Crash Master

I am putting together a plane that uses a dowel with 2-56 wire at each end. With this plane, I can't afford any flex in the control rods.

My question is, will a 4-40 rod be as strong or stronger than to dowel and wire set-up? I would much rather use the 4-40 rods to even save a bit of weight as well.

Any and all comments will be greatly appreciated.

Thanks,

FlyingPilgrim

My Feedback: (26)

4-40 rods will be stronger, but may not be necessary. The main concern with the solid control rods is that they are straight with no bends in the metal rods. You may want to consider using carbon fiber or fiberglass control rods as well. These are available with titanium rod ends if you want the ultimate in strength. What plane is this on? There is nothing wrong with the wooden rods with metal ends, but like I say, keep 'em straight! As soon as you put a bend in it, it becomes very flexible.

Azcat59

4-40 rods are probably stronger than a dowel, but unless the steel rod is inside a nylon tube, well supported by braces inside the fuselage, it will bow "on the push" and you may find yourself running out of up elevator at an embarrassing moment.

I use the threaded rods and nylon tubes that come with some kits, but if it is a "serious" airplane, I use basswood or fiberglass rods with wire ends.

If the pushrod is made of the same material as the fuselage, i.e. wood, glass, etc. it will stretch and shrink at about the same rate as the fuselage, with weather and humidity changes, and thus change trim less. Metal rods will show more trim changes.

Clair

FlyingPilgrim

My Feedback: (26)

Ditto what Azcat said. I took for granted that if using the rod in a tube design that the tube should be supported every six to 9 inches or so (usually wherever a frame former is). I don't care much for the Great Planes design of control rods which have you cut and glue little bushings every few inches. I buy the DuBro tubes and run the 2-56 or 4-40 steel rods through those. I think they are smoother than the bushing design.

Azcat59

Ditto on Pilgrim's comment on the Gt. Planes idea of gluing small bushings every few inches on the steel wire running in the outer tube. I think this is adding a lot of unnecessary drag on the system, which will decrease the servo centering. Sometimes I add a small bushing near each end but no other.

Clair

MinnFlyer

My Feedback: (4)

Ditto to Azcat's first post, but I like the GP way of adding the 1/4" bushings to the wire. It adds no extra drag (in fact it adds less drag) and eliminates a lot of slop in the tube.

Consider this...

The "bushings are made from pieces of inner Nyrod tubing which have a "Star" shaped outside. They are 1/4 - 3/8" long. This means that there is much less surface area touching the outer wall resulting in less binding.

They also keep the push rod centered in the tube to provide less slop.

FlyingPilgrim

My Feedback: (26)

MinnFlyer,
In theory, GP's design sounds great (as your nice diagrams show), but in my experience it has caused MORE resistance than does the plain rod in a tube design. I have tried sanding the little "stars" to reduce this, but have never been happy with the results. If it works for others, great, but I have not have good luck with it. Goldberg had some perfect diameter tubes to use with 2-56 rods, but I have not been able to find them "after market". The DuBro's are larger diameter than need be for 2-56 application, but I have used them without any appreciable slop. Bottom line: Use what works for you! That's why there are so many brands and designs.

MinnFlyer

My Feedback: (4)

I know the tubes you're talking about. Try one of the larger hardware stores like Home Depot.

FlyingPilgrim

My Feedback: (26)

Thanks for the tip MinnFlyer, I'll try Home Depot. I would have thought it should be available in bulk somewhere as a hydraulic line or something.

Azcat59

I agree with Flying Pilgrim....I think some of the Gt. Planes tubes were pretty inconsistent......short pieces on the wire would fit tightly in some cases, and sloppy in others. The old Goldberg (?) sets were pretty good.

Further, if you put just a slight bend in the outer tube, the wire will ride against the bend just a little and never create a probem with bowing or rattling. Works for me!

Clair

Papa Tango

Auto parts stores sell windshield washer tubing which a 4-40 rod is almost snug inside. A 2-56 rod might be better depending on the tubing you find. It is not very rigid though so you will have to anchor it at every former and make sure it is running straight and true.