Vertical Stabilizer

Time: 6 Hours

I flew home from Grand Rapids this morning and had about 7 hours before I needed to head back to the airport and fly my passengers back home and return to Chicago. So I wanted to put that time to good use in the Hangar. Now that I had the HS bolted in place I grabbed the vertical stabilizer (VS) and placed it into position, I did this ahead of step one which has you trim 9/16″ off the bottom of the VS forward spar. I have read that most people don’t need that much removed and had issues with edge distance on the lower rivets on that spar so I chose to wait to cut. You use one centered 1/8″ hole in the rear spar to grab the fuselage with and place two clamps on the forward spar at the bottom along with a spacer, attach angle and the forward spar of the HS. You have to do 3 alignments on the VS, first is the lean left and right, the second is twist left and right and third is lean forward and backward. You start with the lean left and right by picking a place to measure from on the top of the VS to a spot on the outboard edge of the HS, using the same reference point on both sides. I was easily able to get them with a 1/32″ of each other. I tightened down the clamps to hold that position so I could drill the rear spar.  

 This is where the fun begins, measuring for 3 bolt holes on the lower end of the rear spar. The bottom single hole is drilled centerline vertically and 1/32″ above a line between two rivets. This is pretty tough to line up and mark as the space is tight between the flanges of the bulkhead. I grabbed my laser that creates a line for referencing and marking. I lined it up on center of the two rivets for a marking line.  

 I used the laser line to mark a horizontal line and turned the laser vertical aligning with several holes and rivets to get a vertical line and mark the intersection of it and the horizontal line.  

 Now that I had the lower hole marked on the vertical and horizontal I needed to find the two upper hole locations. The plans call for the two holes to be 1 23/32″ above the bottom hole and 7/8″ outboard of the centerline. Again this was really tough to get measured. These holes go through the lower flange of the bottom rudder hinge plate, the spar and the tail wheel weldament. Vans make note to watch for edge distance problems with the weldment and the hinge bracket. I must have measured and examined for over an hour to make sure that I wouldn’t have any issues. I found that making sure that I had edge distance on the hinge bracket meant that I would probably have an issue with the weldment. After talking with my buddy Glen I decided that the edge distance of the weldment was much more important than the bracket as all of the waning force for the tailwheel will be transmitted to that weldment. So I lowered the line I came up with by a 1/16″ to make sure the weldament was okay. I took some deep breaths and stood back to make sure I looked at all the measurements one last time before drilling. Once I was completely sure I had them right I drilled the lower one first and put a clecko in place. I then followed with the two upper holes.  

   I checked all the holes in the inside with a flashlight and mirror and found that they all looked great. I then enlarged the holes with my 3/16″ reamer followed by my 1/4″ reamer and put the bolts in place.  

   I then moved up and drilled the two holes for the AN3 bolts, a lot easier since you just match drill and then enlarge them.  

 Next up was the two other axis that needed alignment. The lean forward and back is pretty easy as you just need a long straight edge like my long level and place it on all three rudder hinge brackets. You just need all three to touch and only requires a little movement. At the same time you need to get the twist left and right so that the rudder is aligned with the centerline of the fuselage. To do this you need a straight edge that can be clamped to the middle rudder hinge. I clamped a piece of 1″ angle and clamped it into place. I marked to spots at 10″ outboard of the rudder skin on each side. I grabbed my pink string and ran a line from the center of the instrument panel crossmember, there isn’t a center hole but rather two holes equal distance for the center of the crossmember. I ran the string in one hole and out the other. Each end of the string was then run back to the angle I clamped to the rudder hinge. I pulled the string tight and secured it so that the lines landed on the 10″ marks I made. The distance is not important as long as they are just equal. Now that you have lines that are at a know setting, crossmember to the 10″ mark on both sides, you have a reference line to measure the twist of the VS. I measured from the same place on the VS skin and got the measurements within 1/32″ 

   After tweaking all the measurements I clamped the forward spar tight and match drilled the 11 bracket holes thru the spacer and spar.  

 Remember the step I skipped for cutting the forward spar bottom? Well here is a photo of what would have been cut off and the little line where I will cut it.  

 I will match drill the 4 bolts holes tomorrow as its getting late to run the drill. I finished up the day with a little painting including the pilot and passengers control sticks and support mount.  

   Not a lot of physical work done but a lot of mental items and they are the toughest! Another great day in the Hangar!

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