Got the Aileron Pushrods welded!

I went to a local shop were they build custom choppers to get my aileron pushrods welded. I figured these guys must be into finesse. Lonnie, at Denton County Choppers in Frisco, TX, did a fantastic job on these puppies. He told me that he scotchbrited everything down, did the welds, and even primed everything after he finished, making sure not to get any primer on the screw ends. Very nice!

Just curious, about what did you pay to have the two rods welded and what type of welding was it, TIG or what?

I struggled getting these properly riveted... ended up having the same thing done for my RV-9 aileron push tubes. Helped with rear spar clearance too!! My local FBO shop TIG welded mine. Think I paid $30.

If you wanna squeeze 'em, checkout this thread:

http://www.rivetbangers.com/cgi-php/forums/viewtopic.php?t=1044&highlight=eddie+squeezer

I made up my own squeezer just for the occasion. It is really slick!

CJ

Hi Mike. It was 75 bucks an hour for the machinery and 10 bucks labor. That's probably a lot I know, but I really feel good about the whole thing.

Smitty,

Mine cost me $50.00 for the TIG welding, but it was worth it! I, too, went to the pros to get this done.

Don't want to trust "Bubba" with this weld....

Listen to this!

I liked the idea of welding over just the rivets for additional strength. I work at a high school which has a welding shop and thought I could get it welded there. OH! was that a mistake! BTW, it costs about $40 plus shipping and handling to replace those pushrods! I'm going to redo them with rivets (thousands are flying with no problem) but prior to riveting I'm going to epoxy the ends on for that additional strength I was looking for. (we live and learn, eh?)

I welded mine with oxyacetylene. Pretty straightforward, though I wouldn't recommend it as a first welding project. Anyone doing this themselves should be aware that you want to remove the plating from the threaded studs prior to welding. Otherwise you will get toxic fumes, just like welding galvanized steel. I soaked mine in some phosphoric acid metal prep solution for several hours to get the plating off. Then did a little final polishing with my Scotchbrite wheel prior to assembly and welding.

I TIG welded mine, they came out quite nice:

I caution anyone who welds their pushrods to properly normalize and heat treat the assembly after welding. A friend of mine lost his beautiful Velux unlimited aerobatic airplane when the welded elevator push rod broke. The welding caused the threaded portion to become brittle.

Ron Schreck
RV-8, "Miss Izzy"
Gold Hill Airpark, NC

ronschreck said:

I caution anyone who welds their pushrods to properly normalize and heat treat the assembly after welding. A friend of mine lost his beautiful Velux unlimited aerobatic airplane when the welded elevator push rod broke. The welding caused the threaded portion to become brittle.

Click to expand...

I think pushrod ends are heat-treated to a yield strength similar to a standard AN bolt, 125,000 psi or a little more. Welding would return it to some unknown lower strength, 80,000 psi or so at the normalized level and as low as 50,000 at the annealed level. I'm working from memory here; you can look up the exact figures easy enough.

"Brittle" usually comes hand-in-hand with hardness, which has a direct relationship to tensile strength. The plastic range at the top of the stress-strain chart is short; not far beyond maximum strength the part snaps rather than deforming. The opposite is "ductile". A ductile steel has a lower maximum strength and much wider plastic region; the stress-strain chart has a shorter straight line section and a longer plastic curve at the top.

Point is that welding lowers maximum strength but is unlikely to make it more brittle.

Two caveats. One, the highest stress is found at the surface of the material. Welding can introduce a variety of undesirable contaminants to the material at the surface, as well as pitting and other surface damage. Two, if the pushrod end was quenched (cooled rapidly) after welding, it would indeed become hard and brittle.

Heat-treating would require placing the entire welded pushrod assembly in a oven.

BTW, pushrods are tricky. If the designer forgot to do a natural frequency check, a long pushrod may be resonant at some given engine RPM. I once strobed a pushrod on a popular design while looking for an airframe "buzz" felt by the builder in a particular RPM range. It was a pushrod linking the aileron system; when resonant the center of the three-foot pushrod was describing a circle about 6" in diameter. Such behavior would indeed fatigue a pushrod end, the probable failure point being the root thread.

Welding Pushrods

I welded mine also (tig). If I'm not mistake, my plans for the 9A show this as an option. That being the case, I assume Van's at least did some checking or the part is significantly "over" designed. At any rate, I'll check my plans this evening to make sure.
I agree with DanH though, just because two parts are welded doesn't mean that they are not weaker as a result.

FWIW, I generally reserve welded-in AN490's for short, low stress pushrods. Longer or higher stress pushrods get a machined steel plug welded into the end of the tube, which is then tapped for a male rod end bearing. Any changes in material properties due to welding are thus restricted to the plug and tube...not the weak-in-bending threads, which are part of the heat treated male rod end.

In the context of this particular RV application, OK with Van works for me.

I found these pushrods the more difficult part of the plane. If I had to remake them, I would not be sure to make them good.

I ended to have one end of one pushrod welded AND riveted. I'm now worried for the thread problem. I thought the problem could have only been the joint itself!

Just wondering...what would happen if one of the ailerons gets disconnected? Death for sure?

I also

welded mine. I beveled the tubes and fittings, drilled for a plug weld, tig welded one end. In respect to my tube and fabric days, put about a half teaspoon of tube oil inside the tube and then welded the other fitting on. I am not too concerned about the heat affecting the fitting and the oil takes care of the corrosion inside the tube. For those that have welded or even riveted theirs on you can still put oil inside by drilling a hole and using a rivet designed for just that purpose.

DanH said:

if the pushrod end was quenched (cooled rapidly) after welding, it would indeed become hard and brittle.

Click to expand...

Indeed! I guess I'm not sure why welding is better than riviting.

I just pounded in the specified rivets are poured in some boiled linseed oil, letting it drain out. The stresses on this rod, to me at least, are pretty small and the tube is short and stiff enough that I would be surprised to hear of any resonances that would cause the rivets to shear. Weld embrittlement would be more of a concern to me, but maybe even that isn't much of a concern. It just seems that if I am apply enough force to shear those rivets, then I am already about to die due to something else failing. I do like the idea of adding some T88 to the joint to help further seal and afix things.

Vans definitely lists the small pushrods on the plans as being weldable, but the larger stick to bellcrank pushrods only calls for the blind rivets. I wonder if welding as well as riveting those would be the way to go.


I wonder if they didn't list welding as an option on that because most people aren't setup to weld aluminum.

Hmmm... I guess I'm glad I gas-welded mine, which mostly obviates the concerns about rapid quenching or need for normalizing. There are a lot of old airplanes flying over us with gas-welded structures. Which is not to say that that there is zero risk that some unspeakably horrible act has been committed upon my pushrods as the result of being gas welded. As pointed out though, these things are really short- and therefore quite stiff for their size. If a bellcrank-to-aileron pushrod on an RV-(something) starts inscribing a 6" circle under flight conditions, I suspect that the pilot may have a subtle cue feeding back through the stick.

For what it's worth, I built the bicycle I ride regularly, about 16 years ago. Thickest tube is .030 4130 chrome molybdenum steel, down to .020 on some parts. TIG welded everywhere; I ride the **** out of the thing, on all kinds of roads. I've probably put 25,000 miles on it since I finished it. I'm still waiting for a crack to form. I was told all sorts of horror stories about how it would fail when I was building it, because I was (a) not using lugs or (b) not planning to heat treat the thing when finished, or (c) using the wrong rod or (d) drinking the wrong whiskey when I finished up for the evening. Of all those, (d) was probably the closest. I didn't have the money for the single malt scotch that I would've preferred But it still hasn't cracked, despite endless miles of being beat up on the roughest California roads that I can find.

I'm not too worried about my aileron pushrods.

I used oxy-acet. on my aileron pushrods also, and I don't worry about it. There is probably only a hundred pounds or something like that max load on those, and only occasionally at that. Like others have said, if you do it, be sure to get good penetration and let it air cool.

realistically, even if there is a significant loss in tensile strength due to the heat treating, the overall strength of the weld and the rod end is still going to be greater than the strength of those two AD rivets.

If you were REALLY worried about the strength of the weld, then you ought to have used monel rivets there!

Camillo,
<<I'm now worried for the thread problem.>>

Don't worry. I only mentioned the strength reduction issue to clarify what happens when you weld a heat-treated part.

Builders can often eliminate worry by spending a few moments with a calculator. First think about the applied load, then calculate strength.

Alex is probably right; aileron pushrod load is probably low. However, do consider the worst case. For example, the typical inflight elevator pushrod loads are also quite low, but the typical case isn't the worst case. The elevator stops are at the control horn. The worst case would be a panic-pull on the stick with the elevator against the up stop. Likewise, rudder controls shouldn't be sized for just the inflight rudder deflection load. The worst case is a panic push with both feet at the same time. You need to assign a value to the worst case; perhaps 400 lbs divided by two cables would be appropriate for the rudder example. The common sense question would be "how hard you can push with your feet?"

As for strength, just work your way through the system calculating and looking for the weak link. Don't forget the anchor points. In particular check long pushrods for failure due to bowing and buckling in compression.

Here we can cheerfully assume the engineers at Van's did all that, and our only concern is the welded AN490. Assume 50,000 psi yield for annealed condition after welding. The root diameter of the 1/4-28 thread is about 0.2 inch. So, 0.1^2 x 3.14 x 50,000 = 1570 lbs load capacity. Pretty safe if you think actual load is about 100 lbs, yes?

Bored today; when we have sleet in south Alabama, not much happens here at the store <g>

Design loads...

DanH said:

Camillo,
<<I'm now worried for the thread problem.>>

Don't worry. I only mentioned the strength reduction issue to clarify what happens when you weld a heat-treated part.

Builders can often eliminate worry by spending a few moments with a calculator. First think about the applied load, then calculate strength.

Alex is probably right; aileron pushrod load is probably low. However, do consider the worst case. For example, the typical inflight elevator pushrod loads are also quite low, but the typical case isn't the worst case. The elevator stops are at the control horn. The worst case would be a panic-pull on the stick with the elevator against the up stop. Likewise, rudder controls shouldn't be sized for just the inflight rudder deflection load. The worst case is a panic push with both feet at the same time. You need to assign a value to the worst case; perhaps 400 lbs divided by two cables would be appropriate for the rudder example. The common sense question would be "how hard you can push with your feet?"

As for strength, just work your way through the system calculating and looking for the weak link. Don't forget the anchor points. In particular check long pushrods for failure due to bowing and buckling in compression.

Here we can cheerfully assume the engineers at Van's did all that, and our only concern is the welded AN490. Assume 50,000 psi yield for annealed condition after welding. The root diameter of the 1/4-28 thread is about 0.2 inch. So, 0.1^2 x 3.14 x 50,000 = 1570 lbs load capacity. Pretty safe if you think actual load is about 100 lbs, yes?

Bored today; when we have sleet in south Alabama, not much happens here at the store <g>

Click to expand...

Dan... the FAA let slip some design loads in an old 1962 book I have...

They do admit the arbitary nature of the design loads on the stick... but give these numbers...

Elevator - 75 lbs. fore and aft

Rudder - 100 lbs. one pedal only, 200 lb on each pedal simultaneously

Aileron - 50 lb laterally, or as part of a couple applied to the control wheel.

You could easily use these numbers and use the change in lever lengths of the stick and aileron bellcrank to get a load.

A wild guess (no drawings in front of me) is 8 to 1. If so, this gives a maximum load in the aileron pushrod of 600 lbs. - still lots of margin...

gil A - playing with numbers again...

<<some design loads in an old 1962 book I have>>

You 'da man Gil. Those old CAA and FAA books can be hard to acquire.

<<They do admit the arbitrary nature of the design loads on the stick... but give these numbers...Elevator - 75 lbs. fore and aft...Rudder - 100 lbs. one pedal only, 200 lb on each pedal simultaneously...Aileron - 50 lb laterally>>

Excellent.

<<You could easily use these numbers and use the change in lever lengths of the stick and aileron bellcrank to get a load.>>

You got it. Took my coffee to the shop and measured a few parts. For the RV-8, the stick ratio is 17/3.5 = 4.85 and the bellcrank arms are equal. So, 4.85 x 50 = 243 lbs, and 1570/243 is a margin factor of around 6.5 for the welded AN490 (less caveats).

BTW, noticed a clever detail in the Van's aileron system design. The stops are at the aileron arm. The arrangement of system components puts the pushrods in tension when the system is against a stop. Smart because it eliminates concern for the buckling weakness of pushrods in compression. That's not to say they are undersized. In compression the 1/2" steel pushrod would be good for about 520 lbs and the long aluminum pushrod would be good for 370-380 lbs.

<< playing with numbers again...>>

It's a shared affliction <g>

This is great reading! I do those sorts of calculations all the time at work (yet another engineer geek), though in the case of the pushrods, since welding was listed as an option on the plans, I decided to blissfully accept that one of Van's engineers had studied the problem and concluded that melting metal was an acceptable solution to joining the parts. Besides, it was fun to use a technique that doesn't get dusted off and practiced much in the construction of these things

If I ever build another airplane, it'll likely be some tube n' fabric job, from plans.

Polishing the pins just a little here, education as well as recreation:

Cutting the tube end square and welding around the rim of the AN490 is quite likely more than adquate for a Van's aileron pushrod. However, the generally accepted best-practice is a wee bit different among the serious tube and fabric crowd.

One method welds around the rim as we've seen, but adds two small rosette welds.

The other method is to V-notch the end of the tube and weld the edge of the notch. The photo below is a fine example; elevator pushrods for a Pitts Model 12 (credit to Kimball Enterprises).

serious joint prep

Good info. Same techniques I've used when fabricating suspension and driveline parts for my various offroad projects. Especially important for joints that will react a moment.

Camillo said:

Just wondering...what would happen if one of the ailerons gets disconnected? Death for sure?

Click to expand...

Assuming the aileron is not blocked in an extreme position, then one aileron is probably enough to get you on the ground. I would not want to experience this particular failure!