CHM

My Feedback: (28)

That would be nice, but when playing with this on the bench I had quite a bit of slack. My fear is that in the transition between full rudder and then relaxing the stick you will have a huge flying surface with no tension on either cable. I believe that could cause flutter, and flutter on a giant scale plane is very scary. At least I'll try to avoid it

I agree with Stickjammer about tightening. That can't be good. And I suppose most of us could get away with having one cable go slack, but it just bugs me to see that. Figuring the offset is easy, and now Sullivan and Dubro have rudder horns that make it easy to get the pivot point on the hinge line.

Stick Jammer

We are talking about a very small amount of slack. Any slack is instantaneously gone as soon as the servo begins to rotate in the opposite direction. The cables are tight long before the rudder is back to a neutral position. This situation won't in itself cause any flutter to occur.

CHM

My Feedback: (28)

I set this up on the bench. There is quite a bit of slack. It does not instantly go away, and flutter takes less time than that to rip an airplane apart. I just don't want to take that chance, but that's my opinion.

On an H9 Sukhoi, and I'm sure on most other 33% and larger planes, it's really hard to use rudder horns much under 3.5" in span. If you run straight cables on a system like that your slots could be cut with a circular saw. Crossing them works and allows a small slot or even a tube in some cases.

Chuck

mglavin

My Feedback: (31)

We've owned two H9 Sukhoi’s, I used a 3" servo arm and 3" control arm with maximum surface deflection. The overall deciding factor is the width or chord of the rudder where the control arm is placed nothing else! Of course you have the cumulative total of the control arm spacing off the surface on both sides of the rudder to the pivot points. Some models do require a wider arm at the rudder and accordingly you provide an equal size arm at the other end. Thus far I have always used the on the hinge line or offset tiller arm method without issue. YES, you will realize a slight amount of slack fully deflected, it has yet to be a problem. However the next time out I intend to apply the Silly's aforementioned method. What the heck it can't hurt.

JoeAirPort

My Feedback: (41)

I have my 25% CAP232 all set to have the cables installed. I'm thinking of starting with sewing thread or fishing line installed temporarily to test all these theories. I might even have enough cable to do two of them so I might just connect the cable temporarily. I have the adjustability all around but I don't have the offset servo arm. I also put my rudder control horns so the holes where the clevis goes in is right dead nuts on the hinge line. So there is no offset anywhere on my system. I'll try a straight shot and also try crossing them. I will also try using a different cable separation on both ends to see how that works. This is all only a test so no damage will be done.

When I find the one that gives me:
1) the smallest slot
2) least slack
3) largest deflections

That will be the one that I use.

Stick Jammer

Not sure what you mean by "quite a bit" but if it's a lot, there is something else wrong. At any rate, think about what causes an unstable surface to flutter. It's the air passing over a neutral surface that is sloppy for one reason or another. Sorta like how a flag flaps in a stiff breeze. When the rudder is deflected to one side it only has air pushing on that side. It would need the same amount of force from the opposite side to create any flutter. The passing air wants to push the deflected rudder back to neutral and unless there is slop at neutral there won't be any flutter. As always, everyone should do what makes them the most comfortable, but rest assured, this condition won't cause any flutter.

JoeAirPort

My Feedback: (41)

I agree with Stick. Just make sure you have no slack at neutral position. Slack on one side at the extreme side of throws is not as big an issue as some people think. The force on a deflected surface is pretty big and will keep the one in tension very taught. It's the center position that both sides need to be tight. According to Scott at SWB, using a perfect rectangle, non-crossed cables, is the only way to have constant tension at all angles of deflection. Of course your control horns have to have the pivot points right on the hinge too. He said he spent hours experimenting with crossed cables and never was able to get it perfect.

CHM

My Feedback: (28)

Okay, there seems to be a general consensus that slack at deflection is no big deal. Hmmm, would you guys feel comfortable with that condition on your elevators too?

Like I said earlier, on the H9 Sukhoi I would have to have a huge slot if I went with straight cables. That's why I wanted to cross them. When I cross them, I get slack. I don't like slack, so I'm going with an offset arm to keep the cables tight. One thing I haven't mentioned is that I'm using the Sullivan yellow fiber cable. I have had this stuff fray if it rubs on the fuselage, so that is why I'm being so anal about a small exit hole. I have seen some guys just use a nylon tube on uncrossed cables, but that looks like it would wear on both the tube and the cable.

Chuck

Stick Jammer

If it were a pull-pull system on the elevator, absolutely. Flutter isn't picky, it doesn't know an elevator from a rudder from an aileron. If the set up is slop free at neutral, there won't be any surface flutter.