Quick Answer
A drone airspeed sensor measures how fast air moves over the aircraft using a pitot tube and differential pressure sensor. Unlike GPS, which only measures ground speed, an airspeed sensor tells the flight controller the actual speed through the air, which is essential for preventing stalls on fixed-wing drones.
What Is an Airspeed Sensor?
An airspeed sensor is a small board with a pressure-sensing chip that connects to a pitot tube mounted on the outside of the drone. It measures the difference between the air pressure rammed into the front of the tube and the ambient static air pressure around it. That pressure difference, converted using Bernoulli's principle, gives you airspeed.
The sensor sits inside the fuselage and talks to the flight controller over I2C. The pitot tube sits outside, usually mounted near the nose or on a wing.
How Pitot Tubes Work
A pitot tube is a simple hollow probe with two channels. The front opening faces into the airflow and catches the total pressure (static air pressure plus the dynamic pressure from the moving air). Small holes on the sides of the tube, set back from the tip, measure static pressure alone.
Two silicone tubes connect these channels to a differential pressure sensor like the MS4525DO. The sensor measures the gap between total and static pressure. Because dynamic pressure increases with the square of airspeed, the sensor calculates airspeed using the formula: airspeed = sqrt(2 x pressure_difference / air_density).
That square root relationship means readings are less stable at very low speeds. That is normal behaviour, not a fault.
Airspeed vs Ground Speed: Why GPS Is Not Enough
This is the critical distinction. A GPS tells the flight controller how fast the drone moves over the ground. But the wings do not care about ground speed. They care about airspeed: how fast air flows over them.
Imagine a fixed-wing drone flying at 50 km/h ground speed into a 40 km/h headwind. Its actual airspeed is only 10 km/h. Without an airspeed sensor, the autopilot sees 50 km/h and thinks everything is fine. The aircraft is on the verge of stalling and the flight controller has no way to know.
PX4's documentation puts it bluntly: "The autopilot does not have other means to detect stall." GPS ground speed cannot replace airspeed for fixed-wing flight control.
Which Drones Need an Airspeed Sensor?
Fixed-wing drones need one. Wings generate lift from airflow, and if that airflow drops too low, the aircraft stalls. An airspeed sensor is the only sensor that can warn the autopilot before this happens.
VTOL drones need one during forward flight mode for the same stall-prevention reasons.
Quadcopters and multirotors do not need one. They have no wings to stall. The flight controller manages altitude by adjusting motor RPM directly, and GPS ground speed is sufficient for position hold and navigation.
PX4 recommends airspeed sensors for all fixed-wing and VTOL builds. ArduPilot considers them helpful but acknowledges they add tuning complexity. For calm-weather sport flying with large speed margins, you can sometimes get away without one. For autonomous missions, survey work, or any flight in variable wind, an airspeed sensor is worth fitting.
Digital (I2C) vs Analog Sensors
Analog airspeed sensors (like the older MPXV7002) output a voltage proportional to pressure. They are cheap but noisy. Long cables pick up electromagnetic interference from ESCs and power lines, and temperature drift throws off accuracy over time. Many also output 0-5V while flight controllers expect 0-3.3V, requiring external voltage dividers.
Digital I2C sensors like the MS4525DO have largely replaced them. The analog-to-digital conversion happens inside the sensor, so the signal stays clean over cable runs. Built-in temperature compensation keeps readings accurate across a wide operating range (-25 to +105 degrees C). ArduPilot's documentation notes that analog sensors are now "largely discontinued" and recommends digital for all new builds.
The MS4525DO: Why It Is the Standard
The TE Connectivity MS4525DO sensor chip is found in most modern drone airspeed kits. It measures differential pressure up to 1 psi (roughly 360 km/h equivalent airspeed), has a total error band under 1%, and runs on 3.3V or 5V supply through an I2C connection. It also includes a built-in temperature sensor for true airspeed calculations.
The Holybro MS4525DO kit bundles the sensor board with a pitot tube (available in 40cm or 100cm lengths) and a GH 4-pin cable. It is compatible with all Pixhawk flight controllers on both ArduPilot and PX4, and can be found in our maker collection.
FAQ
Q: Can I use an airspeed sensor on a quadcopter?
A: There is no benefit. Quadcopters hover by varying motor RPM directly and have no wings to stall. Save the weight and complexity for fixed-wing builds.
Q: How do I calibrate an airspeed sensor?
A: The sensor auto-zeros when the flight controller boots. Cover the pitot tube before powering on in windy conditions to prevent offset errors. ArduPilot also supports automatic ARSPD_RATIO calibration by flying direction-change patterns in loiter mode.
Q: Where should I mount the pitot tube?
A: Away from propeller wash and fuselage turbulence. On a nose-mounted prop aircraft, the wing at least 30cm from the fuselage is a good location. Keep the side holes (static ports) unobstructed and past any surface edges.