I've been playing around with this pattern for a while now. It presents very gently on the water,is extremely buoyant without the need for floatant treatments and seems to be very effective. Even though the body is of CDC it is remarkably robust: I fished this LDO/BWO version (#14) on a small Welsh stream last Spring and it was still in tact after a dozen sharp-toothed wild brownies.
so how do I tie it?
I like to use light wire emerger hooks, maximum gape, minimum shank.
First you select a large CDC feather, appropriately coloured for the abdomen. Hold the feather by the tip and stroke the fibres toward the butt. The fibres at the tip become the tail fibres. Tie the feather in such that you have the right abdomen length to match the natural. Trim the centre of the tip, leaving 1-3 tail fibres on either side.
Tie in a length of Tiemco Aero wing or other buoyant wining material, angled three quarters backward.
Using a split thread technique create a dubbing loop of long CDC fibres to match the legs and wing colours of the natural. I have used one natural and one olive feather here.
Trim the wing to about abdomen length. Trim the underside and neaten, just a little, it works better when a little untidy.
I tie them to imitate a range of uprights from the big E. Danica in #10's through to little #16's. I've not tried smaller, yet.
Have fun and let me know how you go.
edit: I couldn't resist trying this pattern on a smaller hook, so here's an LDO/BWO on a #18 Varivas 2200...