My main interest is in traditionally constructed scale models, built using a balsa framework covered in tissue. Motive power is usually electric, CO2 or the traditional rubber strip motor. It is years since I built a model with an internal combustion motor in it - nowadays there seems to be a move towards quieter, more "enviromentally friendly" power units, so CO2 and Electric are becoming more popular, and there are even compressed air power units available. The appearance a few years ago of Rapier solid fuel propulsion units has also lead to an entertaining detour into the wonderful world of small free-flight scale jets.