The original Andean flutes that I have are thicker than either aluminum or PVC pipes. (The one with the best airy tone is quite thick walled.) The embrochure on both of them (and on all that I have seen) is cut at an angle, producing a very sharp "V" notch. (The sharp edge is on the _inside_ of the tube.) Also, both flutes have the open end slightly restricted. One flute is bamboo with a node at the end and a hole drilled in it and the other is wood that is drilled. In each case, the hole at the open end is about the same diameter as the tone holes. My guess is that it is this restriction of the open end that produces the airy tone by causing back-pressure at the embrochure.