The basics-of-machining class ended today, and I had a chance to do some work on a lathe. Renton Tech has a lot of equipment that dates back to its start as a training center for Boeing’s B-29 plant in Renton. The lathe I worked on was some of that gear.
I was learning how to handle a four-jaw chuck, which is kind of a pain. Nonetheless, I was able to get my work dialed in within a tolerance of a tenth, or .0001″. Not that I’m slick or anything, but that was 10 times more accurate than the work you would do with this lathe. It’s pretty amazing to see the degree of accuracy that is possible with tools from 80 years ago.
There’s been no new progress since completing the first take at a rudder and getting empennage parts delivered. Now that I’ve wrapped up machinist training it’s time to focus on nailing the checkride and making a few changes in the garage to make room for airplane stuff.
A truck showed up last week and dropped off a big box of parts for the empennage. This week I’m getting the garage prepped for storing parts and the finished product I’ll be assembling in the aviation workshop at Renton Technical College.
I sometimes spend time I should be using to pull rivets thinking about the appearance of the final product. Here’s the latest concept, a military/not-military design of the Cascadian Air Service.
It’s not apparent from the illustration that design would use decals on polished aluminum. Stripes are 4 inches high, and the N numbers are 3 inches high. The Renton Technical College logo is 5 inches high. Squatch? 12 inches.
There’s a brief but useful piece in this month’s Sport Aviation (p. 102) with tips on securing engine compartment wiring with zip ties. I had never heard of GripLockTies, designed specifically for use with electrical wiring. Noted for future reference.
I’m driving only blind rivets, which means they’re inserted into a hole, then pulled into shape using a tool on one side of the rivets — commonly called “pop” rivets. On the way to looking up something else, this excellent old-school instructional showed up on how to drive countersunk rivets, that is, rivets that are flush with the skin of the airplane, eliminating a source of drag at high speed. Watching it, I wonder how any homebuilder ever had the time to countersink their rivets.
Work progressed so quickly this week that I barely had time to take photos.
All of the pieces are now firmly attached, and all but a half-dozen or so holes are still waiting for rivets. I spent a fair amount of time drilling out rivets in a few spots where I prematurely went to town along the rivet line for the piano hinge, which I’m attaching in the photo.
The gap between the end of the top cap and the back of the trailing edge seems weird. Here’s what that looks like:
I messed around trying to close that gap as much as possible without distorting the bend. The top cap is about 5 mm forward of the position specified in the plans, but there’s no way to move it back farther without trimming off material and/or bending the curve. Based on a review of a lot of photos online of Cruzer rudders, it looks it is what it is. Hopefully there will be some insights in builders’ forum, but I believe I’ve done this correctly. It seems weird to leave an gap like that, even on the trailing edge, so a little bit of silicone might close it up in the final product.
I’ll still be drilling out some rivets that didn’t get seated properly, as noted earlier. I’ve actually run out so have ordered more via Aircraft Spruce. The concave rivet gun nose I was using may be close-but-no-cigar, and that’s what caused circles around many of the rivets and not-fully-seated rivets. With the Official Zenith riveter and noses in hand there was no problem at all getting the rivets in cleanly. Lesson learned.
Speaking of rivet guns, I picked up a very useful tool that you see in the first photo. It lets you use a drill to smoothly pull blind rivets. This works great, and avoid the “bounce” from pulling out a mandrel with a hand or pneumatic riveter. I love the air tools that I get to use at Tech, but there are some advantages to the smooth action of the drill attachment over the fancier tools. A hundred bucks well-spent.
After a little rivet revision next week I’m planning to move on to the polishing stage with some Nuvite purchased this week and a cheap random-orbit polisher on order. The goal is to see how closely it’s possible to get to a mirror finish.
Considering all of the lessons learned building this piece, including some minor scratches and bangs from driving the part back-and-forth from Tech, I went ahead and included the rudder parts in my order this week for the rest of the empennage. The rudder kit has been a great tool for learning, and the skills and tricks I’ve been learning will be very useful for making airplane parts as accurately as reasonably possible.
I had a busy week on the rudder. The skeleton went together quickly last week, with all mating surfaces coated with an anti-corrosion film (Cortec) and the bits reassembled for riveting.
On Wednesday riveting began, with some missteps. I got carried away and put a half-dozen rivets in the skeleton where they won’t supposed to go yet, so got some experience in drilling out blind rivets without enlarging the hole. That turned out to be easier than I had expected. Everything aligned as expected, and in a couple hours every rivet was in its place on the skeleton and I was ready to put on the skin.
Thursday was a day of great progress. The skin went on with little difficulty — it’s a pleasure to work on an airplane kit where the vast majority of holes are drilled to size and ready for assembly. It didn’t take long to get the skin in place and cleco’d up.
One of the pleasures of this project is where I get to work on it. I’m taking classes in the aerospace program at Renton Technical College, this quarter learning precision machining and related skills like inspection. As part of that, I have access to an incredibly well-equipped aviation workshop, which I’ll detail a bit more in another post. I also have the benefit of working under the instruction of Vincent Phillips McLellan, who founded and runs the aerospace program. He’s given invaluable advice in how to attach the skin to keep it as flat and straight as possible, how to correctly use the tools, and many other skills. A lot of the reason I have confidence in what I’m doing (more on that later) is being able to draw on these resources.
On Friday came the fun part, pulling rivets on the skin. In short time I had the end cap assembled and cleco’d in, and the rudder horn in place. At Vince’s recommendation I’ve started at the trailing edge, in the middle of the rudder, and worked my way out and up. Shop lighting makes the skin exaggerates the waves between the ribs — outdoors and in regular lighting it’s straight. I’m about a third of the way through riveting, but will need to do a little remediation first.
Now, for some mistakes. Putting on the top cap assembly I inadvertently drilled a hole straight through both sides of the skin. After cursing, I followed the advice of the Zenith assembly manual — if you put a hole in the wrong place, just put in a rivet and don’t sweat it. In this case, the extra rivet is at the top a tall rudder, in a place where it will be inconspicuous. And lesson learned.
A bigger concern to me is getting the rivets in true. After wrapping up for the day I did a pretty thorough inspection of the rivets I’ve placed so far on the skin. There are a lot that aren’t sitting as flat as I’d like. The manual says it’s not seated correctly if you can put a fingernail under the rivet, and probably a quarter of what I’ve pulled so far fails the fingernail test.
I’ll be spending the weekend reviewing my Homebuilder Help videos and assembly manual to figure out what I’m doing wrong, and marking the rivets that need a do-over. On Monday I’ll get some help from Vince and starting drilling out some rivets.
Now I’m started to understand why Zenith includes the rudder in the tail kit, whether or not you’ve already built the rudder starter kit. Depending on how this piece turns out, it’s possible I’ll build a second rudder to get my work as high-quality as possible. Hey, it’s a learning process, right?
I had the last lesson before the checkride today, and the instructor and I agreed that I’m not there yet. It’s not that the maneuvers elude me — flying the plane is not an issue — it’s assembling the specific maneuvers within reasonably tight tolerances with a consistency that remains a bit of a pickle.
I’ve scheduled three lessons before the next opportunity for the checkride, and will be working like mad to align my abilities to match the checklist. I never had confidence that I was prepared for Tuesday’s test, but kept working toward that as a goal, so I’m not disappointed. Lindy willing these two (no, three) tactics will help me get there by the end of the month:
1) Fully utilizing the checklist 2) Talking through each step in the checklist 3) Using the checklist
Perhaps there will be more promising news this week on the assembling-the-rudder front.