SIFT Principles of Helicopter Flight Questions and Answers 3

Question 1

What is 'vortex ring state' (settling with power) in helicopters?

Accepted Answer

A dangerous condition where the helicopter descends into its own rotor vortex, losing lift despite high power

Answer

Vortex ring state occurs when the helicopter descends vertically at low airspeed with high power, causing the rotor to descend into its own tip vortex ring, severely reducing lift.

Question 2

How does increasing altitude affect a helicopter's hover ceiling?

Accepted Answer

Higher altitude reduces the hover ceiling because thinner air requires more power to generate the same lift

Answer

As altitude increases, air density decreases. The rotor generates less lift per revolution, requiring higher rotor speed or blade pitch — eventually reaching a ceiling where the helicopter cannot hover.

Question 3

What is gyroscopic precession and how does it affect helicopter flight?

Accepted Answer

A force that causes a spinning rotor to respond to an applied force 90° later in the direction of rotation

Answer

Gyroscopic precession causes a spinning rotor to respond to an applied tilting force approximately 90° ahead in the direction of rotation, affecting how control inputs translate to rotor disc movement.

Question 4

What is 'dissymmetry of lift' in forward helicopter flight?

Accepted Answer

Unequal lift between the advancing and retreating sides of the rotor disc due to different airspeeds

Answer

Dissymmetry of lift occurs because the advancing blade has higher airspeed (and thus more lift) than the retreating blade, creating unequal lift across the rotor disc in forward flight.

Question 5

What is the purpose of 'lead-lag' (drag) hinges on articulated rotor systems?

Accepted Answer

To allow blades to move fore and aft in the plane of rotation, reducing bending stress from Coriolis forces

Answer

Lead-lag hinges allow rotor blades to move forward and backward in the plane of rotation, relieving the cyclic stress caused by Coriolis effect as blades flap up and down.

SIFT Exam Practice Test

SIFT Exam Practice Test

SIFT Principles of Helicopter Flight Questions and Answers 3