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 'vortex ring state' (settling with power)?
Answer: A dangerous condition where the helicopter descends into its own rotor downwash, causing loss of lift
Vortex ring state occurs when the helicopter descends at low airspeed with power applied, causing rotor vortices to recirculate through the disc and destroy lift unpredictably.
What are the three conditions that lead to vortex ring state?
Answer: Low airspeed (under ~15 knots), high power setting, and high rate of descent (over ~300 fpm)
Vortex ring state typically develops with low forward airspeed, an upward flow through the rotor from the descent, and sufficient power to sustain the vortex circulation.
What is the primary recovery technique from vortex ring state?
Answer: Lower collective to reduce power and apply forward cyclic to gain airspeed
Recovery requires lowering collective to reduce power and applying forward cyclic to gain airspeed, moving the helicopter out of the recirculating vortex.
What is 'dissymmetry of lift' and how does a fully articulated rotor correct for it?
Answer: Uneven lift between advancing and retreating blades in forward flight; corrected by blade flapping
Dissymmetry of lift is the unequal lift between the faster advancing blade and slower retreating blade; flapping hinges allow blades to rise and descend, equalizing angles of attack.
What is the purpose of the freewheeling unit (sprag clutch) in a helicopter drivetrain?
Answer: To allow the rotor to continue spinning freely if the engine fails or is decoupled
The freewheeling unit automatically disconnects the engine from the rotor transmission when engine RPM drops below rotor RPM, allowing the rotor to autorotate freely.
What is 'mast bumping' and why is it dangerous?
Answer: Contact between the rotor hub and the rotor mast in semi-rigid rotor systems, which can cause blade separation
Mast bumping occurs in teetering rotor systems when the rotor hub contacts the mast, typically in low-G flight, and can rapidly lead to catastrophic blade separation.
What is 'ground resonance' in helicopters?
Answer: A destructive self-reinforcing oscillation from unequal blade spacing amplified through landing gear during ground contact
Ground resonance is a potentially destructive oscillation where rotor blade lead-lag imbalance couples with landing gear movement to create amplifying vibrations that can destroy the helicopter.