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Building Tips and technical articles. => Building techniques => Topic started by: Rob Killick on April 15, 2007, 09:39:27 PM
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Hi ,
I have quite a few Brodak kits in my stash and I see that the instruction and plans call for a push rod linkage consisting of heavy gage wire (rod) and a sleeve joiner .
For the bigger planes (Oriental , Ares) , I've used carbon fiber tube .
I'm in the midst of building a "Fancy Pants" and was wondering if the wire / joiner type push rod is acceptable for this size airplane ?
I'd rather do it "more correct" , than re-kitting the airplane :'(
Thanks ;D
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Even for a smallish plane like Fancy Pants, I'd go with a CF pushrod - - NO fairlead to align or rub against, and a bit lighter, too. You might go to a smaller CF tube.
Central Hobbies offers pushrod kits in 3 sizes, with Titanium end pieces. Around $16 for enough material to make 2 long pushrods. See:
http://www.centralhobbies.com/control_linkage/pushrod2.htm
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You can also check out Control Line Central or CLC, one of the supportors on this site. Jim Snelson is a great guy to work with. DOC Holliday
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Regarding the titanium end pieces...Titanium seems just a little overkill ( and $$$ ) for our purpose. I've heard there are equivalant steel ends for those pushrods.
Anybody know? Who? Where? How much?
Ward
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Ward, I agree that Titanium is probably like using a sledge hammer to swat a fly, for our porposes. However, consider the total cost of the pushrod "kit" - $16 for enough material to make two longish pushrods. Given that price, how large a price reduction would you expect for steel ends? $1.00? Especially since all the other costss are the same - CF, packaging, advertising, etc. And for those of us who are truly anal about every gram (who, me?), the Titanium should be a bit lighter, too.
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I epoxied a good 4-40 bolt into the end of a carbon rod, and it's been going strong for 8 years or so in a plane that flies a whole lot. The Central Hobbies titanium is so pretty and fits so nicely into the rod end that I'll use it in the future.
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Rob,
To answer your original question, sure it is! As long as you do an acceptable soldering job, the strength is plenty. Roughly speaking, the two ends should be close but probably not touching since you are adjusting the rod length. By the time you finish, there probably is ~3/4 inch of solder contact with the split tube on each rod. If you have any doubt, take some you may have left over from your Oriental and make one. Then see how easy it is to break the joint.
Now you still want some way to support the middle of the rod so it doesn't flex when it is pushing against the elevator. Even then, this is pretty thick rod. I have used it on both my Electric Super Clown, P40 arf, anf my kit Lightning Streak. No issues as far as I see.
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With a bit of pre-planning you can eliminate the solder joint. Bend the pushrod as close to the correct length as you can. A bit short is OK, but try not to go long. Then, adjust the stab for and aft for neutral before gluing it in. Carbon fiber pushrods and titatanium ends have their place in planes intended for the top twenty at the NATS. A piece of music wire and a few in between fairleads works fine at any lower level.
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Glad Howard used the 4/40 bolt. I've been JB Welding those suckers into carbon fiber rods on sport planes, then hanging a ball link on that. Somehow I misplaced the carbon rods that fit the nifty Tom Morris inserts. The rods I've found in my workshop are a tad narrow. (Bought those for 50 cents a piece from a club member.) The 4/40 bolt screws right in. Layered up with JB Weld, not likely to go anywhere. I always bind the ends with a half inch or so of copper wire coated neatly with JB. Prevents splits. Carbon rods don't need a guide. Ball joints allow for adjustment. After spending hours trying to compensate for a long ARF pushrod going to the flaps of Cardinal. That's it. I plan to always build with adjustment. The ball joint/carbon rod setup noticeably reduces friction.
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Howard,
I was curious how you centered the 4-40- bolt in the CF pushrod. I like that idea but was wondering how you centered it. One method I have used that seems to work well is to cut a length of wooden dowel about 1 1/2" long, cut a groove in it to accept the piece of 4-40 threaded rod, seat the rod in the groove, cover that with expoxy or JB Weld and push it into the CF rod. It is a tight fit and when the epoxy or weld dries, you have a really tight connection. You can then attach a clevis or ball swivel or whatever you choose to the thread and attach to your control horn. I have never had one fail doing this but am not saying it is the greatest way to do it. I am always looking for a simpler and smarter way to do it.
Mike Griffin
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Howard,
I was curious how you centered the 4-40- bolt in the CF pushrod. I like that idea but was wondering how you centered it. One method I have used that seems to work well is to cut a length of wooden dowel about 1 1/2" long, cut a groove in it to accept the piece of 4-40 threaded rod, seat the rod in the groove, cover that with expoxy or JB Weld and push it into the CF rod. It is a tight fit and when the epoxy or weld dries, you have a really tight connection. You can then attach a clevis or ball swivel or whatever you choose to the thread and attach to your control horn. I have never had one fail doing this but am not saying it is the greatest way to do it. I am always looking for a simpler and smarter way to do it.
Mike Griffin
Hi Mike,
The CF rods that Central Hobbies, CLC, and Tom Morris, etc., sell are pretty much the same ID as a 4/40 bolt. Not a problem as to centering.........
When I was using the Dave Brown Fiberglass pushrods, I used the dowel for ends like you describe.
Bill <><
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I have found that when I solder a coupler between two pieces of wire that the heat from soldering will "blow" the solder from one end of the joint.
I read in an earlier Stunt News that a small hole drilled in the coupler will prevent this. Been using every since then and it works...
Good luck...
" If a parsley farmer goes bankrupt, do they garnish his wages ??? "
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Hi Gil,
So far I haven't experienced that phenominum with the split steel couplers from Brodaks. They are already open a slight amount all the way along their length. (??)
I would never recommend brass or copper tube as a joiner since it work hardens and willprobably eventually break.
AS to the Fancy Pants, we used all the kit parts to build it and it has survived fror a long time! ;D (actually, thinking back on it, I brazed a flap control horn since the kit maybe had a nylon horn pressed on the wire. ??)
Never the less, that plane is a blast to fly!
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"I was curious how you centered the 4-40- bolt in the CF pushrod. "
It's been so long that I forgot. My plane is eight or nine years old. I used a grade-8 bolt, so maybe the head was still on it.
Regarding the advice above to wrap the ends with something to keep them from splitting, I agree. I was drilling the end of a carbon pushrod the other day and had a heck of a time doing it without splitting the tube. It appears that all the fibers run parallel to the tube axis.
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For relieving the ends of the CF tube when it's too tight, I run a needle nose jewelers file on a variable speed drill in reverse. Go slow and it will do the job. Just run a pipe (the Gieseke type pipe) cleaner soaked with acetone through the tube when finished.
Bill <><
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To Gil C, (was it reply #11?)
When I sleeve-join with brass over steel (which I still do, mostly) I 'notch' the brass tube two or three times between each open end and the space between the steel rods. A "jewelers' file" set usually has at least one flat file with toothed edges. Thickness some under 1/16" is common. I use the edge to file straight across the joiner until a window is open, and usually clean the window with a square/pointy jeweler's file, then run a drill bit through by hand to clean swarf out.
Soldering, done right, shows clearly. NO excess globs outside the joint! Each 'window' gives evidence that the sweated run of solder is good, and cleanly to and past that point. The windows also 'vent' the innards of the joint so the solder isn't blown OUT of the contact area. I prefer the Sta-Clean type for this - the flux assists flow and penetration. (I've mentioned my clean-up procedure to make sure all the acid is neutralized and flushed away...) A damp paper towel also allows wiping any excess off the outside of the joint for less weight, neater appearance*, and removing 'tails' or globs outside the joint that could snag on structure.
(*- I know, I know: most such joints are inside structure... but I see them, don't I?)
This sounds like it takes a long time, but doesn't, really. Longer than just jamming some pieces at each other and pretending to solder them, yes, but I haven't had a joint made this way fail.
I also came across some K&S thick wall aluminum tube, about 3/16 OD, if I recall aright. The ID is a lovely fit to a 4-40 tap drill... pushrod end-fittings made up of 1 1/2" or so of the thickwall, threaded 4-40, mounted into 3/16"ID Al tube, is still going great. ...no fairlead needed, either.
Method: roughen the tapped section of the thickwall tube, by rolling it between two medium fine files. You get practically a diamond knurl appearance if you do it right. Clean oils, etc., off the 4-40 wire to the horn fittings and the inside and outside of the outer tube and the thickwall end piece. Prep some slow JB Weld, apply it to the tang, and run that into the threads, to about 1/4" from the end inside the outer pushrod tube.
Wipe some JB Weld inside the outer tube w/toothpick or some such. Butter the outside of the threaded thickwall tube LIGHTLY with JB Weld and slip it into the outer. Wipe off excesses w/rubbing alcohol.
Drill 1/16" through outer and inner Al tubes where that last 1/4" or so leaves only Aluminum to go through. Apply JB Weld in the drilled hole, and force a length of 1/16" Al tube or rod through. This is, in effect, a retaining rivet. Peen the ends close to the outer surface. When the JB is cured, file down close to - but not cutting into - the outer.
Works for me, anyway...