The addition of nano-sized energetic materials, such as aluminum and boron, has been shown to increase the mass-burning rates of solid fuels. Previous results showed that the addition of 13 wt% Silberline® aluminum flakes to HTPB-based solid fuels increased linear regression rates by as much as 60%. When similar fuel formulations were tested in a larger (~3 times the port diameter) hybrid rocket motor the measured regression rates were nearly identical to those of pure HTPB solid fuels. SEM/EDS analysis was conducted to indicate the reason behind this phenomenon. In contrast, the addition of the same wt% of Silberline® flakes to paraffin-based solid fuels does show a significant increase (~30%) over baseline paraffin solid fuels. The differences in particle entrainment mechanisms for these two types of fuels were attributed to the trend of burning-rate augmentation. Waterfall analyses of pressure-time signals were utilized to study the inherent low-frequency instability of hybrid rockets. Comparisons are made to a universal frequency-scaling formula proposed in the literature, showing agreement to within 25%. To understand the instantaneous mass-burning behavior, a real-time X-ray radiography system is utilized to image the solid fuel surface during combustion testing. Results for both HTPB-based and paraffin-based solid fuel formulations are described. Traditionally, average solid fuel regression rates are correlated to the average oxidizer mass flux by a power-law curve fit. However, instantaneous fuel surface burning behavior does not exhibit the power-law behavior when correlated to the instantaneous oxidizer mass flux.