The Frenchie is a favorite pattern of competitive fly fisherman and Euro nymphers. It's really nothing more than a heavily-weighted pheasant tail with a hot spot.
This pattern is often tied on competition-style barbless hooks but I'm going to tie one here on a Dai-Riki #60 Nymph hook in size 14.
Mashing the hook barb makes it easier on the fish, it also makes it easier to add a bead. To really get the fly down deep, tungsten beads are the way to go, here, a 7/64" in gold.
Place the bead onto the hook, small hole first, and then get your hook firmly secured in your tying vise.
For even more weight, I like to add 8 or so wraps of .015 lead-free wire. Take wraps with the wire around the hook shank and snip or break the excess off close. To stabilize the wraps and the bead, a small drop of Zap-a-Gap applied to the hook shank with your bobbin, before you slide the wraps up, is the way to go.
For thread, I'm going to use fluorescent pink 70 Denier Ultra thread which will help to form part of the fly's hot spot. Start your thread on the hook shank behind the lead wraps and snip or break the tag end off close. Advance the thread forward over the wraps to behind the bead and then back down to insure the weight stays in place.
Coq de Leon fibers are the standard tailing material for the Frenchie and if you can get hold of a Whiting Tailing Pack, it's well worth the investment. The pack I got has two patches, each with more Coq del Leon feathers than I could use in a lifetime. The fibers are thin, stiff and extremely durable. They also have a wonderful natural barring. As good as they look on a Frenchie, on dry flies is where they really shine.
Strip 8 to 10 fibers free from the stem and measure them to form a tail about a hook shank in length. Using the lead wraps as a guide, snip the butt ends off square. You may need to give your bobbin a counter-clockwise twist in order to get the thread to jump rearward on the first wrap. Continue taking wraps down the hook shank to the start of the bend. You can see here just how good a Coq de Leon tail looks.
To rib the fly and protect the somewhat delicate pheasant tail abdomen, brassie-sized gold Ultra wire is a good choice. With the wire butted against the lead wraps, secure it to the near side of the hook shank with tight wraps of tying thread.
Snip 8 or so natural-colored pheasant tail fibers free from the stems. Get them oriented in your hands so you can tie them in tips first. Then snip the very tips off square. Secure them just behind the lead wraps, again giving your thread a counter-clockwise twist so it jumps back. Take thread wraps all the way down to the base of the tail and then wind your tying thread forward to behind the bead.
At this point your Frenchie should have a gently tapered underbody. Get hold of the pheasant tail fibers and begin taking wraps forward to form the abdomen of the fly. Secure the fibers behind the bead with a few firm wraps of tying thread. With the fibers secured, snip the butt ends off close.
Counter-wrapping the rib will make the segmentation more visible and the fly more durable but it does have a down side. When you go to tie it off, the wire and thread are being wrapped in opposite directions and the tying thread tends to push the wire wraps loose. To stop this from happening, I like to take a thread wrap over top of the wire to change the thread wrap direction so it's the same as the wire.
After a couple of wraps, I'll once again use the wire to change the direction of thread wrap back to normal. Doing this isn't absolutely necessary, but I've found it makes for an extremely durable fly. Using the tip of your bobbin as a brace, helicopter the wire off close and then position your tying thread at the start of the abdomen.
Ice Dub, here UV pink, is the standard material used to form the thorax of the fly. A little of this stuff goes a long way. It only takes just a bit to build up a thin tapered dubbing noodle on your tying thread.
With the thorax formed, you want to build up a visible thread collar and successive whip finishes are a really good way to do it. Once you have a nice hot spot collar established, you can snip or cut your tying thread free.
Frenchies are fished on or close to the bottom so I like to apply a liberal dose of head cement to the thread wraps to help increase durability. Leave ample time for the cement to dry and a second drop of head cement isn't a bad idea either. You may want to tie a bunch of these as they're easily lost to the bottom. Different colors of thread, dubbing and pheasant tail can dramatically change the look of a standard Frenchie. My advice is to experiment, you may just stumble upon a secret weapon.