How are hollow composite propeller blades made?

[swiftprop]

I had a look at a Pipistrel's broken prop blade yesterday and noticed that the blade is mostly hollow. I think it is a Vario prop with the inside skin and outer parts made of composite materials, namely fibre reinforced plastic. The leading and trailing edges have a bit of material that looks like foam as a filler but only for a centimeter or so. The rest is hollow. My question: How do they make it hollow? Maybe the blade consists of two pieces glued together? Does any one know how it is done?

[jpage]

Mostly the impregnated fabric is laid up in a mold in two halves, and a latex or silicon bladder put in between. The two halves are then clamped together and the bladder inflated. This squeezes out any excess resin and ensures uniform pressure of the strands against the mold. The whole thing is then heated to the correct temp to cure bladder removed, mold opened etc.

[swiftprop]

Sounds like quite a process! Amazing how light such a prop is. Thanks for the info jpage. :D