Step 3: Flight

In this step you describe how the aircraft flies. The cruise speed sets the wind of the solver. The mass and the centre of gravity turn the coefficients into speeds, power and trim. The air sets the forces and the Reynolds number; the runs are solved in it.

Fields

Cruise speed (m/s): The speed of the air in every run. The hint shows the speed in km/h and the Reynolds number on the mean chord. If the speed is above Mach 0.2, the hint warns that the solver treats the air as incompressible and that lift reads up to 5% low.
Take-off mass (kg): The loaded mass. The hint shows the wing loading in N/m².
CG behind the nose (m): The position of the centre of gravity, measured from the nose. All moments are taken about this point. The hint shows the position as a percentage of the mean chord.
Altitude (m): The altitude of the air, in the standard atmosphere. The hint shows the air density and its ratio to sea level.
Temperature against standard (°C): The difference from the standard atmosphere’s temperature at that altitude. Use 0 for a standard day, and for example +20 for a hot day. The hint shows the temperature and the density altitude.

Checks shown below the fields

Cruise lift coefficient needed: The lift coefficient the aircraft needs at the cruise speed and mass. Values much above 1 mean the cruise speed is close to the stall.
CG within the usual 5–45% of the mean chord: Shows the CG position. A CG outside this range is marked.

Select Choose a package to continue.

Note

The mass can be varied later on the Performance tab, and the mass and CG of the flight model are set in the Aircraft tab, without running the CFD again. The speed, altitude and temperature cannot be changed afterwards: they are the conditions the runs are solved in.