[AJCoholic]

I have a question for the experienced giant scalers..

Regarding rudder pull-pull links, I was under the assumption that when the tiller/servo arms move, the wires (both) should remain taught throughout the travel. This requires keeping the geometry and distances in check, so to speak, all the offsets of the rudder horns and servo tilller have to reamin equal, as do the length of the wires.

That being said, it takes some time to get it just "right". Is it really a big deal if the wire that isnt "pulling" on the rudder goes slack? The wire in tension is doing all the work, aand since the airload on the rudder is also keeping that working wire tight, it seems that the wire not in tension can go a bit slack without a problem.

I just want some other opinions on this matter.

Thanks!
Andrew

[ronm]

I've done lots of pull-pulls on medium size models. It's my opinion that it is good to have both cables taught throughout the range of motion, but I always have the "non-pulling" side "slightly" less taught, so as to prevent excessive wear on all the pivoting parts, which could happen if the cables become tighter as they move from one side to the other.

Ron Mattiuz

[KevinPerry]

It shouldn't matter if the no load wire goes a bit slack. Will prob save wearing your servo out quicker

[Kevin McGrath]

I have pull/pull on a half dozen 1/4 and 1/3 models.It is best to keep the geometry equal and the easiest way to do that is to mount a bellcrank in the centre of the fuse,at the rear of the wing cavity,and connect each arm to the tiller arms at the rudder with your cables which need to be snug but not tight.You drive the bellcrank with one servo and its position vis a vis the the bellcrank isnt critical.Side benefits of this setup include easier adjustment and centering,and far less wear and impact load on the servo.

[AJCoholic]

Kevin,
Thats the method I used in both my AC-1 and AC-2 giant scale planes. I made a tiller arm from 1/8" G10 and have it mounted on dual flanged ball bearings, and the rudder servo drives it with a heavy duty pushrod.

In these two planes, I managed to get the pull-pull cables nice and snug throughout the travel.

The reason I posted this question, is that in the Extra I just got I noticed that one wire is going very slack. Nothing against Randy, or the builder, as I am sure it did the trick - just that it kinda' made me a bit nervous. (and I like to make things as good as I can, or maybe I cant leave well enough alone!) So, today I redid the setup just to be safe. The wires are driven by the servo directly. The mount points on the servo tiller had to be moved back about 3/4" just to keep the same geometry in relation to the rudder horns/ rudder hinge line. Now I feel better, but I still am interested to know if some are flying the system with one slack line, without any problem. Didnt take me too long, maybe an hour to fool with it.

Andrew

[Randy Brown]

Originally Posted by AJCoholic

Kevin,
Thats the method I used in both my AC-1 and AC-2 giant scale planes. I made a tiller arm from 1/8" G10 and have it mounted on dual flanged ball bearings, and the rudder servo drives it with a heavy duty pushrod.

In these two planes, I managed to get the pull-pull cables nice and snug throughout the travel.

The reason I posted this question, is that in the Extra I just got I noticed that one wire is going very slack. Nothing against Randy, or the builder, as I am sure it did the trick - just that it kinda' made me a bit nervous. (and I like to make things as good as I can, or maybe I cant leave well enough alone!) So, today I redid the setup just to be safe. The wires are driven by the servo directly. The mount points on the servo tiller had to be moved back about 3/4" just to keep the same geometry in relation to the rudder horns/ rudder hinge line. Now I feel better, but I still am interested to know if some are flying the system with one slack line, without any problem. Didnt take me too long, maybe an hour to fool with it.

Andrew

There was nothing wrong with the way it was.. only way that rudder was going to move was if you took a sledge hammer to it

Randy

[nony]

My belief is that the wires should remain somewhat taut throughout the control throw. They don't have to be guitar string tight, but having one go slack may be an invitation to flutter during some flight regimes such as sideslips, snaps or tumbles.

I saw a neat set up today called floating bellcranks...two servos (on independant receivers in this case) hooked via pull pull to a suspendened bellcrank the center of which was in turn hooked via pull-pull to the rudder horns. If one servo fails, the other servo is able to move the rudder for half throw, without fighting against the dead servo...slick as a whistle!

[Kevin McGrath]

Before I started using the bellcrank setup I installed several pull/pull setups direct from a buried servo to the rudder yoke.There usually was slack in the non pulling line but it didnt seem to make any difference in taxi or flight.These were all sport scale or bipe models so maybe some unwanted characteristics would show up in a high performance model.Come to think of it though, I had an 80" Midwest CAP set up this way with no trouble......

[KevinPerry]

Just a thought here guys .... Why is it that everyone thinks both wires should tight ? Think about it for a sec ....you can not push a flexible wire , only pull ...sooooo it really wont make any diff if it is lose . ....Just an opinion of course . I don't think I have ever seen a pull pull remain completley tight through full travel both ways .

[AJCoholic]

The articles that I have read in RCM and some other of the magazines allways showed how you can keep the geometry correct and both lines will stay snug throughout the travel.

From "simple logic" you would think that the cable pulling the rudder is doing all the work, as the flight load on the rudder is trying to make it go back to the neutral position. BUT If there is any kind of a load to push the rudder further away from the neutral (as may be experienced during a hard snap, maybe in some fast flying where flutter may be introduced.. who knows) there is nothing to hold the rudder from moving outwards more. It probably will never happen, but being I REALLY like this new bird I wanted to make sure.

When I set up my own rudders pull-pull, I allways got the cables to remain snug throughout the travel, by keeping the geometry identical (all offsets, distances from rotation, length and angles of cables, etc). SO it can definitely be done, I just wanted to know from others experience if it was absolutely necessary.

From some of your responses, I guess it isnt as critical as I thought originally.

Andrew