I hope the stuff we've done more recently doesn't come back to haunt me as badly as the stuff I did that long ago ;-)
The 'wood axe' was a fun little project and it did seem to work surprisingly well on the front of my truck when I drove it down the road. That said - the steel laminates behind the coils like I did that, and all the wood was probably not wise and the single phase alternator is not something I'd ever do again. Hopefully there is a sort of 'warning/disclaimer' at the top of those old pages that suggests folks look for newer stuff.
In your case though - since you are seeing 19VAC from it, I should guess you have the coils hooked up right. Hopefully the bearings spin very freely because it is a tiny machine with a tiny rotor.
Yes - putting a 5' diameter blade on it will not help, the alternator is simply not that powerful and it probably needs more speed in lower winds. If bearing friction is not a problem, then a smaller rotor will spin faster in low winds and you should get more power. The blade for that really does need to be fast.
Hooking it to a lower voltage battery will stall the blades too..... with a larger 5' rotor, you migth do better to try charging a 10V battery or something, but at the end of the day I expect you'll get the most power from a smaller rotor, 3-4' in diameter.
Another factor there.. I wonder what sort of steel laminate you used? I forget what I used, probably something horrible like band saw blades or something - but you will have losses in the laminates and they will make it stiffer to turn, best bet is find some silicon steel for that but it's probably not worth the trouble really.
That was a fun project and it did work - and perhaps the machine could've even held together for a while and produced a tiny bit of useful energy. But it was mostly for fun and today I would do everything differently.
If you're very enthusiastic, I would learn a bit from this (like I did) and move on to a more practical design.