Archive for the ‘Rudder’ Category

Rudder finishing

Sunday, October 16th, 2022

If you are building a taildragger, you want to wait to fit the bottom rudder fairing until you can test-fit the rudder to the fuselage to make sure the fairing is not rubbing on the tailwheel. I dug my untouched rudder bottom fairing out of storage and iteratively trimmed away at it until I had it fitting pretty well. I used a Norton cutting disc and a variety of Perma-Grit tools, which made it go fairly quickly:

The fit around the rudder horn is not completely perfect, but you need a little extra room in the cutout to get the fairing installed anyway, so I'm acceptably happy with it. I taped the fairing to the rudder and drilled the mounting holes, stepping up to #27 and countersinking for Tinnerman washers:

I added a connector to the wire bundle that emerges from the vertical stabilizer spar, and added a layer of snake skin to hopefully protect it from chafing as the rudder moves:

After fiddling with the wiring bundle, I went back and removed more material from the forward end of the bottom fairing, including a semicircular cutout to keep it from sawing its way through the cable bundle:

Rather than try to install nuts for the nav/strobe light inside the narrow confines of the fairing, I bought a mounting adapter which simply pop-rivets in place:

I somehow misplaced my old Whelen beacon light unit, so I had to order a new one. In the intervening years they have greatly reduced the thickness of these little lights, so I had to make a new mounting bracket out of stuff I had laying around. You can also just barely see the O-ring I added to hopefully keep rain from running down around the light and getting into the rudder:

The new beacon light also comes with a small LED driver as part of the cable assembly. I added a connector so I can remove the top fairing, and attached the LED driver to the rudder using an adel clamp and one of the nutplates I had fortuitously decided to install in the top rib tooling holes:

I did a very minor amount of surface work on the bottom fairing – I'll let the painter take care of the rest – and shot a coat of grey primer just to make it look nicer and to make it match the top fairing:

I made a little wiring harness that lives inside the bottom of the rudder, connecting the fuselage to the beacon light and the nav/strobe light. Although this shouldn't move around much, I used snake skin here too since unfinished fiberglass is very abrasive:

I installed both fairings and mounted the rudder on the airplane with the proper hardware, after struggling to avoid dropping any fasteners down into the bottom of the rudder. The final full-up test confirmed that all the lights are working, which was gratifying to see:

The nav/strobe light is a Whelen 550 unit, which fits great into an RV rudder. I attached it to the mounting plate with some stainless screws from the hardware store:

I got the rudder cables hooked up, with cotter pins installed, before I ran out of steam and out of weekend:

Rudder fit fiddling

Sunday, October 2nd, 2022

Working on a number of annoying issues related to how the rudder fits on the vertical stabilizer…

First, with the hinge bearings set to the correct length, the forward face of the counterbalance horn is too close to the vertical stabilizer skin. Not exactly surprising, since I had to deal with the same issue on the elevators, and the fix is the same: just make it fit.

I marked the desired cutout, and clamped a piece of steel to the vertical stabilizer to give me a straight edge to file to. Then I just went at it with a series of files of various shapes.

Result – an even gap all around (despite how it looks in this photo). Not too bad, I'm happy enough with this:

This mini-project I spent many hours on, but forgot to document until I was finished. Between my original rudder stops being slightly too short, and the new rudder perhaps being slightly different, I ended up with a little too much rudder travel – the rudder was able to get too close to the inboard edges of the elevators. I didn't want to remake the rudder stops, since drilling out and replacing the existing rivets would likely have damaged the fuselage, in addition to just being difficult generally. Van's support suggested a couple different fixes, and this is the one I chose – supplemental rudder stop extenders screwed to the existing stops. This is actually similar to what they did with the factory RV-9A, which I confirmed via inspection the last time I was up at Aurora. The screw heads (AN858-8xx) are on the bottom to avoid interference with the rudder cables.

These weren't difficult to fabricate, just tedious – install, test, mark, remove, file, repeat. And if you file off a few thousandths too many – throw it away and start over. I think I ended up making four of these to get two that would work. I sure wish the RV rudder stop design was field-adjustable like a Cessna. To make the process a little easier, I lifted the tailwheel onto my little work table… sketchy to be sure, but easier than laying on the hangar floor.

Then there was some rubbing between the rudder and the vertical stabilizer skin when the rudder was deflected all the way to the left. I shaved the VS skin slightly with a vixen file until the interference was eliminated, although the gap here is still pretty small. I may need to revisit this before the airplane is painted, but at this point that's a problem for the far future.

RV-14 rudder

Monday, September 19th, 2022

My old rudder didn't make the cross-country move to our new house, partly due to damage during packing (my fault) and partly because I was still unhappy with the trailing edge (also my fault). So, finding myself with an RV-7 lacking a rudder, I needed to build another one. But this time, instead of building another RV-7 rudder – which is actually an RV-9 rudder – I decided to build an RV-14 rudder. Confused yet?

The original RV-7 rudder design was similar to the RV-8, with a folded trailing edge just like the elevators. Then later – for aerodynamic reasons that were, depending on who you ask, maybe necessary and maybe not – the kit was changed to use the same rudder as the RV-9. That rudder (i.e. the one I originally built) was bigger, had thinner skins, and a different method of construction involving the dreaded trailing edge wedge. Then much later the RV-14 was introduced, which presumably had yet another new rudder design, or so I thought. However, one day while perusing the RV-14 plans, I saw that a lot of the part numbers were similar or identical to the RV-7/9 rudder, plus some internal structural changes that would seem to make the RV-14 rudder a stronger and better design. So I decided to order the parts to build an RV-14 rudder and see if my hypothesis that it would fit on an RV-7 was correct.

First things first… I've been working on Systems tasks for so long that I almost forgot how much of your time building the sheet metal parts is spent on deburring!

Unlike the RV-7/9 rudder, whose skin stiffeners are simply left floating and not connected to anything, this rudder has a proper internal structure – essentially a set of built-up ribs:

I cut the proper angle (about 5° if I recall correctly) on a piece of scrap wood, to act as a guide for drilling the trailing edge:

With my table saw, I cut the same angle from the edge of a 2×4, and used it on the drill press to drill a series of angled #40 holes in a piece of hardware-store aluminum angle. The hole pattern has the same 1" spacing as the trailing edge.

I used the guide block to hold the drill at the correct angle while match-drilling the skins to the trailing edge wedge, and clecoed the trailing edge to the guide angle as I went. The idea is to always use the guide angle to keep the trailing edge perfectly straight until it is riveted:

More deburring, and then I riveted together the spar, counterbalance rib, and the collection of parts at the bottom of the rudder:

To countersink the trailing edge wedge I used the Cleaveland jig that's made for this purpose. It worked great – I only wish it was slightly longer, as it was very close to being too short to clamp to my large drill press table. The countersink cage is temporarily safety-wired to the drill press quill to stop it from spinning:

I used an edge-rolling tool to slightly break the edges of the trailing edge, and clecoed everything back together with the guide angle to check the fit. Looking nice and straight so far:

Back-riveting the stiffeners to the skins. You may notice I decided not to apply anything to the inside of the rudder other than fingerprints… I'm trying to get this airplane done and I didn't want to spend time messing around with primer. If it's good enough for Cessna it's good enough for my RV. (actually I did prime one part, the rudder horn which is made of 6061 aluminum)

In the time I've been away from control-surface-building, Van's has switched their recommended trailing edge bonding process from Proseal to VHB tape. Fair enough, should be less to clean up.

I cleaned and scuffed the mating surfaces, peeled the tape backing from one side of the trailing edge, stuck it to the skin, and left it all clecoed to the guide angle overnight to let it cure fully:

At this point the assembly process diverges from the RV-7/9 rudder – they have you riveting the internal stiffeners and clips together, while progressively bonding the remaining skin to the trailing edge. It pays to have a helper for this step. And yes, there are two rivet holes at the aft end of each pair of stiffeners, but the plans tell you to rivet only one of them.

My only modification to the rudder design was to add a 1/4" lighting conduit for the top light. It's held in place with a few lightweight clips I made from scrap aluminum, with blobs of RTV in strategic places to stop it from rubbing.

The rudder counterweight is the same design, except they've replaced the inaccessible nuts with a pair of nutplates. This is a good improvement since you can now re-torque the counterweight mounting screws from the outside if you ever need to.

Everything here is riveted except for the leading and trailing edges – time for the hard part:

I polished up my steel back riveting angle and used it to partially set all the trailing edge rivets, following the pattern suggested in the plans. So far so good:

This is the point where things started to go less well. I decided I'd use the Cleaveland trailing edge squeezer set I bought to finish setting the rivets… in retrospect I would have gotten better results if I'd just continued back riveting. I have now tried to squeeze trailing edge rivets on two different rudders, and I just cannot seem to get the results I want.

The angle of this photo makes the trailing edge look much worse than it actually is – it really only varies about ± 0.040" over its length, which is less than half the allowed maximum amount. And if you're standing more than two feet away it looks perfectly straight. But darn it, I wanted it to be perfectly straight. If I ever have to do one of these wedge-type trailing edges again, I hereby resolve to leave the squeezer in the toolbox and do it all on the back rivet angle.

I used the J-hook method and a piece of 1" OD conduit to roll the leading edges together. Happily, the required spacing for the hooks matched the hole pattern on my woodworking assembly table, so I didn't even have to come up with a way to mount the hooks. I used Gorilla tape to attach the pipe to the skin and just cranked away. Once the hooks started getting in the way, I removed them and finished the bends by hand and by eye.

In retrospect it might have been better to use 1 1/4" OD pipe for the middle and lower sections, as the 1" diameter pipe seemed to produce a bend that was slightly too sharp. But I still got the skins to fit together with just a little finger pressure:

Pop rivets in the leading edge, and now the RV-14 rudder is done. Nothing to do next but see if it fits.

Here's proof – yes, an RV-14 rudder does fit on an RV-7. I strongly believed all along that it would, but it was still nice to see it slot right into place.

I still have some messing around to do with the fit of tip fairings and the and the geometry of the rudder stops, but those are specific to my airplane and aren't related to the type of rudder I built.

Overall I'm happy with the outcome, although I wish I'd been able to achieve a perfect trailing edge. I think the original RV-8 rudder would have have made it easier to achieve this, and if I had it to do all over yet again I might go that direction. Still, I'm happy to have the internal structural improvements from the RV-14, as the new rudder is obviously better-engineered than the old ones.

Red beacon

Sunday, October 28th, 2012

I've been planning to put some kind of red flashing ground-recognition beacon on the airplane all along, and this weekend I finally got around to making it happen. For years I've been pondering exactly what kind of beacon I need and where to mount it – see here and here for details of previous plans that didn't get completed, plus thoughts on red beacons in general. What ended up working in my favor is the fact that, while I was trying to figure out what to do, the state of the art in LED technology has advanced to the point where it now makes more sense to use LEDs rather than xenon strobes or halogen flashers for this application.

The particular unit I picked is the Vertex LED lighthead by Whelen. These guys are known in aviation circles for making certified strobes and nav lights, but they make lots of automotive products too. This one is designed to work as a warning light for a cop car or other emergency vehicle, but it happens to also be the perfect size for an airplane too. Here's a photo I grabbed from the internet since I forgot to take a "before" shot prior to getting started:

I played with various mounting positions until I decided which one I liked best – it turned out to be the top of the tail, just like on your grandpa's Cessna. Then I got out the rudder cap and started cutting away at it with a unibit and Dremel tool.

The light will be held in place by two little pieces of scrap angle that will attach to the inside of the rudder cap.

A view from the bottom side. The beacon heatsink just fits into the widest point of the rudder cap.

That has the added advantage of putting the beacon about halfway back from the leading edge of the vertical stabilizer – farther back than on a Cessna – where the light shining directly forward will be blocked instead of getting into the cockpit and annoying me by glaring off the instrument panel.

The circuit board inside the beacon is flush with the top of the rudder cap. Now we just need to do something about the exposed shoulders of the heatsink sticking out into the breeze.

I covered the beacon with saran wrap and then laid up several plies of glass tape over it in a smooth shape:

It's a little late in the season to be doing fiberglass work – i.e. the temperature is a bit low in the garage – but for small projects you can cheat and use a heat lamp to get the resin to cure in a reasonable amount of time.

After sanding the initial layup, I installed the beacon again and followed up with a flox/cabosil mixture to build up the contour and give me a nice sharp edge around the opening for the lens.

I also laid up some flox inside the rudder cap to give the body of the beacon a nice solid shoulder to sit on, as well as thickening up the inside of the lens opening to avoid having a knife edge there.

After letting that cure and sanding it back down, the general shape of the "bump" for the beacon was basically done.

I applied one more coat of dry micro with a squeegee to fill in the low spots, then sanded it smooth.

A quick spray of primer dressed it right up. I'm quite happy with how the shape turned out. There are some small surface imperfections but I'll let the painter deal with those.

The beacon lens is very low profile. I still need to countersink the mounting holes in the sides, but that can wait until I get back the drawer full of #4 tinnerman washers I loaned out.

Now that it's all sanded smooth and blended in, the slight swell for the beacon is hardly noticeable:

What's that, you say you want to see my new rudder-mounted ground recognition beacon in operation? Very well:

It's hard to properly capture with the camera, but trust me, this thing is plenty bright.

Empennage fairings part IV

Wednesday, February 21st, 2007

One more application of filler to the rudder cap – hopefully the last one, save for the inevitable pinhole filling. I'm really happy with the way the rudder cap has turned out.

I'm much less happy with the elevator tip I did the other day. I will probably throw this away and start over with a new one from Van's. The stupid counterweight is totally in the way, and it's looking less likely with every try that I'll be able to have removable tips on the elevators. Darn.

Here's the other, mostly untouched tip fairing, just to illustrate the situation.

Once again, I'm really glad the whole airplane isn't made of this crap.