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Stability and Control

A typical civil aircraft is kept stable by a horizontal tail and a vertical fin. The aircraft is controlled in roll by ailerons on the wings, in pitch by an elevator on the horizontal tail plane and in yaw by a rudder on the vertical fin. It is critical to the safety of the aircraft that the control surfaces perform their function throughout the operational envelope at all speeds and attitudes.

A Typical Test

Wind tunnel tests enable aircraft designers to check how an aircraft model performs both within and beyond its operational envelope in a safe and controlled environment. A typical test may involve the design and manufacture of control surfaces such as spoilers or ailerons, larger items such as engine nacelles and pylons, or the complete aircraft model followed by a wind tunnel test. The aerodynamic loads on individual components can be measured by attaching each component to the parent aircraft with a purpose built balance (there can be up to 19 balanced components in addition to the main balance) which measures the loads on that component. The model loads are tested to the CL MAX and beyond into post-stall regime.

Alternatively, ARA uses Pressure Sensitive Paint (PSP) to test stability and control as it allows the measurement of the pressure affecting the aircraft surface. PSP is specifically useful on areas that are unattainable by pressure tappings.  

Technical Information

Model Attitude:

  • Incidence range: -10° to +40°
  • Sideslip range: ±20°
  • Roll range: ±180°

Model Loads: 

  • Test beyond positive and negative buffet onset
  • High speed failure cases including spoilers and undercarriage
  • Overall model and control surface load measurement

Data Acquisition:

  • Up to 220 channels measured at up to 10 data points per second
  • Measurement of up to 1000 steady-state pressures recorded at up to 10 data points per second

Flow Investigation:

  • Use oilflow visualisation to investigate surface flow phenomena such as separation bubbles and trailing edge separations
  • Use high speed pressure transducers to measure unsteady pressures to investigate regions of separated flow