RV-8 rudder tab

cdr.rschultz · #1 09-21-2011, 12:10 PM

Howdy. Have been playing around with rudder tabs on an RV 8 fastback and was wondering about other builders experiences? Curious if a "fin" type blade
works any better than the wedge I've been experimenting with? The "wedge" type in various lengths and thickness, positions, etc has been only very mildly effective. A "centered ball" at cruise speed is about all I'm after, but so far have not found an acceptable tab? Appreciate your thoughts on the matter. Thanks for your time.

L.Adamson · #2 09-21-2011, 09:45 PM

My 6A has a vertical stab, with no offset. It took quite a bit of rudder pressure to keep the ball centered in cruise. I guessed at the length for a wood wedge, and duct taped it on. It was just about perfect, but ugly. After a few months, I guessed once again, for the size of a pre-bent tab, which I riveted on. It was a good guess too..........as the ball stays centered for the cruise speed I prefer.

L.Adamson

Scott Hersha · #3 09-22-2011, 06:25 AM

I used a wedge that I made out of a piece of bass wood I got at Home Depot. I started with a 6" long piece and cut it down during flight test to get a trimmed rudder at cruise speed. It ended up being about 3" long and is mounted right on top of the tail light blister, flush with the trailing edge, and faired in with some micro. Once painted with my checkerboard tail on my RV-8 Fastback, you can hardly even see it.... even if you're looking for it. If I can find a picture I'll post it and I doubt you'll be able to see it.

Bob Axsom · #4 09-22-2011, 06:58 AM

When I built our RV-6A I taped on a wedge and test flew with it to get the proper size to center the ball in cruise. When that effort was completed all was well in the yaw trim area. Then I filletted the edges to blend it in with the rudder skin with epoxy resin and micro balloon before painting. The paint job was beautifully completed by Gray's Aircraft Refinishing (I may not have that name exactly right) in Ozark. Arkansas. After flying for a while I saw the epoxy was delaminating where it joined the rudder skin and I applied a silicon bead to stop it - if you use the wedge don't do what I did. I began a long term process of modification to increase the speed of the airplane and after a while the yaw trim wasn't perfect anymore. I have an auto pilot and I use it to race in the RV Blue class (360 engine) and even though it accurately followed the race legs it bothered me that the ball was not centered indication the ailerons were holding the line in opposition to the yaw control with some loss in efficiency - drag - and I started riding the rudder. Years later an incident happened where I kinked the rudder below the wedge when I climbed on the step with my wife and all of out luggage in the back and the plane settled back on the lower rudder cap. I took this as a good opportunity to get rid of the wedge and install a removable and ground adjustable rudder tab. That worked out quite well and I prefer it to the out of trim wedge but the wedge was fine before I started changing the plane. The skin back there is very thin and you should not assume that there can be no problems with either installation. There are a lot of details in my rudder tab installation that make it good for our airplane but I would not want to recommend it to anyone else other than generally. I think there is a thread on it in this forum.

Bob Axsom

gereed75 · #5 09-22-2011, 08:19 AM

I have a wood wedge. My story follows Bob's very closely - Worked great, faired in nicely. Now flying faster and it is too much trim. The wood wedge is not easily adjustable as trim needs change.

I suggest an aluminum trim tab would be better. I suggest that it be attached low on the rudder. I suggest that it be attached to "bridge" two stiffeners. I suggest that it be doubled (think of a piece of paper folded in half, one side on one side of the rudder, one side on the other).

In this way you are adding structural rigidity to the rudder and trim tab therefore increasing flutter resistance. If properly done, it could be adjusted by bending or triming it's size as trim requirements change.

Good luck. Fly Navy

Randy Erwin · #6 09-26-2011, 08:17 AM

Would someone mind posting a picture or two of the size and location of your wedges or trim tabs? I am very interested in putting one on my RV-8 and am curious about the choice between a tab or wedge. Thanks in advance.

Scott Hersha · #7 09-26-2011, 09:01 PM

https://picasaweb.google.com/hershas...eat=directlink

https://picasaweb.google.com/hershas...eat=directlink

First pic is Jon Thockers trim tab, prior to SNF '11. Second one is mine. Same idea, slightly different application, same results. You will need to zoom to see the tabs. On mine (the second one) you may not be able to see it even if you zoom. It is faired in just above the tail light blister and is mostly in the red area of the checkerboard. Both tabs results in zero rudder input required at normal cruise speed.

8CW · #8 09-27-2011, 03:51 AM

I can't pull the links come up. They come up, "Sorry page not found"

Randy Erwin · #9 09-27-2011, 02:29 PM

Same here Scott.

Scott Hersha · #10 09-28-2011, 02:40 PM

Sorry. I download the pics the same way every time and sometimes it works, sometimes it doesn't. This is the only site I have trouble downloading pictures on. I don't know what I need to do differently.....