The RS2 was originally designed by Rim Chung nearly 40 years ago. It's an absolutely amazing fly and if you've never fished it, you need to. Tying a proper RS2, however, can be extremely frustrating for many tiers, myself included. Fortunately, author and fly tier Matt Grobert has really got this pattern down and was willing to share how he ties an RS2.
Matt's going to tie one here on a Dai Riki #310 Straight Eye hook in size 18. Sizes 20 through 24 are also very popular. For thread, he's going to use 6/0 olive Danville. Start your thread a hook eye length behind the eye and wind back to about the half way point on the shank. Save the tag end of the thread you snipped or broke off as you'll need this later.
Microfibbets are the standard tailing material on an RS2. You're going to need to separate two of them from the clump and snip them off at the base. Measure them to create a tail that's about 1 1/2 to 2 hook shanks in length. As you secure them, make sure the two fibers lay side by side directly on top of the hook shank, not down the sides. Take a few wraps back up the shank to further secure the microfibbets.
Now, find that tag end of thread and fold it around the bend of the hook. With your dubbing needle, carefully separate the two microfibbets. This can be somewhat of a chore but stick with it. Once you get the tails separated, pull the loop of thread up between them. As you gently pull the loop forward, you'll notice the tails splay outward. When they're at about 80 degrees, take a wrap to secure the thread loop and thus maintain the angle. Carefully take a few more wraps to lock everything in place. Then continue wrapping forward before lifting the butt ends of the microfibbets and the thread loop up to snip them off.
Using extremely fine dubbing, here Super Fine in a light olive, begin making a thin dubbing noodle on your thread. Go very light, this fly is easy to over dub. Once you have a nice thin noodle established, take wraps rearward so the dubbing starts right at the base of the tail. Slip the dubbing under the tail and pull forward to lift the fibers up slightly. With that done, begin taking wraps to form a thin, segmented and tapered body. Make sure to leave some space behind the eye.
For the wing, Matt uses about half the fibers of a standard CDC puff. Fold the CDC around your thread and bring it up to on top of the hook shank. While holding the tips, take a couple of nice tight wraps rearward to secure the CDC. Then snip the butt ends of the CDC puff off close to the hook shank. Use just a few thread wraps to cover the butts.
You can use the same dubbing for the thorax as you did for the abdomen, but again, go easy. Matt starts the dubbing noodle up near the eye to form a dam to hold the subsequent wraps back from crowding the eye. Sneak a wrap or two behind the wing to hold it up near vertical and then take a few more in front to finish the somewhat bulbous thorax.
Finish with a 4 or 5 turn whip finish and carefully snip or cut your tying thread free. Trim the wing at a downward angle, like so, and your RS2 is complete. Although Matt has made this tie look easy this is a pattern that demands practice. Don't expect to sit down and start cranking our perfect flies right away. Experiment with different colors for the body and thorax. And try different colors and materials for the wing. A box full of nothing but RS2's is a worthwhile addition to just about any fly vest.