This one is long. I’ll break into 2 parts

Linkage work part #1

First remove the masking tape form the tips of the elevators so when you power up the servos you don’t break something.

Plug the servos back in to the RX and turn it on. The servo wheel screws are still missing from the servo wheels. This is good it will help us make adjustments easier.

Adjust the length of the control horns from the middle of the hinge to the center of the 2mm clevis pin (bolt) Make sure both sides are identical. Mine were set at 31mm. Match both side as absolutely close as you can. My servo wheel connection choice was a hole about 12mm out from the center of the servo wheel screw. This gives me a mechanical advantage of over 2.5 to 1. This gives the servo better power over the surface and minimizes any slop or wear in the servo. In a precision setup you never want 1 to 1. Not even on the pull-pull rudder, but we will discuss that later. For now think using the maximum servo resolution. Servo wheel 12mm and the control horn on the elevator is 31mm. These are just starting values and we may change them later. Taking your time now will mean matched up changes later. If you need to shorten the control horn length to less than 31mm to get more travel…then its easy just a turn two on both sides and they stay paired up. Making these measurements accurately is very important to how the model will fly and trim later. I like to do it one time and that is it. This is the reason I use the more expensive MK clevis and NMP DARE links. Once you do this work it will not need to be changed. Even changing out servos the linkage will not need to change. Some folks don’t mind putting in the work… That’s cool I prefer to fly it and not have to spend time in the shop trimming…and adjusting.

Back to it; the servo wheels were setup at the 90degs pint as close as we could get. For now ignore the elevator and if it is centered up on the stab tip. Instead look at this 90deg pushrod to servo arm again using the Days Inn card key tool. This time it needs to be spot on. Align the card key down the center of the pushrod and slide it up to get the center of the bolt in the DARE link to align with the center of the servo wheel screw. This is super important here also. The more it’s off the variation you are going to have to put in electronically in the TX to get the elevators moving together. If they are matched mechanically then the differences will be very small as you will see in a bit. Use subtrim to get the servo arm pushrod relationship just right. Small changes in subtrim make a difference so work hard to get it as close as you can.

Since the servo wheel screws are not installed its easy for the next task. Look at the elevator and its relationship to the stab tip. For now I want you to get one side adjusted perfectly to the tip. For adjustments just pop the servo wheel off and rotate the pushrod in the clevis. This will have to be whole turns at a time. For the first side get it as close to aligned as possible. Don’t freak out if its not dead on. We are going to match the other side to it. Right now we don’t know where the elevator trim is going to end up so aligned with the tip is good for this one side. Knowing that Dave Guerin designs a model that is really close here we know the eventual center or neutral point will be close to this tip location. Once you have the linkage adjusted for length to get the elevator centered up on one side you are ready to move to the other side. Install the servo wheel screw on the side you just finished. I turn off the radio so that tightening the servo wheel screw will not strip the gears in the servo. The 3421Sa servos have a small nylon gear train. If you really crank on them while they have power the gears will easily strip. So power them off and tighten the servo wheel screw.

Next elevator side. Dial in the pushrod to servo arm relationship to the 90degs again. Subtrim is the way to do this and ignore the elevator location to center for now. Get that 90degs right. If you screwed up in picking which side of the servo wheel to use and your sub trim is high values….then switch the servo wheel around and re-attach the DARE connector. I screwed mine up and had to do this. In the end one servo had zero subtrim and the other ended with a value of 6. This is a good and low value. Next is to adjust the length of the pushrod to get the elevator in the proper center or neutral location.

This process is the same as the first side….get it close to the tip as you can…but this si not the definitive reference. We want the two sides to match each other. If the tips are sanded just a little off or maybe a little extra heat on the covering can pull one tip down or up. These tips are small and can bend a little bit one way or another. So don’t trust the tip….We used it on one side as a reference. This time eye ball the surfaces of the two elevator halves from the rear. Align your eye with one surface on the original reference side. Use the first side as your reference and adjust the current working side to it. In my case it was up compared to the tip about 1/64th of an inch. This is OK. It doesn’t mean the stab is warped. It just means the tips could be sanded a little different. You likely will not feel it flying. Just make sure the elevators match perfectly. I learned this from Tony Frackowiak. The Mark One Eye Ball is awesome for setting this up. Make full turn adjustments at first to get it close. If you have to, remove the clevis pin bolt. And turn it over to get a ½ turn adjustment.

Note: the MK clevis doesn’t come with a nut for the bolt. So if you turn the clevis over the threaded side of the clevis will be on the head side of the bolt. This means tightening the bolt will not pull the clevis together. That is OK for now…We are going to put little 2mm hex nuts on these bolts later. Its more important to have precision in this setup now. ½ turn on a 2mm clevis is pretty small movement. This is why I use the 2mm over the 4-40 or 2-56. The 4-40 is heavier and not needed due to the titanium…and the 2mm is more threads per inch than the 2-56. This means finer adjustment.

Once you have these elevators all setup at the center position and the servo arm to pushrod relationship is all 90 degs shut the radio off and tighten the servo wheel screw in the second elevator servo.

Now is time to match the servos or rather the elevator surfaces as they move. The servos and linkages are setup the same and we need to make sure for any given stick movement the elevators will track together. Our reference of centered and matched at neutral elevator will be our basline.