Split Elevator
 

I am building a plane that has a split elevator. The two elevator halves are not connected to each other. Each has a push rod. The two push rods are connected together inside the fuse and then to a single servo. This is essentially a "Y" with the two upper sections of the "Y" going to the elevator halves (about 12 inches long) and the bottom portion (2 inches) going to a single servo.

My questions are:

1. Does the part that connects to the servo have to be in the exact center line of the plane.
2. If it is off center by about 1/2 inch, how will it effect elevator deflection (major, minor, none at all)

Thanks,

RE: Split Elevator
 

I dont think the 1/2" would hurt you. Figure that with a large servo arm, the normal servo arm travel at full deflection will move that end of the pushrod about that much anyway. I would think you could position your servo just about anywhere and lengthen/shorten the hookup ends as required unless it is an extreme amount.

P.S. I would be interested in what others say on this subject as to whether or not anyone has actually measured any different throws with this setup. Personally, I have never used the setup (usually convert to a torque rod or double servos if the plane is big enough)

RE: Split Elevator
 

I've used this setup on two different planes and have had no trouble.

RE: Split Elevator
 

I avoid trusting the wheel collar for the Y connection... I THOUROUGHLY clean the wire, coat with solder flux the wire wrap with #24 solid copper, then more flux and silver solder it. The silver-soldered joint is stronger than the pushrod.

RE: Split Elevator
 

Off center won't hurt you unless you are really close to the elevators....but if the servo is in the wing saddle area, you are ok. I am sure with FHHuber on the wheel collar idea, which I know Gt. Planes shows on some of their kits, guess they don't think the modern modeler can solder. Wrap and solder, as instructed above.

Another option is the "U" shaped wire connector between the two elevator halves, and run one push rod to a control horn on one elevator only. This is pretty workable, unless you are talking about a precision contest plane, or a much larger airplane.

Clair

RE: Split Elevator
 

Vic:

The rotary motion of the servo arm will give a slight differential in movement, but a "Y" rod has been used by many, and no one has had any problem with the slight angularity difference.

Bill.

RE: Split Elevator
 

Off center will not matter. Unequal rod lengths will be a disaster. I agree completely that you should not use a wheel collar for a joiner. Try drilling a hole on opposite sides of the rod (dowel?), one of them 1/4" or so farther up the rod than the other. Make a "L" bend in the rod to slip into the holes. You can file a small groove on both sides of the rod for your wires to rest in. Temporarily hold them in place with CA and then wrap the entire section from the holes to the end of the wood dowel with a heavy thread and saturate the thread with thin CA after wrapping.

OR, you could just use a piece of heat shrink tubing over the wires to hold them in place. Whichever you think will suit you needs best.

RE: Split Elevator
 

Thanks for your help and advise. I will take all of these tips into consideration. This is a Great Planes model and I have used the wheel collar on other planes with no problems, however I do understand your concerns. I can solder but I only have a pencil iron about 5 watts. These pushrod wires soak up the heat and you end up with a "cold" solder joint - bad Juju.

Again, thanks for your help.

RE: Split Elevator
 

Mount the servo sideways, and the problem goes away.

BTW Sullivan make a nifty litte splitter... but I found you really must be concerned about differential motion if you use it - mounting the server sideways is a must. I had a setup, as in your picture, using the Sullivan splitter and there was noticable differential motion. Using a soldered Y connection fixed it. The rod pair seem to move side to side a bit as the servo arm rotates. With the Sullivan splitter the "dumbell" (double ball joint) that connects the rods will rotate as the servo arm rotates and you get noticable differential motion.

RE: Split Elevator
 

Well, I did a trial fit that resulted in very little difference in deflection (about 1 degree at full up). I don't think that will cause any visable effects during normal flying as I rarely need full up elevator. I bolted the servo tray in place and we will see how she flies when the weather permits flying here in Baltimore.

RE: Split Elevator
 

1 degree could make a difference in a loop. I always put my pushrod with the split-Y right in the middle of the fuse just to be safe.

RE: Split Elevator
 

Not to complicate this issue, but this might be of interest. I built a GB Sukhoi some years back and installed a strong JR servo inside the fuselage about 12-15 inches from the elevator hinge line. Looking in the bottom of the fuselage, the servo was right side up, and the control rods (wrapped and soldered as described above) entered the servo wheel exactly on the fuselage center line. Old pattern flier, I just knew I had a perfect set up. Nope. Picture this if you can....on up elevator, servo pushing the rods, the servo driving the left elevator is getting a pretty linear push, while the rod driving the other elevator is going somewhat sideways. And the reverse was true when the servo is pulling the rods for down elevator. Result was that everytime you used very much control, the deflection was different from side to side, and of course the airplane would slightly roll. Requiring correction on loops, split S turns, etc.

Had I mounted the servo on its side, all would have been perfection, with the servo wheel moving in the same vertical arc as the control horns.

Learned one the hard way that time:) However, had the servo been up in the wing saddle area, the difference would have been minor.

Maybe this will help someone to avoid my mistake.

Clair