Flap Horn / Elevator Slider material. 4130 Chrome moly vs. A1008 CRS

[Brent Williams]

In practical terms, for flap horns and elevator sliders does 4130 Chrome moly have tangible advantages over regular A1008 cold rolled steel? 
Are there enough meaningful changes of the anealing / temper that occur during the brazing process that would make one select 4130 over CRS?
I've witnessed a flap horn made from mystery, probably hot rolled type steel fracture mid flight.  It was also soldered, not brazed.  Vibration killed that one, I believe.  I want to avoid that failure mode completely if it is material properties related.
I'm thinking about having some batches of horns laser cut, so I'm stuck in my typical material selection analysis paralysis.

[Brett Buck]

In practical terms, for flap horns and elevator sliders does 4130 Chrome moly have tangible advantages over regular A1008 cold rolled steel? 
Are there enough meaningful changes of the anealing / temper that occur during the brazing process that would make one select 4130 over CRS?
I've witnessed a flap horn made from mystery, probably hot rolled type steel fracture mid flight.  It was also soldered, not brazed.  Vibration killed that one, I believe.  I want to avoid that failure mode completely if it is material properties related.
I'm thinking about having some batches of horns laser cut, so I'm stuck in my typical material selection analysis paralysis.

   I always use mild steel of uncertain provenance. I wouldn't worry too much about it, 4-strokes are not really a "thing" any more and that was sort of a unique situation. I would pick it based on its ease of brazing. 

         Brett

p.s. on further consideration, if I was going to use a large 4-stroke (Saito 72/82 or whatever) I would use a double upright, based on Gordan's experience.

[Dan McEntee]

   I always use mild steel of uncertain provenance. I wouldn't worry too much about it, 4-strokes are not really a "thing" any more and that was sort of a unique situation. I would pick it based on its ease of brazing. 

         Brett

p.s. on further consideration, if I was going to use a large 4-stroke (Saito 72/82 or whatever) I would use a double upright, based on Gordan's experience.

     I was going to say increase the thickness if in doubt.  Or doubling up on the horn. Kind of depends on what airplane and other size circumstances I guess.
    Type at you later,
    HAPPY HOLIDAYS!!
  Dan McEntee

[Dave Hull]

The 4130 is the better material. Do you need it? That will depend a lot on the mass of your pushrod and the severity of the vibrations your engine puts out. I have seen a number of carbon-tube pushrods that are overdone to the point of excessive weight--but they don't fail. Instead, the horns or the ball joints fail....

One reason that 4130 is better is because the strength in normalized condition is higher than the 1008 CRS. If your brazing temperature is kept below 1500F, you likely won't anneal the material from its normalized condition. Importantly, the fatigue strength of 4130 is much better than 1008 or other low-carbon CRS. Fatigue is likely our most stressing design case. Fatigue is the failure mode of a part under high-cycle alternating stresses that are below the normal yield stress.

One caution about using 4130 is that most sources will tell you that as a higher strength alloy, it is susceptible to hydrogen embrittlement from processing. In practical terms for making horns, I would not nickel or zinc plate the parts afterwards unless followed immediately by a bakeout. (The horns in my most recent kit were plated, and I didn't have much confidence that these went thru a bakeout. But they also were probably low carbon steel, and thus not susceptible....)

The normalized 4130 is going to be harder that the low-carbon CRS, so if you are using a slider adjustment and worry about the screw or washer digging in and marring the smoothness of your adjustment, that might be another reason to choose the 4130.

One difference that you might want to ask your fabricator is whether either laser waterjet cutting would add difficulty and cost for a 4130 part as compared to the 1008 CRS. One of our club members has some 4130 parts cut a few years ago and I don't seem to remember any issues with waterjet.

To me, the only reason for not using 4130 for horns is simply cost and availability. It has virtually the same machineability as the 1008, and excels 1008 in every other way I can think of. But is 4130 necessary? A lot of planes have been built using lesser materials....

Dave

[Jim Svitko]

For what it is worth, I have been using the 4130 from McMaster-Carr.  6" X 12" sheet, 0.071 inch thick.  None of my planes with horns of this material have hundreds of flights on them but the material has worked out for me.

[Motorman]

I also use 4130 plate (1/16th or .071 thick) with no failures on my 575 sq. in. planes. I basically copy the Tom Morris design. I use 1/8 drill rod for the wire. The trick is to use silver solder for the joint and keep the heat to a minimum and you'll stay just below critical temperture that makes it brittle. If you want to braze it you'll have to do some heat treating after soldering as you will reach critical temp. It a kin to chaos if you don't have a temp controlled oven and know the colors to look for. So much simpler with silver solder.

MM

[Brett Buck]

Nothing to do with the upright materials, and I am not sure who was making them, but I don't recommend using the ball by itself as the slider, or at least, not without a hardened washer underneath it. I have seen several cases where the ball spread the arms of the horn, and eventually slipped, causing a crash. At least it needs a hardened or very thick washer, so the washer doesn't flex under the force of screwing it down and spread the load all away from the slot.

    I don't use ball links at the elevator, but a slider with a separate screw, with a hole for the 3/32 pushrod end and a keeper. Same thing would work if you just threaded the hole and screwed the ball to the slider.

     Brett

[Dennis Moritz]

You guys. Overthinking again. Plywood horns as in Sterling kits. No problem. Many function Perfect like the tanks. Besides. They take dope well.

[Ken Bird]

 Brent,
Although I use 4130N for my flap and elevator horns, I do so only because I am literally using left over scrap material I have and I cut process everything manually by hand. I think 4130 is overkill for the application from a strength standpoint, however there are some issues specific to 4130 (and all chrome moly steels) that you may wish to be aware of that might affect the fatigue life of your part.
4130 will harden from a heat cycle such as welding or along a kerf when using thermal processes (such as laser) to cut. There are ways to address this but some will be more practical than others dependent on the item.
Thinner material (less than .120) does not seem to be as affected probably due to a lesser quench effect from thinner parent material. The hardness is not throughout, it will be restricted to the edges that have been cut. One way that can address this is to grind the edges of the material that have been thermally cut. Maybe not so practical with a relatively large quantity of parts. 
If you have the holes in your horns laser cut and wish to tap threads in the upright, for example, you will find that the hole will be hardened and you may end up breaking taps. More importantly, the slot cut in an adjustable elevator horn might create enough of a discontinuity from the hardness that it could be susceptible to fatigue failure at the thinnest points.
If I were looking at a production run of parts, I would just go with your non-alloyed cold finished material with a modest carbon content (e.g. C1020) if you wish to laser cut. I am not a big fan of water jet cutting only because of my experience with its kerf shape and roughness, but you could definitely get past all of the thermal cycling challenges related to cutting by using water jet.

I should add that I think the bigger issue with respect to low temperature brazing your horn will be with respect to the technique of the one doing the work as well as how it affects the wire used (drill rod, music wire, TIG rod, etc) rather than the upright itself. FYI, I use Easy-Flo 45.

Hope this helps you get past your analysis paralysis!

Ken   

[Brent Williams]

Thanks guys.  This is all excellent info! 

[Ken Culbertson]

In practical terms, for flap horns and elevator sliders ....

This may be a dumb question (I am not blond) but what is an "elevator slider".  All I can think of is that small brass "T" nut that goes into on adjustable elevator horn.  You know, the one that falls out and gets lost in the fuselage when you unscrew it too far.

Ken
 

[Brent Williams]

These are the parts I'm referring to.

[Brett Buck]

This may be a dumb question (I am not blond) but what is an "elevator slider".  All I can think of is that small brass "T" nut that goes into on adjustable elevator horn.  You know, the one that falls out and gets lost in the fuselage when you unscrew it too far.

Ken

    The slider is about how you describe, although mine is steel (with a brass bushing). It goes up and down in the slot in Brent's drawing.

      Brett

[Steve Dwyer]

Some of you may find this interesting. I did a quick price comparison between McMaster Carr and OnLine Metals.

 Price Comparison Sheet Steel:                            McMaster-Carr             OnLine Metals
       
4130              .063 (1/16”) 12” x 12”                         $38.12                      $24.79
A-1008 CRS    (16 g) 12” x 12”                     .0598     20.41             .062      7.45

Aluminum Sheet:

2024-T3       .090 12”x12”                                        45.91                        23.14

[M Spencer]

ACTUALLY , in the Motorcycle frame neck of the woods , theres a Mid way Grade of Steel , thats not as heat sensitive as the olde 4130 , which wont weld in open air . Brazed for lower Temp.

Whereas the middle of the road one is argon arced or some such . I see now Renolds is up again but engineless , as its Cycles to the hilt . The 4130 was the Manx Norton Chrome moly frame tube . BRAZED .