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.
Playing with the look
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.
A nearby Cruzer builder recommends videos of builders and their projects in progress. I’m turning into a YouTube junkie.
Zip ties, duct tape and wire hangers
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.
Speaking of which, the four methods of countersinking
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.
Rudder is riveted. Mostly.
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.
It’s time to pull some rivets. And make a few mistakes.
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?
Let the drilling begin
I finally broke the seal today and started assembling the rudder from the pre-drilled kit.
It was a slow start, as I needed to get up to speed with the Renton Technical College instructor whose shop I have the pleasure of using as I toy with the idea of building a plane. As you’d expect from a shop that prepares Boeing assemblers, it has all of the tools I’ll need — pneumatic drills and rivet pullers; air chucks at every workstation; all of the right drill bits, tool chests full of files, fussy little clamps, deburring tools, machinist’s rules, well-organized clecos, cleco pliers, and everything else you might need to assemble an aluminum airplane. For a sloppy-workbench guy like me it’s a dream!
I’m starting with the skeleton of the rudder. In the course of an hour I got a groove on assembling the spar, first by cleaning off labels and markings off of the pieces, which all have been cut, bent and mostly drilled at the factory.
So far about two-thirds of the work is done to clean, deburr and drill the holes needed to attach the doublers to the spar. It’s super-easy because the spar already has the holes, it’s just a matter of putting in the doubler holes and enlarging holes in the assembled pieces to the final size. Honestly, as a kid I made more complicated plastic models.
I won’t be back on the project until Wednesday. Next week’s goal is to see if I can complete initial assembly of the rudder skeleton in preparation for adding corrosion protection and starting to pull rivets. I’m guessing that dry-assembly work will take no more than several hours.
A friend on the Facebook Pages version of this blog loved the STOL video I posted earlier. Here’s another that shows the incredible short-takeoff performance of these planes.
Not to confuse matters, the version of the CH 750 family that interests me is the cross-country type. But some builders, including Jonathan Fay, have modified their Cruzers as excellent back-country planes that have great short-takeoff performance, as well. Without much sacrifice of a higher cruising speed.
What is a Zenith 750 Cruzer?
It’s an all-metal, two-seat aircraft that meets the requirements of the sport pilot license. The Cruzer is the cross-country member of the CH 750 family, which includes a STOL “off-airport” plane and a stretch “super duty” version.
|Stall Speed||34 knots|
|Never Exceed Speed||126 knots|
|Rate of Climb||1200 fpm|
|Range||450 nautical miles|
|Empty Weight||780 lbs|
|Gross Weight (LSA)||1320 lbs|
|Useful Load (LSA)||540 lbs|
|Design Gross Weight||1440 lbs|
|Design Useful Load||660 lbs|
|Load Factor||+6/-3 g|
|Take-off Roll||350 ft|
|Landing Roll||350 ft|