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  #1  
Old 09-26-2021, 10:10 PM
RVFan671 RVFan671 is offline
 
Join Date: May 2020
Location: Seattle
Posts: 75
Default How to rig the aircraft to begin measuring rigging

I have a -4 that has a trim tab on the left aileron and still has a heavy right wing. I also can see the left flap trailing edge is .5” recessed from the bottom of the fuse compared to the right flap trailing edge which is flush.

I would like to go through the rigging top to bottom following vans suggestions but I’m not sure how I should level the plane. Are there any instructions in the -4 plans (have the USB) on how to level and begin checking? Do I need some jacks that go into the tie down locations under the wings or just wheel it up onto a proper size shim for the left/right level?

Should I be leveling front/back to center the bubble or be about 3 degrees nose low which I think is close to level flight attitude?

There are some great threads on how to perform the measurements so I planned to leverage those but if anyone wants to share more info in this thread, happy to take a look at the suggestions too.

One thing I haven’t found yet is, what do I do if the wing incidence is off between right and left wing? If they were drilled with different incidence each side (if that is my conclusion), what is my remediation? Vans instructions linked above say “fix it” but I thought drilling the spar was a one shot deal. So then do I just raise/lower one aileron as the only possible bandaid?
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  #2  
Old 09-27-2021, 05:15 AM
fixnflyguy fixnflyguy is offline
 
Join Date: Jan 2006
Location: Winston-Salem, N.C.
Posts: 1,457
Default A couple things

I built my -4 and did the best I could do with strings,plumb bobs ,ect. to make it as close to perfect as I could. While the drawings and construction manual have basic symmetry instructions, no 2 RV-4's are identical, and variations are not uncommon. I "leveled" mine by jacking at the firewall cross-member just under each lower engine mount to get the wheels off the ground, and used a level on the cockpit side rails in both lateral and longitudinal direction, supporting the tail to the level position. When everything is measured a zillion times and seemingly spot on, the rear spar attach hole is clamped and drilled and the wing incidence is set. it cant easily be changed later without oversizing, eccentrics or other means. I installed electric aileron trim during my build for fuel burn reasons, but found during phase one, I always had a heavy right wing. After careful inspection a zillion more times, I found my L/H aileron outboard hinge (steel U-shape) was "low" by nearly an 1/8" inch which creates a flap like condition on the left wing. Wala, remove and drill up new hinge bracket..poof, heavy wing gone. The newer RV kits have the holes pre-drilled and less prone to this occurrence. I would start by checking for this scenareo, then follow the VANS "heavy wing" dialogue.
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  #3  
Old 09-27-2021, 04:30 PM
RVFan671 RVFan671 is offline
 
Join Date: May 2020
Location: Seattle
Posts: 75
Default

Did you level along the longerons lateral and longitudinal to lake the levels bubble right in the middle or did you orient slightly nose low which is the level flight attitude? Where in the -4 plans does it walk you through the setup/drilling of the wings? I'll have a closer read there.
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  #4  
Old 09-28-2021, 04:50 AM
fixnflyguy fixnflyguy is offline
 
Join Date: Jan 2006
Location: Winston-Salem, N.C.
Posts: 1,457
Default Leveling

I leveled the longerons "bubble centered". When building the -4, the fuselage longerons are level from the the rollbar back, but bend downwards at the front slightly. All measurements are taken from the longerons for the most part when the fuselage is upside down in the jig during build. When it comes time to mount the stabilizer and wings, there isn't a bunch of variables, other than stabilizer shimming which is covered in the build manual. The wings are rigid and the spar carry-through will determine the general angle of incidence, and the rear spar attach can only be "flexed" a little in the pitch direction (fuselage fair with belly skin overlap mating controls this). getting the wings parallel with no sweep FOR/AFT is another story, and this is where measure a zillion times before drilling the AFT spar carry-through is critical. Hypothetically, all this could be done with the aircraft nose high/low but measuring/shoring would be difficult, and the end result would likely be the same. Alot of builders leave the empennage fairing unfinished for phase 1 so they can change the stabilizer shimming and vertical fin offset to achieve faired trim tabs and no rudder tab before doing the finish glass work. In your case, chasing a heavy wing on a finished/flying plane has some tricks to work with if no major build problems are detected.
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  #5  
Old 09-28-2021, 06:44 PM
Christopher Murphy Christopher Murphy is offline
 
Join Date: Feb 2007
Location: colorado
Posts: 932
Default Be careful with the rear spar.

I know of a rv3 buyer that fixed his incidence issue by screwing up his rear spar attachment and shed the wing.

Cm
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