No way should fiberglass ducting be that rough. This type of ducting should
have as much attention as the surface of a wing. What that means is that the
interior should be coated in Micro, sanded, painted etc. to provide the
smoothest surface and avoid boundary layer separation. I am currently building my ducting in this manner and allowing for a felt
weather seal on both sides of the coolers (oil and rad.)

........ at least I feel it is an important detail.

T Mann

-----Original Message-----

Specifically be aware of the potential danger of fiberglass ducting rubbing on water and oil coolers. Fiberglass is a great abrasive.

Finn