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What shape is a typical rocket engine nozzle?

Convergent-divergent: it narrows to a throat, then widens like a bell.

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  1. A straight tube of the same width
  2. Widens first, then narrows to a point
  3. Narrows to a throat, then widens ✔

Why: Hot gas squeezes through the narrow throat, then expands in the widening bell. That shape speeds the exhaust up to supersonic speed, which makes more thrust.

Huh, didn't know that: Engineers call it a CD nozzle for short.

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Why was the rocket nozzle so calm? It knew how to expand its horizons.
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References

Answer: Narrows to a throat, then widens. Hot gas squeezes through the narrow throat, then expands in the widening bell. That shape speeds the exhaust up to supersonic speed, which makes more thrust.

  1. NASA Glenn, Nozzle Design www1.grc.nasa.gov/beginners-guide-to-aeronautics/nozzle-design
    This nozzle configuration is called a convergent-divergent, or CD, nozzle.
    Checked 2026-10-10.

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