Fighter aircraft are designed with some degree of inherent aerodynamic instability, requiring close control by fly-by-wire computers. Therefore it is vitally important that the stability and control aerodynamics of the aircraft are fully understood throughout the flight envelope at all speeds, attitudes and payload combinations as these data form the basis of the flight control software systems. It is important to acquire stability and control data for a large number of store payloads to provide sufficient data for aircraft flight control systems. The safety of the aircraft and crew are therefore dependent on the fidelity of the aerodynamic data base.
For military aircraft, control panel loads determination is also important since control panel loadings are affected by the payload carried on the aircraft, more especially by external stores. Loads on various control panels may be derived either directly, by use of panel balances, or by measuring pressures using Pressure-Sensitive Paint on the upper and lower surfaces of the panel and integrating these data.
ARA has many years of experience in the measurement of stability and control aerodynamic data for a wide variety of military aircraft throughout the global market, including Tornado, Typhoon and JSF (F35). This has enabled highly accurate stability and control data acquisition methods to be developed coupled with excellent productivity.
Individual control panel loads may also be measured simultaneously with the overall stability and control loads. ARA has extensive experience in the measurement of payload forces and moments for both individual stores and multiple stores on racks/launchers etc. This experience has enabled ARA to couple stability and control data acquisition together with store loads measurements simultaneously during a wind tunnel entry to maximise data acquisition whilst keeping tunnel entry time to a minimum.
Alternatively, ARA's use of Pressure-Sensitive Paint with a standard forces model provides the customer with component load data from the first test of a new aircraft programme.
During the wind tunnel test a sequence of different control panel settings together with various store configurations are tested. Some of the typical measurements made during such a test are listed below:
- Change in aircraft handling characteristics due to the presence of stores before and after release.
- Control panel loads due to the presence of stores before and after release, using either panel balances or by the integration of measured pressures.
- Incidence range: -40° to +40° (dependent on model scale, model tested upright and inverted to accommodate full range)
- Sideslip range: ±25° (model tested at appropriate pitch and roll angles to cover required incidence and sideslip ranges)
- Roll range: ±180°
- Overall model loads
- Control panel load measurements
- Individual store/multiple store assembly loads
- Use of oilflow visualisation to investigate surface flow phenomena such as separation bubbles and trailing edge separations
- 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
- Use of Pressure-Sensitive Paint to provide whole surface pressure data and component loads