Re: How do you tie a "folded feather"?
It plays for me.
Looking at the fly in your link I think the feather is folded over with the shaft along the shank and not folded and wrapped. I may be wrong. I think you could get it to work iether way. I used to tie a fly for Trout called a Professor that has a folded wing the way I am thinking it is. Smaller section and tied upright more in a Trude kind of angle.
One trick in getting them right is how you get the first wraps of thread on. If you hold them in place with one hand, finger and thumb over the head, then holding light pressure on the feather, kind of sneak the thread into where you are pinching it. Then go over the top and sneak it into the other side. While holding pressure on the feather, slowly tighten the thread. It helps to make this wrap as far back as the head will go so subsequent wraps don't roll the wings.
I wouldn't worry about it floating the fly. Once it has been cast a few times that feather will be more hair-like and won't hold air.