Empirical Earth · Flight & Navigation

Aircraft, gyros & the attitude indicator

The claim

“A level plane would fly off on a tangent; pilots never dip the nose; gyros would drift.”

What is true

A plane flying straight and level would leave the surface if the surface curved away and nothing corrected for it. The geometry in the claim is right.

What is measured

To hold altitude at cruise an airliner keeps pitching its nose down ~8° per hour (v/R) to follow the curve. On a flat plane no such correction would be needed.

What would show this is wrong

aircraft requiring constant nose-down trim to hold altitude, as flying level over a flat plane would demand.

Sources

  1. Ring-laser / fiber-optic gyros & inertial navigation. Sagnac-effect optical gyros; gyrocompass alignment senses Earth rate (15.04°/hr). Standard avionics/IRS references (e.g., Honeywell/Nort link
  2. MEMS vibratory (Coriolis) gyroscopes. Performance grades and bias stability; tactical/consumer applications and GPS aiding. Standard inertial-sensor literature. MEMS gyroscope link
  3. FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25). Attitude indicator operation, gyroscopic instruments, and flight at constant altitude. FAA PHAK link
  4. Schuler tuning: inertial platforms stay level via Earth’s radius. An inertial navigation platform is tuned to a natural period of ~84.4 minutes — that of a pendulum whose length equals Earth link
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