Autopilot Open Closed Loops

What open-loop and closed-loop control mean in general system theory, and how they apply in aviation (autopilots, autothrust, etc.) 👇

🧭 1️⃣ General Concept — Control Systems (Systems of Regulation)

In engineering, a control system is any system designed to regulate or control something — temperature, speed, altitude, position, etc.

There are two main types of control systems:

Type	Description	Feedback?	Example
Open Loop	Performs an action without checking if the output is correct	❌ No	Electric kettle without thermostat
Closed Loop	Continuously measures output, compares it to the desired target, and corrects any error	✅ Yes	Thermostat-controlled heating system

These concepts are universal — used in engineering, biology, economics, and aviation.

⚙️ 2️⃣ Examples in General Systems

Field	Example	Type	Explanation
Engineering	Washing machine runs fixed time	Open loop	No water-level feedback
Engineering	Washing machine with water-level sensor	Closed loop	Adjusts automatically
Automotive	Driver manually adjusts speed	Open loop	No automatic correction
Automotive	Cruise control	Closed loop	Monitors and maintains speed
Biology	Human body temperature regulation	Closed loop	Uses feedback via nervous system
Economics	Market adjusting supply to demand	Closed loop	Feedback via price signals

🛫 3️⃣ Applying the Concept to Aviation

In aircraft systems, the same principle is applied to autopilot, autothrust, and flight control systems.

Open-Loop in Aviation

The system acts but does not check the result automatically.
Examples:
- Pilot trims the elevator manually.
- Manual throttle setting (no autothrust active).
- Basic servo test without feedback sensors.

→ The pilot must monitor and correct any error — no self-correction.

Closed-Loop in Aviation

The system continuously measures actual performance, compares it with the target, and corrects automatically.
Examples:
- Autopilot ALT HOLD: compares selected altitude vs. actual altitude and adjusts pitch.
- Autothrust (Speed Mode): compares target speed vs. actual speed and adjusts thrust.
- Yaw Damper: senses unwanted yaw rate and applies rudder correction.

→ These are self-correcting feedback systems.

🧩 4️⃣ Visual Overview

 OPEN LOOP
  Command → Actuator → Output
   (No feedback to correct errors)

 CLOSED LOOP
  Command → Actuator → Output
                     ↑
                 Feedback
   (System measures result and self-corrects)

🧠 5️⃣ Simple Analogy

Scenario	Type	Why
You turn on an oven and leave it running for 10 minutes	Open Loop	No feedback — may overheat
Oven with thermostat that maintains set temperature	Closed Loop	Uses temperature feedback to self-adjust
Pilot manually holds altitude	Open Loop	No automatic correction
Autopilot ALT HOLD	Closed Loop	Uses pressure altitude feedback to maintain selected altitude

✅ 6️⃣ Summary

Feature	Open Loop	Closed Loop
Feedback Present	❌ No	✅ Yes
Automatic Correction	❌ None	✅ Self-correcting
Accuracy	Depends on operator	High
Used In	Simple or predictable systems	Advanced, precise systems
Aviation Example	Manual trim, manual thrust	Autopilot, autothrust, yaw damper

✈️ In short:

Open-loop and closed-loop control are universal regulation concepts used in all control systems. In aviation, autopilot, autothrust, and flight control systems are specific applications of these principles — using feedback to maintain altitude, speed, and stability automatically.