A Bunny's Tale/Tail -- The Rudder

The Rudder

(30 hours)

"The rudder and elevators of the RV-6 are quite different than the surfaces you have built up to this point. Instead of having internal ribs to support the skins, there are ribs only on each end. Stiffeners, made of aluminium angle and riveted to the skin (but not the spar), help the skin keep its shape. The skins themselves are only .016" thick and are very easy to damage through careless handling. Laying a rudder or elevator skin on even a small drilling chip or other piece of debris can result in a dimple that can't be removed. Gripping an edge too tightly or lifting the skin from one end can cause an unsightly crease. Handle these skins with care: lift them from both ends and always keep the surfaces you lay them on spotlessly clean."

Have a look at David Carter's rudder construction notes.

This is where you get onto learning some new stuff; back-riveting in particular.

Be very careful handling the rudder and elevator skins; that light .016" skin is very easy to dent or crease.

I found cutting the stiffeners to length to be a slightly tricky exercise... they're supposed to finish ³/₁₆" from the trailing edge of the skin. But where is the TE position? It hasn't even been bent into shape yet. And the TE slopes, so is that ³/₁₆" at the top of the stiffener, or at the bottom? Slightly tricky. In the end, I just measured the distance from as far as my little ruler would reach. It's awkward to work in there too. And I made the TE of my stiffeners slope so that the whole end of the stiffener was ³/₁₆" from the TE. This in turn means that the left and right side stiffeners are different, so that I couldn't mix them up later.

Be careful with getting a right angle off the spar, NOT from the edge of the skin. It does say this in the manual, but at least one person has got it wrong! Easiest way to do this is to Cleco the spar in place (you need to do this to drill it to the skin anyway), and use a set square against the spar.

To overlap the stiffeners, I thought I'd be smart (uh-oh, famous last words) and NOT drill the rivet holes down the centre of the stiffener; instead, I drilled them ¹/₁₆" on the flange side of the centreline. That way, with the rivet lines neatly lined up on each side of the rudder (OSH Grand Champion, here I come), the stiffeners would overlap by the required ⅛". Except that dimpling holes that close to the flange tended to twist the stiffeners, so I had to untwist them later. And back-riveting that close to the flange wasn't easy either. And I hadn't got everything lined up that neatly, so that the holes on the outside of the skin don't line up exactly opposite each other. Suffice to say, I didn't do this on the elevator.

To cut the taper on the stiffeners, I put a mark on my set square 6" from the inside angle, and another ⅛" down. After cutting the stiffeners to length, it was a quick and easy job to put each one in this little 'jig' and mark the ends of the taper. Then join the points with a line, and cut with snips. Another cut to make the taper to match the TE, and one at the other end for the 15° (³/₃₂"), and the other sharp corners. Then file all the tapers smooth and round the corners, and they're done.

Marty Emrath <emrath@msn.com> wrote to the RV-list: I followed the "Bunny" method (I don't understand this... I think I might be getting the credit for someone else's idea!) and put a ³/₁₆" rod in the TE for clearance and butted up the stiffeners to the rod prior to drilling the holes. The first holes at each TE of the stiffeners were drilled ⁹/₁₆" from the end. Each end of the Stiffener was angled to follow the TE slope vs 90°. This means the first hole is 0.020" from the outside TE of the skin (I'm using 0.020" skins in lieu of the 0.016"). IMHO that is close enough to the TE measurement of ¾" since I have a hard time measuring 0.020" using that 100th increment scale anyway. I will epoxy down my stiffeners using Scotch Weld 2216 the full length and put in the RTV in the TE and the leading edge also. I spaced my rivets 1.5" from the spar to the last two or three TE rivets and then equally spaced them per the plans.

Drilling & riveting stiffeners to the skin

No real problem drilling stiffeners to the skin; just follow the video.  Pre-drilling the end holes makes them a little easier to put in. That's useful when working at the TE, where you're holding the other half of the skin out of your way whilst drilling. Since I wrote the following for some-one, I'll include it here: Here's my technique: I back-rivet one stiffener at a time, starting with the middle stiffener and working outwards (don't know whether this makes any discernable difference, but I guess it won't hurt)... put the rivets in, put a strip of masking tape over their heads, turn the skin over, and put the stiffener in place over the rivets.

I do the rivets starting at the spar end first, working towards the TE: Line up the first couple of rivets over my backing plate (set into the bench-top, but only about 6" in diameter). Place the gun on the rivet, press down with fingers of free hand to hold the stiffener and skin flat. Use one or both elbows to keep the other half of the skin out of the way. Drive the rivet. Same again for the next rivet. Check both rivets with the gauge, give them a touch more if necessary. Repeat for each pair of rivets... the last two *are* more difficult, but you only need to keep the skin flat and pressed down for an inch or so round the rivet.

It seems that Vans offers extra thick (.020" instead of .016") skins, which are recommended for high (180+) HP RVs and Harmon Rockets (don't what the RV-8 has). Seems these are more difficult to fold back and hold open for drilling; it may be necessary to clamp the skin down near the TE to prevent the bottom skin from bowing up when the top skin is held back.

Dimpling the stiffeners is also easy. However, dimpling the skin caused major drama. The dimples were fine, except for the last couple nearest the trailing edge of each stiffener. As you bend the top skin up to get the Avery tool in there, the bottom skin tends to bend away. If you do as I did and dimple it like this (and I didn't look until I'd done one entire side), then you'll get the outline of the dimple die pressed into the skin. The solution (once found) isn't difficult; press the dent out with your fingers. The back-riveting process will NOT fix this; instead it will leave you with a dent that you can't press out with your fingers because there's a stiffener riveted in the way. Hammers and such like are overkill for this situation too, and will make matters worse.

Prevention actually isn't too difficult (once you figure it out!): don't hit too hard! Lots of little taps with the hammer is good; two fairly hard taps is bad. You also need to ensure that the skin round the dimple die is quite flat. Hard to do when you have one hand holding the hammer, and the other holding the dimple die down. I used a couple of cushions and foam rubber pads to support the skins, and pressed down from above with another foam pad. Not entirely successful, and on two occasions (in the Right Elevator) the dimple die tore and elongated the hole. No answer to this problem, I'm afraid. I think I may need to put a ⅛" rivet in here.

Don't forget to take the plastic off before riveting! I just used masking tape to hold the rivets in place for back-riveting. Don't even bother moving it to the next row of rivets... I'd just leave it in place until you're ready to prime. On reflection, this isn't smart. The masking tape is a major nuisance to remove, especially if it's been left on for a while. I've since bought some of Avery's Magic Tape. This stuff really is magic... it sticks fine, but it peels right off.

Actually riveting was kind of tricky; it was always hard to know exactly where the back-riveting plate was. My plate is set into my workbench; *twice* I managed to drive a rivet that was half-on, half-off the plate, and once I missed the plate entirely. These are not actions I recommend; I have a couple of dents in my rudder skin now. It's hard to drill out these little rivets too. I used the Avery back-riveting set, which seemed to work well.

After riveting the stiffeners to the first side of the rudder, I found a small piece about 2" in diameter near the TE which oil-canned. However, after the stiffeners were riveted to the other side, that went away all by itself. Whew!

Dave Lundquist <DLUNDQUIST@postoffice.worldnet.att.net> wrote about the spring-back when squeezing the rudder TE to the RV-list: I VERY gently squeezed the trailing edge with my hand seamer. I put padding on the jaws and moved along the length of the trailing edge, and applied a barely perceptible squeeze as I moved along. After a few passes, perfection (well at least by my definition. I would agree that it seems nearly impossible to get a full closed rudder/elevator using the hinged jig alone.

Joe Larson <jpl@showpg.mn.org> reported to the RV-list: Paul McReynolds (ex-OSH Grand Champion) talked at a US fly-in about rigging your RV.  During the talk, he discussed his method for squeezing the trailing edge of the control surfaces, most notably the ailerons.

Paul does NOT use the method listed in the plans. I can tell you from personal experience the hinged 2x4 method just doesn't work that well. Paul does something similar, but different.

He does use 2 2x4s, but they aren't hinged. Instead, he uses 6 large C clamps and slowly, carefully, clamps the 2x4s closer together until everything is Just Right.

Other notes on this -- the definition of "just right" he has determined to mean that the 2x4s should be flush with the trailing edge of the skins. Stop tightening the C clamps when the 2x4s are ³/₁₆ apart. If the 2x4s have a slight radius on their edges, either remove the radius (carefully and straightly) or adjust positioning of the 2x4s slightly.

The clamps themselves should be places along the trailing edge of the 2x4s almost such that they fall off. You just want to tighten things at the trailing edge, not forward of that point.

When you think you have ³/₃₂" between the 2x4s, take it all apart, then hold the skins trailing edge to the sky and see if they hang with the right distance at the spar point. Remember, the idea is to have them just touching the spar with no pressure on them. But if you do it on the table, the top skin will be affected by gravity and you'll get a slight cheating action to close the skins further.

The Rudder Skeleton

David L. Macintire <dave_mac@bellsouth.net> wrote about dimpling/riveting the aft holes in the rudder ribs to the RV-list: Did you try using the dimple die set pop rivet dimpler with a copper nail? I could usually bend the copper nail enough to reach just about any hole. Otherwise, put a rivet in the hole, put two small pieces of 0.032" aluminium with a #40 hole drilled in them (stack them together) to act as a bucking bar; and clamp these pieces in there snug. Put another piece of aluminium over the rivet head. Then take a small vise grip pliers and squeeze lightly. That should provide you an adequate dimple. Buck the rivet with a cold chisel and use a rivet gun very carefully to finish the job.

Drill the holes to connect the rudder cable to rudder horn (³/₁₆", near front of horn) now... it's easier than when the rudder is assembled. If you've decided to build a -6 rather than a -6A, drill the holes to connect the tail-wheel steering chains (#30, near aft of horn).

The rudder skeleton is otherwise straightforward, except for the rudder horn brace. Riveting this on involved holding the bucking bar (a small one) through the lightening holes. 

Jeff Orear <jorear@mari.net> wrote to the RV-list: Regarding the rudder horn brace, part R410 (the part from hell!), I ended up flaring the sides out and then bending a tab on each side to parallel the rib flange that it gets riveted to. This was required to close a gap left after the factory bent the stock that R410 is made from. I also placed a .04" shim, made from cutoff from making the R410 part, on each side of R410, again to further close the gap. I just couldn't get a nice tight fit otherwise. With making these bends and using the shims, I now have a nice fit.

On bucking the 4 AN rivets that attach R410 to the rudder horn, have I got a deal for you! I found that if you use the heavy stainless steel base from a machinist's square as a bucking bar, you can slip it right along all the rivets and buck them with no problem at all.  I used a medium sized one that I got from Harbor Freight. Just support it with two fingers through your *required* lightening hole in R410, and away you go. It really worked slick. No damage to the square, either.

RV-List message posted by: Bill Von Dane<bvondane@atmel.com>:
I figured out a way to rivet the two inside rivets on the rudder's horn bottom. I have posted the "tip" on my web site

RV-List message posted by: George McNutt<GMcNutt@compuserve.com>: Went to the local scrap metal dealer and bought some assorted pieces of stainless steel. Found a piece ⅝ x 1⅛ high and about 10" long, polished the ⅝ face on the belt sander and it worked well as a bucking bar.

Clamped the rudder spar to workbench in horizontal position with area to be riveted hanging over end of workbench, poked bucking bar up through bottom of boxed in area and riveted the four rivets working from top to bottom.

According to recent (May 98) RV-list postings, Vans has changed the shape of the R410 so that it now fits much better.

The rudder and elevator jig measurements are shown in Drawing 8PP in the upper left hand corner -- VB1 and VB2 for the Rudder ("V" Block 1 and 2). The dimensions shown don't seem to make much sense; with the jig Vs set up as per the plans, they don't match up with the skin as shown. I moved them in a little.

Before rolling the LE, fold the last ¼" or so of the edge down; much easier than doing it after rolling the LE. On my elevators, I did this with hand seamers, and that worked fine.

Rolling the leading edge smoothly was difficult; I've got a couple of discernable corners at the start of the curl where the spar is. (There may be clearance problems once the part is mounted; I don't know more at this stage).  To get the radius right at the top, temporarily fit the top & bottom fairings.

Rather than build/buy one of those edge-bending tools with the two little wheels, I tried bending the edge down with my hand-seamer. Not a good idea: the back of the seamer has left a whole lot of grooves on the other half of the skin :-(.

Note that the trailing edge of the rudder is not parallel with either side of the spar, but should be with the centreline of the spar. If you lay the spar flat against the table either side, there should be a gap between the table and the outboard trailing edge. The same goes for the elevators.

RV-List message posted by: jerry calvert<calverjl@flash.net>:

1. Use the edge tool to put the slight bend on the edge of the skin before you start bending with the pipe (just easier to do it now before it's bent).
2. I found it easier to bend one section at a time with a short ¾" pipe than trying to do all three sections at one time. Just get the skins rounded over and then do the final moulding by hand.
3. When the skins are curved about how you want them, take a ⅜" wooden dowel and hold it at the edge that was bent with the edge tool. Squeezing it between your fingers and thumb, curl the edge a little more around the dowel. This makes the edge bend down a little more and rounds it so that it really fits the curve of the skin.
4. Cleco together and check to see how the edges are laying down. If you're not satisfied, un-cleco and bend some more until it meets you liking.

RV-List message posted by: "Fesenbek, Gary"<gfesenbek@meridium.com>: A recommendation I have on the rudder is to drill and cleco in the top cap. Using a Dremel tool I gingerly cut away at the cap until it fit very well with the rudder skin. I noticed that I had to move one of my pre-punched holes in order to get the cap to fit just oh so right on the skin. Sure, sure you can't really move a pre-punched hole, but you can drill in another place and skip the pre-punch.

RV-List message posted by: Mark Fredericks (Mlfred@aol.com): When building the Rocket empennage, we don't do that LE in that manner. We simply bend the LE into the proper curve after trimming the skin fwd of the spar and re-flanging it. No rivets, no problems, finished quickly.

Mounting the Rudder

RV-List message: Richard Bibb<rbibb@fore.com>: Get a pair or needle nose pliers and file (I ground on bench grinder) a small V groove in the jaws near the tip. This enables one to hold a round bolt by the shaft easier. Use the needle nose pliers in one hand holding bolt while you work the elevator into position with the other.

RV-List message: Bob Skinner<bskinr@trib.com>: Using some scrap .032", I made a tool to hold the bolts. The handle can be bent to suit and is 3 or 4 inches long. To the handle, I riveted another piece of scrap with a slot cut in it to accept the shank of the bolt.  You then pry the two pieces apart and insert the bolt with the head against the solid part (the handle) and this set up will hold the bolt firmly.

I made a couple of temporary hinge pins by putting a right angle bend ¾" from the end of a couple of 4" long ³/₁₆" bolts. File the end of the bolt down to a bullet point to make it easy to insert.

A few years after mounting the rudder using bolts and so on (and un-mounting it and re-mounting it and the elevators dozens of times), I've had a really bright idea for a tool! For each hinge (2 on the rudder, 4 on the elevators -- ordinary bolts can be used for the bottom rudder and elevator centre bearings), make a temporary hinge pin as follows:

1. Put a right angle bend ½" from the end of two 2-3" long ³/₁₆" hardware store bolts.
2. File the ends of the bolts down to a bullet point to make them easy to insert.
3. Grind off the side of the bolt head, on the same side as the bend.
4. Drill a ³/₁₆" hole near the end of each of two pieces of aluminium (1"x½"x.025 or so) then bend at right angles, maybe ¼" from the hole centre.
5. Put the first bolt through the hole in one piece, and tie the assembly to one leg of a spring clothes-peg using a piece of twine.
6. Similarly, attach the second bolt to the other leg, aligning it with the first so that when the peg is closed the ends of the two bolts just touch.
7. For better rigidity, use Araldite to glue the bolts in place.
8. I covered the twine and glue with masking tape, to hold the bolts in place while the glue set, and to stop the two halves from permanently sticking to each other.

You can now squeeze the clothes-peg to open the 'hinge pin', align the two bent ends of the bolts with the holes in the rudder bearing, and let go. Tada! The bent ends of the bolts go into the bearing and hold things in place.

I also made a "bearing socket" by grinding slots in the sides of a ½" socket. That made inserting and adjusting the bearings quite painless. Someone the RV-list suggested making it out of a piece of PVC pipe. Note that one of the bearings is a larger size than the other 6. That one goes in the bottom of the rudder. 

Make sure all the rudder rod-end bearings line up by sighting lengthwise through them all using Mk1 Eyeball. Get two about right, then sight through the three rod-ends to ensure that all three are lined up properly. The VS hinge brackets should already line up since they were all lined up on the jig. Note that the VS spar to rudder spar distance is 2" at the top and 2½" at the bottom.

The rudder will be removed when mounting the VS to the fuselage... don't permanently mount it to the VS yet.

Tip Fairings

The rudder top fairing was no problem... it just slots right in there. Except that there was a small (less than ⅛") gap at the front. I've redone the LE roll of the rudder to match the shape of the fairing.

I followed instructions from Jim Cone's newsletter, rather than those in Vans manual, in fitting the rudder bottom fairing. Basically, make a horizontal (when fitted) cut round the front of the fairing with a hacksaw, back to the front of the rudder horn. Next cut down along the vertical line of the rudder horn to meet the first cut, and remove this piece. Then cut a slot each side for the rudder horn to protrude from. By adding some tabs, either to the offcut piece or to the main fairing, the offcut could be reattached with screws (to give access into the rudder bottom if you have a tail light on it) or pop-rivets. I chose to make up an aluminium cover for this gap. There are two parts to it, rivetted together. The inner part goes inside the fibreglass of the fairing, and provides a flange for the outer part to be rivetted to. The outer part is made from .032" -- this thickness gives a pretty good match to the thickness of the fibreglass, to make for a nice butt joint between them.

Bottom Fairing Light

As far as the rudder bottom goes, it doesn't have to be removable to service the tail light. Leave an extra 6-8 in. of wire in there so it can be pulled out to work on the rear of the socket if necessary.

RV-List message posted by: ABAYMAN@aol.com: All I did was mark and drill the hole a little smaller than the fixture.  Used my Dremel with a drum sander and kept taking off a little at a time till the round recessed part fit into it tightly. Then I marked the screw holes, drilled them so the small bolt would be a tight fit.  This is where I think I am alone in how I mounted my light. I inserted both the screws with the heads inside and the threads facing out.  Installed the fixture over the screws and used the little lock nuts that came with the light to hold the fixture down. Then I placed the globe and gasket with the retainer with Nyloc nuts. If the bulb burns out, all I have to do is remove the top 2 nuts change the bulb without worrying about the rest of the fixture falling out. Looks good. Seals tight.

I did the same thing, more or less. I used a holesaw to cut a 1⅛" hole in the fairing, and drilled holes above and below for the two screws. I used M3x16 (3mm diameter 16mm long) machine screws to mount the light because the screws that came with mine didn't have locknuts. M3s were the smallest screws available with locknuts. I inserted the screws into the fairing, with the heads inside and threads out, and a washer to spread the load a little. I then epoxied them in place. Beforehand I had ground a little off one side of the head of each screw so that even if the glue didn't stick to the head, it wouldn't turn. I took some care to ensure that both screws were exactly parallel. On the outside, I have two washers, with metal on one side ground off for clearance, on each screw, and a locknut.

RV-List message posted by: Gary Van Remog (Vanremog@aol.com): Graft on a flat piece of fibreglass (FR-4) circuit board material and install rivnuts or something similar for the two holes that will attach the taillight housing. A single Adel clamp accessible from the front of the bottom front rudder opening stabilizes the wiring. If this is done, the whole shebang comes out easily for replacement.

RV-List message posted by: Scott Gesele<scottg@icsnet.com>: Secure a piece of ³/₁₆ aluminium in the rudder fairing. This piece should be filed to fit the contour of the fairing and is located where the mounting holes are in the tail light are. I used two pieces of aluminium about ¼" high x ³/₁₆" wide x ⅜" long. These sizes are approximate as it was two years since I installed them. The size description is to give you a better idea of how I made the blocks.  Once these blocks are fit into the rudder fairing, they can be drilled and tapped to accept a machine screw that will hold the tail light on. Two other holes are drilled sideways through the rudder fairing and each block, perpendicular to, but not through, the drilled and tapped hole. This is used to pin each block to the fibreglass fairing.  These pins are covered up and secured with a light piece of fibreglass cloth.

RV-List message posted by: RICKRV6@aol.com: I cut out a piece of ³/₁₆" model aircraft plywood the shape of the base of the tail light. This shape should match the fibreglass fairing. I then cut a hole in the ply large enough to fit the light shaft. I then drilled the light mounting holes in the ply.  I bought two blind "T" nuts from my local hobby store. These nuts will mount on the inside of the ply. I epoxied the ply to the inside of the fibreglass opening being careful not to get any glue in the blind nuts (a bit of Vaseline will protect the nuts). After painting you simply mount the light to the wooden mount. Some Loctite will ensure the bolts remain in place.

RV-List message posted by: Patrick Kelley<patk@megsinet.net>: I am using the same method except I made my plate out of .040" aluminium instead of wood. The nuts are tack glued to the plate with thin cyano-acrylate glue and I smeared mould release on the screws and ran them into the nuts.  Next, I glued the plate assembly in place with a flox/epoxy mix.  When set, I removed the screws and put a dot of scotch tape over the holes (make the dots with a hole punch). Finally, two layers of glass over the plate to fair it into the fairing and add strength. Once set, trim out the centre hole and screw holes with an X-acto knife.

Originally, I intended to make a connector at the front of the fairing, but that turned out to be a complicated idea (too many problems to overcome).  I am currently putting a grommet at the front of the fairing and will simply run the wiring from the fuselage back to the light with a connector at the light. To remove the rudder, first remove the light and grommet in order to release the wiring. Reassembly will be just as simple.

RV-List message posted by: "Dan Checkoway" <dan@rvproject.com>: Just leave slack in the wire(s) with a connector inside the fairing. You run the wires out the bottom of the VS and UNDER the lower rod end bearing and into the opening in the front of the bottom fairing. You need enough slack to be able to remove the screws in the light then pull the wire out of the opening to undo the connector. The light comes out with the 2 screws, then disconnect the mate-n-lok connectors...light assembly is removed. Pull the rudder right off the fuselage and the wires/connectors pull out the front of the rudder at the lower rod end bearing hole. Need to pull the wires back into the fuselage? Just remove the plastic mate-n-lok shells and the wires/pins will slip right in through the hole in the VS.

No problems so far, and nothing is "permanently attached."

RV-List message posted by: "Dan Checkoway" <dan@rvproject.com>: "How to prevent the wires from chaffing/cutting (from rudder movement) as the wires ride on that fibreglass edge where they drop down from the rod end bearing down inside the fibreglass fairing?"

In my case, the edge doesn't even come close to the wire. Granted, I opened the "mouth" of the fairing up a bit and lowered the edge, but the wire exit hole in the VS spar is high up enough, and the front edge of the fibreglass fairing is forward enough so that the wires droop right down into the fairing and there's basically no chance of contact.