I am installing a Kevlar Pull Pull on my 120 size Extra. I plan on using an aluminum bell crank.

Since I have never installed something like this, I am unsure about the alignment of the bell crank/ servo set-up to the rudder horns.

I assume ideally, there would be a straight line from the rudder horn to the bell crank. But, what would be the problem with having the cables angle up on there way to the bell crank.

i.e. The rudder horns will be mounted at the bottom of the rudder. Due to the set up of my plane, it may be easier to mount the bell crank on the top of the servo compartment. Therefore, the cables would travel in an upward angle to the servos. I realize the cables would be pulling "up" as well as back, but don't know how big of a problem this would be.

Confused? Any ideas?

Mike

Mike.
I have plenty of smaller planes with pull pull on the tial sections but I won't use kevlar. although it strong I question it at the linkage..
I prefer to use nylon coated fishing wire. you can either crimp it or twist it and melt. the nylon melts into each other and will not come apart.
email me if you need photos.

some of my pull pull systems are straight to the control serface and others are not so straight but none have a bell crank.
How that would change the servo's ability to move the serface someone else in here might be able to say.

How much of an angle are we talking about here? I've never tried it myself, but on the surface it seems like a pull pull setup operates in a 2 dimentional plane. It doesn't matter what angle the plane is on, the geometry of the mechanics will remain constant. As long as you remember to make sure that the distance between the clevises at the control surface is the same as the distance at the bellcrank, (that parallelagram again) you're in business.

OK, now somebody will come along and point out how stuipd I am, and give you some actual good advice.

BTW, I very excited that I got to use "geometry", "2 dimentional plane", and "parallelagram" in conservation. Even if it is just a cyber-conservsation

Frank

BTW, instead of "agua" or "water" you should say "unflavored-clear-wet"

the angle doesn't matter,go to the engine and back if you wish,Kevlar is on some of my pull/pull,also you can cross the lines or go straight.Have fun.

I just did a pull/pull rudder on a Stinger, using a Sig tiller bar driven by servo. Cables cross between tiller bar and rudder horns, so the cables run in a straight line from bar to horn, but exit the fuselage just 4-1/2" forward of the hinge line. Tiller bar is about 1-1/2" higher than the rudder horns. Works great. Tension on cables is snug but not tight, so friction of cables crossing is negligible.

I would not trust any cables that cross each other if they make contact where they cross. Sooner or later one will saw the other into two pieces. I prefer the nylon coated fish line leader also. I have quite a few 1/4 scale with pull-pull on rudder and elevator, some over 12 years old with hundreds of flights and no failures. I do run the cables inside nylon tubes (to more easily string the lines and to guide the lines around some rather sharp turns. I do use a pulley at the servo end, no bell cranks, as the pulley always pays out as much line as it pulls in with no tension changes. Lines just taunt enough to not come off pulley.

Rodney, Could you provide a picture of your setup? for us engineeringly challenged :stupid:

Regards
mark

The angles won't affect the working of the rudder, however it will put more stress on the linkage at both sets of horns. If you use a typical clevis, it will want to work itself loose because it will try to rotate perpendicular to the direction of travel. Hold the system in your hands and over-exaggerate the angles and you will see what I mean. You could use a ball link to acommodate this rotation, but I don't trust those to stay on.

The system will work great, however, if you can mount the servo on an angle parallel to the direction of travel, as well as mounting the rudder control horns parallel. This way the linkage is only moving in 2 dimensions.

I just did this same thing in an Ultimate Bipe.

Thanks Dannost,

I toyed with that idea also.

Mike

I do not have real clear pictures (cheap digital camera) of two of my installations but; if anyone wants to view them, send me a request via E-mail and I'll send you copies. If any of you have access to the May 1993 issue of Model Airplane News, I have an article on "How To" on this topic with full descriptions and photos as well as how to build your own pulleys and systems.

When do you use straight vs. offset bellcranks?

ML

Hello Rodney,
I read all the posts concerning the set up of a pull - pull rudder system. I am planning to use this set up in my son's Viper once we start construction. I would greatly appreciate it if you would send me any drawings or pictures that would show how to get it all to work. If you'd like, you can e-mail me at [email protected].
Thank you in advance for your time and help.

Best regards,
Mike

Mike, I triedto E-mail those picture to you but they came back as undeliverable. I tried both [email protected] and [email protected] and get the message that they are undeliverable. What am I doing wrong?