The Lockheed L-1011 TriStar had a unique S-duct air intake for its tail engine (No. 2 engine). Instead of mounting the engine on the tail like the DC-10, it was placed inside the fuselage.
✅ S-duct benefits:
- Less drag → More fuel-efficient ✈️
- Better balance → Stable flight ⚖️
- Quieter → Less noise 🔇
This design made the L-1011 advanced, but it had limited success due to financial issues.