Stiffeners clecoed to the Rudder Skin

If you are confused from the previous posts about the siffeners and what they are used for, perhaps these last pics will help clarify. Here they are clecoed to the skin on one side. When the rudder is finished each side of the skin will have its own set of stiffeners. You can see how they taper to a small point or edge as they move further back towards the end if the rudder, and are wider at the front. The angle is used to counteract any torsion moments of the skin, and is the real reason why the term stiffener is used. If you simply applied a strip of aluminum without the angle to the inside of the skin, you would not get the same stiffening quality that is needed here. As more of the rudder comes together you will see how these parts interact with the rest of the structure.

Smoothing the rough cut stiffeners

Here are some pics that show the finished stiffeners after smoothing all the edges on the Scotch Brite wheel. What an amazing tool for working with aluminum. Sometimes the chemical folks come up with the some really amazing things to benefit mankind. Dangerously jagged edges are all made as smooth as a babies bottom. The corners are rounded, and the parts are completed.

The idea here is that the stiffeners must conform to the tapered shape of the rudder. (Small at the tip or trailing edge, and much wider at the front. The rudder is actually a very complex shape that contains multiple tapers from top to bottom as well as in width from side to side. So the stiffeners must be very small at the trailing edge where they essentially come together with both sides of the skin, and they then widen out as the skin gets wider towards the front.

Trimming Stiffener Cont'd.

This is a pic of the safety glasses, ear plugs, dremel tool, and the scrap aluminum pieces you end up with when you are done cutting all 16 stiffeners. Note how sharp looking these are. it is important to clean these up and ensure that they are picked up off the floor as soon as they are cut. I could think of no useful purpose for any of this scrap material, so it ended up in the 86 files (trash). Recyclers will now respond and attack me "En masse" for doing such a foolish thing. So it goes I guess.

More on trimming the stiffeners

The process to trim them is basically to secure the angle to the work bench with the clamps. I absolutely must use two hands with the dremel tool in order maintain control of the tool while it cuts, so it is imperative that the clamps are positively securing the work. If you even suspect that the part is starting to move, turn off the tool and re-clamp the piece before continuing. You line of the cutting wheel so that it si just outside of the trim line for each cut.

I basically started with the cuts that separate each stiffeners from the angle stock, and then reclamped each one individually to make the angle cuts on the flange and do the final trimming. Using the Dremel tool makes this process go quite quickly, but it is also very easy to make a mistake. The key, as with all things about this process, is to take your time and follow the same process for cutting each one.

Tools, Safety, and Trimming the Stiffeners

I used my dremel tool to cut the stiffeners from the aluminum angle. Other tools included clamps, Safety glasses, ear plugs, and several REINFORCED dremel cutting wheels on the standard Mandrel. Do NOT use the small standard NON-REINFORCED cutting wheel as these will shatter as soon as you hit the aluminum. The reinforced cutting wheels will work fine, but you will go through at least 4-5 of them in the process of trimming all 16 rudder stiffeners. The wheels dissipate quite rapidly when cutting the aluminum, so you will need several of them. You MUST where safety glasses and ear plugs, and, as I found out the hard way, even some gloves to keep from burning yourself on the hot dremel tool.

The last thing you need is tiny shards of aluminum in your eyes. Believe me, there are plenty of them hitting your face as you cut the metal. If you are less inclined or do not possess a Dremel tool then a good hack saw or metal cutting blade will work fine. I set my Dremel to a 9 power setting (Almost full speed). I did not want to experiment with a slower setting for fear of binding the aluminum causing the wheel to jump and cut things other than those you originally intended to cut.

Marking the stiffeners

Here is a series of pics that shows the various markings to be made in order to trim the stiffeners from the aluminum angle. You can see the semicircle notches that Vans made and the lines drawn to connect the marks to create the correct trim lines for each stiffener. The only thing I did not like about this process was that Vans attempts to show this in their plans with the angle drawn "flat". They say this is for "clarity," but I found this to be quite confusing. They really need to show a better diagram so that you can understand how the trim lines need to be drawn. Nevertheless, I managed to figure it out.

More on Rudder Stiffeners

In my research, I found that any detail concerning the fabrication of the stiffeners for the rudder and elevators is woefully lacking on most builder sites, so I am attempting to fill that void by providing a bit more detail. This pic shows the labels forsome of the stiffeners, which are labeled from A through H. There are eight per side, for a total of 16 for the rudder. All 16 had to be trimmed from the angle provided from Vans.

The stiffener basically "stiffens" the thin rudder skin to keep it from flexing to much. The only ribs for the rudder are the two end-ribs, one on top adn one on the bottom. I'm not totally certain why the rudder does not contain a more robust skeleton made of fully formed ribs from end to end, but perhaps this has to do with the fact that this is a critical moving part of the aircraft that controls a force called yaw, or the left and right turning capability of the airplane. Perhaps hard formed ribs that would attach to both sides of the rudder skin may be subject to failure and cracking due to the amount of force that this surface will endure over time. It could also be related to weight concerns, since this is the aft-most structure of the entire airplane, and therefore has a large affect on the center of gravity.