Cutting My Wing Spar Webs

I should have posted this before the picture of the cut blanks below, but I had lots of video editing to do.

Preparing to cut:

Cutting:

Observations during construction:

Final Layout:

I also drilled the lightening holes, but did not film the process. It was a 2-person job using the drill press and feeding the material, so rather than fool around with video camera angles and footage quality, we just concentrated on making good parts. I'll post a few pictures of the spar webs with the lightening holes drilled out. It took about 3 hours to drill and de-bur them (18 holes in all for the spar webs).

Accounting for Material Thickness

Hey, Everyone. Here's a short video about interpreting the measurements on your blueprints. A number have people told me that you have to adjust the measurements in the blueprints to accommodate the thickness of material where parts nest together. An example is where the rear wing ribs nest into the channels that you have to bend. Some folks have told me that you have to subtract or add material thickness to the measurements to get the parts to fit together properly. My experience has shown this to be false, as long as you build within the tolerances allowed by the blueprints. Check it out:

Wing Spar Webs

Well, they don't look like much, but they are the backbone of the wings. Every structure in the airplane hangs on the wings, literally. The wings bolt to the cabin. The wing spars support the wing structures, and the wing structures hold the plane in the air. I was nervous about cutting these because they have to be perfect. Well, I'm happy to report that I've cut them perfectly, to well within the 1/2-mm tolerance specified by the blueprints. Lots of construction left to go before they are complete spars, but this was the hard part. Each 4'x12' piece of .032"-thick aluminum is $200. Make a mistake on these babies, which are nearly 12' long, and you're flusing real cash down the toilet.

Revising Form Blocks and Making Wing Ribs

Here's another video...trials and tribulations of getting form blocks and cutting templates correct for all the ribs you have to make. In this case, my wing ribs!

 

Making complex bends on the homemade brake.

Here's a rather long video (16 mins) detailing how difficult it was to form my elevator trim tab, a relatively small part in the airplane. I was very happy with the way this part turned out. The video details some tips and tricks to forming aluminum sheet when you have several long straight bends.

And finally an actual structure: The Rudder!

So after all the hammering, running the router, bending in the brake, I finally put one of the structures together!

Here is the rudder skeleton clamped together. Starting to look like a piece of an airplane!

Rear skin of the rudder clamped in place:

Full rudder skin clamped in place:

Lots of rivets for such a small piece of the plane...

Some easier parts...

The other day, I decided to cut all of the parts in the 1/8" thickness (.125") that were shown in the blueprints. These are the heavier brackets, and high-wear items:

Here we have various items such as tie-down rings, bearing doublers, wing root mounts, door center latches, rudder stops, etc.:

And here are the Flaperon Arms. My plane uses full-span flaperons, which are a combination of flaps (which allow you to land and/or take off more steeply) and ailerons (which make the airplane bank in order to turns). These arms mount the flaperon below the trailing edge of the wing. They were cut on the router using a cutting template:

 Here's the rudder horn. This piece was bent over a piece of oak with a 1/4" radius routered into it and clamped to the table. I used a mallet to hammer this to shape. Took me an hour!

The only parts I haven't made in this thickness are the door handles. They have complex bends, and the 1/8" material is almost impossible to bend without an industrial brake.

More parts!

The Flaperon Nose Ribs shown below are pretty small...about 1.5" tall with a tight radius around the nose. It took me a while to get the geometry on the flat blanks correct before they would form the radius around the nose without looking like a crimped bottle cap or cracking:

Generally, anything that has curved surfaces or complex bends gets formed around a form block. Other things like channels or L-angles can be bent up using the bending brake. For example, here is my rudder spar. It is the backbone of the rudder, and made up of .032" thick aluminum. It has 2 simple bends, but is about 4.5' long:

Looks like a simple enough part, but it took me a few hours to get my bending brake set up correctly to bend this properly. Plus, 60601-T6 aluminum is very stiff. It's a bit counter-intuitive, as aluminum is softer than most other metals, but it resists bending like crazy. So you can easily drill it out or cut it, but bending is another story! This really strained my DIY bending brake.

Finally making some parts!

 Rudder nose rib...only had to make one of these, but it was a complex form block!

Flaperon Rear Ribs:

Rudder Rear Ribs and Horizontal Stabilizer Rear Ribs:

Rudder Bottom Rib:

The Starting Point: Part 4 - Your first cuts in aluminum!

Once you have acquired or built most of your tools, built your work table and built your form blocks, you're ready to start making actual parts for your airplane. It took me over 50 hours of work just to get to that point, and I finally arrived here:

Yep, one big giant overwhelming flat sheet of aluminum. I'm supposed to make an airplane out of this? What? Well, yes, actually, I started by laying out all the parts blanks on the aluminum sheet. Some of them were traced from the cutting forms I made from wood, and some were measured and drawn directly onto the aluminum from the blueprints.

Once the parts are laid out, you start cutting!

And you end up with flat pieces of aluminum sheet that still need to be bent in the brake or formed around form blocks.

More to come...

The Starting Point: Part 3 - Building up your tooling.

"Tooling" refers to the special tools you have to fabricate to build something. So while you can run down to your local tool store and buy a drill press, you probably can't buy the special holding fixtures, form blocks and other things you need for each part you need to make. You'll be making things that only apply to your specific project. So in this case, you need specially-shaped form blocks to bend your aluminum around to create the shapes you need for parts in the wings, fuselage, tail section, etc. Unless you have an unlimited  budget, you'll probably also need to build DIY versions of more expensive tools like bending brakes. You can build a homemade bending brake for around $150, and it will be just fine for your project. Conversely, a professional bending brake will cost many thousands of dollars, and has much more capability than you will generally require. In  my case, I built 2 bending brakes, numerous form blocks and lots of other special forming tools.

My bending brakes are built from angle iron and piano hinges. One is 4' long and the other is 8' long. Remember what I said about carefully examining your blueprints? I recently discovered that I have 3 bends in aluminum that are 8.5 feet long. Fortunately, a friend has a professional grade 10' brake, so I don't need to build another one. My 4' brake was more proof-of-concept, but works fantastically on smaller bends.

I spent many hours laying out form blocks from measurements in the plans. My form blocks are made from 3/4" plywood, and I used the table saw, band saw and belt/spindle sanders to create them. There are many pairs of them, even though some of them only create one right- and one left-handed version of a part. In other cases, I might make as many as 16 of each part.

  

Lots of form blocks, lots of wood!

The Starting Point: Part 2 - Examine your blueprints

You have to thoroughly examine the blueprints of your chosen aircraft before building and/or acquiring any of the tools you need. I had many of the tools needed for this build already, but I had to acquire a few more, and build some DIY examples of still more. By examining the blueprints carefully, you will determine, for example, what the longest bend in any piece of material will be and therefore, how big your bending brake needs to be. Further, by examining the materials you'll be working with, you'll figure out what sizes of drill bits to buy, whether you needs sanders, cutting equipment, sanding equipment, etc. You will learn all the dimensions of the various form blocks you have to build to shape your aluminum:

The Starting Point: Part 1 - Tools

So building an aluminum aircraft from scratch requires a few tools (well, a lot of tools, actually). Here's a relatively short list:

• Sheet metal bending brake 
• Band saw
• Belt, spindle and disc sanders
• Table saw
• Drill press
• Router
• Cordless and/or pneumatic drills
• Rivet guns (hand and pneumatic)
• Various clamps, jigs and other holding fixtures
• Bench Vise (a sizable, good quality one)
• Hammers and mallets
• Files
• Metal snips/shears
• Clecos (temporary rivets)
• and many many more...

Some of these tools you can actually build or modify from existing tools. Many of the tools are for woodworking, but can also be used on soft aluminum. However, you have plenty of woodworking to do (Wait? I said this is an aluminum airplane, right?). Much of the tooling consists of wooden form blocks, which you use to form the aluminum sheet into the complex shapes required for the plane.

Really, the process starts with examining your blueprints, but having a running inventory of the tools you already own is a good starting point.

Welcome

This blog is intended to photo and video chronicle the construction progress (and hopefully, flight experiences) on my Zenith CH 750 STOL airplane, an aluminum short take-off and landing aircraft with two seats. It will be powered by a 1965 Chevrolet Corvair air-cooled, 164 cubic-inch, horizontally opposed, 6-cylinder engine. It will be registered under the new Light Sport Aircraft regulations with the U.S. Federal Air Administration. When it's done, it will look like this, though I will have a different paint scheme:

I am mostly building this airplane from scratch. That is, it is not a kit airplane put together with pre-made parts. I am forming most of the parts from flat aluminum sheets and some bar stock. Since I am not a skilled welder, I may purchase certain welded parts from Zenith, or pay to have them fabricated locally. But the bulk of the airplane will be made from scratch. Follow along as I try to make steady progress and have a flying airplane in 3-5 years...