SIFT Principles of Helicopter Flight 3

Question 1

What is ground effect in helicopter operations?

Accepted Answer

Increased rotor efficiency when flying within one rotor diameter of the ground

Answer

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.

Question 2

What does the term 'effective translational lift' (ETL) refer to?

Accepted Answer

The airspeed (typically 16-24 knots) at which the rotor becomes significantly more efficient

Answer

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.'

Question 3

In a hover, what primarily causes the helicopter to require more power than in slow forward flight?

Accepted Answer

The rotor must work in its own downwash, creating induced drag

Answer

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.

Question 4

What is the 'deadman's curve' (height-velocity diagram) used for?

Accepted Answer

Showing combinations of airspeed and altitude that may not allow safe autorotation after engine failure

Answer

The height-velocity diagram identifies dangerous airspeed-altitude combinations where, following engine failure, insufficient altitude or airspeed exists to successfully complete an autorotation.

Question 5

What is 'lead-lag' (hunting) motion in rotor blades?

Accepted Answer

The fore-and-aft movement of blades in their plane of rotation to accommodate Coriolis effect

Answer

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.

SIFT Exam Practice Test

SIFT Exam Practice Test

SIFT Principles of Helicopter Flight 3