Control linkages on bigger models

RknRusty wrote:I'm using clevises(clevi???), for my .25/.35 size planes like the Skyray and Shoestring. I think the Akromaster would be fine with that too. But those boys over there are flying .60-.90 size ships and they probably need some more substantial tackle. They also build them for a thousand flights or more and can't get to the linkages to inspect them.
Rusty

Where do you find the threaded rods. I have a great hobby shop here, is that a standard item they would have?

Jim

Rusty, are you implying that my model won't make it to 1000 flights? 

I get them at my hobby shop. It comes with a coupler to solder to the music wire and a threaded rod about 3" long. I also use a lock nut to jam the clevis. That will keep vibrations from wearing out the threads. They seem plenty trustworthy to me.

If anyone here can put their mind to achieving a kiloflight, I'd bet on you, JP.
Rusty

EDIT: That's so long as you don't try tying anymore knots in Spiderwire.
  ............ Just kidding.

Carbon fibre rod/arrow shafts will be going on my Twister along with ball links for linkages.

I sometimes use standard hardware as well. I would consider using large as possible control horns. The thick black ones or the white ones with the brace to prevent flexing.

JPvelo wrote:
Where do you find the threaded rods. I have a great hobby shop here, is that a standard item they would have?
Jim

If your LHS is well stocked, then they should have fully threaded rods and rods threaded only on one end.  Typical sizes are 2-56, 4-40 and 6-32.

As far as clevises are concerned, I would not use a ball link in a location I could not reach.  The nylon socket will eventually wear and harden over time.  I really like the Sullivan Golden Clevis --- they have inner locking ears where the clevis is rolled for the threaded portion and a steel retaining clip that will prevent accidental opening.  After I've set the length of the control rod, I use a locknut that I run up against the clevis -- this keeps the clevis from turning on the rod and will stop vibration wear between the rod and clevis.

Cribbs74 wrote:Carbon fibre rod/arrow shafts will be going on my Twister along with ball links for linkages.

I sometimes use standard hardware as well. I would consider using large as possible control horns. The thick black ones or the white ones with the brace to prevent flexing.

Do the ball joints require special horns. How does the ball joint attach to the carbon rod.

Thank you,

Jim

The heavy duty ball link on the control bell crank threads through the same hole as the rod would go through.  The 3/32 rod is the same OD as the link I bought (and decided to not use due to kiloflight logic, I think a new term was coined) The significantly larger wear area is the reason for using a ball link.  I used the solder on brass ends Rusty mentioned.  

Compared to a rod directly on the bell crank there is a HUGE difference in contact area.  The insert in the ball joint is close to 3/8 inch diameter instead of a mere 3/32 diameter rod.  This will reduce wear.  Also consider that many full fuselage stunt models have access to the bell crank location and flap linkages through the fuselage.  

Incidentally a allen head cap screw can be used as the head will fit the rod, but there is an effort vs cost trade.  The brass couple is not very expensive and very easy to install, the screw is even less expensive, and somewhat harder to keep in line properly.  I have also used a die to thread rod directly, but don't know where said die is, it may be at my parents, or one of my brothers...

The ball link assembly attaches to a threaded portion of steel or brass that is epoxied into the CF tube.

Phil

Thanks Phil great explaination!

What he said Jim...

You can also use CF tube and epoxy standard steel rod or threaded rod into it. Bend the steel rod at a 90 degree at one end drill a hole in the side of the CF tube or arrow shaft hook the 90 into the drilled hole then shim with a piece of hard balsa and dump epoxy into the tube.

Ron

When I mate the CF tube with music wire I'll use  copper wire wrap and JB Weld rather than epoxy. My current build no longer has access to the bellcrank unless I cut a door in the sheeting. Not structurally a sound idea.


Phil, can we get a picture of this?

pkrankow wrote:The heavy duty ball link on the control bell crank threads through the same hole as the rod would go through.  The 3/32 rod is the same OD as the link I bought (and decided to not use due to kiloflight logic, I think a new term was coined) The significantly larger wear area is the reason for using a ball link.  I used the solder on brass ends Rusty mentioned.  

Compared to a rod directly on the bell crank there is a HUGE difference in contact area.  The insert in the ball joint is close to 3/8 inch diameter instead of a mere 3/32 diameter rod.  This will reduce wear.  Also consider that many full fuselage stunt models have access to the bell crank location and flap linkages through the fuselage.  

Incidentally a allen head cap screw can be used as the head will fit the rod, but there is an effort vs cost trade.  The brass couple is not very expensive and very easy to install, the screw is even less expensive, and somewhat harder to keep in line properly.  I have also used a die to thread rod directly, but don't know where said die is, it may be at my parents, or one of my brothers...

The ball link assembly attaches to a threaded portion of steel or brass that is epoxied into the CF tube.

Phil

Wire wrap is a good idea. Why JB weld? It's an epoxy. Or are you concerned about fuel?

I've always considered JB stronger than the regular stuff, especially where metal is involved. But I don't have any real knowledge or evidence of that, I could be completely wrong. Besides if you bend a tang in the wire and put it through a hole in the tube like you said, I don't think it's in danger of pulling loose anyway, with either kind of epoxy.
Rusty

RknRusty wrote:I've always considered JB stronger than the regular stuff, especially where metal is involved. But I don't have any real knowledge or evidence of that, I could be completely wrong.
Rusty

I did pushrod testing back in 2005 using carbon fiber tubing, music wire and various adhesives, including JB Weld. The results are in RCU if anyone is interested. JB Weld was tested in Post #13.

http://www.rcuniverse.com/forum/1-2-1-8-airplanes-70/3037672-pushrod-testing.html

Oh ok, I thought maybe you had some inside scoop.

I have only ever seen Epoxy, but I don't see anything wrong with using JB.

Ron

Thanks, Andrew. Great work for someone only in their mid 50s!  
Rusty

Here's a pic of the metal horns I use, a lot stronger than nylon, no flex or chance of snapping, unless it's subjected to a figure ''9''.

Arrow shafts work great for pushrods, but most hobby shops sell some type of carbon fiber or fiberglass. I wrap my ends with nylon string and CA, but here again there's several ways to do it.

While the carbon style pushrods work terrifically, this isn't the only backbone of the control system subject to flexing. They have the strands of graphite and carbon orientated in different directions. Depending on which style you choose to use, this is why the end needs to be wrapped due to the forces on the rod wanting to spit in the direction of the fibers. Protruded carbon rods probably wouldn't require this and have  a much stiffer spine deflection but in addition is heavier. Many times I see the incorrect choice of wire size for pushrods for instance, the bellcrank to pushrod. A Sig or Brodak bellcrank is designed to accept .093 music wire and that's what one should use for a .35 size model. The threaded couplers suggested above are designed to properly fit certain size wire. The 4-40 threaded coupler is designed for the .093 wire. 2-56 clevis's should not be used on .35 sized models. They will fail and regardless of who's using them currently, I've witnessed many failures due to this.2-56 hardware is fine for 1/2A and .15 size models. When you move to .35 size equipment, the loads are heavily increased  on the flying surfaces. The threads are formed within the clevis and if the locknut isn't used, the threads will quickly diminish due to vibrations. Keep the loads in a straight line and don't have the wire or pushrod at a angle to your horns when using a clevis. The flexing of the clevis will cause the spring steel to fail and one side of the clevis will just break off. This won't happen immediately, but when it happens it certainly is spectacular.

I see many Ringmaster's built and I've built many myself and for a plane like this, one needs to realize the size of the elevator. If one screws or bolts a control horn directly to the wood surface, you might as well jump on the model prior to flying it. The elevator will split and or the horn will pull directly through the balsa. Putting ca or epoxy may prolong the area by hardening the balsa but it will eventually fail. Place a round pad of 1/64" ply just slightly larger than the footprint of the horn on the top and bottom of the elevator. This will stop the  flexing of your control surface and could also save your model someday.

I personally see no advantage to be gained using a ball link aside from smoothness and longevity. When other methods are done correctly such as properly sized and bushed areas, bellcranks, control horns, flap horns, all will not only work smoothly, it should outlast the model's life. There's always that one model that defies others we've all had them. Ken