An experimental program has been conducted in the LTV Hypervelocity Wind Tunnel at M = 17 to investigate the effects of ablation product characteristics and thermal lags on re-entry vehicle dynamic stability. The free oscillation method of dynamic stability measurement was used and the ablation processes were simulated by the controlled mass injection through four sections of the porous model skin. The flow rates through the top and bottom quadrants were oscillated at the same frequency and at an amplitude proportional to the model motion. The thermal lag effect was investigated with nitrogen injection into nitrogen tunnel flow at several different mass flow rates and phase angles between the oscillating mass flow and the body motion. The ablation product study was conducted by injecting gases other than nitrogen with specific heat ratio and molecular weight being the test parameters in addition to mass flow rate. The results obtained from these tests indicate significant effect on dynamic stability with both injection phase angle and some characteristics of the injected gas. The effects of model frequency, Reynolds number and mass injection distribution were also investigated and some static pressure measurements were made near the aft of the model. Appendices to the report contain tabulations of the pertinent data and discussions of supporting analytical studies and data analysis.