ez2bgman

My Feedback: (4)

Hello Eveyone,

I have a few questions: I am building an H9 Aresti 40 and am converting the standard rudder system to Dubro's Heavy Duty Pull Pull system. First, how can you get the wire to pass through the crimps 3 times as the picture shows on the package? Second, the heat shrink that came in the package is way too big, is it necessary to have the heat shrink on, or is more for cosmetics? Third, should the servo arm be the same length as the control horns on the rudder? This is my first attempt at a pull pull setup. Any advice would be greatly appreciated. Thanks.

Gary

MinnFlyer

My Feedback: (4)

1 Don't know

2 Probably just cosmetic

3 No. Use whatever lengths give you the desired amount of movement.

bhole74

Gary, I just looped my cable through twice, made sure I had a good strong crimp. The heat shrink tubing keeps you from stabbing youself with the excess wire when working on the plane.

Ed_Moorman

My Feedback: (1)

I forget what the DuBro set-up looks like, but the 3 passes through the crimp tube used to be the required way to do control line ends. At least it was when I flew CL in the 50s & 60s. You run the pull-pull wire up through the tube, then come back down through the tube. You take the end of the wire and loop it back around and go back down through the tube a second time. This is to keep the end from pulling out is the crimp isn't tight enough.

The spacing of the clevices on the servo arm should be the same as the spacing of the clevices on the 2 control horns. If the spacing is different, when you deflect the control, one wire will loosen up and the other wire will tighten. This usually results in a long servo arm because the thickness of the rudder spaces the clevices fairly far out.

ez2bgman

My Feedback: (4)

Ed,

Thanks for the info. I was thinking the same thing for the servo horn. What kind of tubing could I buy to use as crimps. I crimped 2 ends already, but only passed the wire through twice (I couldn't get it to loop around again due to the size of the wire versus the diameter of the crimp). I may try to strip off the plastic coating on the wire (where it passes through the crimp only) and see if I can get it to loop 3 times then. Looks like another trip to LHS for more tubing and a longer servo arm. I'm glad the weather's been lousy and I have time to build this thing right. Thanks again.

Gary

jaka

Hi!
I get my wire and crimp tubing at a sport fishing store (use thinnest wire possible).
Always pass the wire 3 times through the crimp tubing.
Servos in the picture is for rudder and elevator on my Great Planes GEE BEE R-2.

Regards!
Jan K
Sweden

Stick Jammer

I disagree Minn. The servo arm should be the same length as the control horn for pull-pull.

ez2bgman,
The cable should pass through the crimp tube a total of three times but I'm not sure you're looking at this correctly as it's not three times around so to speak. Thread the cable through the sleeve, that's one. As it turns 180 degrees at the control horn and heads back into the sleeve, that's two. You then loop it around the sleeve and pass it through again, that's three. I've used the Dubro stuff and had no problem doing this without stripping the plastic off. I also used the supplied shrink tube and it worked fine. You did not ask this but it's also important to have the control horn pivot point exactly on or slightly behind the hinge line.

ez2bgman

My Feedback: (4)

Stick,

Thanks for the help. No matter how hard I tried, I could not get the cable through the crimp with the plastic on. As soon as I stripped it off it went through all 3 times with no problem. I will post pics hopefully by this weekend of the finished conversion on my Aresti 40. As far as the heat shrink, I had the heat gun (on high heat) on it no less than 3 inches away and it barely shrunk. I think I'll just hit Radio Shack and pick up a bunch anyway. BTW, my pivot point is maybe 1/16th of an inch behind the hinge line.

One more question: I am putting an O.S. 50SX for power, what size APC prop would you guys recommend? The manual says it can handle a 12x6. This is my first time with any type of pattern plane and I'm not too sure as what size/pitch prop to use.

Thanks again for everyone's help.

Gary

MinnFlyer

My Feedback: (4)

Why?

jaka

Hi!
Control arm and servo arm doesn't have to be same lenght!!!
See Picture of my GEE BEE R-2. The servo arm is aproximately 1,5cm from center to hole/linkage... and the control arm is aproximately 5cm from center to hole/linkage.
Control arm is made of a 8mm Easton aluminium arrow shaft and 3mm pianowire and my elevator halfs are glued together through this Eston arrow. Picture shows one part of the elevator contoll arm (3 mm pianovire) with its wire atachment.
Why the contol arm is so long is because I want a firm and stiff set-up with a small amount of movement at the elevator. With this set-up the elevator is so stiff and firm that the elevator is hardly moved by pushing on the elevator.
Regards!
Jan K
Sweden

Stick Jammer

Geometry. I know everyone has their own opinion on this subject but the fact is, when using a straight servo arm with the control horn pivot point on or close to the hinge line, the non-pull cable will tighten as the servo rotates if the servo arm is shorter than the control horn.

ez2bgman

My Feedback: (4)

Sup Guys,

I finished the conversion and used as long as a servo horn as I could. THe Aresti 40 doesn't exactly have the widest fuselage. Everything worked out great. I had to modify the servo tray a bit, but it works out great. Absolutely no binding, or rubbing on anything. I plan on taking pics of the completed coonversion, hopefully by tomorrow, and have them posted here. Thanks for everyone's help

Now that the pesky little tropical depression went by, maybe I can get her out flying this week. Only thing left to do now is mount the receiver and battery and she's ready. Wish me luck.

Gary

jaka

Hi!
A Fact!???
The fact is that the control arm can be as long as you wish without having one wire slack and the other tighten as long as the servo arm is 90 degrees to the servo output axle AND the control arm is 90 degrees to the hinge line.
Regards!
Jan K
Sweden

Stick Jammer

Not sure of the nature of what you are trying to describe with these statements. How is a servo arm anything other than 90 degrees to it's output axle? And what does that have to do with this issue? At any rate, if the completed set up does not form a parallelogram (with the cables NOT crossing), the resulting geometry will not remain constant as the servo rotates. It is geometrical fact (do a search), that if the servo arm is shorter than the control horn and the control horn pivot point is on the hinge line, the non-pull cable will tighten as the servo rotates. The further it rotates, the tighter it will get.

mikeboyd

I didn't read anything about telling this new guy to cross his lines and shroud them to prevent them from shaffing each other. Most of us doing large scale IMAC do it that way. If the "servo levers" (arms) are of a larger moment than the rudder control arms, the following cable will tend to slack. If this is the case, then it is extremely important to ensure your cables are nice and tight at center to prevent flutter. Most of us, use a seperate control lever to take the load of tight cables, keeping from over-pulling on the servo gear train and couple the servos to the control lever. This can be another pull pull mini system or push pull system, which ever is most ergonomic for your application. Hope I didn't muddy the water too much, but had similar concerns years ago with my first pull-pull system. They are great, reliable, and lightweight, and nearly flutter proof when done properly.

ez2bgman

My Feedback: (4)

Mike,

Is crossing the lines more efficient than running them straight? I noticed one problem with my setup: since the Aresti 40's fuselage is so narrow at the back, the wires do not go straight back. They end up rubbing on one of the formers toward the rear of the fuselage. Could I rectify this problem by crossing them? It works great, but I'm sure that over a long period the lines will end up sawing throught the former. This has me concerned.

Gary

Stick Jammer

Crossing the cables is fine and should be done if there is a clearance problem. Don't allow the cables to rub on the formers as they will cut through. Glue in a piece of nyrod sleeve somewhere between the crossed cables so they don't rub together. Check this site for more info on pull-pull.

http://www.swbmfg.com/rudex.html

ez2bgman

My Feedback: (4)

Ok, I crossed the cables. Clearance in the fuselage is perfect. The cables even exit the fuselage better, straight through the cutouts. But now when I fully deflect the rudder to the left, one of the cables has slack in it. Yet when the rudder is deflected fully to the right, neither cable has slack. What gives? I made sure the control horn is straight on the rudder and the servo arm is straight on the servo. The cables have good tension on both side when the rudder is in the neutral position. Also, to prevent the cables from rubbing, I used Dubro Ball Links on the servo arm, one on top and one on bottom. There is approximately 1/4" between the cables where the cross. Any and all help is appreciated. Thanks.

Gary

Stick Jammer

A little slack in the non-pull cable at full deflection is fine and won't hurt a thing. Can't say for sure why there is no slack in the opposite direction. Possibly the right control horn pivot point is a tad behind the hinge line. Possibly the left control horn pivot point is slightly ahead of the hinge line. It doesn't take much and it's very hard to see by just looking at it.

ez2bgman

My Feedback: (4)

Stick,

Thanks for all the help. It didn't appear to hurt the rudder. I was concerned about it returning to nuetral, but it returns fine. I'll try to play with it a lil' more before I take her out for her maiden flight this weekend. I think that the hole through the rudder may have become enlarged from the constant adjustments. I'm going to check that out and, if necessary, add a small light ply piece to each side to reinforce the attachment point. I think that this may solve the problem (hopefully).

Gary

ez2bgman

My Feedback: (4)

Well I finished the pull pull conversion on the Aresti 40. I ended up having to cross the cables. On the servo arm, I used Dubro ball links and mounted one of the cables on top the arm and the other on the bottom of the arm. This provided more than enough clearance where the cables cross (absolutely no rubbing during deflection in both directions).

I put 3 flights on her today and she performed flawlessly. The pull pull setup provided great authority. Stall turns were accomplished with ease. Hammerheads were effortless and straight. I did notice some roll/pitch coupling during knife edge, but it is easy to fly the maneuver. I may set up a mix for knife edge. I am very pleased with this plane. Although not a true pattern, she is a good sport/pattern plane to learn on.

Here a few pics of the pull pull rudder: