Aviation and rotorcraft: What did Igor Sikorsky invent and pioneer in practical, modern form? Focus on his most famous contribution to powered flight technology. Choose the correct invention.

Given data

• We must identify Igor Sikorsky's key invention.

Concept / Approach
Igor Sikorsky is renowned for developing the practical helicopter, especially the single-main-rotor with tail-rotor layout (e.g., VS-300, R-4).

Step-by-step reasoning
Parachutes, jet engines, and rigid airships are associated with other inventors; Sikorsky's principal contribution is the helicopter.

Final Answer
Helicopter (practical single-rotor configuration).