j2 Elements

No Data, No Problem

The j2 Elements plug-in provides an integrated Aerodynamic Strip Theory approach for aerodynamic modelling.  This means that the aerodynamic data can be added quickly and easily for all lifting surfaces.  There is no need to calculate dynamic derivatives in order to model the aircraft as these are calculated automatically based upon the motion of the aircraft and the distribution of the aerodynamics.  This enables rapid prototyping of multiple designs and concepts to easily identify key behaviour characteristics.

By combining aerodynamic strip theory and aircraft kinematics to calculate the velocity profile across the complete airframe j2 Elements takes into account not just the position of each strip on the airframe but the orientation of its axes too.  The contributions are then totalled using local areas and dynamic pressure to produce the complete aerodynamic contribution at the aircraft’s aerodynamic reference location.

A Horizontal or Vertical Stripped Item can be added to any Aerodynamic and Dynamic Item on a model in j2 Builder.




Once added, the geometry of the surface can be added.

This starts with the Maximum and Minimum Y/Z values being added to define the span.

The location of the leading edge (Ref Point.x_i, Ref Point.z_i) relative to the datum is defined in terms of spanwise position.

The chord distribution (c_i) and wing twist (twist_i) can also be added in.

The location of the centre of the aerodynamics (NP_i) is included.

This has then defined the geometry of the lifting surface.

The local aerodynamics are added based upon the 3-D characteristics of the airfoil section (CDrag_i, CLift_i, Cm_i).  These too can be varied based upon spanwise location to account for changes in airfoil section.  These characteristics are functions of the local angle of attack (alpha_i) rather than the free stream angle of attack (alpha).  These characteristics are based upon the airfoil section only and not the aircraft geometry so it does not matter whether the surface is horizontal or vertical.

The local angle of attack is not just based upon the free stream and the twist, but the velocities of the strip in its own axis system based upon the motion of the aircraft (see Aerodynamic Strip Theory).   For each strip along the surface, the local angle of attack is calculated each calculation step and this is then used in the aerodynamics to find the local set of coefficients.  This provides distributed characteristics which influence the motion of the aircraft.