rudder pull-pull setup, please HELP !!!!
09-04-2004, 06:33 PM
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rudder pull-pull setup, please HELP !!!!
Hi
I'm finishing a CAmodel 27% Extra 300L but I have some problems installing the rudder pull-pull system.
On the rudder I'm using nelson hobbies hardware, it's 3 in. wide and the rotation point is 6 mm behind the hinge line.
I need to cross the pull-pull wire because the fuselage is very narrow where the exit slot are.
I can make any servo arm for the rudder servo using phenolic panel but I don't know what size need to be in this situation. I know when you are using cross wire the servo arm is shorter with an offset to the rear of the plane but the rudder horn is on the hinge line. [
]
Anyone of you know how to calculate the length and offset that I need on the servo arms to get a good pull-pull ??
Best Regards
Fernando.
I'm finishing a CAmodel 27% Extra 300L but I have some problems installing the rudder pull-pull system.
On the rudder I'm using nelson hobbies hardware, it's 3 in. wide and the rotation point is 6 mm behind the hinge line.
I need to cross the pull-pull wire because the fuselage is very narrow where the exit slot are.
I can make any servo arm for the rudder servo using phenolic panel but I don't know what size need to be in this situation. I know when you are using cross wire the servo arm is shorter with an offset to the rear of the plane but the rudder horn is on the hinge line. [
]Anyone of you know how to calculate the length and offset that I need on the servo arms to get a good pull-pull ??
Best Regards
Fernando.
09-05-2004, 06:11 AM
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RE: rudder pull-pull setup, please HELP !!!!
Don't worry so much, just make up an arm and try it. If it works, you've got yourself a vorking arm, if not make up another one. Begin with the standard servo arm and the hole furthest from the centre. Then work up from there if that is not enough.
It is OK if one of the lines goes slack while deflecting the rudder (the left one in a right-hand turn), the other one is still pulling and doing the job needed.
It is OK if one of the lines goes slack while deflecting the rudder (the left one in a right-hand turn), the other one is still pulling and doing the job needed.
09-05-2004, 09:42 AM
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RE: rudder pull-pull setup, please HELP !!!!
I agree with the above. Just make it 1:1 (distance from cable connect point to the servo arm axis of rotation verses the distance from cable connect point to the control horn axis of rotation). Try it out as is. I have some slack at full deflections on my 25% CAP232 rudder and it flies just fine. In fact they are not even fully tight at zero deflection and I just haven't bothered to adjust it yet. BTW, mine are 2 inches on both sides and crossed (2 inches from cable to cable). I have no offset on either side and it works great. With bigger planes, maybe you have to be more exact but not on my 25% CAP232. Check out the following link on pull pull systems. It might be helpful. This guy has done a lot of R&D on this topic.
http://www.swbmfg.com/rudex.html
You might want to go with a 2 inch wide servo arm instead of a 3 inch if a 2 inch wide control horn clears the fuse in back at full deflections. That way your cables will swing a more narrow path when the surface deflects from one extreme to the other (and the slots can be more narrow). Your setup sounds like example B on the SWB site. Your servo arm will have to be slightly shorter than your control horn (cable to cable distance) and a slight offset to the rear of the plane for the servo arm. See example B. Like I said, I did similar to example B except with the servo arm and control horn the same width, 2 inch, and I have no offset on either side. Works great.
http://www.swbmfg.com/rudex.html
You might want to go with a 2 inch wide servo arm instead of a 3 inch if a 2 inch wide control horn clears the fuse in back at full deflections. That way your cables will swing a more narrow path when the surface deflects from one extreme to the other (and the slots can be more narrow). Your setup sounds like example B on the SWB site. Your servo arm will have to be slightly shorter than your control horn (cable to cable distance) and a slight offset to the rear of the plane for the servo arm. See example B. Like I said, I did similar to example B except with the servo arm and control horn the same width, 2 inch, and I have no offset on either side. Works great.
09-05-2004, 11:15 AM
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RE: rudder pull-pull setup, please HELP !!!!
fdo300,
The servo arm should be the same length as your control horn. If the pivot point of the control horn is 6mm behind the hinge line you're likely gonna get extreme slack in the non-pull cable as the rudder is deflected unless the servo arm has the same offset. If you can make your own servo arm, put 5 or 6mm of offset (to the rear) in it to match the control horn.
The servo arm should be the same length as your control horn. If the pivot point of the control horn is 6mm behind the hinge line you're likely gonna get extreme slack in the non-pull cable as the rudder is deflected unless the servo arm has the same offset. If you can make your own servo arm, put 5 or 6mm of offset (to the rear) in it to match the control horn.
