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Push-Pull control tube fabrication

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REVAN

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I need to build some push-pull control tubes like the one shown at the end of the tutorials shown on this page (scroll to the bottom):

How to install Push-Pull Tubes & Cable Rigging in Aircraft

The instructions reference a part "CC-29 End Plug". I have not been able to locate a source this part with any Google searches. Does anyone know where this part can be found? Does anyone have other reference material on good methods for building control tubes? My application is for an ultralight. I expect to use both 3/4" and 1" diameter control tubes in the design.

Any help would be much appreciated.
 

proppastie

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not the number you are looking for but the same function...did not find the female in those size.....but did not look very far.....I have a lathe so have been turning my own.
 
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BoKu

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The drawing at the linked website appears to be from an excerpt of some kit airplane assembly instructions. The part number is probably specific to that kit.

I bid out things like that in batches of 50 or 100 on mfg.com. When I just need one or two I sweat them out on my lathe. The only size I keep in stock is 5/8" x 0.035" wall.
 

REVAN

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So, it looks like most folks make their own end caps, at least when it comes to larger diameter tube sizes. I guess I'm surprised there aren't more COTS parts available to complete push-pull tubes. I would have thought that is such a common assembly that there would be more available.

Looking at my design, I think I may be able to take the 3/4 inch tubes down to 1/2 inch and use the COTS parts with the 1/4 inch threaded ends. For the larger tubes, I am considering welding end cap fittings from 0.058" walled steel tube, sleeve sized to fit an 0.058" walled aluminum tube. I can weld a nut to the end cap for a female interface, or weld a bolt to the end cap for a stud interface.

Does this sound like a reasonable plan for someone without a metal lathe, or would you recommend spending the money to outsource the parts to a machine shop for only 4 end caps (2 male and 2 female)?
 

cluttonfred

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REVAN, what overall length and what types and sizes of ends do you require? Such items can be had relatively inexpensively from the aircraft surplus (scrap) market for engine controls and you can also built up very solid ones using automotive Heim joint rod ends and threaded rod or sockets welded or riveted or even epoxied to the tubes. For example....

 

Hot Wings

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I guess I'm surprised there aren't more COTS parts available to complete push-pull tubes.
So am I. It almost sounds like an opportunity for someone with access to a CNC lathe to fill in during the slow times. 5 tubes sizes (5/8", 3/4", 1", 1 1/4", 1 1/2" all .035" wall) with 1/4" and 3/8" threads (10 total part numbers) would probably cover 90% of the homebuilt market.
 

wsimpso1

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Revan,

I would be really surprised if you need anything like 3/4" or 1" on a Part 103 Ultra Light. The reason there are not more sizes is because the ones that are AN standard are about all the sizes ever needed. I have some turned on a lathe, but that is because the they are fiberglass and thus non-standard sizes.

What ever size you are thinking about, I would recommend doing a check on tube strength. Buckling in compression is the usual worry. Do this by calculating your biggest control moments at a modest overspeed (TOWS has this), then calculate the forces in the control pushrods, then check them for buckling using either the standard charts for aluminum and steel tubes (Summerill Co curves as reproduced in Evans or by applying Euler's method (Shigley is my favorite). In Part 23 airplanes, the Regs used to state forces at the control stick and pedals, unless you have better info. The old version was pretty safe, but in airplanes with light controls resulted in significant overbuild. Better to do the math for your bird and make sure the tubes selected will answer to the helm.

How to do it without a lathe? Hate the idea of building it up - heavy. I would design a light plug type with 1/4-28 female threads in each diameter I need and bid them out with some spares. You do not know ANYONE in your EAA chapter with a lathe?

Billski
 

radfordc

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You might check with some of the ultralight manufacturers and see if they have the part available. My old CGS Hawk used that part in several of the push/pull tubes. I still have one in my scrap box.IMG_20200529_143028245.jpg
 

Hot Wings

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How to do it without a lathe?
I was a cheap kid and wanted nosecone shapes that were not available from Estes. Made my own with a hand drill clamped in the vise.

You might be surprised what you can do on a drill press, in aluminum, with a 4 inch grinder, a file, a sawed of bolt shank, some scrap wood for jigs and a bit of imagination. The Silver and Deming drill to bore out the end fitting is probably the only tool that isn't already within arms reach of a well equipped drill press.
 

proppastie

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If you use 5/8 x .049 wall you can insert a 1/2 solid alum rod. If you are handy you should be able to drill and tap that rod very close to the center with a drill press. Maybe even with a hand drill. But you should have at least one of those cheap Chinese drill presses.
 

Markproa

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If it was a yacht we would epoxy (with flock) a nut or two into the end with maybe a rivet into the plug to prevent it loosening. Not sure if that is acceptable in an ultralight.

Mark
 

cluttonfred

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I seem to remember that the British BCARS microlight design standards require the control circuits to hold up to normal maximum pilot inputs in the case of a jammed control. That makes them overbuilt for normal use but does simplify the design process. I don’t, offhand, remember the forces used for the various control circuits (elevator, ailerons at stick, rudder at pedals, flaps separate). Anyone know those?
 

crusty old aviator

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Be careful with reducing your tube OD! 1/2” is pretty small unless it’s sliding through a roller fairlead every 2’, like in many Euro gliders. Use 2024-T3: it’s much stiffer (and more expensive) than 6061-T6, and you’ll want to paint the outside and ACF-50 the inside, as 2024 is also less corrosion resitant.
 

REVAN

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I would be really surprised if you need anything like 3/4" or 1" on a Part 103 Ultra Light.
The reason for the large diameter has to do with how the control limit happens when the push-pull tube swings sideways into air frame structure. This can put a lot of bending load on the tube. As an alternative, I'm considering how to put a limiter on the control input to prevent that from happening, in which case, I can use a smaller tube. However, with the tubes exposed alongside the pilot, I don't want to make them too small. I expect people will bang into them and they should be strong enough to take it without fear of damage or misalignment resulting.

For simplicity and overall durability, my initial strategy is to just greatly oversize the tube diameter up near the pilot. That tactic would seem to favor low cost which I think is fairly critical to ultralights. If that fails to be adequate then I'll add complexity to solve the problem with limiters and downsize the tube diameter.
 

BoKu

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...Use 2024-T3: it’s much stiffer (and more expensive) than 6061-T6...
All aluminum alloys have about the same stiffness, and consequently about the same resistance to column buckling. Since that's what dominates push-pull tube strength, the corrosion resistance of 6061 usually makes it the better choice.
 

Yellowhammer

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You might check with some of the ultralight manufacturers and see if they have the part available. My old CGS Hawk used that part in several of the push/pull tubes. I still have one in my scrap box.View attachment 97355

What size and type is that jam nut? I am having trouble finding some on Aircraft Spruce.

Thanks
 

BJC

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Is this what you are looking for?



BJC
 
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