Got a Hangar 9 value series Cessna 40 ARF for Christmas from my loving but highly non-model airplane oriented wife. I am not getting a warm fuzzy feeling about the pushrod system that came with it. It utilizes ~1/4" balsa dowels connected with metal ends glued and shrink wrapped to it. I assembled the first one (rudder) which exits on top of the fuselage but am not satisfied with the fit of it. It kinda appeared that there would be serious interference at the last former. The instructions give no clue as to how the rod ends should be bent for clearance. What I am thinking of is installing Sullivan Gold-N-Rods and Ernst pushrod exits on it. My biggest problem seems to be how to attach the rods to minimize outer sheath torque movement. My thoughts on this are to install the rod from the tail and then slip a piece of ~1/8" X 1/2" X 1" with a 3/16" hole to one side and adhesive (wood glue, epoxy, etc.) to the other, place it against the middle of the tail former, and hold it down with a dowel till set/cured. I will then stabilize the rod sheaths near the servo arms.
I can't quite picture what you are proposing. However with the Goldenrod type pushrod, theoretically, if both ends of the housing are anchored securely, it doesn't matter where the pushrod (housing) goes in between. I feel better having the house supported somewhere in between also. You may have to be creative with a dowel and chewing gum to glue a block of wood between the servos and the tail. Again, be sure both ends of the housing are securely glued - sand the outside of the housing for glue to adhere. Epoxy is good, silicone is ok. The inner pushrod can extend a few inches from the housing, a little longer if you put that piece of metal rod in it that the clevis screws onto, extending into the pushrod. Happy landings!
Earle
Here is a hint from "the model doctor" An easy way to secure Ny-rod or Golden-rod type push rods to the sides of the fuselage is to use small pieces of light fabric. Take a strip of the fabric and lay over the outer case of the push rod and press against the surface to which you wish to attach the push rod casing. Flow thin CA on to the fabric to bond the fabric to the surface. Oh yea, unless you also want to be bonded to the airframe, use a piece of Saran Wrap between your fingers and the fabric.
hint below from the Sun Lakes Arizona club newsletter
Another thought, with pushrods, is to align the outer sleeve using a piece of hard piano wire inside the sleeve with as tight
a fit as possible, and then aligning the servo output and the control horn in a straight line. Support the sleeve at the rear
of the fuselage where it exits and then another support about 3 ½ to 4" behind the servo output, and finally a support
about ½ way between the two other supports. When these are completed, withdraw the stiff piano wire, and reinsert the
inner pushrod.
I prefer "GoldenRod" brand pushrods using the red colored sleeve as it is a bit flexible. Then I use a ¾" piece of the 2/56
threaded rod and a nylon clevis from either Goldberg or Dubro. I find that the nylon clevises fit the control arm of either
the servo arm or the control arm on the movable surface, and that they last
50 to 60 hours of flying time before they
should be replaced. Notice that I stated "Servo Arm" and not "Servo wheel". I buy and servo "X" outputs, and then cut off
the unneeded/unwanted arms so that regardless of servo movement, the clevis never binds on the output when the servo
is moved to the full forward position. On surfaces such as a slanted rudder, I recommend the use of a Dubro Ball and
socket, where the ball is screwed into the surface control arm and the socket is attached to the 2/56 threaded rod at the
back of the goldenrod. That way, the ball and socket take up the twist action that would normally eventually break the
clevis pin leaving you without the use of that control surface. BUMMER!!
On Tue, 22 May 2007 22:27:52 -0500, "Mark Daughtry, SR" wrote in :
I usually worry about the sheath only near the servo.
The other end is secured as it exits the fuselage.
If I'm not mistaken, Sullivan recommends putting an S in the middle if you're worried about making the pushrods less sensitive to temperature changes. I've never tried that. I just trim as needed for the day's conditions.
If the two ends are secured, what happens in the middle really doesn't matter.
That would be true if the tubes and rods were inelastic. They are not. Consideradable lateral force can be exerted down the length of the snalke outer under compression..enough to bow it sideways even if its secured at both ends. Its epscially likely to do this if it is curved already,.
I lwayss secure my runs, in even smll models, every couple of inches. This need be nothing more tan two notched pieces of balsa glued across the fuselage wit the rod outer trapped between them but its necessary, or one day you will call for full up elevator in a dive, and NOTHING will happen..
That sort of push rod has always served me well, although 1/4" balsa is about the minimum that I'd consider for a 40 sized plane -- I'd maybe go up to 5/16, but I'd maybe over do it.
I bend a right angle in the end of the wire & drill a hole across the pushrod about 1.5 or 2 inches back. Then I wrap the end with carpet thread & use CA thin to hold it. Trim the end of the rod past the hole to a point if clearance is an issue.
On Wed, 23 May 2007 18:18:45 -0500, Charles & Peggy Robinson wrote in :
I've already conceded that the materials may flex under load.
Since the manufacturer recommends and S-turn in the middle of the run to compensate for temperature changes and since I have had satisfactory results from securing just the end points, I argue that the amount of flex is, for all practical purposes for the type of aircraft in which I would use this arrangement, negligible.
In my pattern planes and my gasoline-powered planes, I don't use nyrods.
I agree, Marty. For planes like a Q-Tee, Whimpy, or the average 20 to
40 size trainer, Nyrods are great. But on the average aerobatic plane I usually use a 30" metal rod with 2-56 threads on one end, through a white nylon tube available at the hobby store. That's become my default pushrod on most of what I build. Sometimes I like using old fashioned wooden stick pushrods, just for nostalgia I guess. That's what I put in the Royal Coachman I just finished, even though the plan shows Nyrods.
Thanks for all the info guys. From the discussion I have decided that the Gold-N-Rod procedure is sound and should meet my requirements as long as I can anchor them "mid-tail".
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