Like driving a car, the speed of an aircraft is based on the movement of the aircraft relative to its surroundings. However, there are multiple surroundings to consider when talking about airplanes.

When flying a fixed wing, there are three speeds to measure and consider.

Air Speed

The first, Air Speed, refers to the speed at which an aircraft is traveling through the air. This is the most important speed to consider for fixed wing aircraft because these these aircraft are kept aloft due to the the lift generated by the movement of the vehicle through the air. The aircraft must maintain a minimum speed in order to generate lift and prevent a stall condition. Check manufacturer recommendations to find your aircraft's minimum speed. For more on the physics of flight, click here.

Wind Speed

The second, Wind Speed, refers to the speed that the air is traveling across the ground. This is the wind that you can feel and is displayed on the weather report. When checking weather conditions, be sure to check that wind speed is below drone manufacturer wind limits.

Ground Speed

The final, Ground Speed is simply the speed at which the aircraft is traveling across the ground. While this is the speed we can perceive as observer on the ground, ground speed is not relevant to the actual aircraft during regular flight. However, this speed does become very relevant during the takeoff and landing phases of flight.

When we put all of these speeds together, we can see how they are all closely connected. As long as we know what two of the speeds are, we are able to determine the final speed is. If we are flying North at 30 mph into a 15 mph wind out of the North, we are able to determine that our ground speed will be 15 mph. If the wind was instead out of the South, our ground speed would be 45 mph.

Takeoff and Landing

Takeoff

When performing a takeoff or landing with a fixed wing drone, it is important to always launch with the nose of the aircraft pointed into the wind. The reason for this is that we are able convert the current wind speed into usable airspeed to generate lift. We can make up the extra airspeed required with our launch. If we were to takeoff into a headwind (into the wind) of 10 knots with an aircraft that requires a minimum airspeed of 25 knots, our launch will only require an extra 15 knots. However, if we launch with a tailwind (with the wind) with the same aircraft and wind speed, our launch will require an additional 35 knots. 

Survey Mission

When we fly a survey mission, Botlink will automatically orient survey passes perpendicular to the wind direction in order to have consistent ground speed. This ground speed allows us to capture images in an even matter. Botlink will also start the survey on the downwind side so that every turn is into the wind rather than with the wind. Turning into the wind allows us to make much sharper turns.