Meteorology for Commercial UAS Flashcards

What is the significance of the 'dew point' for UAS operations?

Answer: When temperature approaches the dew point, fog, mist, or low cloud may form, reducing visibility

The dew point is the temperature at which air becomes saturated and moisture begins to condense. When the air temperature is close to the dew point, fog, mist, or low cloud is likely to form, significantly reducing visibility. For VLOS operations, this can make it impossible to maintain visual contact with the UAS.

What is the Beaufort Scale and how is it useful for UAS pilots?

Answer: A scale that classifies wind speed based on observable effects on the environment, useful for estimating conditions on site

The Beaufort Scale classifies wind speed from Force 0 (calm) to Force 12 (hurricane) based on observable effects such as movement of leaves, flags, trees, and surface water. It is useful for UAS pilots conducting site assessments when anemometer data is unavailable, allowing them to estimate wind conditions from visual cues.

Why are 'thermals' a concern for UAS operations, particularly over urban areas?

Answer: Thermals are rising columns of warm air that can cause sudden altitude gains and turbulence, affecting UAS stability

Thermals are rising columns of warm air caused by uneven surface heating. In urban areas, dark surfaces (roads, rooftops) can generate strong thermals. For small UAS, thermals can cause sudden uncommanded altitude changes, unexpected turbulence, and difficulty maintaining precise position — particularly hazardous near buildings and during inspection work.

At what wind speed (as a general guideline) should most small commercial UAS operations be suspended?

Answer: When sustained winds exceed approximately two-thirds of the UAS maximum airspeed

A widely accepted guideline is that operations should be suspended when sustained wind speeds exceed approximately two-thirds of the UAS maximum airspeed. This ensures the drone retains sufficient control authority and can return to the pilot against the wind. Gusts must also be considered, as they can momentarily exceed the drone's capability.

What is the 'lapse rate' and why does it matter for UAS operations?

Answer: The rate at which air temperature decreases with altitude, affecting density altitude and UAS performance

The lapse rate is the rate at which atmospheric temperature decreases with increasing altitude, typically around 2°C per 1,000 ft in the International Standard Atmosphere. This matters for UAS because temperature affects air density, which in turn affects motor efficiency, propeller thrust, and battery performance at different flight altitudes.

How does high density altitude affect UAS performance?

Answer: It reduces air density, decreasing propeller thrust and degrading UAS performance

High density altitude occurs when the air is less dense than standard (due to high temperature, low pressure, or high humidity). Less dense air means the propellers generate less thrust for the same rotational speed, requiring motors to work harder. This reduces climb rate, maximum altitude, payload capacity, and battery endurance.