Archive for the ‘Empennage’ Category

Connected elevator trim

Saturday, May 20th, 2023

I pulled the elevator trim servo and associated parts out of storage so I could finish the pitch trim installation. The wiring here requires some kind of connector so you can remove the servo and/or the entire elevator, and furthermore whatever connector you use has to be able to pass through the 7/16" ID bushing in the elevator spar. Taking a page from RC aircraft, I decided to use a model airplane servo connector for the trim position wires, and an XT30 power connector for the servo motor itself. These I soldered to the wire pigtail and secured with heatshrink:

The above job was pretty easy since I was able to do it on my spacious, well-lit workbench using my good soldering station. By contrast, the mating connectors on the airplane were more of a pain since I had to use my crappy old Radio Shack portable iron while laying awkwardly on the ground under the tail. If I was smarter I would have done this when I was originally fabricating the wiring harness for the tail, but I clearly wasn't thinking far enough ahead.

After testing to make sure it was correct, I bundled up all this wiring and stuffed it into the elevator along with the trim servo. The power wires are shielded in accordance with the G3X manual, and the shield is grounded to the airframe using one of the servo mounting screws:

I don't have the cockpit trim controls installed yet, but I am able to run the trim by selectively grounding the individual loose wires that will eventually go to the stick grip switches. I did some minor fiddling with the trim linkage until I had roughly equal travel up and down, a little over 22° each way. The plans say this should be "25-35 degrees maximum", which isn't particularly clear or helpful. If I need more or less trim at some point down the road, I can always come back and adjust this.

I installed the clevis and cotter pin, so the elevator trim is properly connected now in all senses:

I did a quick calibration of the G3X elevator trim gauge, and happily everything seems to be working electrically:

So that's one more flight control surface finished, a small but satisfying milestone:

Empennage fairing fine-tuning

Monday, May 8th, 2023

While waiting on some parts to arrive I spent a weekend on one of the million little jobs on my seemingly never-shrinking todo list… improving the fit of the empennage fairing.

Maybe they've improved the quality of these parts in recent times, but the fit of my empennage fairing has only ever been "just okay". Look at that wavy gap along the top seam where it meets the vertical stabilizer:

I also have some problems at the leading edge of the horizontal stabilizer on one side:

I marked the areas that needed building up (visible in the photos above) and laid down a protective layer of clear tape over the metal parts. Then I mixed up batch of filler (epoxy, flox, microballoons, and cabosil) which I spread over the inside face of the fairing before I screwed it in place.

The FAA wants me to show my face in the build log periodically, so here I am declaring that sanding fiberglass is a messy job.

I repeated the above process a couple times before I was satisfied with the results. Here's the result after sanding to 220 and shooting with a primer coat just to gauge the finish. It's not perfect but it looks a lot better:

Still a micro-gap in places along the top, but the overall result of this effort is a much nicer fit in general. Everything else I will leave for the professional painter:

Tailwheel upgrades & rigging

Wednesday, February 8th, 2023

I noticed the steel tailwheel spring was looking a bit ragged, so I pulled it off the fuselage for reconditioning prior to hooking up the tailwheel controls. With the wheel removed, I propped up the fuselage on a small work table with plenty of cushioning:

I scoured off the rust and old paint with a scotchbrite pad, and masked off the ends where necessary:

After a coat of primer and two coats of Rustoleum matte black, it's ready to go back to work:

While I had it all pulled apart, I decided to upgrade the wheel itself to a Flyboy Accessories unit with sealed ball bearings, so no more greasing will be required. I also picked up one of their extended axle kits, to give the towbar something more substantial to grab onto. Everything here is very nicely made:

With the help of a helpful forum thread, I put together a collection of hardware for the tailwheel steering controls that will allow me to omit the terrible wire clips, which tend to break and are generally a pain. I retained the stock steering chains and compression springs, but substituted better hardware in place of the clips.

In the center of this picture are some Maillon Rapide Links (part number 7350SF-1/8), a pair of AN42B-4A eye bolts, and some AN115-21 cable shackles. And at the bottom, another upgraded Flyboy Accessories part – a tailwheel steering arm with a lug for a tiedown rope.

Here's how it all looks when installed:

At the forward end, eye bolts and removable links replace the chain clips. These links are rated for a working load of 440 pounds, well in excess of what the chain itself will bear, and are Loctited closed.

At the back, the cable shackles connect the springs to the steering arm. I had to expand the inner dimension of the shackles slightly to fit over the arm, but they are malleable enough that this wasn't difficult.

I may need to adjust the tightness of the chains in the future – right now they are slightly slack when the weight is off the wheel – but this should be good enough for now.

Horizontal stabilizer fairings again

Sunday, November 6th, 2022

While working on the rudder fit and the vertical stabilizer fairing, I decided to re-check the clearance between the elevators and the horizontal stabilizer tip fairings. I was surprised to find that I had inadequate clearance (less than the minimum 1/8") on the starboard side. Not sure what happened there, perhaps I had the elevator hinge bearings adjusted differently during fitting versus how they are installed now.

I sanded the fairing to fix the clearance issue, which resulted in me sanding right through the epoxy layer and into the balsa wood underneath. So something needed to be done about that:

I had been regretting using balsa anyway, so I carved it all out and replaced it with fiberglass just like I did with the vertical stabilizer fairing. Of course I had to do both sides so they'd be identical, otherwise I wouldn't be able to sleep at night. The process here was identical to that used for the VS fairing: popsicle stick supports, glass panel bonded with flox bead, additional glass layer on the inside. I promise it turned out nice even though this in-progress picture makes it look terrible:

I sprayed all these fairings with several coats of SEM high-build primer, then sanded lightly with 320 grit. I like this stuff – it's expensive but it gives a decent result, and it comes in a handy spray can.

As before, I followed up with a cosmetic coat of 7220 and installed the fairings on the plane. And just as before, the results are not perfect but close enough that I'm happy for now. The pro painter will have a few pinholes to fill, but the shape is correct and the clearance problems are gone:

So now all the fairings on the tail of the airplane are technically done, although I still want to work on improving the fit of the empennage fairing. But that will have to wait for next year's fiberglass season – it's now too cold and rainy for that kind of work.

Vertical stabilizer fairing

Sunday, November 6th, 2022

With the rudder finished and installed on the airplane, I'm now able to fit the vertical stabilizer fairing. Here it is clecoed to the skin:

Unfortunately the shapes of the vertical stabilizer and rudder fairings don't match at all. Given that Van's can produce metal parts with holes that align perfectly, I'm not sure why their fiberglass parts are so troublesome – you'd think they'd be able to turn out properly-sized fairings in some kind of CNC-produced mold. But anyway, this mismatch needs to get fixed:

The back face of the fairing also needs to be closed up with something. I decided to use the method currently given in the RV-14 plans, and laid up three plies of glass over a flat piece of aluminum (visible at left). Oh fiberglass mess, how I have not missed you.

While that was curing, I cut some popsicle sticks to the correct size and super-glued them inside the fairing, flush with the edge. These will keep the fairing from collapsing when it's removed from the plane:

I ended up with a thin, flat sheet of stiff plastic, which I marked and trimmed slightly oversize:

Then I bonded it to the fairing with a flox bead, and an additional glass layer on the inside. The RV-14 plans tell you to do this step on the airplane, which seems like it would be messy; the popsicle sticks allow you to do this on the workbench where you can control the mess easier. I left it to cure overnight under an incandescent lamp due to the arrival of winter weather here in the northwest:

After curing I sanded the edges flush, and the result is pretty good. The popsicle sticks are now sandwiched between glass layers, which will prevent them from soaking up water and swelling:

The little tongue at the bottom took a few iterations to sand to the right shape:

Making the fairing structurally complete is easy enough – the hard part is making it look nice. I protected the vertical stabilizer with tape, stuck in a piece of vinyl-covered aluminum as a divider, and slathered on the first application of micro filler:

After sanding most of it off, the shape is starting to improve… note the built-up areas at the nose as well as on top:

Another round to fill the low spots:

Sanding flush with the skin:

Here's the finished result, which looks terrible visually but is now the correct shape and smoothed to 320 grit:

I did the usual thing with nutplates mounted on aluminum strips:

After a few coats of high-build primer, more sanding, and a final cosmetic coat of 7220, this is the finished result. Not perfect, but good enough for now. Eventually I'll have a pro painter take care of the last 10% and make it look really nice.