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Mounting the Horizontal Stabilizer

Dean Pichon

Well Known Member
I built a new HS (and elevators) for my -4. I'm leveling up the fuselage in preparation for mounting the HS and have a couple of questions for those that went before me.

I used my laser level to level the top longeron. That went smoothly as shown below. I'm struggling with what reference to use for level in the roll direction.

IMG-1792.jpg


I pulled the wheels off and tried the axles, but I'm concerned that jacking on the axles individually may put unequal bending loads on the gear which may introduce errors.

After leveling axles, I find one wingtip is about an inch different from the other (relative to the laser level line).

Tomorrow, I will put a spirit level across the cockpit coamings to get a 3rd reference. What is typically used to establish level in the roll direction? (I don't recall what I did when I built the plane 25 years ago...)

Thanks,
 
Spirit level (or electronic) across the cockpit gunwales and then across the span of the horizontal stab ... block the fuselage until it's stable and level, then proceed to the Hstab.

Guess the point being that you want those two (wing and Hstab) to be on the same plane.

Pretty easy to set up.
 
as a second reference i would also pull the seat and put a small level on top of the spar in the center of the carry through.

bob burns
RV-4 N82rb
 
Thanks for the help all. I went back to the hanger this morning and leveled the fuselage in the roll direction using the cockpit rails and checked using the spar. Shimming under the axles allowed me to level the rails nicely. The spar level was close, but I decided to use the rails as the reference surface. Both forward and aft of the roll bar measured the same.

IMG-0654.jpg


IMG-0649.jpg


Once the fuselage was level in pitch and roll, I was able to attach the HS. Here it is leveled span-wise using the laser. I have drilled holes for the 4 aft bolts. Now, I have to figure out how to drill up from inside the fuselage to drill into the angle on the forward spar.

IMG-0656.jpg


Thanks again,
 
... I have drilled holes for the 4 aft bolts. Now, I have to figure out how to drill up from inside the fuselage to drill into the angle on the forward spar.

...

Take your time here - there is not a lot of edge distance, if I recall correctly. On the 8 we are able to drill top down. A mistake here will be painful to correct. And I believe this is an attachment that will see some stress when you fly aerobatic.
 
Drilling up from inside fuselage

I am betting this is thru the existing holes ? I too would interested in your solution ….I thought of using correct ( obviously) sized transfer punch up from bottom to mark and then removing horizontal stab to drill on the transfer punch marks ….small pilot hole …then reinstall to check . Or making a drill guide to keep 90 degrees,clamping it in place and using angle drill up from bottom . Not completely sold on either idea ,but leaning towards the drill guide . Please post your solution, Dean. Cheers. Stew
 
90* drill & bushing

Dean,

I recently mounted a new horizontal & vertical stab on our -6. On the horz stab I got the horz stab exactly where I wanted it and then clamped well into position. Then I used an 90* air drill with a #40 bit to make the initial hole. I found an appropriate drill guide bushing for the AN bolt size for OD of bushing. And the inside of bushing is sized for a #40 drill bit. I got it from Granger. Will post photo of bushing and part number when I get back home today. I had to run the air hose through the fuselage and getting it all lined up to drill from underneath was a bit blind and uncomfortable, but it worked. Then I updrilled the holes. Worked very well.

HTH
 
Drill guide bushings

The #40 guide is sized for AN3 bolts. The #30 is for AN4.
 

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Thanks all for the help. I tried to drill the holes using 2 different right angle drills, but could not seem to get good access while outside of the aircraft. I ended up using a #12 transfer punch to mark the holes. See the photos, below.

I located the HS using the aft spar and started the front spar attachment with this view:

IMG-0672.jpg


I then clamped the angle in place with a couple of C-Clamps.

IMG-0671.jpg


I reached in thru the 4" hole in the F-419 deck skin and marked the underside of the angle with the transfer punch. I colored the bottom of the angle with black Sharpie to make the mark easier to see. The prick marks where well-defined, so I felt ok with the approach.

IMG-0673.jpg


I put the angle on my milling machine and carefully aligned to each punch mark. (This photo shows the tool used to align to the punch marks. I forgot to get a photo of it, so this one is "staged" as the thru-holes have been completed.)

IMG-0675.jpg


I drilled thru with a #12 bit.

IMG-0674.jpg


I then dropped all 4 bolts in place and clamped the angle to the forward spar. Details to follow in a subsequent post.
 
The bolt dropped in smoothly. I clamped the angle to the forward spar, again, and drilled thru the angle using pre-drilled pilot holes in the spar.

IMG-0676.jpg


Yesterday afternoon, I primed the part. This morning, I riveted it to the spar and placed the horizontal stabilizer back onto the fuselage. All the holes aligned and all bolts went in smoothly.

Now, my next plea for help. How do I get the washers and nuts back on these bolts. It was all I could do to get a wrench on them during disassembly. I seem unable to get my fingers to the bolts to start the nuts.

Do I need someone to climb into the tailcone? I don't recall how I did this 20+ years ago. If it had been so hard, I thought it would have been more memorable....

Thanks,
 
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