IMUs are those black boxes that tell aircraft which way is up. Actually they tell which way everything is – attitude, acceleration, rotation. Critical for when GPS drops out or you can’t see outside.
What’s Inside
Accelerometers measure linear motion. Gyroscopes measure rotation. Put three of each together at right angles and you can track movement in all directions. Magnetometers sometimes too, for heading reference.
Modern ones use MEMS – tiny mechanical sensors etched onto chips. Older ones had actual spinning masses. The new stuff is smaller, cheaper, and generally more reliable.
The Drift Problem
IMUs accumulate errors over time. Small inaccuracies in each measurement add up. Fly long enough on pure IMU and you end up thinking you’re miles from where you actually are.
Solution: combine with GPS. IMU handles short-term, high-frequency motion. GPS corrects the drift. They complement each other. Lose GPS? IMU carries you for a while. Bad IMU data? GPS catches it.
Where They Live
Every modern aircraft, obviously. Also missiles, drones, spacecraft. Your phone has one – that’s how it knows which way you’re holding it.
Self-driving cars use IMUs. Submarines navigating underwater where GPS doesn’t reach. Any situation where you need to know position and orientation without external references.
Aviation Grades
Consumer grade IMUs drift fast – minutes to useless. Aviation grade holds accuracy much longer. Military/aerospace grade is even better. Price difference is massive. Your phone’s IMU costs cents; aircraft INS costs thousands.
Failure Modes
Triple redundancy in most aircraft. Three IMUs, vote on the outputs, flag disagreements. If one goes bad the other two outvote it. Catastrophic failure requires losing multiple units simultaneously – rare but not impossible.
