It’s easy to use “pitch angle” and “angle of attack” interchangeably to talk about an aircraft’s flight—but it can also be dangerous.
They’re both small angles, and they’re similar enough in what they describe. So it shouldn’t be that big a deal, right?
But here’s the problem: many UAV autopilots only provide pitch angle in their output telemetry. All autopilots have an inertial measurement unit (IMU) on board, which functions similarly to our inner ear—it helps the aircraft determine its attitude in space, like if it’s right-side-up or rolling. The IMU measures pitch angle because it needs to use it for guidance and control.
Getting an angle of attack readout requires more thought. Remember, your angle of attack is the angle between your UAV’s centerline and your relative wind—i.e., the direction and speed of the air the aircraft is flying through. You need to do something like install another sensor on your bird or add some smart calculations into the autopilot code in order to collect it.
So if
- Angle of attack is the angle that matters for your airplane’s lift and stability,
- Your aircraft is only reporting pitch angle, and
- You’ve been using “pitch angle” and “angle of attack” interchangeably,
You may not recognize when you could be getting into a bad situation in the air.
You may have local turbulent conditions that create an updraft and crank up your angle of attack, because suddenly your relative wind is coming from in front of and BENEATH your aircraft. Within seconds your UAV’s wings stall and it loses control.
You’d never see the problem because both your pitch angle and airspeed were in the “safe” zone the entire time—until the bird began nose-diving.