I can't help agreeing that a commercial ducted fan unit will give better results... However, I really want to see if you can get this off the ground with a modified cooling fan. Go for it! It's obvious this model isn't going to be the most efficiently or well designed plane out there, but at least it's interesting.
Skyman, that wouldn't be practical for a few reasons... Firstly, as Jetplaneflyer already pointed out, you are only going to lose energy by having the electrolysis rig on the plane. Electrolysis is horribly inefficient, and water is not an energy source so you're just sacrificing energy in the conversion from electrical to chemical energy. Secondly, the size of the electrolysis rig in order to feed a model sized engine of any sort is going to be absurd... These things really don't produce an awful lot of hydrogen unless they're huge.
And JetPlaneFlyer, I'm not sure he was suggesting that the water would act as a power source (unlike the hundreds of HHO scammers). I think what he was getting at was to use the battery as the only source of energy, but use the electrolysis rig as a way of making the system more 'jet' like, by using ignited fuel to propel the model foward.
At any rate, if you want to experiment with hydrogen powered models, you'd be much better off producing the hydrogen on the ground and simply filling a tank on the plane.
And now I'll try and stay on topic.