Asymmetric rudder load due to steering link?

[rv8ch]

At cruise, my RV-8 is about half a ball out of trim. I have read others also need a bit of left rudder.

With the steering link, I have additional drag on the left side, pushing the rudder right. I wonder if that could be the cause of the out of trim conditions in cruise?

Does anyone with chains, which are (more) balanced, also need left rudder in cruise?

 

[Ralph Inkster]

Most RVs have a small trim tab (wedge) on their rudders to compensate for this.

Also in my case, I have a bit of slack on my tail wheel chains that would allow a bit of rudder deflection without bothering how the wheel was positioned in flight.

 

[wcalvert]

Mickey,

I like the way you're thinking but think you're likely barking up the wrong tree. IMO assuming the link is adding some force to the rudder horn (and it is, although small), the lever arm it's acting on is so small compared to the arm and loads on the rudder that it would have almost no effect.

Other things like trailing edge radius, some small misalignment of the vertical stab, wing incidence, leg fairings etc. act on a much bigger arm and will have much greater effect on the yaw issue.

Just for reference, my plane needs a little right rudder in most conditions, decreasing as speed increases in cruise, and left rudder with the power pulled back. Just what you would expect.

Keep looking with a critical eye and you may find something like what I mentioned that is suspect. Good luck!

 

[Mikeyb]

I have stock Vans chains slightly loose. My flies very close to center over a wide range of airspeeds. Maybe a bit to the right.

 

[Jpm757]

I have used rudder pedal return springs on both my RV's which has worked very well. In addition to keeping the rudder cables taught, you can adjust the spring tension on either rudder pedal to compensate for a out of trim rudder. In your case you would have a slightly tighter spring on the right rudder pedal.

 

[D-Dubya]

I agree with Wild Bill. The drag from that link is insignificant.

You can't do much about how the VS was mounted, but what about the wheel pants? Van's manual states that a small misalignment here can have a pretty big effect on whether the ball is centered. Did you build the plane? If not, Van's provides a pretty good write-up on how this should be done. You've got to jack the plane up and get the load off the gear, and it involves strings, plumb bobs, and careful measurements. It's fiberglass, so anything can be re-worked if it's off a bit.

It takes some effort to set up for these measurements, but a buddy and I have done this for both our planes and they both fly straight in cruise with our feet flat on the floor.

 

[bjdecker]

Testing...

I doubt the presence of the steering link (Silverbullet, JD Air, Flyboy Rocket, et al.) causes much (if any) biasing of the rudder.

You could always swap sides (flip the arm over) and see if the ball changes positions...

 

[Dan 57]

I've had different steering links on the same ship, Vans bathtub chains, then Lynx, and recently changed to JD's link...
Guess what, no difference between them all
Which in the case of my steed means ball slightly right in stabilised cruise conditions.

Haven't read the building instructions for the -8, but -4 builders surely remember setting a slight VS offset...

 

[riobison]

Could it be your wheel pants?

Tim

 

[rv8ch]

Thanks for the feedback. There was a post a while back where someone added a very small "tab" to the tail light, so I thought if that tiny tab can move the ball, perhaps the steering link can move it.

https://vansairforce.net/community/showpost.php?p=1515376&postcount=5

There is a difference in the leverage between them on the rudder.

I'll move the steering link to the other side and see if it makes a difference. Got an oil change coming up...

 

[CHEMENG]

Rudder pedal return springs.

I have used rudder pedal return springs on both my RV's which has worked very well. In addition to keeping the rudder cables taught, you can adjust the spring tension on either rudder pedal to compensate for an out of trim rudder. In your case you would have a slightly tighter spring on the right rudder pedal.

I to installed these springs and keeps my ball centered at cruise. Also does not allow the rudder to flap in the breeze on the ground during winds.