Load measurement tests are performed to determine aerodynamic loads. External balances and internal balances are used to find aerodynamic forces and moments acting on the model in different speed, angle and model configurations. MSS is used to set the test model to the desired angle. Balances consisting of various hardware and software components make the measurements accurate and reliable during wind tunnel test. External balance system is located outside of the test section whereas internal balances with different diameters and load limits are mounted in the model. Load ranges and operating principles of balance types are different from each other. All balances have 6 components. The type of balance and the diameter of internal balance to be used in the test is decided according to geometric and aerodynamic properties of the test model and pre-test evaluations. Balancing systems operate between -10 and +45 ˚C temperature values.
External Balance System
External balance system in Ankara Wind Tunnel was located under the test section. High load limit model can be tested by six component external balance system. It includes many load cells and different types of steel framework structures.
External Balance Limits
|Component||± Load Range||Full Scale Precision (0.02%)|
|Axial Force (N)||3560||1,42|
|Side Force (N)||8900||3,56|
|Normal Force (N)||8900||3,56|
|Roll Moment (Nm)||1900||0,76|
|Pitch Moment (Nm)||3500||1,40|
|Yaw Moment (Nm)||1100||0,044|
Internal Balance System
22 mm, 35 mm and 44 mm diameter six component sting type internal balances with different load limits are used in AWT. Internal balances have a calibration precision of less than 0.2%. Calibration accuracy of the 44 mm diameter internal balance varies between 0.03% and 0.15% with respect to different aerodynamic components. A maximum model weight of 10 kg can be tested using 22 mm diameter internal balance while 35 mm balance is limited up to 30 kg and 44 mm balance is limited up to 50 kg. Load limits of internal balances are given in the table below. Normal force values in the table include weight of the model. Internal balance to be used is decided by structural analysis, considering the aerodynamic loads expected in the scaled models Internal Balance Limits
Internal Balance Limits
|Axial Force||±80 N||±375 N||-500/+200 N|
|Side Force||±225 N||±1000 N||±1250 N|
|Normal Force||±225 N||±1000 N||±2500 N|
|Roll Moment||±10 N.m||±150 N.m||±200 N.m|
|Pitch Moment||±15 N.m||±150 N.m||±400 N.m|
|Yaw Moment||±15 N.m||±100 N.m||±200 N.m|
MSS in the AWT was made ready for use after installation and commissioning. MSS can operate in an integrated manner with the external balance system and in harmony with sting type internal balances. High positioning accuracy, quick and precise force and moment measurement are possible in this balance system. Tests can be carried out automatically at different angles of attack, sideslip and roll angles. Angle of attack is given to the test model by the movement of the arc sector on the guide rail and roll angle is given by the rotation of the Roll head at the back of the sting. Sideslip angle is given by using the rotating frame structure (Turntable) seen at the bottom of the external balance system. Technical features and load limits of the MSS are given below.
|Axis||Angle Limit||Precision||Sweep rate|
|Angle of attack (α)||-20º -> +50º||0.025º||0.1-2°/s|
|Sideslip angle (β)||-30º -> +30º||0.025º||0.1-2°/s|
|Roll angle||-90º -> +270º||0.025º||0.1-6°/s|
|Positioning precision||± 0.01º|
MSS Load Limits
|Components||Min – Max Load Limit|
Integrated MSS and external balance are given in the figure below.