Study Guide
Impact of Ground Obstructions & High Winds on sUA Flight
Features like hills, valleys, and large buildings can drastically change wind patterns, creating unpredictable gusts and turbulence. These local wind conditions often differ from the broader area and can lead to unexpected gusts or downdrafts that impact your drone’s stability and control. Understanding these potential hazards is key to safe and successful flight operations.
High winds, gusts, wind shear, and microbursts posing unique challenges that every remote pilot should understand and prepare for.
High Winds:
Sustained strong winds blowing consistently over a period of time
Wind Gusts:
Brief increases in wind speed that can cause abrupt changes in flight conditions.
Wind Shear:
Abrupt change in wind speed and/or direction over short distances.
While wind shear can occur at all altitudes, it often occurs near passing frontal systems, thunderstorms, and temperature inversions, particularly when winds exceed 25 knots.
Microbursts:
Microbursts are intense, localized downdrafts within a thunderstorm, causing sudden and powerful wind gusts that can exceed 100 mph and pose significant dangers, especially to aviation.
Urban Drone Operations: Wind Gusts and Building Effects
When flying a UA near buildings, understanding the effects of airflow and wind patterns around structures is crucial. Buildings can significantly disrupt the natural flow of air, causing unexpected wind patterns.
How Buildings Alter Wind Patterns:
Strong updrafts occur because wind flows toward a building and is forced to move upward along its vertical surface. This creates vertical air currents that can lift the drone suddenly, potentially affecting its stability and control.
Additionally, the edges and corners of buildings can cause turbulent airflow, leading to rapid changes in wind direction and speed.
These unpredictable gusts can make it difficult for the Remote PIC to maintain steady flight and avoid obstacles, increasing the crashing into buildings, loss of maneuverability, or total loss of control as your UA gets swept away by the wind never to be seen again.
Flying Your UA Over the Windward and Leeward Sides of Mountains
When flying your UA near mountainous terrain, understanding the wind dynamics on both the windward and leeward sides of a mountain is necessary. These wind patterns can significantly affect your UA’s stability and performance.
Windward Side: Updrafts and Their Effects:
The windward side of a mountain is where the wind hits the mountain and is forced upward.
On the windward side, wind flows smoothly up the windward side of the mountain and the upward currents help to carry
Leeward Side: Downdrafts and Their Effects:
On the leeward side of a mountain, the wind flows downwards, creating a different set of challenges:
- Downdrafts: As the wind descends, it can cause downdrafts that push your UA downward. These downdrafts can be particularly strong and sudden, leading to a rapid loss of altitude.
- Turbulence: Similar to the windward side, the leeward side can also experience turbulence. The wind moving down the mountain can interact with the terrain and create turbulent conditions that affect the UA’s stability.
- Wind Shear: The transition between the updrafts on the windward side and the downdrafts on the leeward side can cause wind shear—a rapid change in wind speed and direction over short distances. Wind shear can make the flight more challenging and increase the risk of sudden altitude changes.
Shape and Appearance: Lenticular clouds are lens-shaped clouds that form perpendicular to the direction of the wind. They resemble saucers or pancakes and can sometimes stack up in a series.
Turbulence: Lenticular clouds can be associated with significant turbulence, especially near their edges. The turbulent air can create challenging flying conditions for unmanned aircraft (UAs) and manned aircraft alike.
Wind Patterns: The presence of lenticular clouds often indicates strong and turbulent wind patterns. Pilots should be cautious of these conditions and plan their routes to avoid areas where such clouds are present.
Sea Breezes & Land Breezes
Land breezes themselves are generally not known to be turbulent. They are characterized by cooler air from the land moving towards the warmer air over the sea at night, typically creating stable and steady airflow conditions.
Unlike sea breezes, which can sometimes cause turbulence as cooler air moves inland during the day and encounters rising warm air, land breezes tend to produce more predictable and calm atmospheric conditions at night along coastal areas.
Sea Breeze
While a sea breeze during the day feels refreshing and cool on the skin, it can cause a lot of turbulence for your UA. These sea breeze drafts can lift your UA unexpectedly, causing turbulence and requiring careful control to maintain a stable flight.
Sea breeze occurs when during a warm day, the land heats up more quickly than the waters of the sea. As the air above the land continues to warm, the air also continues to rise and create a low-pressure area. Cooler, denser air from the sea then flows into that low-pressure area, creating a breeze.
In other words, this cooler air flowing inland form the sea creates the breeze, which we call a sea breeze.
Land Breezes
As the sun sets and the temperatures begin to drop, the land and water start to cool at different rates. This temperature difference creates a natural movement of air known as a land breeze.
Land breezes are generally gentle and can vary in strength based on the temperature difference between the land and water. They typically occur during the night when the temperature contrast is greatest.
Understanding how this breeze works can help you anticipate and manage wind conditions, especially if you’re flying a UA near bodies of water.
What Is a Land Breeze?
A land breeze occurs during the night when the temperature of the land drops more quickly than that of the nearby water. Here’s a step-by-step breakdown of how it works:
After sunset, the land cools down faster than the water because it loses heat more quickly. This results in cooler, denser air over the land. As the land cools, the air above it also cools down, becoming denser and heavier compared to the air over the warmer water. The cooler, denser air from the land starts to move toward the warmer water. This movement creates a breeze that flows from the land to the water.
