Density Altitude

The key to remember for this module is that aircraft operate better in denser air as opposed to less dense air. Denser air provides more air molecules to flow over the wing to create lift and more air molecules for the propeller to push against.

A few relationships to remember for the exam:

• As air pressure increases, air density increases
• As temperature increases, air density decreases
• As humidity increases, air density decreases
• As altitude increases, air density decreases (in general)

The term Density Altitude refers to the altitude that the aircraft "feels" like it is in. The denser the air, the lower the density altitude (since air is denser at lower altitudes), and the less dense the air, the higher the density altitude. So, in the relationships listed above, you would need to remember that each time air density INCREASES, density altitude DECREASES, and vice versa. For instance, if temperature went from 75 degrees to 80 degrees, this would mean the air became less dense, thus the density altitude would go up (since less dense air means higher density altitude).

Density altitude is depicted by the pressure altitude and ambient temperature. Density altitude can have a large effect on how your aircraft will perform. Density altitude is the altitude that your drone feels like it's flying at. For example, high density altitudes occur at higher altitudes, lower atmospheric pressures, high temperatures, and higher humidity. A hot and humid day can create high density altitude conditions. Hot and humid air makes the air thinner because the air molecules are spread out further from one another. The separation of air molecules makes the drone work harder because there are less air molecules for the drone to grab onto. Hot and humid conditions mimic the conditions of a higher altitude because of the thin air.

The higher in altitude you fly, the thinner the air will get. Higher altitudes are cooler, but that does not make that altitude denser. At higher altitudes, the atmospheric pressure is low which means there is not enough pressure to push air molecules closer together. A low-density altitude occurs at lower altitudes, higher atmospheric pressures, lower temperatures, and low humidity. The density altitude will be lower because at lower altitudes the atmospheric pressure is greater. If the air is cool and dry, the air molecules will be closer to each other. This means there will be more air molecules for the air to grab onto. It is easier for a drone to create lift in a low-density altitude than it is in a high-density environment.