# Air

Air is the domain above water and land and below space, and is also a category of components.

## Atmosphere

Air is defined as the region where the atmosphere exists (density is greater than zero). At base the density of the atmosphere starts at 1 from an altitude of 0 m (sea level) to 300 m. From 300 m to 500 m it decreases to zero. The density scales the effectiveness of jets and heliblades.

Air is much less dense than water. This allows lower drag and therefore higher speeds. However, it also means air provides less buoyancy, requiring lighter materials or greater thrust to maintain altitude.

Altitude Domain
0 - 300 m Thick air
300 - 500 m Thin air
500 - 900 m Suborbital space
900 m and above Orbital space

## Components

### Propulsion

Most forms of propulsion may be used as maneuvering thrust as well as primary thrust.

#### Hot air balloons

Balloons consume no resources and provide a large amount of lift at low altitudes, up to about 300 kN below about 100 m. Lift decreases drastically above 100 m but is not directly proportional to atmospheric density. A rough approximation is

$L = 300 \min \left(1, \left( \frac{100}{y} \right)^2 \right)$

Make sure to account for the craft likely hanging significantly below the balloon.

Helicopter blades can be used with spin blocks to produce thrust.

Suppose

• $\rho$ is the atmospheric density in atm.
• $\omega$ is the rotation speed in radians per second (maximum 30).
• $\alpha$ is the "motor drive" setting of the rotor.

The thrust produced per blade (in kN) is

$T = 0.5 \rho \omega \left( 1 + \alpha \right)$

This is up to 165 kN with maximum motor drive and 15 kN with no motor drive.

The thrust produced (in kN) per blade unit is

$T = 0.5 \rho \omega \left( 1 + \alpha \right)$

Note that the radius of the rotor does not matter, only the number of blade units.

Power use at maximum motor drive is 15 per spinner or pole unit plus 3 per blade unit.

One blade produces 165 kN thrust. This can be expected to hold up 15 t at sea level with about a 12% reserve.

At 0 motor drive no power is consumed, and one blade unit develops 15 kN thrust.

#### Simple jet engines

Simple jet engines are a quick way of getting a large amount of thrust, but require significant exhaust space.

• Huge Jet Engine: Produces up to 4500 kN thrust for 180 MW power.

#### Custom jet engines

Main article: Custom Jet Engines

Custom Jet Engines consume fuel instead of power. Power and efficiency increase quadratically with size, making them an excellent choice for large vessels.

### Control surfaces

Control surfaces provide an alternative to maneuvering thrusters. Their effectiveness is proportional to airspeed.

• Wing: Provides lift of 0.05 kN per m/s forward speed, up to 1.5 kN at 30 m/s. Produces five times as much lift underwater.
• Aileron: Provides roll thrust of 0.1 kN per m/s forward speed.
• Tail Plane: Provides yaw and/or pitch thrust of 0.2 kN per m/s forward speed.

### Stabilisation

• Jet Stabilizer: Attempts to reduce the pitch or roll of the vehicle. The thrust comes out the ends of the barrel, while the mounting face determines whether pitch (front/back face) or roll (left/right face) stabilisation is provided.