I've read a lot about folks trying to setup their pull-pull systems and not being able to get them tight or pull correctly. I wanted to setup my profile with a pull-pull setup and then read about the Ackerman setup and it works great. I'm just getting my radio gear installed in this plane and was pretty amped how well this looks to work. Used the line termination method I read about on a few other threads here on RCU.

The gist of the Ackerman setup is that at neutral, both lines are taut but as you move to deflect either way, the pulling side stays taut while the non-pull side gets a little slack in the line. It's a pull setup so you don't need the non-pulling side to be taut.

Neutral - both lines taut...



Surface deflected - pulling side taut - non-pulling side has slack...



The main setup item that contributes to slack on the non-pulling side is having the control line pivot point behind the control surface pivot point.



The other item that can contribute to slack on the non-pulling side is having your control horn connection points on the servo side slightly more narrow than your surface control horn connection point width... which is the case with my setup. The front horn connection points are about 1/8" more narrow than the back control horn connection points.



The materials I used...



The metal fishing leader is multi-stranded cable material...



Dubro threaded coupler drilled with a 1/16" bit...



Cleaned up the hole for the cable by filing the path where the cable sits so there are no sharp edges...



To terminate the control line on a threaded coupler or directly to a horn you first slide a crimp sleeve onto your working line...



Next, thread the tail through your connection point and back through the crimp sleeve...



Next, thread the tail back around and through the crimp sleeve (this is a little added insurance to keep the line from slipping through and to fill the crimp sleeve so it gets a good bite when crimped)...



Pinch the line and work the slack out of the sleeve...



Then crimp the coupler three times on alternating sides of the crimp sleeve...



I felt the narrow bite helped get more pressure in a smaller area to better grip the line.

I cut off the line so I had about 6" extra past my servo. I then repeated this on the other side. I connected the couplers to the plastic clevises and connected them to the rudder control horns.

With having both cables connected and crimped at the back control surface horns, I ran the cables to the servo horn and threaded the front connections on and dressed in the crimp sleeves at the servo but did not crimp them. I then pulled one side taut to the point where the rudder was straight and then pinched the line at the connection point to keep this length. Next I worked the slack out of/dressed the cable into the crimp sleeve with my other hand by pulling on the tail end of the cable. I crimped the sleeve in three positions. I repeated this with the cable on the other side.



Both lines are pretty taut at this point. I adjusted the lines at the coupler to be taut at neutral. I used plastic clevises... this is a smaller plane setup so they will do the trick and they grip the 2-56 threads well enough that I don't require a nut to keep it tight. After this, I trimmed the tail ends off and put one drop of CA into each crimp sleeve for a little more insurance.

I imagine the neutral setting will get a little slack after a few flights as the control lines bend a little more at their connection points. Once this slack is removed, I think I'll be set.

Pretty amped with how easy this was and is a light setup to boot! Hope this helps someone.

somegeek

You did an excellent bit of reporting here Somegeek. I use nearly the identical procedure with great success. All my large planes use pull-pull on elevator and rudder and all have a slight bit of Ackerman built in. I have the cables just snug enough to have no sag at neautral. I've never had a failure duing it that way and some of my planes are 15 years old or older with literly hundreds of flights on them.

Great job, A bit big but A good job of reporting on A how to. I have been making up my own pull/pulls for years and pretty much do it the same way. I buy Dubro rigging couplers instead of drilling the brass types. Only because my drill press isn't very good. I get them in both 4-40 and 2-56. I have the wire leader on hand in several sizes from 15 pound to 30 pound test. It's nice to have A Bass Pro close at hand.

Thanks for the kind words guys!

I read a lot of posts regarding pull-pull systems but didn't see many pics so figured I'd add to the collective.

somegeek

I have started using these from swb.
And if you go to servo arms, they have offset arms, this provide the ackerman without moveing the control horn up or back.

http://www.swbmfg.com/

FYI, they are a little pricey, but they make life really simple when adjusting the tension as the wire stretches.
Also, great job somegeek, nicely done and explained.

Good stuff Geek! This one's going straight to the hard drive. Thanks!

-MA

Why would you want slack on the non-pulling side... when you begin moving the surface in the other direction... nothing happens with stick movement until the slack is taken up especially in manuevers with low airflow over the surface... or am I missing something?

The slack this setup causes sets things up so you're not pulling tight on both sides at all times. With prop wash and/or forward movement, you will always be pulling if not in the neutral position.

somegeek

There is no slack at the neautral position, only on the non pulling side after some movement off center has been made. It is just a safer method of doing it as, if you make a slight error and have the opposite of Ackerman, you put a big strain on the servos and most everything else which gets worse the further the suface is moved. Improperly installed pull-pull can eat up your batteries (increased current drain) in a hurry. Properly done, very reliable and light.

I add my thanks for this tutorial as well. Xlnt photos and description and as MasterAlex said, straight to the hard drive! [sm=thumbup.gif]

OK.One thing I failed to ask. Do I hook the servo to the tailwheel & then use springs to the rudder? Or, do I go directly to the rudder & then to the tailwheel ? I'm thinking the later would be the way to go. Again, thanks to everybody !!!

Go direct to rudder then use springs to go to the tail wheel. This saves the servo as no shock loads when the tail wheel hits an object that deflects it.

Thanks again guys. I'll have it working tomorrow!!!!

One more question since I'm going to be using pull in earnest on my next build....

I heard it better to get Ackerman by having the control pivot point behind the surface point thereby allowing the lines to be parallel as opposed to a slightly less diameter servo arm leading to a trapezoidal type setup..   Not sure if this is the case but parllell lines are better or it doesnt really matter?

it may be worthwhile to explain/mention that with ackerman geometry, the amount of slack on the non-pull side is proportional to the amount of surface deflection........ when the deflection is small, the slack is very slight and as the deflection gets larger, the slack gets greater........ this keeps the likeliness of flutter in check at small angles of deflection, where it's more likely to happen and is more detrimental to responce, but allows a no-resistance pull at larger deflections, where the control surface is really loaded against the prop wash/ airflow and flutter is most likely not going to happen anyways.