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ignacio

Active Member
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
 
Hmm...

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.
 
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 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?
 
ignacio said:
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,...
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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.
 
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ignacio said:
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.
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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... ???
 
LifeofReiley said:
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.
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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.
 
Kind of what I figured with the early RV's, If I built an RV4, it would have the offset built into the airframe.
 
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
 
Yep... on my 7A, the ball stays centered and the plane flies straight no rudder required in straight and level... :D Oh, and no stinken tabs...
 
Ignacio,
The newer designs have a very small offset built in. It's approximately .25 inches. This is nowhere near 7 degrees (closer to .7 degree).

In any case, Vans will have a simple solution for you when you call them.
 
LifeofReiley said:
Yep... on my 7A, the ball stays centered and the plane flies straight no rudder required in straight and level... :D Oh, and no stinken tabs...
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I also have one of those vintage 6A's with the good looking & shorter "classic tail". The plans called for a straight vertical stab, and a trim tab IS required. But what the heck............trim tabs as well as seeable rivets are just part of what makes an airplane an airplane. :D

Unfortuanely, I couldn't "cheat", :) and claim that my airplane flew hands off on the first flight, as so many offset tail owners can. Without doubt, my plane required a good dose of right rudder to keep the ball centered in cruise. Yet the tab is small, and not that much of a bend. I'd even think of installing an electrically operated rudder tab in the future. Oh well....

L.Adamson --- RV6A

P.S. --- the tab was installed after 20 hrs or so.
 
szicree said:
Ignacio,
The newer designs have a very small offset built in. It's approximately .25 inches. This is nowhere near 7 degrees (closer to .7 degree).

In any case, Vans will have a simple solution for you when you call them.
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Sorry... it's more like .45" when you get to the front of the vertical overall. Van's calls for shimming on my set of plans, I elected to offset the angle bracket... yes somewhere around .1875 on my 7A.

Ignacio,

I really don't think you'll have a problem.
 
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thanks guys. i will call vans 1st thing in the morning. dont think i will have to rebuild and im sure they're going to agree. i found the fwd spar on vert stab a little slanted on the inside and think thats what caused the twist. lets see what vans says, thanks.
 
ignacio said:
thanks guys. i will call vans 1st thing in the morning. dont think i will have to rebuild and im sure they're going to agree. i found the fwd spar on vert stab a little slanted on the inside and think thats what caused the twist. lets see what vans says, thanks.
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good deal... Van's will have your answer. I check my notes and put the real numbers in my post as to the offset... it's been a while since I was at that point in the construction mode. :) I know when you look down the fuse the looks HUGE, but it really not that much.
 
When I was building my -4 I asked Vans about offsetting the rudder. Their position was "build it to plan", they had no idea what offset was appropriate. That was what I did.

In retrospect I wish I had ofset it, but I dont know by how much. To do it now I would have to rebuild the glass fairing at the fuse' junction, so the trim tab sits there.
 
Vertical Stabilizer offset does work - but not in plans

My RV4, plans #2042, had absolutely no design offset and certainly no twist. The RV8 I'm building now doesn't employ offset either. Like Larry said, all the flying surfaces on the RV's are built straight and flat.

After flight testing my unpainted 4, I determined the amount of rudder deflection needed in cruise to keep the airplane trimmed (ball centered). The offset in the leading edge of the vertical stabilizer could then be determined. Turned out to be 1/2". Before paint, I re-drilled the forward VS attach point to obtain the 1/2" offset, and the airplane flew perfectly. Had to build a new empennage fairing for it, though.

Keep in mind, there are a myraid of factors that affect yaw trim, including installed HP, propeller dynamics, weight & balance, etc. So, the 1/2" I used for my 4 probably wouldn't work for your airplane. The solution used by nearly all builders is to put a fixed aero trim tab (in the form of a wedge) on the rudder.
 
i agree bill. it just hurts knowing you have gotten this far just to find out one of the first parts you built is, well twisted. having the eng, prop, paint and controls and so on will change things heck it might even fly straight, highly doubtful but hey we will see.
 
well i got lucky, but might have lots of adjusting to do once i get up in the air. i spoke to vans tech supp. and they agreed i didnt have to rebuild the stab but suggested i move the lower leading edge on the stab to compensate for the top where its twisting. the vertical aft spar hinges are lined up perfectly with the horizontal stab hinges so im ok there and the measurments from the tips are fine to. so in the end i might just have to use tabs, oh well. didnt expect a perfect airplane. hey even us airplane techicians make mistakes. remember dont put to much pressure on the skins when strapping them down for riveting or drilling, and always make sure things are straight. lesson learned. now i can continue and finally stop twisting and turning in bed
 
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