Center of Gravity
The point where the entire weight of a drone is balanced in all directions.
The center of gravity (CG) is the point where the entire weight of a drone is balanced in all directions. Imagine it as the exact spot where all the drone’s weight is concentrated.
Maintaining the correct CG is essential for stable and controlled flight. If the CG is off—too far forward, backward, or to the side—the drone may become difficult to control or even unsafe to fly.
When adding or removing equipment, such as cameras or sensors, it’s crucial to make sure the CG stays within the limits specified by the manufacturer. Always check your drone’s CG after making changes to avoid issues with stability and performance during flight.
Introduction
How Center of Gravity, Angle of Attack, and Stalls Impact Flight
Lesson Breakdown:
First, we’ll start by explaining the center of gravity (CG), which is essentially the “balance point” of your drone. The location of the CG influences how your drone behaves during flight, especially when making turns or adjusting altitude.
Next, we’ll dive into the critical angle of attack (AOA). This is the angle between the drone’s wings and the airflow, and when it becomes too steep, the airflow can’t smoothly pass over the wings, leading to a stall.
Finally, we’ll look at stalls—what they are, how they happen, and how understanding the CG and AOA can help you avoid them for smoother, safer flight.
By the end of this lesson, you’ll have a clearer understanding of these interconnected concepts and how to manage them to keep your drone flying at its best.
Center of Gravity
The point where the entire weight of a drone is balanced in all directions.
The center of gravity (CG) is the point where the entire weight of a drone is balanced in all directions. Imagine it as the exact spot where all the drone’s weight is concentrated.
Maintaining the correct CG is essential for stable and controlled flight. If the CG is off—too far forward, backward, or to the side—the drone may become difficult to control or even unsafe to fly.
When adding or removing equipment, such as cameras or sensors, it’s crucial to make sure the CG stays within the limits specified by the manufacturer. Always check your drone’s CG after making changes to avoid issues with stability and performance during flight.
Critical Angle of Attack
The angle between the drone’s wings and the airflow
The critical angle of attack is like the “no-go” zone for your drone’s wing, where it’s saying, “Whoa, that angle is too steep!”
In simpler terms, the critical angle of attack is the steepest angle at which the wing can meet the oncoming airflow while still generating enough lift to keep the drone flying.
A stall happens when the wing exceeds this critical angle, disrupting the smooth airflow and causing a rapid loss of lift, which can lead to the drone stalling.
Critical Angle of Attack
The angle between the drone’s wings and the airflow
The critical angle of attack is like the “no-go” zone for your drone’s wing, where it’s saying, “Whoa, that angle is too steep!”
In simpler terms, the critical angle of attack is the steepest angle at which the wing can meet the oncoming airflow while still generating enough lift to keep the drone flying.
A stall happens when the wing exceeds this critical angle, disrupting the smooth airflow and causing a rapid loss of lift, which can lead to the drone stalling.
Stalls
When Your Drone’s Wings Lose Lift and Flight Becomes Unstable
A stall for a drone occurs when the airflow over the drone’s propellers or wings (if it’s a fixed-wing drone) is disrupted to the point where they can no longer generate sufficient lift. This typically happens when the angle of attack — the angle between the propeller or wing and the oncoming air — becomes too steep.
How A Stall Unfolds:
Below, you’ll find a step-by-step breakdown below explains what happens from a smooth, stable flight to the point where a stall occurs and how to recover from it.
As a drone’s angle of attack—the angle between the wing or propeller and the oncoming air—increases, it reaches a critical point where the airflow becomes turbulent, diminishing lift capacity.
This leads to a stall, causing the drone to lose altitude and potentially spin out of control. With the right recovery action preparedness, you can regain stability and continue flying safely.
Click image to enlarge:
- 1Normal Smooth Flight: The aircraft is flying smoothly, maintaining a balanced angle of attack, which is the angle between the wing and the oncoming air.
- 2Approaching the Angle Limit: As you increase the drone’s pitch, the angle of attack gets steeper.
- 3Reaching CRITICAL ANGLE OF ATTACK Point: When you hit the critical angle of attack, the airflow over the wings starts to get turbulent.
- 4Experiencing Disrupted Airflow: Beyond this point, the airflow gets turbulent near the wings, destabilizing the smooth lift the wing usually creates. If you keep pushing, the UA can’t handle it anymore, and the lift looses its stabile ascent.
- 5STALL: A stall happens when your UA’s propellers can’t generate enough lift to keep flying level. This is when your drone is pushed to its breaking point.
- 6Experiencing Drone Drop: The increased angle of attack, with all that turbulence and drag, causes the lift to drop rapidly, and the drone starts to lose altitude and might even spin out of control.
- 7Prevent Crash: Recover & Stabilize: To recover, you ease off the pitch, lower the angle of attack, and let the airflow smooth out again. Once the airflow is back to normal, the drone stabilizes, and you’re good to go.
Nose-Heavy vs. Tail-Heavy Center of Gravity
Impact of Weight Distribution on Drone Stall Behavior
The location of the center of gravity (CG) affects how fast your drone needs to fly to avoid stalling.
If you move the CG forward, like by adding a camera to the front of your drone, the drone might stall at a higher speed. So, instead of stalling at 55 mph, it might not stall until 65 mph because the weight is more forward.
The angle at which the drone stalls doesn’t change. What’s changing is how fast you need to go to keep flying without stalling, depending on where the weight is.
So, while the speed at which the drone stalls can change, the angle where it loses lift stays the same.
Nose Heavy Drone:
- What It Means: The front of the drone is heavier.
- Effect: The drone needs to fly faster to avoid stalling. If it normally stalls at 55 mph, with the extra weight in the front, it might stall at 65 mph.
- Why: The heavy front makes it harder for the drone to stay level, so it needs more speed to keep flying.
Tail Heavy Drone:
*In aviation, “aft” refers to the rear part of the aircraft, or towards the back.
- What It Means: The back of the drone is heavier.
- Effect: The drone can fly slower before it stalls. If it normally stalls at 55 mph, with the extra weight in the back, it might stall at 45 mph.
- Why: The heavy back makes it easier for the drone to keep its nose up, so it can fly at lower speeds without stalling.
In both cases, the speed at which the drone stalls changes, but the angle at which it stalls (the critical angle of attack) stays the same.
