Rudder Pedals and Elevator Brackets

I've been making small amounts of progress here and there. I'd been putting off the rudder pedal swingarms, because I wanted them offset to work with the offset seating. In order to generate more shoulder room, the pilot's seat will sit 3" forward of the pax seat. That doesn't sound like much, but it causes shoulders to overlap rather than push against, which makes things much more comfortable. My shop really isn't set up for metal work, so cutting, grinding, and jigging this 4130 has been a challenge.

This was my first jig attempt, and while I did get it to work well enough, it was a huge hassle. The second jig turned out a lot better, and was much easier to build.

These were sent off to be welded, and are now ready to be cleaned and painted. I'll be cleaning and painting the steel parts of the control sticks assembly at the same time.

While I was set up for it, I went ahead and cut my elevator pushrods to length. I have a 5/8" rod from my control sticks to a T lever, which transitions to cables, which run back to another T lever and a 3/8" rod to the elevator.

The pushrods are not yet connected to the rod ends in the picture, but that's not an oversight. I wanted to hook everything up before drilling holes and riveting, to make sure the length was right!

The main reason for my slow progress has been my own work in adjusting existing designs to fit my needs. Specifically the brackets/T-lever assemblies. It takes me a while to fabricate the metal bits, so I try to make absolutely certain that I don't have to re-make any parts due to unforeseen problems.  A few of my sketches are below, showing the bracket and T-lever setups.

This is a 4x scale drawing of my forward T-lever setup. From left to right: sintered bronze (SB) bushing, 3/4" aluminum spacer, aluminum T-lever, SB bushing inside the T-lever, 3/4" spacer, SB bushing. I have SB bushings on both ends, so that's what will contact the bracket, and I have a SB bushing through the actual lever itself to facilitate smooth rotation.

Next is a 1:1 drawing of the rear T-lever, which also incorporates an arm for counterbalancing the elevator. I will preempt this drawing by saying, I did not use this design. Rather, I adjusted it with spacers.

And here's a 4x drawing of the center of the assembly, or the pivot point:

From left to right: SB bushing, T-lever, 3/4" square tubing for counterbalance, 1/4" angle, SB bushing. The problem with this design is, the cables will rub the counterbalance arm when it pivots. As a result, I'll be adding a spacer between the T-lever and the 3/4" square tubing. 

This gives you a better view of the problem. The second and fourth "nut" from the top will have cables attached, and anytime the elevator isn't slightly up the counterbalance will intersect one of the cables. Adding an 1/8" spacer to the pivot point and the pushrod point should give me enough clearance.... or maybe 1/4". I'll be mocking this up *not* in the plane, to make sure I get it right, before I start drilling holes in the wrong spots. Anyway, I hope to have most of this finished after this weekend. 

Frustration

I've been waiting for a hardware order to come so I could finish putting my control sticks together for the last time. Unfortunately, once again I seem to have ordered the wrong length bolts. However, this time I have enough of various sizes to put together a formula, so (hopefully?) I'll get the right stuff every time from now on. The problem is as follows:

When a person wants to order AN hardware, they have two numbers and two yes/no options for standard bolts. The yes/no options are for a drilled head (for safety wiring) and a drilled shank (for using a cotter pin and a castellated nut.) The first number denotes the diameter, and is in sixteenths of an inch. AN3 is 3/16, AN4 is 4/16, (¼, if you will) so on and so forth. Nice and easy. The second number denotes the length, and the only way to know what it stands for is to have a lookup table. The good news is, lookup tables are readily available online. The bad news is, they only give you two lengths, and those are NOT ENOUGH.

The first number I'll address is *nominal* length. This is the total length of the bolt, (minus the head) which is important to know. Obviously you want to make sure the bolt is long enough to get through the material it's holding with enough room to spare for washer(s) and a nut. In addition, it is sometimes important to know how far the bolt will stick out beyond the nut (as you'll see when I build my control-stick-pushrod-to-cables-bracket.)

"But Matt," the reader may ask, "Why don't you just order a bolt that's a little longer than you think you'll need? You can always just grind it off if the extra length gets in the way." Oh, that it were that simple. Unfortunately, there is another number that's just as important, and it makes precision quite necessary. It's called the *grip* length.

Grip length is the length of the bolt that is *not* threaded. That's right, there's a *lot* of bolt that isn't threaded. In fact, on a 3/16" bolt, only a little over ⅜" is threaded, no matter how long the bolt is. Even that isn't so bad, though; just pick a bolt that has a slightly shorter grip length than the material you're bolting through. Unless, of course, you need a castellated nut with a cotter pin.

Castellated nuts and cotter pins are used when it would be very, very bad for something to come apart. On this plane, the main things I'll have this type of hardware on are the control systems, since they're very important, and they'll be in motion pretty constantly. It's a great system, and pretty hard to mess up. If you get the right length hardware. The length, however, is determined by adding the material thickness to the amount of castellated nut that is below the cotter pin, then subtracting the distance the drilled hole in the bolt is from the end of the threaded portion. This would be feasible, except NONE of these variables are published... at least, not anywhere I found.

If you're still keeping up, you've figured out that neither nominal nor grip length will help with this problem. Therefore, I took some measurements against several different length bolts, both 3/16 and ¼" diameter, and wrote a spreadsheet that gives estimated minimum and maximum material thickness along with nominal and grip length. I've checked it against all of the hardware I have, and it all matches up for me. I'm publishing it here in hopes that I can save some other poor homebuilder a few weeks of guessing and frustration, not to mention extra shipping costs.  Currently it only features AN3 and AN4 drilled bolts, but if I get data from other diameters I'll add that to it.

*The lengths listed for max and minimum material thickness are based on the use of an AN380-2-3 cotter pin. Minimum thickness was based on my personal comfort level of how much bolt needed to stick up and grap the cotter pin, and maximum thickness was taken as soon as it was possible to push the cotter pin through the hole.

**I should mention that I used two different sized bolts for each diameter, and noticed ~.002 inch variations between same diameter bolts. I decided that was an acceptable variation to assume standard hole placement was used throughout the entire lineup of same diameter bolts. However, I do not claim to have tested each length, and therefore my numbers may not be correct in every instance. Your mileage may vary.

Permalink: https://drive.google.com/open?id=0BzhVbe_jC3gDQ0ZoTm96MHVFZkU

Instrument Panel

I've been waiting for various hardware and tubing, but I haven't been twiddling my thumbs. I'm slowly acquiring the instruments for my plane, and I realized that having a plan in place would make picking up the right instruments a whole lot easier. I spent a few evenings trying to come up with panel arrangements using a photo editor, but I just couldn't get a feel for how it'd look in real life. So I had my local print shop print out a full-scale template of my instrument panel, overlaid with a ¼" grid. I then printed out full-sized instruments, as well as two glass screens I intend to incorporate. I cut all of this out, then used contact paper to make them more wear-resistant. What I ended up with was a completely customizable panel that shows me exactly how large everything will be in the plane. For some reason, this is a lot easier for the spatial reasoning part of my brain to work with. Here's a picture I took, not of a well thought-out layout, but just a quick proof of concept. (It's super blurry because of crummy lighting; the graphics are actually quite crisp. :D)

Control Sticks (Part 6)

Continued from Control Sticks (Part 5)
I finished cutting, shaping, and drilling the aluminum brackets, as well as the nylon bearing surfaces. I was very careful to make sure there would be no slop in the system when I was drilling the holes. Somehow, once again, I managed to order the wrong size hardware, so everything is temporarily assembled with other bolts I had on hand. I'm going to write up a list, or maybe a spreadsheet, that lays out what length bolt is ideal for various depths of material, because I can't seem to get it right. I test assembled everything on my workbench, and marked my layout so I could transfer the brackets to the plane.

Next I marked on the front spar where I wanted the brackets to be, lined them up and clamped them, and started drilling holes. I drilled one hole at a time, making sure everything lined up before committing to another hole. I really didn't wanna screw this up!

Everything in place, at least temporarily:

As you can see, I left the actual sticks long because I wasn't sure what length I'd want. I'm going to have to give them both a slight bend so they'll have enough throw to clear the front spar, whilst remaining far enough forward to be comfortable. I'll have to disassemble when the correct hardware arrives, and I may paint everything for corrosion resistance. I also need to redo the cables - only one of the three cables has a turnbuckle, which means if the cables ever stretched or needed adjustment, you'd have a heck of a time getting things realigned. Regardless, I'm much happier with this setup - lower profile, much better geometry, and working on this gave me an idea for a really simplistic aileron trim that'd be pretty easy to implement.

Control Sticks (Part 5)

Continued from Control Sticks (Part 4)
I got my brackets and sticks back from the welder today. I forgot to take a picture of the bracket, but this is how I fitted and attached the aluminum "fingers" to the sticks for welding.

I cut a square wooden peg to match the OD of the aluminum tube, drilled a hole where the aileron cable connection will be, then chucked it up in my lathe and turned the other end down to the ID. I turned far enough along the peg to set the depth of my jig.

This is the jig inserted into the tube, with the fingers already welded on. A small C-clamp held the fingers to the tube for tack welding, and then was removed for the full passes.

I realized after I got these sticks back that I had forgotten to mark where I needed the other set of holes. The main problem I faced was getting the holes in the center of the tubing and lined up with the existing holes. My drill press vise is just far enough off of level and plumb that I didn't trust it, so instead I used a speed square to find the center on both sides, then drill and ream the holes.

I drilled and tapped a length of ¼" 4130 tubing to connect my two control sticks along the horizontal axis, which turned out to be a little bit of a trick. I chucked the tubing in my lathe in order to drill it out so I could tap it, then locked the lathe up and tapped it by hand. I didn't drill quite far enough on one end, so I broke the tap... luckily, enough was sticking out that I could grab it with pliers and screw it right back out. Another trip to the hardware store for a new tap, and I was finished. I threaded in two AN42B "eye bolts," and it was ready to connect.

The last of the metalwork for the control sticks was to make the mounting brackets. I needed a set of brackets to hold the control sticks, and a set of brackets that will mount to the back of the rear spar where the pushrod will transition to cables. I did some adjusting to Mark Langford's drawings for the former, and did some math and drew up the latter on some graph paper. Here they are, attached to ⅛" 6061 T6 aluminum angles, but not cut out yet. I started by drilling all the holes, since that can be a difficult procedure once everything is cut out.

Tomorrow I hope to finish the mounting brackets and begin assembly in the fuselage.
Continued in Control Sticks (Part 6)

Control Sticks (Part 4)

Continued from Control Sticks (Part 3)
I made progress on a lot of little things today. I laid out, drilled, and cut the nylon bearing surfaces for the control sticks. Forgot to take pictures of that. I redesigned the brackets that'll bolt to the front spar, because the plans I'm using account for a flap design I'm not using. I'm still waiting on the material I need to fashion the brackets, so I couldn't work any further on that. I also drew up plans for the bracket assembly to hold the bellcrank behind the rear spar,  where my pushrod will transition to cables for elevator control.

I've found no matter how much I work with various CAD software, the easiest and fastest way for me to design things is still on paper. (Partly because I usually spend about an hour fighting with my printer when I want the finished design printed to scale.)

I'm not a very proficient welder, and I don't have the right tools, so I sent my jigged-up assemblies out to be welded. Once those come back and the rest of my material shows up, I'll be able to finish this project and move forward. I believe I'll finish the rudder pedal assembly next. Sometimes I feel like I'm going to run out of work that isn't fiberglassing before it warms up, but I'm well known for taking *way* longer than I say I will to finish projects.

Control Sticks (Part 3)

Continued from Control Sticks (Part 2)
I finished cutting the steel for the main body of the assembly today.  I saved the diagonals for last, since they're the only set whose length is critical. I found a great site that allows you to input tubing diameter and thickness, angle, offset, and generates a template you can print out and transfer to your tubes. Check it out here.

I set up my shop for woodworking, so I had to get creative to cut and grind some of these pieces. I do have an angle grinder, so that got clamped to my workbench, and I cut the curved portions (where the round tube nested inside another round) with that. It was a lot easier than I envisioned it.

I used the RAS to cut my 45* to the rectangular tubing, then used my bench sander/grinder to make the fit really precise. Finally, I attached them to the jig, which will be welded after I cut and fit all my aluminum (in case there are any surprises).

I measured and cut the pushrod/shuttle that will connect the two control sticks, and drilled the ends to accept a 10-32 tap. Unfortunately, I cannot find my 10-32 tap, so this is where I quit for the day.
Continued in Control Sticks (Part 4)