Cracking on steps

[CanadianAce]

Originally Posted by XOverZero

Shane:

Could it be that the steps that cracked before engine start were anomalous? In a production environment, it is possible that some steps could be overlooked and not get normalized after welding. With 4130 and the way the steps are loaded, that scenario would practically guarantee exactly the sort of failure in evidence. The failure in my partner's step is right along the edge of the weld, all the way across the chord.

It could be an anomaly; however, it would be unusual to see a failure in the compression zone unless it was caused by fatigue. (I am assuming the reporting of these pre-startup failures are accurate, and the QAQC process by Vans precludes a cracked part from being sent from the factory.)

Originally Posted by Kyle Boatright

Have we established that the steps are supposed to be normalized after welding? I'd bet against it.

Typically, it is not necessary to normalize (or better yet anneal) thin wall 4130. If the part is properly prepared (near perfect fit and at least 16'C before welding) and welded correctly (not at an excessively high temperature) then it should be sufficient to allow it to cool in air at room temperature.

It would be interesting to see if this failure would repeat if several owners who experienced early (<500 hr) failures replaced their steps with sand filled ones (ingenious solution to the harmonic prop wash issue btw). If these new steps made it well beyond the initial failure age of the originals, I think it would be safe to say the solution was found for most cases.

As for the others that failed before startup... be gentle when using your steps. Or strengthen the steps to allow for an increase in loading. This is where I like the Van's solution, since it corrects for both the prop wash and heavy foot issues.

The best solution is perhaps Guilherne's... just don't install them. This is my plan... now I only need to make up my mind on having a vertical or horizontal induction.

[RV7A Flyer]

Originally Posted by CanadianAce

The best solution is perhaps Guilherne's... just don't install them.

I didn't, and I'm glad of it. I carry a small, lightweight plastic stepstool for passengers. Yeah, it's a big step up to the wing on the -A model, but I can do it pretty easily. And if the day comes when I can't, maybe I'll install a step then (perhaps by then they'll have the cracking problem sorted out ).

Also, less weight, less drag...so I can go faster

[grayforge]

Ditto. I'm building a 7A and am also going stepless.

[8 ball]

Those breaks are caused by nitrogen embrittlement. It has nothing to do with how you step on it or whether you are a few lbs. heavy. There is a very easy fix. It has to be done during the welding process. If they would use stainless steel welding rod (tig) this will end the problem. There is no need for additional trussing.

[David Paule]

If it were hydrogen embrittlement, we'd be seeing these effects:

* The cracks would occur anywhere on the weld,
* Other stressed parts, like the engine mount and landing gear mounts, would crack.

If you're concerned about hydrogen embrittlement, you can bake the parts - you'll have to look up the baking process and follow it carefully.

Welding with a rod of the wrong material, and perhaps an incompatible material, might prove to be more problematic than the current design. It would certainly be harder to correct. Again, best to follow an established process here to get reliable results.

Dave

[rvbuilder2002]

Originally Posted by CanadianAce

Prop wash is likely the culprit in most cases, but some have failed prior to first engine run...



This is a complex problem with likely several issues at play...



And that is why Van's own fix is to add the stiffener plate. It solves the vibration and the overload (heavy/jumping passenger) issues.

Keep in mind that Van's airplanes do not experience a typical step usage.....
Some of them get climbed in and out of more times in a day, than a lot of builders planes do in a year... by 100's of people in all shapes and sizes....

The repairs that have been made previously to Van's planes are all for damage that was clearly from load cycles. I am not yet convinced of cracking being cause by in flight vibration. I am not saying it isn't possible.... since there is likely a broad range in the level of vibration based on prop balance, etc., within the fleet. I just haven't seen any indications (so far) of any data to support it.

[Mark Burns]

On a 7A install both steps!

That's my advice after 1200+ hours.
I can't imagine having to look after a folding step stool.

As many rides as I've given the stool would have been a royal PITA.

I'm 5-11" and I want that step on my side also!
It's a real stretch not to use it.

My .02

Mark

[8 ball]

Nitrogen embrittlement always occurs in the base material where the heat line pushed the carbon back away from the weld. 308 stainless is an acceptable filler for 4130. Been doing this process for over 50 yrs. whoever is concerned would do well to listen.

[boom3]

Originally Posted by rvbuilder2002

The repairs that have been made previously to Van's planes are all for damage that was clearly from load cycles. I am not yet convinced of cracking being cause by in flight vibration.

I think your statement leads new builders to believe that it won't happen to them. Then one day down the road when it does they'll be back on this thread.

Whatever the reason the current design could be improved or an optional upgrade could be offered. Yes this may take a little effort on Van's part but double the price or something. It's just no fun drilling out rivets, sandblasting off your paint, paying a welder to add a support, then repainting.

I just don't buy that hundreds of people who otherwise baby their airplane somehow show no regard for their passenger step. (Constantly letting overweight passengers just jump on it backwards.)

Pretty please???

[CanadianAce]

Originally Posted by boom3

Whatever the reason the current design could be improved or an optional upgrade could be offered. Yes this may take a little effort on Van's part but double the price or something. It's just no fun drilling out rivets, sandblasting off your paint, paying a welder to add a support, then repainting.

This statement is bang on. There is a recognized issue that is ongoing. If the current part design is problematic it only makes sense for the manufacturer to change to design. The fact the manufacturer has upgraded this part on thier own demo unit says a great deal. The best way for this issue to progress forward is a new part design from Vans. Once implemented it will be clear soon enough if it resolves the issue.