Probably the most successfull of the microhybrids so far designed, Rene offers a complete kit or plans to Microhybrids. If you don't know what that is, a microhybrid is just what it sounds like. It employs both a solid propellant and a liquid oxidizer. In the case the grains are rolled paper and the oxidizer is NO2 available in the form of whipcream refill cartridges.
Have a look.
http://rlmac.com/
Plus here's the link to the yahoo forum dedicated to RC site.
http://groups.yahoo.com/group/microhybrids/
Rene Caldera Microhybrids
Moderator: Mike Everman