapping helps balance lift across the disc.
• CIncorrect. That is the lead-lag hinge.
• DIncorrect. Flapping is a flight motion.

Answer: C) Changes all blade pitch

• AIncorrect. That is the antitorque pedals.
• BIncorrect. That is the cyclic.
• CCorrect. The collective changes main rotor blade pitch collectively, controlling lift.
• DIncorrect. This is unrelated.

Answer: B) Blade flapping about the flapping hinge

Dissymmetry of lift is mainly compensated by blade flapping. The advancing blade flaps up (lower angle of attack) and the retreating blade flaps down (higher angle of attack), and cyclic feathering adds further compensation.

• AIncorrect. Lead-lag motion about the drag (vertical) hinge lets the blades speed up and slow down in their plane of rotation, which relieves stresses from Coriolis effect. It does not change blade angle of attack to equalize lift.
• BCorrect. The advancing blade flaps up, which lowers its angle of attack and its lift. The retreating blade flaps down, which raises its angle of attack and its lift. This evens out lift across the disk, and cyclic feathering (less pitch on the advancing blade, more on the retreating blade) adds further compensation.
• CIncorrect. Collective pitch changes the pitch of all blades by the same amount at the same time. It cannot correct a lift difference between the advancing and retreating sides.
• DIncorrect. Tail rotor thrust counteracts main rotor torque and gives yaw control. It does not balance lift between the two halves of the main rotor disk.

Answer: B) Rolling over a skid

• AIncorrect. That is loss of tail rotor effectiveness.
• BCorrect. The helicopter rolls about a skid or wheel in contact with the ground.
• CIncorrect. It is a hazard.
• DIncorrect. This is different.

Answer: B) Engine rpm on one needle and main rotor rpm on the other

A helicopter dual tachometer shows engine rpm and rotor rpm on one dial. The needles are 'married' when the engine drives the rotor and 'split' when the freewheeling unit disengages.

• AIncorrect. The tail rotor is geared to the main rotor at a fixed ratio, so it does not need its own needle. The two needles compare engine speed with main rotor speed.
• BCorrect. When the engine is driving the rotor, the needles are superimposed ('married'). When the freewheeling unit disengages, for example in autorotation, the needles split.
• CIncorrect. The second needle is not a maximum-reading (drag) pointer. It shows rotor rpm in real time, so the pilot can compare it with engine rpm.
• DIncorrect. The needles are not redundant engine indications. One shows engine rpm and the other shows rotor rpm, so they read differently when the needles split.

Answer: C) The tail rotor, engine or drive train

• AIncorrect. Skids do not rotate.
• BIncorrect. The main rotor turns slowly and causes low-frequency vibration.
• CCorrect. These parts rotate much faster than the main rotor.
• DIncorrect. Fuel tanks do not generate high-frequency vibration.

Answer: D) Slows and stops the rotor after shutdown

• AIncorrect. It is not a steering device.
• BIncorrect. It slows the rotor.
• CIncorrect. That is the swashplate.
• DCorrect. It also keeps the rotor from turning while parked.

Answer: C) It changes the drive direction, often 90°, and may adjust shaft speed to tail rotor rpm

The tail rotor gearbox changes the direction of drive from the tail rotor drive shaft to the tail rotor, usually by 90°. Its gearing may also adjust shaft speed to the best tail rotor rpm.

• AIncorrect. The main rotor transmission reduces engine speed and drives the mast. The tail gearbox only serves the tail rotor.
• BIncorrect. This is the job of the freewheeling (overrunning) unit between the engine and the main transmission, not the tail rotor gearbox.
• CCorrect. The tail rotor gearbox gives a right-angle drive from the tail rotor drive shaft to the tail rotor. It may also use gearing to set the best tail rotor rpm.
• DIncorrect. The tail rotor drive shaft is supported along the boom by hanger bearings, and on some designs by dampers. The tail gearbox is a power-transmitting component.

Answer: A) A freewheeling unit

• ACorrect. It disconnects the engine so airflow can drive the rotor.
• BIncorrect. It does not disengage the engine.
• CIncorrect. This is unrelated.
• DIncorrect. This is unrelated.