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  #1  
Old 02-21-2015, 12:00 AM
xblueh2o xblueh2o is offline
 
Join Date: Apr 2011
Location: SF East Bay
Posts: 770
Default Shimming the horizontal stab

QB fuselage. I have it leveled laterally and longitudinally. After a ton of measuring I discovered the fus has about a 1 degree twist built in to it. With the wing spar level the aft deck is about a 1/8 bubble out. Initial fit up of the horizontal stab requires an additional .120" shim on the left side (in addition to the .125" spacer) in order to get the Horizontal stab level to match the wing spar. I can shoot a laser through all the holes in flight control attach points on the horizontal stab so I feel it is pretty straight and not the culprit.

Here is how I did it. Tell me if I am doing something wrong.
1. Level laid across the main wing spar at the front seat crotch belt. Shows laterally level.
2. Second level on the 819 aft deck shows longitudinally level.
3. Turn the level on the aft deck to measure laterally and it shows slightly out.
4. Place and clamp the horizontal stab per the instructions with the .125" spacers in position.
5. 2 small blocks of wood on the horizontal stab equidistant from the centerline and along a rivet line with a 3' level laid on them shows essentially same error as the aft deck.

What I did next.
1. Quadruple check level. Confirmed.
2. Swap positions of all levels. Same readings.
3. Put a digital level on everything. Pretty much the same readings as the bubble levels.

Has anybody else had to put that much shim on the stab? What awaits me further in the build? Searching reveals a couple other threads about this but none with this much shim required. Thoughts?
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RV-8 with the Showplanes Fastback conversion
Emp completed except for glass work
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  #2  
Old 02-21-2015, 07:24 AM
Tnikkel5 Tnikkel5 is offline
 
Join Date: Jun 2014
Location: Sully, IA
Posts: 37
Default

I have a quick build fuselage also and my was not straight either. When I leveled the fuselage longitudy my aft deck differed from the front of the airplane. Also when I shot a laser down the center line of the airplane my turtle deck is a little off also.
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  #3  
Old 02-21-2015, 08:55 PM
xblueh2o xblueh2o is offline
 
Join Date: Apr 2011
Location: SF East Bay
Posts: 770
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Do you recall how much shim you put under the stab?

I spent today doing everything again from the beginning. Same result. It is just going to take a huge amount of shim to get the stab in line with the wings. The big problem is there is so much shim on the left side, the right side is only touching the shim at the outboard edge. I will need to make a taper shim or something like that to put under the angle.
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RV-8 with the Showplanes Fastback conversion
Emp completed except for glass work
Wings completed except for bottom skin and glass work
Fuselage underway
N18451 reserved
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  #4  
Old 02-21-2015, 09:54 PM
Tnikkel5 Tnikkel5 is offline
 
Join Date: Jun 2014
Location: Sully, IA
Posts: 37
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I actually had to shim the horizontal stab where it bolts through the rear spar to get mine straight. I didn't have to add any more shims in the normal place it tells you for the front spar, like your talking about. You might give vans a call bc that's does sound like a lot.
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  #5  
Old 02-22-2015, 12:15 PM
CMW CMW is offline
 
Join Date: Mar 2007
Location: Livermore, CA
Posts: 165
Default

Sam,

Before you spend too much time on a shim, I would temporarily mount the vertical stabalizer. If you need a 1/8 shim under the horizontal stabilizer, I think the vertical stabalizer will be your next problem. It might help determine what the best fix will be.

-Chris
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  #6  
Old 03-06-2015, 07:48 PM
xblueh2o xblueh2o is offline
 
Join Date: Apr 2011
Location: SF East Bay
Posts: 770
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Follow up question.
After talking with Van's I made a tapered shim so the horizontal stab is now laterally parallel with the wing spar. Because the shim ended up with about a .100" delta between the thick and the thin side, I made the thin side less than the stock .125" in an effort to retain as close as possible the same angle of incidence. The instructions say the incidence is correct when the stab chord line is level with the upper longerons and to use the tooling holes in the ribs to get the chord line. The question is, how do I use the tooling holes to get the chord line? I have been looking at this for about 30 minutes trying to come up with a good way to do it aside from just eyeballing it.

Anybody?

Side note. I had wifi installed in my hangar today and I am finally able to actually search and post while working instead of stopping and going home. This is my first post using the new abilities.Little victories.
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Sam
RV-8 with the Showplanes Fastback conversion
Emp completed except for glass work
Wings completed except for bottom skin and glass work
Fuselage underway
N18451 reserved
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  #7  
Old 03-06-2015, 08:38 PM
engineerorange engineerorange is offline
 
Join Date: Apr 2008
Location: Catawba, NC
Posts: 168
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Put appropriate size clecoes in the tooling holes and lay a straight edge on top of them.
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  #8  
Old 03-07-2015, 02:02 AM
xblueh2o xblueh2o is offline
 
Join Date: Apr 2011
Location: SF East Bay
Posts: 770
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Honestly, sometimes the simplest things elude me. I even had the buckets of various clecos sitting nearby and didn't put two and two together.
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Sam
RV-8 with the Showplanes Fastback conversion
Emp completed except for glass work
Wings completed except for bottom skin and glass work
Fuselage underway
N18451 reserved
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