7.1 Standard Conditions and Density Altitude - Quiz Questions

What is the standard air temperature and pressure at sea level?

• 15° C 29.92” Hg

• 59° C 1013 millibars

• 17° C 1013 millibars

Answer explanation

At sea level, standard air temperature is 15º C (59º F), and standard air pressure is 29.92” Hg, or inches of mercury (1013 millibars).

At these standard conditions, density altitude and pressure altitude will be equal to each other.

What effect does high density altitude have on the efficiency of a UA propeller?

• Propeller efficiency is increased.

• Propeller efficiency is decreased.

• Density altitude does not affect propeller efficiency.

Answer explanation

When density altitude is high, the air is less dense, and your propellers become less efficient in thin air. As your density altitude increases, the performance of your aircraft decreases.

Remember that it’s not just literal altitude that can affect density altitude. It’s the temperature as well. If you’re flying on a hot and humid day, you’ll also experience reduced aircraft performance. Higher density altitudes occur at higher elevations, lower atmospheric pressures, higher temperatures and higher humidity.

What is true altitude?

• The height above the surface.

• The vertical distance of the aircraft above the surface.

• The vertical distance of the aircraft above sea level.

Answer explanation

There are a few different ways to interpret altitude. True Altitude is another way of describing the height above mean sea level, or MSL. It's the "true" altitude your aircraft is flying at.

Which combination of atmospheric conditions will reduce aircraft takeoff and climb performance?

• Low temperature, low relative humidity, and low density altitude.

• High temperature, low relative humidity, and low density altitude.

• High temperature, high relative humidity, and high density altitude.

Answer explanation

When density altitude is high, the air is less dense, and your propellers become less efficient in thin air. As your density altitude increases, the performance of your aircraft decreases.

Remember that it’s not just literal altitude that can affect density altitude. It’s the temperature as well. If you’re flying on a hot and humid day, you’ll also experience reduced aircraft performance. Higher density altitudes occur at higher elevations, lower atmospheric pressures, higher temperatures and higher humidity.

If the outside air temperature (OAT) at a given altitude is warmer than standard, the density altitude is

• higher than pressure altitude.

• lower than pressure altitude.

• equal to pressure altitude.

Answer explanation

At sea level, standard air temperature is 15º C (59º F), and standard air pressure is 29.92” Hg, or inches of mercury (1013 millibars).

At these standard conditions, density altitude and pressure altitude will be equal to each other. If the outside air temperature is warmer than standard air temperature, then the density altitude will be higher than pressure altitude.

Density altitude is defined by

• humidity and braking friction forces.

• headwind and landing weight.

• pressure altitude and ambient temperature.

Answer explanation

Density altitude is the altitude relative to the standard atmosphere conditions at which the air density would be equal to the indicated air density at the place of observation. Those standard conditions include pressure altitude and ambient temperature.

What effect, if any, does high humidity have on sUAS performance?

• It increases performance.

• It decreases performance.

• It has no effect on performance.

Answer explanation

High humidity increases density altitude which decreases sUAS performance.

Which factor would likely increase density altitude?

• An increase in ambient temperature.

• A decrease in relative humidity

• An increase in barometric pressure.

Answer explanation

An increase in ambient temperature increases density altitude which decreases sUAS performance.

When is pressure altitude equal to density altitude?

• When the temperature and dew point are beginning to converge

• When advection fog is present

• On a standard day (15° C and 29.92” Hg)

Answer explanation

At sea level, standard air temperature is 15º C (59º F), and standard air pressure is 29.92” Hg, or inches of mercury (1013 millibars).

At these standard conditions, density altitude and pressure altitude will be equal to each other.

How would high density altitude affect the performance of a small unmanned aircraft?

• It would increase the performance.

• It would decrease the performance.

• It would have no effect on the performance.

• It would stabilize the performance.

Answer explanation

When density altitude is high, the air is less dense, and your propellers become less efficient in thin air. As your density altitude increases, the performance of your aircraft decreases.

Remember that it’s not just literal altitude that can affect density altitude. It’s the temperature as well. If you’re flying on a hot and humid day, you’ll also experience reduced aircraft performance. Higher density altitudes occur at higher elevations, lower atmospheric pressures, higher temperatures and higher humidity.