hi guys

i know the phoenix atlantis isnt exactly at the top of the list for pattern, but it should help "whet my appetite"... my question is concering the pushrod arrangent which requires using hard balsa dowl with a threaded rod at each end.
However, the elevator is in two pieces so the elevator pushrod requires two threaded roads in a y-shape; one to operate each elevator half.

I have found with these sorts of setups, that any sideways movement results in an "aileron effect" on the elevator halves which is totally useless.

I dont know too many other modellers; what methods do people use for this sort of setup?

regards


mike

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If you make the pushrod extend beyond the Y joint to the tailpost, and support the pushrod in the tailpost and before the Y joint, you will get very stiff elevator control. Even better is the Dual Elevator Control System (DEPS ) described elsewhere in this forum.

I don't remember where I first saw this many years ago, (maybe in Dean Pappas' column in Flying Models?) but I've used it several times in pattern planes. It has zero slop and is very precise.

The pushrod is a hollow rod, like an arrowshaft or CF tube. There is a threaded rod (a long 4-40 screw works well) that passes through it near the rear of the fuse, and exits just clear of either side through slots in the fuse that are long enough to allow full travel of the pushrod. The rod ends get those milky white nylon aileron horns screwed onto them, and then two short regular steel pushrods to the elevator horns. The front of the pushrods get solder clevises for attachment to the aileron horns.

The end of the hollow pushrod rides on a wood dowel glued into the tailpost (shown in red), which is long enough to engage and support the rod during it's full stroke. The dowel needs to be a relatively loose fit so the slight lateral displacement the pushrod will have from servo rotation won't make it bind on the dowel.

Here's a very crude drawing to help illustrate. Drawn looking from the top/bottom:

Rick

Mike,

MK products makes a ball bearing dual elevator setup just like described above. As for the Y pushrod setup. I have done that many times w/Dave Brown pushrods. The think you have to remember is that the elevator servo output must be in the exact center of the plane to get the Y pushrod to push/pull evenly on both sides of the plane. If you do not have the output in the center, you end up with "differential" elevator which is always good for a solid 5 for inside/outside loops since they will look like a corkscrew. I still use Y pushrods with the servo output exactly centerline and have no problems with loop trimming.

Dan

thanks for the input.. i never thought about the differential factor... funny how the manuals never seem to say anything about that!
what are Dave Brown pushrods? do you have a link to a page i can view them?
regards

mike

I think that putting the servo in the centre of the fuselage will not remove the differential effect, as the servo arm will move in an arc.
Putting the servo on it's side, will however.
Magne

Yeah, that's correct. Putting the servo in the "conventional" way will not work as desired. Put the elev. servo on it's side. Make sure the pushrod is in the center of the fuselage and the motion is along the center too. Make sure the servo arm swings parallel to the center line of the fuselage (it may be offset slightly depending on the type of end link you use. This works very well and it's not hard to do. If you make a ply servo tray - be sure the servo is isolated from the airframe somehow (rubber grommets). Futaba has a ready-made plastic tray for their standard size servos that may also be used but sometimes it doesn't fit into the small (40 size) planes.

John Pavlick