Horizontal Stabilizer 

Time: 6 Hours

After a good Sunday breakfast this morning with my girl I got to work in the Hangar for a little work before I had to head out to fly a rare weekend trip. First up was to rivet all the parts for the two rear baggage area mods. This went pretty quick with my rivet squeezer and back riveting set. 

     Now that I had the few items that needed riveting I decided to take on the horizontal stabilizer(HS)! I was a little nervous right about this task as it’s pretty important to get it right the first time as changing drilled holes is not an option after they are drilled. First up was to find the center line of the aft deck which will end up being a reference line for the spars.  

 I then needed to get the fuselage level forward to aft and left to right.  

     I then placed the HS into position with the rear spar tight against the fuselage spar attach bars and centered on the line I drew on the aft deck. You need to give a space of 3/16″ under the rear spar which accounts for the incedence of the HS which is 0°. They suggest a 3/16″ drill bit under the center of the spar. Whit that in place I clamped the rear spar to the attach points. Now I needed to see if the HS was level in reference to the fuselage, if perfect it would be at 0°. Since the HS tappers as it goes outboard you need spacers to sit a level on. These can be of any height just as long as they are the same. I used some 3/4″ angle and turned it so that it looked like an A so the level would sit on the tip. You then need to place the spacers at the same spot on each side of the HS so your measurement will be equal.  

       I was amazed to see that it was spot on and perfect, man I love this RV-8! With everything level and perfect I really tightened the clamps and then rechecked the level. Once I was satisfied it didn’t move I matched drilled the four #30 holes thru the spar attach bars into the spar cleckoing as I went.  

   Now that the rear holes were set I needed to make sure that the HS was perpendicular to the fuselage. To do this I would take a measurement from the corner of the outside rear skin of the HS to a point along the mid fuselage on both sides. I picked a rivet hole on both sides of the middle of the fuselage and drew a line using a square at the corner of the longeron. 

   Now I had an equal reference point on both sides of the fuselage that I could measure to. When I first measured I was off by 1/16″, with a little tweak I was able to get it with in 1/32″ at 99 3/4″

   Now that everything was squared up my clamped the forward spar to the cross angle. This is where it gets a little trickier, as there are no holes to match drill from just measurements from the plans. Ok so now I need to measure in a tight space and with somewhat of a good accuracy.  Then drill a hole that is perfectly straight down thru the spar angle, spacer, fuselage angle and longeron.  The plan I came up with from help of Glen was to mark the edge of the longeron, which is the reference point for these measurements on the underside of the spar angle with a sharpie as well as the edge of the spacer.  I then removed the HS and flipped it over on the workbench to make my measurements and drill the #30 holes using my drill cup to be square.   

 I clamped the spacer in place based on the sharpie line and flush with the leading edge of the spar angle. Flipped the HS back over and used the holes I just drilled as guides to drill the spacers. I then returned the HS and spacers to the fuselage keeping everything lined up. After rechecking the measurements and making sure they were both back at 99 3/4″ I reclamped it in place.  

 I grabbed the 90° drill and put the #30 drill bit in and took a really deep breath and drilled down thru one hole trying to keep everything square using the spar angle and spacer as a guide. With one done I grabbed the #12 drill bit that I borrowed from Glen and enlarged that hole. I placed a AN3-10A bolt, washers and nut in place and tightened them down. I grabbed the tape measure and rechecked the measurements and found that they were perfect. So I drilled the opposite hole and repeated the process. Next up was the two outboard holes that go thru the longeron. Everything turned out perfect with good edge distance.  

   Whew those all turned out great so I went the aft holes and enlarged those to a #12 hole placing a bolt in place as I went.  

   Another big step today and the HS is drilled! It will come off when I get to rivet the aft top skin but now I will be able to set the elevators and controls as I go. Next up will be the vertical stabilizer (VS), another great weekend in the Hangar!


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