In summary, NASA and Boeing decided to use three existing TDI model 2700 TPS units for the powered testing of the HWB model in order to save costs. These units were originally developed for testing a high wing transport configuration in the 1990s and had similar mass flow characteristics to the predicted requirements for testing the HWB model. However, modifications were necessary to achieve proper flow scaling and to accommodate the inverted position of the TPS units on the HWB. Additionally, concerns about the oil lubrication system led to an additional goal of running the TPS units upside-down during risk reduction testing.
