Rapid Prototyping

The hierarchical structure for developing rotary models that is present in j2 Builder enables the aircraft and proposed systems to be laid out in the model so as to mimic those in the real aircraft.  As the aircraft evolves so whole sub-assemblies can be relocated quickly and easily and the j2 software will take care of all changes in locations and moment arms to recalculate the various contributions. The Main Rotor, Tail Rotor, and Gearbox are added as a rotor assembly using j2 Rotary. Engine characteristics are added through Drive Shafts and can start with ideal (torque matching) engines and be further developed later to cover higher fidelity engine performance characteristics.

The airframe can be kept separately from the rotors and it too can be constructed using the hierarchical structure. With limited information relating to fuselage, horizontal and vertical tail geometry and location, the complete aircraft model can be developed within j2 Elements.  This provides detailed dynamic characteristics based upon the local flow at any point on the aircraft.  These items can include the downwash and sidewash characteristics from the rotors.  Legacy tools as well as existing data frameworks can easily be added into the j2 model framework using j2 Developer.

Preliminary Handling through to Certification

From initial investigations into the stability and control of the helicopter across the complete flight envelope to identifying the basic pilot control settings through trim analysis in j2 Freedom, dynamic manoeuvres can be analysed using response analysis.  Response analysis can start with initial disturbances from the trimmed condition to establish basic stability through to more test based manoeuvres and control inputs.  The primary Stability Augmentation System (SAS) can also be developed and tested with the Washout Filters, PID Controllers and Rate Limiters already built into j2 Builder. More complex control laws and logic can be developed through the j2 Matlab Toolbox. This plug in enables the complete helicopter model to be dropped into a Simulink model as a completely self contained block.  The AFCS is then wrapped around the Airframe and the Simulink model file is integrated back into the j2 Universal Tool-Kit as a Matlab Aircraft Model.  This simple routine  provides a consistent environment to develop and test the rotors, the airframe, and the AFCS simultaneously in a fully version controlled and configuration managed system.

Simulation

From the very beginning of any project, as soon as an aircraft model has been developed and saved it can be flown ‘straight out of the box’ in real-time with a pilot in the loop using the j2 Pilot plug-in.  This enables a test pilot to provide early opinions on the design and overall handling qualities, leading to improved design and handling.  Pilots can test and evaluate failure modes and envelope excursions without risk and can feedback information to the design team.

Flight Test and Envelope Expansion

As the aircraft design evolves, so the aircraft certification manoeuvres can be tested and evaluated across the complete flight regime.  These can also be tested ahead of any flight test to establish a safe test envelope.  Flight test data can be brought back into the j2 Universal Tool-Kit using j2 Flight and the model can then be automatically tuned.  The separation of the rotors from the fuselage aerodynamic characteristics means that any corrections can be focused on the correct area which leads to improved model tuning.

From the initial tests, the model can be reviewed and updated.  This provides improved confidence in the model and enables the next set of manoeuvres to be tested.  As the flight test program expands so the model becomes more and more accurate.  This means that the model can be used to confidently demonstrate stability and control for certification purposes, both during and in support of validation and verification flights.