I have other hobbies, one is archery. The way to make changes in the length of the bow string or cam cable is to twist it. Bow strings are made of kevlar these days. You can buy kevlar as fishing line. I did that, 150# test.

I am working on a 1/4 scale BUSA fokker D-7. I absolutely want pull-pull for the elevator and rudder, probably the ailerons as well. What is wrong with making my pull-pull cabels out of say, a half dozen strands of the kevlar fishing line? 900# test now! To make my fine ajustments in length I could simply twist the bundle. I am envisioning using quality snaps from swivels instead of clevisis. The ends would be finished with a bunch of half hitches and CA glue.

How about going right off the servo arm? I read some guys don't like the idea. There is no need to make the cabels banjo string tight. In fact the steel cabels on my current daily flyer are steel and a bit loose. The play in the surfaces is less then a push-pull lash up.

Scota,

I have a big bird with Kevlar pull/pull on the rudder. It was a purchased kit. The one down side I have experienced was that the cable did not stand up too well to abrasion. I had to replace both sides after a year or so. The second set has lasted longer, but I inspect them frequently.

I do not subscribe to the high tension design approach. Once you have the slack out of the Kevlar, more tension is only adding stain to the servo and surface. My bird is a slow flyer. I assume your Fokker is too. I cannot imagine real high loads requiring all that much tension capacity. Geeze, you are not hanging the model from the cable!

Have fun!

Bedford

It's best to build a 'tiller' so that the servo connects to it via an adjustable link. The tiller takes the tension loads (which shouldn't be much). By having multiple attach points on the tiller for the servo's link you can adjust the throw and get better mechanical advantage. It's easier to match the width of the hole from the horns to the tiller, too. Servos connected to the flying surfaces may give too much throw unless you adjust travel rates. The throws are smoother in flight if servo connects outboard to where control cables do. If a servo needs changing it is easier with a tiller setup. It's easy to duplicate the rudder bar in a scale fashion so the control runs will be more accurate. What DVII are you going to replicate? I have one of these BUSA kits and have a Proctor kit on the way.

I have not decided on the paint. There is a German guy who did a nice one on the rcscalebuilders site. It is read and white. I like it. I did not buy any losenge fabric. Mine is all "natural" color. I'll get more decisive on that as I get more excited toward the end of the project. Goering's white D-7 looks nice but, it has probably been done a bunch of times. It might be hard to see. I find that an airplane that visually pops is easiar to fly. The Swiss paint looks easy and would be different. I like to be different. I think the Swiss colors might be easy for me to see against a blue sky. My color vision is slightly sub par.

On the chafing problem........Bow strings use something called "serving". It is another piece of line, wrapped around the main cable very neatly and tight. Black monofiliment is used a lot. It would take a lot of wear to get though 100# mono. Serving is where the arrow nock goes and the end of the string hooks on the limb or cam. Serving is waxed to make it last longer. I have bowstring wax.I was going to bring the control line out the fabric and make some leather patches to feed them through, like real airplanes. Since I have the tools to do that I probably will serve the cabels. Basically, I will be making bowstrings.

The thing that intrigues me is the idea of using a twist to regulate length. How simple, strong and light is that? It should look really cool too.