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How Vertical is Vertical Enough?

M

MK77

Well Known Member
Hi fellow RV'ers,

I'm in the midst of final assembly of the RV-7 project I took over from a previous builder. I'm mounting the empennage right now.

Like many of the sub-assemblies that I thought were finished and ready to bolt together, upon closer look it appears that the VS to fuselage assembly may not be quite to the level of accuracy that I would like.

1. I have the HS mounted. I temporarily installed the VS and measured the distance from the top tip of the VS to the tip of each end of the HS. Naturally, these measurements should be equal to indicate a truly vertical VS. Here's what I'm reading:
Left HS tip to VS = 66 5/8 inches
Right HS tip to VS = 67 1/8 inches

Total delta is 1/2 in. So my question is how far off can this be without a dramatic effect to the flight characteristic? I know perfect is ideal but that's going to take some real re-work. The rear VS spar is well centered in the rear bulkhead. If I take out all but the bottom bolt in the rear spar, I need to push the VS rear spar all the way until it's hitting the right side before I get equal measurements.

2. The hinge line is not perfect. The top hinge bracket is aft almost a 1/16". Ideas on how to fix this?

Thanks!
Matt
 
The half inch lateral dimension is not really a problem.

The 1/16" off on the hinge line is a problem and has to be fixed.
Redoing the fwd spar attach is the only way to fix it.
 
rvbuilder2002 said:
The half inch lateral dimension is not really a problem.
Click to expand...

I was hoping you'd say that! I did the math and it's less than 0.5 degrees so I figured it was probably ok.

To fix the hinge line, is the only way to remove the F-781 attach plate from the spar, replace and re-align?
 
Last edited:
BillL said:
It has been a bit since i checked mine, but you know the VS is rotated to the right, right? You said "tip".

I certainly don't want to second guess Scott, but you might want to recheck.
Click to expand...

Don't get this backwards, double check but I think the leading edge of the VS is mounted to the Left.....
 
Stab

I think you are right Brent , but I mounted mine center and it flies feet off in cruise.
Bob
 
Yep, I measured the offset and the correct value called out in the manual is there, 1/4" to the LEFT so I'm good with that. The measurements I was concerned about were from the top of the VS to the HS tips. Manual specifies they should be equal.
 
MK77 said:
I was hoping you'd say that! I did the math and it's less than 0.5 degrees so I figured it was probably ok.

To fix the hinge line, is the only way to remove the F-781 attach plate from the spar, replace and re-align?
Click to expand...

The best way to fix this would be to redo the fwd spar attach.
Another alternative would be making a shim to bolt between the bottom of the vert stab spar and the fuselage. This would effect a number of other things though (non standard shape to rudder stops, etc) and it would be difficult to get the hinge line exactly straight so it would not be the method I would choose.
 
Last edited:
Pardon the newbie question, but how do you know it's the vertical rather than horizontal that's out of alignment?
 
StuBob said:
Pardon the newbie question, but how do you know it's the vertical rather than horizontal that's out of alignment?
Click to expand...

The horizontal should be leveled with respect to the main wing spar carry-thru.
 
Also, I think, if the rear deck plate was put on without the longerons being parallel perpendicular with the center section, that would put a twist in the rear with the HS front spar not able to make the right angle with the VS rear spar????
 
bret said:
Also, I think, if the rear deck plate was put on without the longerons being parallel perpendicular with the center section, that would put a twist in the rear with the HS front spar not able to make the right angle with the VS rear spar????
Click to expand...

If there was a twist in the rear portion of the fuselage it would effect the alignment of the horizontal and the vertical stabs equally, so they could be properly aligned with each other but not aligned with the wing.
 
Good point. I did a quick measurement from the HS tips to the floor and the distances were pretty much spot on. Next time I'm at the plane, I'll throw a level on the main spar and compare the reading to the HS spar to confirm they're the same.
 
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