I'm having this problem fairly regularly with the latest Cura 15.04.2 where it will leave some overhanging geometry entirely unsupported. In the past, when I notice in time, I have been able to resolve the issue by orienting the model in a different way on the build bed, but sometimes that doesn't even work or it results in super long print time that shouldn't be necessary if Cura would just be smarter about the placement of the support material.
here is one example:
The geometry indicated with the green arrow should go up at an angle and eventually meet the main dome structure, but it will never make it that far because all of its initial layers are being printed in mid air... I already reoriented this model once to fix a much worse floating overhang, but still Cura insists that these hooks (which are an important mechanical attachment feature in this print) can be printed in mid air. Unfortunately I didn't see this one in time and now more than halfway through my 16 hour print, there is a wad of spaghetti hanging off of my model where attachment hooks should be.
I suppose changing the value for overhang angle for support could fix the issue, but this also would add a significant amount of support material to the domed inside of my model where it actually isn't necessary.
Very frustrated. Any ideas or suggestions are greatly appreciated.
Thanks.
-Blake