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Technicalities: Speaking of Jets

**Garrison's proposal for a four-seat
single-engine jet. It was judged less cool
than an X-tailed design with an engine
on a pylon above the rear fuselage.
**
Gemini Sparkle

Key Takeaways:

  • A turbojet engine cannot exceed its own exhaust velocity because thrust is generated by accelerating the working fluid, and if the aircraft's speed were greater than the exhaust velocity, no net acceleration (and thus no thrust) would occur.
  • The article then discusses Austin Meyer's project to develop a four-seat jet for homebuilders, initiated by a misunderstanding of specific fuel consumption for jets at cruise.
  • Meyer's project faces significant challenges in acquiring suitable engines from manufacturers and complex design hurdles related to engine placement, weight balance, and aerodynamics, which he plans to explore using his X-Plane simulator.
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Certain universal questions pop up over and over, like “Why is there something, when there could be nothing?” or “Can a jet fly faster than its own exhaust velocity?” Let’s look at the second one; I’ll get back to the first in a future column.

Reciprocating engines inhale about 15 pounds of air for every pound of fuel they burn. This is the so-called “stoichiometric ratio” — the ratio at which every oxygen molecule in the air gets combined with a hydrocarbon molecule in the fuel, leaving no unconsumed oxygen or fuel at the end. Chemically combining the oxygen and fuel releases energy in the form of heat — which makes the engine go — as well as, in the ideal case, just carbon dioxide and water.

Peter Garrison

Peter Garrison taught himself to use a slide rule and tin snips, built an airplane in his backyard, and flew it to Japan. He began contributing to FLYING in 1968, and he continues to share his columns, ""Technicalities"" and ""Aftermath,"" with FLYING readers.

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