Principles of Helicopter Flight Flashcards
7 cards from real SIFT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Principles of Helicopter Flight flashcards as text
What is ground effect in helicopter operations?
Answer: Increased rotor efficiency when flying within one rotor diameter of the ground
Ground effect occurs when the rotor system is within approximately one rotor diameter of the surface, where interference with ground-reflected airflow reduces induced drag and improves efficiency.
What does the term 'effective translational lift' (ETL) refer to?
Answer: The airspeed (typically 16-24 knots) at which the rotor becomes significantly more efficient
ETL is achieved around 16-24 knots when the rotor fully leaves its own downwash, resulting in a noticeable increase in rotor efficiency and a vibration sometimes called the 'translational lift bump.'
In a hover, what primarily causes the helicopter to require more power than in slow forward flight?
Answer: The rotor must work in its own downwash, creating induced drag
In a hover, the rotor recirculates its own downwash, increasing induced drag and requiring more power than in forward flight where fresh air is encountered.
What is the 'deadman's curve' (height-velocity diagram) used for?
Answer: Showing combinations of airspeed and altitude that may not allow safe autorotation after engine failure
The height-velocity diagram identifies dangerous airspeed-altitude combinations where, following engine failure, insufficient altitude or airspeed exists to successfully complete an autorotation.
What is 'lead-lag' (hunting) motion in rotor blades?
Answer: The fore-and-aft movement of blades in their plane of rotation to accommodate Coriolis effect
Lead-lag is the fore-and-aft movement of rotor blades in the plane of rotation, accommodating Coriolis forces as blades change their distance from the rotor hub during flapping.
What is the main advantage of a semi-rigid (teetering) rotor system?
Answer: It is mechanically simple with fewer parts because blades teeter as a pair
Semi-rigid teetering systems are simpler and lighter because the two-blade assembly teeters as a unit, eliminating the need for individual flapping and lead-lag hinges.
What is 'torque effect' in a single-rotor helicopter and how is it countered during a hover?
Answer: The fuselage tends to rotate opposite to the main rotor; countered by tail rotor thrust via pedal inputs
Torque reaction causes the fuselage to rotate opposite the main rotor's direction; the pilot uses anti-torque pedals to adjust tail rotor thrust and maintain heading.