# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/DaRuoWMA0BR
- **Gondola URL:** https://gondola.cc/posts/67391858-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/bc430fad19.jpg
- **Posted:** 2026-07-02T04:29:20.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

Both a turbojet and a turbofan burn kerosene to spin a turbine, yet they solve the problem of thrust in opposite ways. The difference comes down to a single principle from Newton’s second law: thrust equals mass flow multiplied by the change in velocity of the air passing through the engine.

A turbojet is the purist. Every molecule of air is drawn through the core: compressor, combustor, then turbine. Fuel ignites in the combustor, the expanding gas drives the turbine, and what remains is blasted rearward as a thin, blisteringly fast jet. It accelerates a small mass of air to an enormous velocity. Simple, compact, and capable of supersonic flight, but thermodynamically wasteful at subsonic speeds and deafeningly loud.

A turbofan reframes the question. A large fan sits ahead of the core, and most of the air it moves never touches the flame at all. That air is ducted around the engine as bypass flow, generating thrust cold and quietly.

The governing metric is the bypass ratio, the mass of bypass air divided by the mass passing through the core:

- Low bypass (0.3 to 1): military engines chasing raw speed and afterburner compatibility
- High bypass (5 to 12): airliners chasing fuel economy and a quiet cruise

Propulsive efficiency is the reason. Efficiency scales as 2 divided by (1 plus the ratio of jet velocity to aircraft velocity). Move a large mass of air slowly and that ratio approaches unity, so efficiency climbs toward its ceiling. The turbofan trades exhaust velocity for mass flow and wins decisively on fuel burn everywhere below Mach 1.

The turbojet screams past. The turbofan simply moves more air, and lets Newton do the rest.

#stemantics #aerospace #jetengine #propulsion #aviation

## Stats

- **Views:** 0
- **Likes:** 718
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- **Comments:** 5

## Tags

propulsion, jetengine, aviation, stemantics, aerospace

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