Category Archives: Section 08, Horizontal Stabilizer

This week I finished squeezing all the spar rivets, which concluded the standard build portion of the horizontal stabilizer.  My technical counselor suggest 5 drill-outs on the inner spar sections, so these have also been completed.

Squeezing the spar rivets is a one-man job, so these were completed alone.

Eric did stop by for bucking the inner spar rivets and setting the final 25 inch/pound torque on the center hinge bracket bolts.

The final product is good, but not as clean as I would have liked. A few minor optical dents and dings, but should be safe otherwise.

All the finished parts so far (rudder, VS, HS) are stored on the overhead shelf to avoid “shop rash” from being bumped during the processing of other parts.  I used 18″ bubble wrap between the parts, and eventually covered all with thin plastic to keep out dust and dirt.  The nice part is being in the bonus room, temperature controls and humidity are not a problem.

Done with Section 8 of the manual.

This week was all about riveting the horizontal stabilizer parts together.  The whole job is not yet complete, but good progress was made on bucking the nose, spars and some inboard ribs.  I had help from both Eric and Rich during the period.

Oops. Notice the small, but still visible blemish near the most forward rivet.  This came from the tungsten bucking bar pounding the reverse side of what we were processing.  The bar as I held it was wide enough to span from one skin side to another. Drats.  For later rivets I rearranged holding the bar parallel to the rib, not perpendicular to it as in this case.  Hopefully this can be smoothed away with filler before painting.  The only saving grace is this appears on the underside of the horizontal stabilizer.  People will have to bend over and look from beneath to see it.

During the week and after doing the nose ribs, I prepped for riveting along the spars.  AN426AD3-4 rivets are used for the outer section, AN426AD3-4.5 for the inner parts where the spar caps are located.

Eric comes over after work most nights for dinner.  On this occasion I pressed him into service for a few hours doing the outer skin-to-forward spar rivets.

Here are the prep stages for the inner spar riveting.

Rich came over on Saturday to help me complete the upper skin riveting in its entirety. The small cells between the stringers, inboard ribs and spar are quite tight for my big hands.  It takes lots of repositioning of the bucking bar to see well into those cavities.

Here’s what it looks like on the outside as of Sunday morning.  All the upper skin rivets are set (actually the bottom on this photo), the lower skins have been riveted to the forward spar.   The inner rivets and placing the rear spar up for next week.

Upon inspection I found a number of scratch marks where the bucking bar had rubbed against the spar during rivet setting. This happened despite putting duck tape on the forward spar and the bucking bar for protection. My plan is to get a small Preval brand sprayer to prime over this spots before closing off with the rear spar.

Another trick employed was fitting a felt chair leg cushion to the end of the bucking bar. When used in conjunction with duck tape against the spar, this seemed to eliminate any scratching.  Another prime example of live, innovate and learn.

Although I have not posted in a few weeks, much activity has been occurring on the horizontal stabilizer.  Three long weekends in a row have gone into drilling, scuffing, washing, brightening, alodine, priming and assembly.

May 24 – final stages of jigging and match drilling complete.

May 25 – Rita, the not-yet Riveter. Here she is helping me dimple the HS skins with the DRDT-2 machine.

May 26 – mixing the DP401LF catalyst with the DP40LF priming for the HS skins.  First the skins were washed with Pre-kote, then dried in the shed.

May 26 – suited and ready for skin priming.  Not much can be seen inside the shed once priming starts.

May 31 – dunk tank extended to 12′ to hold the HS spars.

May 31 – brightening underway. This was the first time I used the garage for corrosion treatments.

May 31 – another view of the extended dunk tank.  One of the spars is bubbling in the phosphoric acid brightener on the right, a rinse tank is on the left.

May 31 – the alodine is on the right, rinse on the left.

June 7 – all parts are primed and ready for riveting.

June 7 – Rich came over to help rivet on hinges, attachment brackets, spar doublers, caps and stringers. We squeezed as many rivets as possible, only had to buck 6 rivets on the custom made attachment brackets.  Turns out the bracket, spar flange, and doubler combination is too thick for my Main Squeeze 3″ yoke (takes a 4-10

June 8 – the internal parts of the stingers and ribs must be riveted together before attaching the skins, because afterwards there is no access.

This past week saw the initial stages of fitting and match drilling the horizontal stabilizer parts.

Front HS Spar Doubler and Attachment Brackets clecoed ready for match drilling.

Front spar completely match drilled with #30 bit.

Tracing the outline of spar ribs as a template for the cradles.

Completed cradles.  I used 1/2″ copper pipe insulation foam to cover the 5/8″ plywood cradles.  The wood is USA-made birch plywood of high grade.  It came from a throw-away set of shelves, the board were scavenged from the good pieces.

Skins inserted in the cradles after removing vinyl strips on the outside, completely removed vinyl on the inside. Note how the cradles are held with clamps – I wanted the ability to position as needed on first fitting.  This allowed the cradles to fit between ribs to allow easy access.

Forward spar and ribs ready for insertion…

Inserting the spar assembly into the skins.

Clecoes being applied.

Ready for deburring the skin edges and match drilling the holes.

Another angle showing everything lined up.

I manually prep the skin edges with a flat needle file before using a 1″ diameter Scotchbrite wheel in an electric drill to finish off the smoothing.  It could be done on the raw sheets, but I prefer having the skins stabilized with spars and ribs clecoed in place.  My confidence in not bending or kinking an edge is much greater with this setup.

All done, next steps are with alodine / priming.

Much of the metal preparation work on the horizontal stabilizer was done before I primed and assembled the rudder and VS.  This weekend saw the start of jigging and match drilling on the rear spar of the HS.

As usual, all the parts are laid out and checked before any alterations are started.

An initial task is riveting a flange bearing between two powder coated pieces to construct the inboard hinge brackets.

Looks just right.

Match drilling the hinge brackets and the rear spar doubler is the first order of business.

Spent about 7 hours this week deburring the ribs on the horizontal stabilizer.  This is tedious, but necessary work.

This weekend I started organizing the pieces for the horizontal stabilizer.  This included laying out most of the metal parts, removing vinyl, and starting the deburr process. This section has the most elements, so metal preparation for all the ribs, doublers, and spars will take some time.

Horizontal stabilizer pieces ready to start preparing.

This is the third section I have started without setting a single rivet.  Right now I have all the logistics ready for alodining for corrosion protection, but do not yet have a suitable air compressor for priming.  The shed is almost ready to go now that the paint booth filter has arrived.  I just need to setup the exhaust fan configuration prior to buying the compressor. (a post on the shed configuration will come later).