Compass Remote Reading System
The Remote Reading Compass System
- what it is,
- how it works,
- the role of the flux valve,
- the modes,
- and where the output is displayed.
🧭 Remote Reading Compass System (Gyro-Magnetic Compass)
✈️ 1️⃣ Purpose
The Remote Reading Compass (RRC), also called a Gyro-Magnetic Compass System, provides the aircraft with a stable and accurate magnetic heading for display and navigation.
It combines two technologies:
- Magnetic reference from the Flux Valve, and
- Directional stability from a Gyro.
This system eliminates the errors and lag found in a traditional magnetic compass and provides smooth, reliable heading information to flight instruments and navigation systems.
⚙️ 2️⃣ Main Components
| Component | Function |
|---|---|
| Flux Valve (Magnetic Detector Unit) | Senses the Earth’s magnetic field and produces electrical signals proportional to heading. |
| Directional Gyro (DG) | Provides a stable reference and smooth heading indication, free from short-term disturbances. |
| Slaving Amplifier / Control Unit | Compares the flux valve (magnetic) and gyro (stabilized) signals, correcting any gyro drift. |
| Torque Motor | Physically adjusts the gyro to stay aligned with the magnetic reference. |
| Compass Indicator (HSI/RMI) | Displays the final, stabilized magnetic heading to the pilot. |
🧩 3️⃣ How It Works
The Flux Valve senses the Earth’s magnetic field and outputs electrical signals representing the aircraft’s magnetic heading.
The Directional Gyro gives a smooth, stable short-term heading.
The Slaving Amplifier compares both:
- If the gyro drifts, it sends a signal to a Torque Motor,
- which re-aligns the gyro to match the magnetic heading from the flux valve.
The corrected heading is displayed on cockpit instruments such as the HSI or RMI.
🔄 Simplified Signal Flow
Flux Valve (magnetic heading)
↓
Slaving Amplifier (compare + correct)
↓
Directional Gyro (stabilized heading)
↓
Torque Motor (gyro alignment)
↓
Compass Indicator (HSI / RMI)
🧭 4️⃣ Flux Valve — Magnetic Reference
The flux valve is the system’s magnetic sensor and main reference to magnetic north.
- It’s a soft iron core with three secondary coils spaced 120° apart and one excitation coil in the center.
- The excitation coil is powered by AC current, creating a magnetic field.
- The Earth’s magnetic field distorts this field depending on aircraft heading.
- The secondary coils pick up voltage signals that vary with magnetic direction (sine and cosine of heading).
- These electrical signals go to the slaving amplifier.
📍 Location: Mounted remotely — usually in the wingtip or vertical stabilizer — to avoid magnetic interference from the aircraft structure and electrical systems.
✅ In short:
The flux valve continuously senses the direction of magnetic north and provides the long-term reference for the compass system.
⚙️ 5️⃣ Modes of Operation
| Mode | Description | Use |
|---|---|---|
| SLAVED (COMP) | Gyro automatically aligns to the flux valve’s magnetic heading. Continuous correction for drift. | Normal operation |
| FREE (DG) | Flux valve is disconnected; gyro runs freely. Pilot must manually reset heading. | Used near magnetic poles or in areas of interference |
| SLAVE FAST (SYNC) | Rapid alignment mode to quickly synchronize gyro to magnetic heading (used on ground or maintenance). | Setup or synchronization |
✅ Normally, “SLAVED” mode is used for flight — giving automatic magnetic correction and smooth heading indication.
🖥️ 6️⃣ Where the Output Is Displayed
The heading output from the RRC is sent to:
| Display Instrument | Function |
|---|---|
| HSI (Horizontal Situation Indicator) | Shows heading, course, and navigation data. Most common modern display. |
| RMI (Radio Magnetic Indicator) | Shows heading with pointers to VOR/ADF stations. |
| Compass Repeater | Basic heading display in standby or secondary systems. |
The same heading data is also shared digitally with:
- Autopilot (Heading Mode)
- Flight Director
- FMS / IRS (for navigation cross-checks)
🧠 7️⃣ Advantages
✅ Smooth and stable heading display ✅ No acceleration or turning errors like a magnetic compass ✅ Continuous correction for gyro drift ✅ Accurate long-term magnetic reference ✅ Provides heading data to multiple systems (HSI, autopilot, FMS)
✅ 8️⃣ Summary Table
| Feature | Description |
|---|---|
| System Name | Remote Reading Compass / Gyro-Magnetic Compass |
| Purpose | Provide accurate, stable magnetic heading |
| Key Components | Flux valve, gyro, amplifier, torque motor, indicator |
| Main Display | HSI, RMI, or compass repeater |
| Modes | Slaved, Free, Slave Fast |
| Magnetic Reference | Flux valve |
| Stabilization | Directional gyro |
| Correction | Slaving amplifier + torque motor |
| Advantages | Accurate, automatic, stable heading for navigation and autopilot systems |
✈️ In short:
The Remote Reading Compass combines a flux valve (magnetic sensor) and a directional gyro to give a stable, accurate magnetic heading. The flux valve senses magnetic north, the gyro stabilizes the indication, and a slaving system keeps the gyro aligned automatically. The heading is displayed on the HSI or RMI, and used by the autopilot and navigation systems for precise directional control.