Vert stab twisted ? RV-4

[ignacio]

MOUNTED AND DRILLED THE THE VERTICAL STAB TO THE HORIZ. STAB AND WHEN I WENT TO ADJUST THE VERT FWD SPAR I NOTICED THE THERE WAS A SLIGHT TWIST, BOW OR WHATEVER YOU WANT TO CALL IT, ON THE LEADING EDGE OF THE STAB. I LAID IT ON THE TABLE AND VERIFIED IT WAS TWISTING TOWARDS THE TOP. ALL THE HINGES WERE ALIGNED VIA LASER BOTH VERTICAL AND HORIZONTAL AND THE MEASUREMENTS FROM THE TOP OF THE VERTICAL TO THE TIPS OF THE HORIZONTAL ARE WITHIN LIMITS. BUT WHEN I ALIGN THE VERT STAB TO THE FUSELAGE CENTERLINE THE TOP OF THE STAB IS OFF. AND THE LASER LINE DOESNT MATCH. THE CAUSE I GUESS WAS DURING CONSTRUCTION. WHAT SORT OF PROBLEMS AM I LOOKING AT? HOPING I DONT HAVE TO REBUILD MY VERTICAL. ANY HELP WILL APRECIATED, THANKS

[LifeofReiley]

The vertical stab should be offset on RV's... built into the design. Might this be what you're seeing? The fairing is also offset.

[ignacio]

i was reading on that earlier but could not find it in the plans. if there is an offset, anyone know where i can find the measurements, what dwg.. in desperation i removed the top rib to see if it helped...it didnt. so im stopping there. i still havent drilled the fwd vert spar so i havent fully screwed yet...have i. thanks.

[LifeofReiley]

The offset is established by design when the vertical is mounted to the horizonal and fuse. If you're actually seeing a twist on the table... well you probably have a twist built in the vertical. If I recall correctly, the offset is somewhere near 7 degrees. I don't have RV4 plans to review. Can you email a pic?

[n5lp]

Originally Posted by ignacio

i was reading on that earlier but could not find it in the plans. if there is an offset, anyone know where i can find the measurements,...

Offset and twist are two separate issues. There is no planned twist in any control surface or stabilizer on an RV. They are supposed to be straight. As to how much twist would be noticeable in flight, I don't know.

My RV-6 drawings show no offset and I believe the RV-4 is the same. Some people have used offset in an attempt to avoid a trim tab.

[LifeofReiley]

Originally Posted by ignacio

i was reading on that earlier but could not find it in the plans. if there is an offset, anyone know where i can find the measurements, what dwg.. in desperation i removed the top rib to see if it helped...it didnt. so im stopping there. i still havent drilled the fwd vert spar so i havent fully screwed yet...have i. thanks.

The offset will be from centerline fuse showing the vertical towards the left wing or pilot side. RV4's may not have this in the design. Later plans may show an offset... ???

[szicree]

Originally Posted by LifeofReiley

The vertical stab should be offset on RV's... built into the design. Might this be what you're seeing? The fairing is also offset.

This is definitely not true on a -4. The whole plane is right/left symmetric with the exception of the motor mount.
I would accurately measure the problem and give vans a call. They've seen it all.

[LifeofReiley]

Kind of what I figured with the early RV's, If I built an RV4, it would have the offset built into the airframe.

[ignacio]

i agree with the offset issue, since i havent seen it in the plans. i to have read its to avoid trim tabs. i will try to take a pic but dont think it will appear very clear. stab is not primed and the twist is difficult to see, now im just looking for info and advise on what to correct, and will it affect me in flt and so on, my advice to everyone. do not use to much pressure on the skins while in the jig. thanks

[LifeofReiley]

Yep... on my 7A, the ball stays centered and the plane flies straight no rudder required in straight and level... Oh, and no stinken tabs...