fledermaus

I am finally finishing my 1/6 sport-scale Sopwith Camel scratch-build and I have run into a problem I don't know how to solve.

The exit points for my rudder pull-pull cables are too close to the horn ends if I use standard pull-pull end fittings. I need to have some kind of adjustment at the horn ends, unfortunately, because the way I have the servo ends set up I can't have adjustment. I have just barely 2 inches between the horn end and the side of the fuselage.

Yeah, I know, should have figured this out in the planning stage. Did I mention this is my FIRST scratch-build...

So does anyone have any suggestions? Is there a shorter clevis I could use? What about drilling out a normal clevis closer in to the threaded end and using music wire for the clevis pin?

Help!

abufletcher

Are you absolutely sure you can't switch things around so that you have the clevis with the threaded rod on the servo arm instead on the control horn end? If there's no way to get the adjustability into the pull-pull loop you could just do without and try to get the cables as tight as you can (which doesn't really have to be that tight) just with a crimped tube. That is, don't use clevises at all (which will actually look more scale). Are you using the DuBro 2-56 threaded rod to attach the pull-pull cables. If so, these can also be shortened somewhat.

BTW, let's see some photos! We're always eager to see more photos of WWI models!

allanflowers

Would this work?
http://www3.towerhobbies.com/cgi-bin...?&I=LXDS47&P=7

TedMo

Not sure I understand your situation? are you referring to quick links as the clevis? If so there are some pretty short nylon quick links that may be useable? Or possibly a ball link.

TFF

Just make the adjustment at the servo ,and just loop the cable through the surface control horn with a crimp end. At the surface will be fixed but at the other end you can adjust.

abufletcher

Just remember that fine adjustments aren't really needed now that we have computer radios to make the adjustments. So as long as you get the cables reasonably taut with the flying surfaces reasonably well centered, you don't need the clevises at all.

fledermaus

Ok, maybe I can just use loops through the horns.

The problem with connection at the servo end is this: because the interior of the 1/6 scale camel was very congested I could not align the servos appropriately to run pull-pull cables directly off the servo arms unless I put at least one of the servos pretty far back in the fuselage, where it would not be easily accessible for adjustment anyhow.

So I used a method that is sometimes used in larger models - the pull-pull cables are run around spools which are driven by short pushrods from the servos. The spools are positioned to allow symmetrical pull-pull cables for the rudder, and reasonably even cables for the elevator, but they are behind the hatch region where the servos are.

TFF

The wheel is called a capstan. Very nice.

fledermaus

In the pix I posted you can see the spools and the cramped servo compartment. The rudder and elevator servos are mounted sideways, and beneath them you can see the aileron servo (a Hitech high-torque model) which drives all four ailerons via another spool. The ailerons are in a closed loop just like the full-scale Camel.

If you want to see the complete build saga, I have a "vanity web site" at [link=http://www.mts.net/~mhultin]Phil's Airplane Pages[/link] and the Camel is In My Workshop. Follow the links.

I am just finishing the painting, only have two more roundels to do on the upper wing and then clear-coat for the whole plane. Then its assembly and rigging.

Frankly, now that I have got this far I would not use this servo-driven spool method again. I just needed to modify my plans to make a longer fuselage hatch so that I could place the servos more appropriately, but I didn't realize that when I built the fuselage.

abufletcher

It may not be the most convenient installation, but you can be proud of your solution! In fact, thanks for posting those photos as I may need to do something like that on one of my builds. It's always good to try something new and different.

I'd just go with cable loops through the horns. By the way, one thing you can do to be even more scale AND allow some "adjustment" to the length of the cable is use a little U-shaped loop of metal (called a "shackle") on the horn (attached with a pin) and the cable loops through the shackle instead of the horn. You can fudge the length of the shackle to get the tension of the cable just right. I did this on my Snipe.

fledermaus

Good idea. I had thought of doing something like that on my rigging because I don't trust the smoothness of the holes I drilled in the brass rigging plates, but it hadn't occurred to me to use that method on the control cables.

The one nice thing about the capstan (thanks TFF) method is that I was able to maximize the servo travel and the leverage. The diameter of the capstans matches the spread of the control horns, but the location of the pushrod and its position on the servo were chosen to produce the desired maximum control surface throw at nearly the maximum travel of the servo. It also ensures that there is no slack on the cables because they pay out exactly in proportion to the travel.

abufletcher

I checked out your build pages and it looks very good. Excellent work on the cowl. It does look like you might need significant weight up front though so best to plan for it now.

fledermaus

The Proctor 2C turnbuckle might be a good solution. The overall length of the turnbuckle is just under 1 inch, leaving about 1 inch for the crimp and loop at the end of the cable and for the travel needed in operation. I had looked at Proctor hardware for rigging but decided it was too pricey for me on this project. It hadn't occurred to me that I could perhaps use the turnbuckles on the control system, which needs far fewer of them.

Thanks for the suggestion.

fledermaus

I figured I could screw lead plates onto the firewall if necessary, but in fact my initial check of the balance point on the uncovered airframe didn't seem like it was that tail heavy - if anything it might even be a big nose-heavy. With all the servos, fuel, battery, receiver etc. forward of the lower wing T.E. (i.e. no more than 9 inches back from the CG which should be near the lower wing L.E.) the tail isn't all that heavy.

Still, we shall see now that it is covered and painted.