Our testing experience with hybrids is fairly limited as we just started it a few weeks ago. That being said, hybrids are the form of engine that we intend to pursue for the near future, they offer most of the efficiency of liquid engines without all of the complicated plumbing and ignition systems. After all a hybrid is just a fuel grain that we pump an oxidizer through.
For our hybrids we are using Nitrous Oxide and Paraffin wax, a combo that can hit a specific impulse of 270s or even higher if well designed. And the best part is the materials are cheap and readily available. Nitrous can be purchased at your local hotrod shop and paraffin wax is just candle wax. The cost is so much lower than both solids and biprops and the efficiency and high thrust potential is there, as you can see, its something we couldnt pass up.
For now all we have is a few tests using whiplash as a hybrid, but in the future we plan to make a monotube hybrid and fly it in my Madcow Screech as a mid H class engine.
Whiplash was converted to a hybrid by tapping a 1/4 npt fitting into the forward bulkhead and attaching the nitrous solenoid we purchased for Epoch 2. After that all that was left was to fill the body with a single grain of paraffin. We opted for a single BATES grain on these tests for shear simplicity, however the effects of this can be seen on the burn, as the burn at points fails to stabilize and spikes in thrust near the end of the burn.
Hopefully more to come on hybrids very soon!!