Fitting the empennage...
|Before fitting the empennage the fuselage must be leveled longitudinally and laterally. This is were that fuselage cradle of mine comes in handy to keep it steady. Make sure the aft deck area is perfectly level.|
The HS is clamped loosely in place for fit. I aligned the rear and front spar with the centerline and measured the distance to a centerline point well forward to square the stab. I came out at 1/32" difference on a total distance of 12' from the first time. Not bad at all! I adjusted (very) slightly to get the distances equal.
Also mark the fuselage edges on the front spar lower angle to have a correct reference in order to mark and drill the 4 pilot holes for the bolts. This is best done from the bottom and with the stab on the bench.
Mark the postion of the F-811 attach bars on the rear spar as well at this time and drill pilot holes in the rear spar.
|The stab was again clamped with the two 0.125" spacers at the front and a 3/16" spacer is slid under the center of the rear spar. Then the 4 front bolt holes were drilled.|
|The rear spar drilled and bolted as well.|
|A close-up of the 4 front spar bolt holes. All holes came out at the correct position with no edge distance issues. Remark: the 2 outer holes come at 9/32" from the longeron inner edge, so this is minimum-minimum edge distance, 1.5 x the hole diameter. You need the space anyway to be able to get the wrench socket on the nuts.|
On to the VS fit. Start by laying out the hole location for the spar attachment to the F-812 bulkhead. There are no dimensions specified on the plans. The only thing mentioned is to keep an eye on edge distance. Remark: the plans are more or less at 1/2 scale, so it gives you a rough idea about distances.
The 2 top holes: Measure where the top of F-812B angle/elevator stop will be. The holes are 5/16" below that line. Locate the holes to get min edge distance for the spar re-enforcement, not the spar channel!
The three bottom holes: Two upper holes are located at 12/32" from the bottom edge of the lower hinge bracket. The lower hole is on centerline of the spar. Measure on the F-812 bulkhead where the tooling hole is, so the two holes correspond. I located at 1/2" from the spar bottom edge and came out a bit below the tooling hole. Structurally OK, but a bit pitty...
Start fitting the F-812B angle to the specified location on the VS and centered on the spar. Then hang the VS on the fuselage using this angle and a couple of wooden blocks. Align the VS on the fuselage centerline at height of F-812B angle. My bulkhead must have moved a bit out of vertical while riveting. The only correct centerline is that one at the aft deck.
Next clamp, measure, move, clamp, ... until the VS is vertical longitudinally and laterally. The bottom of the spar does not have to be flush with the bulkhead if necessary, it attaches to the F-812B angle and all the way at the bottom.
Don't drill anything until you are sure. Start drilling #30 and cleco. This way you still have room to move the VS a little if required and drill the holes to final size afterwards.
|It starts to look like an airplane now, doesn't it. Oh well, saying this to myself keeps me motivated...|
|The spar can flex at this point so you need to check the alignment of the hinge brackets to avoid rudder binding.|
|A close-up of the VS attachment. Note that the tooling hole is located exactly between the two flush rivets in the bulkhead.|
|The front spars of both stabs join with the F-681 splice plate. First clamp to the HS to drill the four bolt holes.|
|The front spar of the VS needs to be trimmed to length. A spacer goes between the F-681 splice plate and the VS spar. As per plans the spacer needed to be 0.125" thick. This thickness can vary as required on your particular airplane.|
|The centerline of the fuselage was established with straightedges across the fuselage.|
|The VS was clamped in line with the centerline.|
|Again the string helps you check the position of the hinge brackets before drilling.|
|When everything is triple checked the holes are drilled for the AD4 rivets.|
With both stabs in place it's time to start on the control surfaces and control linkages.
This is the elevator belcranck fitted and drilled.
|The belcranck primed, riveted and installed.|
Next I hung the elevators and clamped them in their neutral position. This is achieved by lining up the counterweight horns with the stab. Using some shims I then fine-tuned the neutral position until both elevators were perfectly in line with eachother.
A 3/16" hole was drilled through the elevator horns for the push-pull tube attachment. Again start with a smaller size drill bit and enlarge in steps. You need to drill perfectly perpendicular through both of the horns which are about 1" from eachother. Failing to do so will get both elevators out of line when attaching the push-pull tube.
I fabricated all the push-pull tubes for the elevator control linkage. The control sticks are ready for fitting and rigging.
Also both rear seat rudder pedal push rods are assembled. I will have these welded instead of riveted. When re-painted they will just look cleaner since they are visible in the cockpit.
|The aft tube is installed first. At the specified length as mentioned on the plans and with the elevators in neutral, the belcranck came right at its neutral position from the first time.|
|At the aft end the tube just clears the F-811 bulkhead by about 1/32". I was afraid of having to trim this bulkhead at this stage, but this will not be necessary.|
|The space between the two elevator horns and the tube rod end bearing must be filled with either washers or alu tube spacers. I choose to fabricate two 7/32" wide spacers.|
|With the elevators installed and in neutral, the rest of the control system is installed and rigged. The sticks as adjusted until perfectly vertical. All jam nuts on the pushrods are tightned. To get the F-840 pushrod in place you need to remove the fwd floor / footwells and aft control column mount bracket. There's no other way around.|
|Next the rudder is hung onto the VS. It took me a while to get those three rod end bearings into the hingebrackets. At this stage the rudder stops are fabricated and installed. I decided to go with a modified system as I've seen on RV7 builder Jef Bordelon's website. The fuselage will look a lot more cleaner in that area too. I will install this later when I get some material from Spruce.|
The rudder assembly with the rear seat rudder pedals connected.
Most RV8(A) builders report unwanted brake application during rudder input and modify their rudder pedals in different ways. Especially on the 8 this is unfavorable. My rudder pedal modification consists of just moving the position of the brake cylinders attach holes at the pedals 5/32" more upwards. This results in the rudder pedals being at a 5 degree angle forward from vertical. Or the top of the pedals being 1/2" more forward. We'll have to wait until test flying to see the results and whether all of this makes any sense.
I also installed these hydraulic brake fluid reservoirs I got from Spruce. Many builders reported leaks in the standard system. The only disadvantage I've noticed is that the pedals cannot move fully forward without interference of the reservoirs with the firewall. I'm planning on installing an aluminum tube spacer around the slide bar trimmed to the required length to keep the slider from going too much forward. I still have some scrap tube left from the aileron pushrods which is exactly 1" ID. We'll see.
Another modification, required by the Belgian CAA and based on the PFA Airworthiness Approval Note, is to install return springs for the rudder pedals. It's also my opinion that this should be standard. The plan is to attach one end of the springs to an MS21919DG18 Adel clamp on the slider forward of the release mechanism and the other end to the inner pedal hinge bolts.
|Before removing the empennage for storage I checked the interference of the VS with the turtle deck. The line shows where the turtle deck intersects the VS. You might need to trim this off to get the 1/16-1/8" clearance as specified on the plans.|
|I finally got up to the third rivet location to get proper clearance.|
|The turtle deck in place for the picture. Unfortunately this all has to come apart again.|
|This is where I decided to route the wiring for the tail light/strobe, right throught the tailwheel weldment. It's location is 2" below the lower hinge bracket. The hole is 7/16" diameter (id of the bushing 1/4"). I might enlarge this to a horizontal sleeve to alow more for rudder deflection...|
|I got some 1/2" thick nylon from Spruce and fabricated these custom rudder stops. I recalculated the measurements using my own empennage as a reference rather than taking those from Jef Bordelons website. I cut it with an electric hacksaw using a very coarse tooth blade. Went pretty easy.|
|I then mounted them on the lower hinge bracket. The geometry must be accurately calculated and cut out so you get exactly 30° of rudder deflection on either side.|
|The rudder stops are attached using two AN3-7A bolts, washers and nylock nuts.|