The CSIR focuses on evaluating the aero/mechanical impact of integrating stores with the aircraft. This work is done in compliance with MIL-HDBK-1763 and covers the following aspects; aeroelasticity (flutter) ; store separation behaviour; loads on aircraft during carriage and impact on aircraft performance and handling characteristics. These aspects are summarised below:
Aeroelastic (flutter) compatibility
Flutter is a dangerous dynamic instability that all aircraft can encounter. It is driven by the mass and stiffness distribution in the aircraft structure, combined with its aerodynamic characteristics. Changes to those characteristics due to the addition of a new store configuration to an aircraft can cause flutter. It is essential that the aeroelastic properties of all new aircraft store configurations are evaluated to ensure that flutter does not occur.
The CSIR is a leader in aeroelasticity technology and has cleared almost 200 aircraft configurations for the SAAF since the 1970s. It has a full range of aeroelasticity-related capabilities including:
• Ground vibration testing (GVT) and modal analysis
• Finite element modelling (FEM)
• Unsteady aerodynamics analysis
• Flutter analysis
• Flutter flight test tools and exciters
Store separation analyses
Stores that are individually stable can behave differently in the flowfield of an aircraft. This can result in unexpected dynamics with the store possibly colliding with the aircraft. It is essential to verify that stores can be released safety over the full release and jettison envelopes.
Store separation analyses are very complex and require the use of advanced computational and experimental tools. The CSIR has developed store separation analysis tools in-house and has led the field in South Africa.
Carriage loads analysis
Stores exert loads on the aircraft structure while they are being carried. These loads include:
It is important to ensure that aircraft structure is not overstressed at any point. The CSIR performs analyses in compliance with the applicable regulations using a range of aerodynamic, simulation and dynamics tools.
Performance and handling analysis
Carrying a store affects the performance and handling of the aircraft. It is important to compare the actual performance envelopes against the specifications for the configurations with the store. It is also necessary to ensure that the aircraft is controllable and has acceptable handling in all phases of flight. The CSIR performs analyses in compliance with applicable regulations.