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ORIGINAL: JohnBuckner

Of key importance in any pull/pull installation is for the two surface horns clevis holes to be lined up perfectly laterally and through the exact hingeline of the surface. If there is any discrepancy in the alignment either fore or aft then differential will be induced and there will be a slack line situation on movement in both directions.

For all practical purposes the chief reason for pull/pull is to save weight aft of the CG for airplanes that may have tail heaviness problems. That sure applied to my Balsa Nova I built some years back. The Morris kits lumber was overly heavy at least in mine and the structure was a bit overdone. Take care in your CG considerations and the airplane is a great flyer however you will enjoy it. I recently gave the old bird away to the gentleman in the photo and he is sure enjoying it.

John

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ORIGINAL: Rodney

As one who uses pull-pull on nearly all my planes, on both rudder and elevator, I have found that you always want some positive Ackerman in any pull-pull. If you do not know what Ackerman is, just google for it as there is a lot of good info available . Basically, it is adjusting the attachment points relative to the hinge point so that the line NOT being pulled on always goes a bit slack as you move the surface away from neutral. The trouble most people get into on their first pull-pull is to get some negative Ackerman built in and that can cause all kinds of problems as it causes excessive current drain on the servos as well as possibly causing binding and/or restriction on amount of throw.

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ORIGINAL: Gray Beard

Life was just so much easier before we heard of Ackerman, who is this person?? How did we ever get our pull/pull systems to work before he invented Ackerman??

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ORIGINAL: CGRetired

To make life simpler, Bill, the bottom line is to center the servo, make the attachements with the straightest connection between the servo and the control horns, and then don't try to remove 100% of the slack. It just won't happen.

I use a vinyl coated cevlar cord (see link below). Great stuff, comes in two sizes. I threw away the steel cable stuff, in favor of this cevlar cord. It's strong, but very easy to manipulate and to tie knots with (hey, Coast Guard Retired, remember? ha.. oops) And, if and when it may become frayed, and it can and will happen, it's easy to replace.

http://www.thunderboltrc.com/index.p...roducts_id=580

They make different thicknesses. This one is .038'' but there is.058 I believe and other thicknesses.

Of course, there are the physics of the connections. Use the same conrol horns on both sides, do your best to make sure the control horns are mounted in as close to exactly the same position on the left as on the right (and, of course, vice versa.. ;) ) and then make sure you absolutely center the servo with your transmitter set to exact center with the trim at as close to center as possible.. then make the connections WITH THE SERVO'S ENERGIZED. Use the strength of the servo to insure maintaining centering.

Once done, you will have a well centered and balanced pull-pull rudder installation.

Oh my gosh.. next project.. having a pull-pull elevator AND an pull-pull rudder ( as in the Excelleron 90 installation.. quite a challenge!!)

CGr.

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ORIGINAL: JohnBuckner

Yes, with that type of crimpinng sleeve you simply crimp after routing as you described. you can also use short peices of brass tubing for crimpers if you don,t want to buy expensive pull/pull sets.

Another method I often use on the airplanes I choose to use pull/pull is to use a clevis threaded onto a solder on thread fitting. Just flatten the end that the wire rod is normally inserted and soldered. Then drill a small hole for spider wire which works great tied directly through this hole and dripped with a drop of Ca. This works well with a lot of lighter aircraft, old timers and such. Have used pull/pull on a fair number of my old timer types even on elevators this of course for the need to minimise weight aft of the CG.

My Balsa Nova was a working airplane that was needed quickly for the use as a pace plane in the old Scale Warbird Racing Association events used at a number of southwestern fields. Typically the airplane would be required fly working normally with three other pace planes for around one minute every fifteen minutes for a total of around fifty flights in a long race day. This required a lot of fore thought to keep the pace planes going with shared pilot duties and refueling and servicing. That why the upright engine for ease of ignitor use and fueling with a visible and accessable fuel tank. In some cases we also used converted Q-500 airplane with taxi capable tri gears for pace planes also. The Balsa Nova is a very easy airplane to land and more importantly easy to taxi and get off the runway quickly. Important for that type of application.

John

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