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Cracking on steps

Fred.Stucklen

Well Known Member
Friend
RV-7A Step Failure

Hi All,

Was spring cleaning today, cleaning the belly, when I noticed a new crack on the back side of the right side step. This step was replaced less than a year ago! Fortuneatly, I had the wisdom to install the new step a year ago with AN-3 bolts and nut plates. I also put an inspection panel in the baggage compartment floor, so removing the broken part only took 15 minutes instead of all day. And I had the old step welded, so, was able to easily replace the broken part and be ready to fly tomorrow morning.
Heres some pictures of the broken part.. I'm planning on getting it welded, but this time with some additional re-enforcements on the back side.....
So what's causing this to happen????
PICT1164.jpg

PICT1172.jpg

PICT1165.jpg
 
In my case other RV pilots asserted that it was due to my excessive mass (weight). Mine failed in almost the same manner and I had reinforcing metal welded on the front and back. Those pics should be here somewhere.

Here it is:

http://www.vansairforce.com/community/showthread.php?t=26071&highlight=crack+step+weld

When in the hangar I almost always use a step stool to get in rather than the step.

Based upon what I have read this is hardly a rare occurrence.
 
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I have heard that this can happen if you step off the wing looking aft. When this happens, people can see the step and almost jump on it. If you step off facing forward, then you kind of have to fish for it and transfer your weight to the step slowly.

I don't really know as I don't have those things on my -9. that is just what I have been told, which may be total BS.
 
Looks like a classic case of metallurgical failure due to "Heat Affected Zone". Heat from the welding process creates an area above and below the weld that is structurally different. Basically the zone is where one side is hardened, and one side is not. Where these two structurally different areas meet can crack with constant flexing. The parts should have been annealed or "normalized" after welding by heating the entire part to a certain temperature and allowing the entire piece to air cool.

IMHO, if this crack was caused by stepping off facing the tail or a person being too heavy it would be cracking on the other side, or the rivets would fail.

Heat-Affected Zone
http://en.wikipedia.org/wiki/Heat-affected_zone

Here is info on normalizing.
http://en.wikipedia.org/wiki/Annealing_(metallurgy)

I hope Vans normalized the engine mounts! I guess that is why we do annuals. ;)


Fred, how many hours on the -7 before you noticed the crack, and if you don't mind publishing it on the internet how much do you weigh? May be a good data point for others
 
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Harmonic vibrations?

Hello,

what I do not understand:

- The left step is mostly used 50-90% more than the right one.

- The crack is on the compression side of the load.

This makes no sence to my knowledge. I understand the heat affected zone and the unleaning. But but why it happen to the right Pax side and on the compression side?

Can it be a harmonic vibration due to prop wash, that cause this happen?

Regards Dominik
 
I have seen the result of fractures along a “heat affected zone” many times and I have to disagree with you this time as the break does not follow the heat affected zone or the weld but rather is simply in a straight line perpendicular to the load. In my 20+ years of working with 4130 I have seen that it never breaks on the tension side, rather it will break on the compression side if the load is sufficient to buckle or compress the tubing repeatedly, it becomes work hardened along the compression line and eventually breaks. The fact that this happens at or near a weld in this case is simply because that is where the most stress is focused, where the lever/step is attached.

I would recommend any one having problems with this, weld a strap on the bottom side that extends down about two inches, Vans actually does this on there demo planes because people of all sizes climb in and out of them all day long all the time.
 
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IMHO, if this crack was caused by stepping off facing the tail or a person being too heavy it would be cracking on the other side, or the rivets would fail.

As you know, that part is a tube. The weld on the outside would have to tear apart to fail. The weld on the under side is held rigid on the upper part of the weld by the mounting plate. The lower part of the weld is connected to the tube. The tube will flex when you step on it.

If you back off of the wing, you will find the step with your foot and rest your weight on it as you back off of the wing.

If you step off of the wing facing to the rear and allow your weight to drop on to the step, the step sees three times more weight than backing off.

Passengers will depart this way most of the time, so explain how to get out.... or get over there and help them find the step.

This step thing is kinda like the nose wheel...... it fails because it is being abused...............:eek:
 
I have seen the result of fractures along a ?heat affected zone? many times and I have to disagree with you this time as the break does not follow the heat affected zone or the weld but rather is simply in a straight line perpendicular to the load. In my 20+ years of working with 4130 I have seen that it never breaks on the tension side, rather it will break on the compression side if the load is sufficient to buckle or compress the tubing repeatedly, it becomes work hardened along the compression line and eventually breaks. The fact that this happens at or near a weld in this case is simply because that is where the most stress is focused, where the lever/step is attached.

I would recommend any one having problems with this, weld a strap on the bottom side that extends down about two inches, Vans actually does this on there demo planes because people of all sizes climb in and out of them all day long all the time.

Listen to Russ...he has it exactly right.
 
Have heard of quite a few stories of the steps cracking.
With my previous plane, Piper Cherokee, I would always hit my shin on the #$%$ step. That's why I opted to not install one. For me, the step up is not that bad.
In the hanger, I use a step stool.
For passengers, I always supply a plastic step stool. This enables me to assist the passenger in & out of the plane.
Also, no step drag in flight.
 

And this is what will happen if you don't notice the crack starting on the back side..................:eek:

This can be repaired...... Clean up the edge. Make a plug that will slide up in the remaining socket, and fasten it with a C/S screw. Do the same with the new part by cutting the leg off and fit it to the exposed part of the plug. Drill and tap it too.
 
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Same failure for me.

Hello,

what I do not understand:

- The left step is mostly used 50-90% more than the right one.

- The crack is on the compression side of the load.

This makes no sence to my knowledge. I understand the heat affected zone and the unleaning. But but why it happen to the right Pax side and on the compression side?

Can it be a harmonic vibration due to prop wash, that cause this happen?

Regards Dominik

My right side step failed in precisely this manner about a year ago (after 5 yrs flying). The left side step is used more than twice as often, yet the crack formed on the right INBOARD side. I don't get it. Luckily a neighbor TIG welded it in place for me and it's been fine thus far...
 
Interesting commentts on my step failure. I tend to agree that it is a compression failure. I'm no light weight, and while working on the plane, I've definately stepped down facing aft.
I'm having the offending part welded, but this time will beef up the backside with extra material. I'll post new pictures when I get the part back from the welder.
 
Vlad.
Thats a nice picture of my " NO STEP" :p
I had noticed a little spring in the step. When I looked under the plane I saw the same crack as everybody else is seeing.
Not wanting to lose the step somewhere in the air, I pulled it off myself.
Last month during my condition inspection I drilled out the exterior rivits, cut a small access hole in the baggage area to unbolt the inner support and had it welded.
I had a small gusset added to the outside for strength.
I hope you wont be confused whe you see " no step" next to a step this year.

Sean
 
crack

Two main factors that i see. 1-Tube fails on the inside of a bend motion or on the compression side first. 2-Cracks will always start at the joint where a solid is connected to a flexible, in this case the mounting plate connected to the fuse is solid and the tube is flexible. With these to facts combined it is simple for me to understand how and where it is cracking. Heavier use or abuse will make the crack show up earlier grow faster. There are several ways to repair and prevent this cracking. Best wishes for your success.
 
Two main factors that i see. 1-Tube fails on the inside of a bend motion or on the compression side first. 2-Cracks will always start at the joint where a solid is connected to a flexible, in this case the mounting plate connected to the fuse is solid and the tube is flexible.

That's correct.

Here's how I fixed the step on my 6A.

http://www.facebook.com/album.php?aid=19363&id=1833677196&l=e4471f22ae

I inserted a one piece plate that transitions through the mounting flange and inside both tubes that takes the bending out of the compression side as well as the tension side. Just make sure that the internal plate sits just under the outside diameter of the tube so that you can weld it up with a tig and dress the weld to the outside of the tube without grinding away all the weld. This makes the step look original without cobbing on a bunch of external metal that really doesn't address the root problem.;)

Dave
 
Fatigue cracks in a welded joints can occur in a location that is on the compression side. The welding process can cause enough residual stress that part of the joint is in tension almost at yield without any load. In this instance the load causes a reduction in stress and the removal of the load causes an increase in tension. In a non-welded component you can ignore the compression to a degree hoever fatigue mostly occurs at a weld.

I am a bit puzzled because I would have thought that the number of times the steps get uses would be low and therefore fatigue unlikely. That makes me suspect that there is some form of resonance issue during flight.
 
I think the most interesting thing I learned at Oshkosh is how many "A" builders have cracks on the INSIDE of the step on the RIGHT side, and it doesn't appear to be from people using the step.

Is this a long-acknowledged situation? It's amazing how many RV "A" builders I met who reported the same thing in a matter-of-fact sort of way.
 
Cracked step

Probably noticed it after about 150 hours on ours. Yup, passenger step. Luckily it was before painting.

Now there's a good topic to poll.
 
I thought I was lucky until someone challenged me to take a looked (at about 1,000 hrs). Indeed my pilot side step has a crack that almost went through half of the tube. Passenger side is still okay though. I had a friend welded it in place and none of my electronics got fried (I was warned by several people about the potential).

It is also a good idea to keep some paint for touch ups.
 
Both of mine cracked!

Passengers step cracked at about 250 hours. Pilot side cracked at about 900 hours.
Both cracked along the weld on the midline side of the arm.

Before I replaced the passengers step I welded an extra bit of steel to distribute the load over a larger area. Seems to have worked.

I still need to replace the pilots side step.
 
Removable Steps

Several years ago I made me steps removable for racing. I made access holes and covers for the baggage floor and two large nut plates containing a platenut for each former rivet location and a couple of extra ones for mounting the nut plates. When set up for racing covers with holes for only the perimeter holes are installed.

You might want to consider this mod.

Bob Axsom
 
Yep, me too. Only on the 'right' side so far, but it isn't because of passengers as that is the side I fly from full time. One of these days, I'm going to step on it and fall on my ***.
 
Mount them with screws and platenuts for ease of service

I thought I had written this type of installation in this forum but maybe not. Anyway it makes the step a completely removable and serviceable unit with no effect on paint, no need to drill out rivets. etc. I e-mailed one fellow photos last night. I did it at the suggestion of John Huft after the plane was built, flying and painted so I could remove them for drag reduction in races. If there is a known chronic cracking problem it makes no sense to rivet then in as an integral part of the airframe.

Bob Axsom
 
Well after reading this thread I checked and sure enough my passenger step is cracked. Pretty much all the way across the inside, just below the weld.

Well shoot, it's gonna suck trying to fix it since it's nicely painted and clearcoated. :(

Might be another good service the Anti-splat guy can provide. Maybe he can beef up the steps a little before installation.
 
I just passed the step install stage on my QB 7A. Decided to skip the step install and maybe toss a light weight stool into the baggage compartment if climbing onto the wing is too difficult for passengers.
 
I have discovered our RHS step is cracking, or the powder coating is..... and I wonder why?:rolleyes:

Looks like a fun job coming up and some careful use of that step for a while.

Are Vans doing anything about this?
 
Pictures

It seems that van ought to look into the weld process from the manufacturer to investigate why it is occuring so frequently. Failure mechanism appears to be cyclical and eventually failing on the edge of the weld (heat affected zone). Anybody have photos of the cracks/failures?
 
I was going to post a picture of mine but it's just like the picture at the beginning of the thread.

I agree they need to do something. My passenger side while rarely used has never been abused. Everytime I have a new passenger I'm over there giving them instruction on how to get in and out. No one has jumped on it or stepped off forward instead of backwards.

Some beleive and I tend to agree that this cracking is caused by vibration and not misuse.

Grayforge, you won't have this cracking problem but let me say it's a big step up onto the 7A wing.
 
Combination

The steps arent failing because of the occasional load that is being applied by people entering the cabin. I believe it is a combination of the high frequency vibration that eventually causes the crack in the most vulnerable (stress riser) location where the tube and the plate join.
 
Might be another good service the Anti-splat guy can provide. Maybe he can beef up the steps a little before installation.

Good idea, and I bet a smart engineer like him would figure a way to vibration-dampen that step. That is, if vibration is the cause...

.
 
Well I stepped up this weekend and removed my cracked passenger step. I'd been dreading it for months but it was really pretty easy.

Ah man, I hate to do it, but here goes...
step1.jpg


Drilling out the baggage floor LP4-3 blind rivets was the easiest part.(for those of you contemplating nutplates) I drilled slow and didn't push and the heads came right off. The solid rivets on the side cover and tunnel nutplates were a little more work but not too bad. I left the back flange riveted and just rolled up the floor to expose the wing step bolt.
step2.jpg


I center punched first then drilled into each rivet with a number #40 drill. I then drilled with a #30 drill and popped of the heads. The rivets were easy to tap out with a bucking bar behind the skin.
step3.jpg


Literally
step7.jpg


The crack
step4.jpg


step5.jpg


step6.jpg


After it's sandblasted I going to have a welder repair and reinforce it. Some repainting and I think I'm going to bolt it back on. (Mainly because I don't want to mess up the paint riveting it back on.)
 
Some believe and I tend to agree that this cracking is caused by vibration and not misuse.

The steps aren't failing because of the occasional load that is being applied by people entering the cabin. I believe it is a combination of the high frequency vibration that eventually causes the crack in the most vulnerable (stress riser) location where the tube and the plate join.

Might be another good service the Anti-splat guy can provide.

Good idea, and I bet a smart engineer like him would figure a way to vibration-dampen that step. That is, if vibration is the cause...

I talked to the AntiSplatAero guy about another product, and he mentioned the step cracking. He thought it might be caused by prop-wash vibration, hence, worse on the passenger (right) side. He thought adding a few ounces of sand into the step (the horizontal part, the actual step part of the whole thing), pouring in a bit of epoxy or Proseal to hold it in place, might change the harmonics enough to reduce or eliminate the problem.

I'd try it but have already riveted the steps to the fuselage. Even so I'm tempted to remove the right-side step and try this.
 
The cracking of the R/H step on my plane was NOT caused by prop wash! My step was cracked on the inboard (compression) side before the first engine run. It cracked from just being used to get in and out during the build process.

What about the portable fan you used during the build? :D

I wish the manufacturer would just beef them up a little. If most people have problems with your product, wouldn't you want to make them better? It seems like they're all destined to crack. (Whether from normal use and or the prop wash.) This is not at all a new problem.
 
What about the portable fan you used during the build? :D

I wish the manufacturer would just beef them up a little. If most people have problems with your product, wouldn't you want to make them better? It seems like they're all destined to crack. (Whether from normal use and or the prop wash.) This is not at all a new problem.
We build these steps for Van?s however it is not our design, we build what we are asked to build, we are not at liberty to change the design of our customer?s parts, if they ask us for a change that would be no problem.
 
Thanks for your input Russ. Your products and work are top notch. I don't believe this cracking has anything to do with your work, but rather the design itself. I apologize for my comment that you that manufacturer had anything to do with the design. My misunderstanding.

I'd be happy to write a letter to Vans explaining the problem. With any complaint it's nice to at least offer a possible solution. Since I don't know much about available materials and welding, can you offer any suggestions? Is there heavier guage chromolly material about that size that could be used? I've heard rumors that the Vans demo planes have beefed up steps although I've never really looked at one.

I just think it be nice to at least have the option for heavier duty steps. I think most people wouldn't have a problem paying a little more and sacrificing a little weight.

Any thoughts?
 
step reinforcement

As a new builder I am reading and wondering, should I have a welder reinforce the area before installation? I'm thinking a small piece welded perpendicular to the tube would prevent cracking. It would add some drag though. I would then have it powder coated again. Of course, this community always find a solution so it may get fixed before I get to that point.
 
If someone has a broken step laying around, I would be glad to look at it and see if I can come up with a solution to help everyone out.

Be glad to pay shipping, and whoever can send one I will make sure they are taken care of.
 
I experienced this failure on our flying RV-7A during the annual inspection (800 hours) in December. The failure occurred along the underside weld where the tube joins the plate riveted to the fuselage. The failure itself was in the tube at the point where the weld stopped. It did not look like a bad weld, it looked more like a fatigue failure of the metal at the junction which would flex every time someone put weight on the step. The pilot side step looked fine.

I fixed the step by rewelding the joint and welding over the crack that had propagated outward from the joint. I made the bead bigger than original to better distribute the load, but I believe this will eventually crack again. A more permanent fix, perhaps, would be to cut a 1/4" - 3/8" (or maybe wider?) strip of 4130, .040 thick, bent to fit the curve of the tube at the junction where the crack is, and weld it to both the tube and the plate. My theory is that this will better absorb the flexing by distributing the forces. Making sure that the rewelded part is fully stress relieved will also increase longevity.

Why it seems to only happen to the passenger step is a real mystery, especially in light of how it has also happened to non flying airplanes. And in our plane the pilot side step gets used far more than the passenger side one.
 
If you don't mind

Russ,

If you could say . . what the material specs (basic steel type) are and do you oven bake the parts at 1250 deg F or so for a hour, after welding, for stress relief.

If this is sensitive, just disregard . . . just curious if there is a stress relief baking in the process.

It is just odd that it always occurs on the lower side of the steps, odd from a stress standpoint. No finger pointing, just thinking that things that repeat, come from a common origin. I would expect your parts are EXTREMELY consistent.

Thanks
 
Too thin of material for PWHT

Not to speak for Russ...but the thicknes of the 4130 plate and tube that is being joined is too thin to need the stress relief. Typically with carbon and alloy steels, a nominal thickness wall material of 1/2" or less will not need the post weld heat treatment. Also as a TIG process the throat of the weld will be much less than 3/8".

It is somewhat of a mystery that only the right side step is failing. Anybody have one on the left that has failed?
 
The material on my steps is much thicker than what is used on my bicycle. I have put thousands of hard miles on my bike and never had a failure of any of the joints. This is really a strange thing. There must be a way to strengthen the step other than adding a big support that causes more aerodynamic problems. There must be steps on other certified planes - do they have a problem? The welds on my steps are beautiful. I can't imagine them failing, but I am putting the baggage floor in with plate nuts. I may use screws and nuts for the step itself.
 
It is somewhat of a mystery that only the right side step is failing. Anybody have one on the left that has failed?

I found the left side cracked at 1,000 hr. At the time right side had no cracks. Now at 1,270 hrs I need to check the right side again.

ed: Checked right side this morning and found a 1/2" crack.
 
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Sent this to Vans today.

Not sure who to send this to at Vans so I thought I’d give support a shot. Please forward it along if need be.
Is there any chance of Vans beefing up the current step design or offering a heavy duty version? Seldom ever used and never abused (babied in fact), my passenger side step cracked at about 200 hours. This compression crack on the underside seems to be the norm on most passenger and some pilot side steps. (There have been quite a few threads on Vans Airforce over the years)
I realize that no matter what you make, someone will find a way to abuse or break it. I just think in this case a little heavier duty design is warranted. I’m sure most of us would be more than willing to pay a little more and sacrifice a little weight. I heard that the Van’s demo planes have beefed up steps. If true, maybe this could be offered on all of them.

Thank you,

Jeff Bloomquist
RV-7A


step4.jpg
 
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