In this chapter the real-time testing technique which has become known as
real-time dynamic substructuring
is discussed. A control systems approach is taken to develop stability and robustness criteria for real-time dynamic substructuring tests. In particular we discuss how delay and uncertainty effects in the experimental apparatus can lead to loss of accuracy, or worse, system instability. Models which take account of the delay effects are developed using both delay differential equations and transfer functions. From these models delay compensation schemes can be constructed either using inverse transfer functions or forward prediction methods. Three methods for improving robustness are described for use in combination with a delay compensator. Throughout the chapter experimental results are presented, and in the final part results from an industrial example of substructuring a helicopter lag damper are discussed in detail.