Homebuilt Airplane Rudder Construction

The purpose of an airplane rudder is to control lateral yawing of the aircraft – nose left and nose right movements.

The GlaStar rudder design is of all aluminum construction, with aluminum spars, ribs and skin.

As suggested in the GlaStar construction manual, we decided to build the wing jig first since the rudder, horizontal stabilizer, and elevator can all be builtusing the wing jig. I believe another advantage in building the wing jig firstis that by the time the tail components are completed, the 4x4 posts will probably have begun to bend or twist if they are going to do so.

Obviously, it's best to know if the posts will remain straight before wing construction begins.

The wing jig design suggested by the manual consists of two 4x4 posts, which are mounted on a 2' wide table. The table is built upon a framework of two 16' 2x6's, with 2x6 cross bracing and 2x4 legs.

Though some builders have opted to modify the suggested design and/or materials with great success, we decided to build the table per the suggested design. The only alteration we made is the addition of a shelve below the table, adding both structural rigidity and a convenient place for the storage of tools and materials.

The jig takes quite a few hours to complete, but when finished, is almost perfectly level, with the posts nearly perfectly vertical (according to the digital level: a great tool!).

After deburring (removing any rough edges left from the manufacturing process) and marking rivet lines on the rudder components, the next step isto make modifications to one end of the wing jig.

A line at least 6' must be drawn upon the center of the table, and a 3' spar support board must be attached at a 90 degree angle to the table. The centerline will be used to position the rudder trailing edge while in the jig, while the spar support board will anchor the rudder assembly to the jig.

The 'yoke weldment' is then bolted to the spar support board, using an extension of the table centerline for positioning.

After fabricating some angled wooden blocks to support the structure from the bottom, the 'forward spar' is attached to the yoke weldment. Before drilling the holes through which rivets will attach the two pieces, it is critical that the forward spar be aligned asperfectly as possible with the yoke weldment.

This step took a looooong time, requiring many cycles of clamp-check alignment-unclamp-adjust before everything was satisfactory. A string - which is stretched through the 'center hinge bearing' of the yoke weldment and exactly above the trailing edge centerline - and a plumb bob are used to check the alignment.

Once the forward spar is drilled and attached to the yoke weldment, the 'root rib' is also drilled and attached to the yoke weldment after assuring that the center of the root rib is on a plane with the trailing edge centerline on the table.

Next, the 'aft spar' is drilled and attached with a bracket to the root rib. The aft spar is centered laterally on the root rib.

Once the forward and aft spars are in place, the 'counterweight rib' is positioned vertically between the two spars, and drilled and attached to the spars with brackets. Once again, a string representing the trailing edge centerline and a plumb bob are used to check the alignment of the assembly.

Now it's time to fit the skins to the internal framework. The main rudderskin is first slid into place while lifting the framework in the jig.

At this point, all of the pre-drilled pilot holes in the skin must be aligned with the centerlines which were earlier marked on the spars and ribs. When the skin pilot holes and the rib and spar centerlines are aligned and the entire assembly clamped, then the pilot holes are used as guides to drill the rivet holes through the skin and the underlying structural members.

As the holes are drilled, special clamps called 'clecos' are inserted into every third or fourth hole. Clecos are inserted and removed with a special type of pliers, and are used to pin the skin to the underlying structural member, maintaining the alignment of the entire assembly.

With the main rudder skin in place, the next step is to fit and drill the 'forward skin' and the 'tip rib.'

I found this step to be the most challenging aspect of rudder assembly to this point. The forward skin must be made to conform to the leading edge curves of the rudder tip, while also keeping the forward skin pilot holes aligned with the forward spar and counterweight rib centerlines.

In addition, the tip rib must be positioned horizontally relative to the forward spar, and vertically relative to the top edge of the main skin.

I found it necessary to trim back the top edges of both spars in order to attainthe proper vertical positioning of the tip rib (the manual approves of doing this if needed).

Now the entire rudder assembly can be disassembled, and the rivet holes deburred. Also, a number of the rivet holes in the skin, the forward spar, and the tip rib are dimpled to allow for the use of flush-head rivets.

The next step is to fabricate the 'lead counterweight'. The purpose of a counterweight is primarily to inhibit aerodynamic flutter of a controlsurface. The rudder counterweight should weigh 1.5 lbs., and is fashioned from lead sheeting provided with the kit.

Several 4-inch long pieces, narrow enough to fit between the flanges of the counterweight rib, are cut from the lead sheeting.

As with most of the rudder assembly, the next step required the learningof a new skill: mixing and applying primer for corrosion protection.

I've discovered that there is anything but a consensus of opinion amongst other homebuilt aircraft builders concerning the materials and methods of corrosion proofing. We've decided to use 'DEFT', which is the corrosion inhibiting primer recommended by the manufacturer of the GlaStar.

We are, however, departing somewhat from the manual's recommendation, in that we've decided to dispense with the intermediate step of applying 'Alodine'. Instead, we are cleaning the parts thoroughly with 'MEK' (using full precautions; MEK is a very hazardous material), and then applying the DEFT.

We've also decided to build a small 'paint booth', which will hopefully allow us to perform all primer applications in a partially sheltered environment outside of the shop.

The application of the DEFT was marginally successful in terms of results, but highly successful in terms of education. We learned a lot!

As the pictures show, we had a lot of runs in the DEFT, some of which will need to be sanded down and retouched.

The next time we apply DEFT, we are going to use a thicker mixture than recommended in the mixing instructions, and we will also use less air pressure than the recommended 60 psi.

The next step is to bolt the rudder counterweight to the counterweight rib.

The counterweight, which was fabricated earlier from lead sheeting, is first wrappedin tape to inhibit the development of corrosion as a result of contact between dissimilar metals.

At this point, the rudder components are ready for final assembly.

The rudder is riveted together using a clearly defined sequence of steps as documented in the assembly manual.

As with most of the GlaStar, 3/32" and 1/8" diameter driven rivets are used in the rudder, along with a few pulled rivets. Driven rivets must be accessed from both ends - with the rivet gun at the head of the rivet, and flattened with a 'bucking bar' on the tail end.

Pulled, or 'pop' rivets, are set from just one end using a special tool, making them necessary in just a few areas where it would be impossible to reach the tail of the rivet with a bucking bar.

Although we did make several mistakes riveting which required that rivets be drilled out and driven again (my mistakes; Dad has years of experience doing this!), overall I believe the rudder turned out nicely.

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