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My step cracked.

RVG8tor

RVG8tor

Well Known Member
I was under the plane doing some work and happened to creep by the step and thought that seems to have more movement than I remembered.

Sure enough the back side right at the weld and gusset is a crack, just logged 216 hours. Step stool used when in the hangar so it is only used when getting in and out for flight. I always step back onto the step and have my passangers do the same.

This well be kind of a big job as I cut my flap fairing to just fit the step, the flap fairing will have to come off or at least part of it. then all those rivets to remove, I know a good welder and will ask if this is something that can be done with the stop on the plane.

I wonder if a wad of JB Weld would hold things for a few months, I really don't want the airplane down for the summer flying season.

Cheers

These are photos of the crack and step and fairing.

2hol0li.jpg


70dgeb.jpg


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29ly1iq.jpg
 
I took a continuing education course titled "Fatigue of Weldments". One thing the professor said that has always stayed in my mind is that weldments are instruments of the devil. I know many who have had similar failures. It can't be repaired as all you'll be doing is chasing the crack to some other location near the affected area. We need to design a step that does not have welds, at least in the portion where the step attaches to the tube.
 
It is mind-boggling that step cracks continue to be a problem that the factory never has had an interest in addressing. "When in doubt build it stout". Doubling the thickness of the steel parts in the steps 2x would solve the problem. Who cares if it gains two pounds in weight.
 
Hi Mike. Kind of a bummer I know. I had the same thing happen to my 9A at about the same time. I watched it carefully and in my case it never extended much further than what you show. When I sold it at 700 hours it was still holding and I never dealt with it.

Your JBWeld idea should keep it from flexing if you grind down the outside, but won't really "repair" it. Only true solution is to remove for repair long term.
 
Interesting

akarmy said:
Hi Mike. Kind of a bummer I know. I had the same thing happen to my 9A at about the same time. I watched it carefully and in my case it never extended much further than what you show. When I sold it at 700 hours it was still holding and I never dealt with it.

Your JBWeld idea should keep it from flexing if you grind down the outside, but won't really "repair" it. Only true solution is to remove for repair long term.
Click to expand...


Andy,

Funny you should say that, I wondered if the crack is done moving and if it has been there a long time. I say this because the good side now kind of acts like a hinge, when weight is on the step it compresses but when off it just relaxes.

My plan is to baby it until winter when I can tackle the real issue, I might just try a new design I was thinking about when building. I was thinking of a telescoping tube system that would stow flush to the fuselage. This would give me a step that will not crack and less drag!

Cheers
 
RVG8tor said:
Andy,

Funny you should say that, I wondered if the crack is done moving and if it has been there a long time. I say this because the good side now kind of acts like a hinge, when weight is on the step it compresses but when off it just relaxes.

My plan is to baby it until winter when I can tackle the real issue, I might just try a new design I was thinking about when building. I was thinking of a telescoping tube system that would stow flush to the fuselage. This would give me a step that will not crack and less drag!

Cheers
Click to expand...

Would love to see a design for a telescoping tube step! Might just have to put some time into this and make a project out of it! Anyone? Alan?
 
....better than steel?

rocketbob said:
It is mind-boggling that step cracks continue to be a problem that the factory never has had an interest in addressing. "When in doubt build it stout". Doubling the thickness of the steel parts in the steps 2x would solve the problem. Who cares if it gains two pounds in weight.
Click to expand...

If the steel is such a problem, why not an aluminum, or ( gasp!) carbon fibre step? surely one of the keen vendors on VAF could come up with a part that is actually stronger, lighter, and faster than they were before! :)
(...cue 6 million dollar man musical interlude here...):rolleyes:
 
JB Weld is a poor idea. It can't pick up enough load to do any good since its modulus of elasticity is no more than 1/40 of the steel. All it will do is hide the crack.

Dave
 
RVG8tor said:
My plan is to baby it until winter when I can tackle the real issue, I might just try a new design I was thinking about when building. I was thinking of a telescoping tube system that would stow flush to the fuselage. This would give me a step that will not crack and less drag!

Cheers
Click to expand...

This has been done. A builder in Tennessee has a RV-6A he built several years ago with retractable steps. They are linked to the canopy with cables so they extend when the canopy is opened. One of the cleverest mods I've ever seen...and I have no idea how he did it.
 
That would be Mr. Mark Phillips of the Possumworks! Met him at OSH one year and marveled at the step. Lots more fussing than I want to do, but it was fun to watch.
 
natural frequency shift...

The fact that the crack develops on the compression side leads me to suspect that the failure is caused by the resonant ferquency of the step being the same as or a harmonic of an
engine roll frequency vibration at cruise. Once the step has cracked half way through it is no longer resonant at cruise rpm. Others have suggested drilling a hole in the outboard end of the step, filling the horizontal part of the step half full with dry sand, and plugging the hole with a screw or weld. This sounds like a good solution to prevent failures in a new step, but I have no conclusive evidence that it works.
I wouldn't recommend the JB Weld on this structural component.
 
I am step-less so keep that in mind. JB Weld will do little to nothing. Either don't use your step or fix it.

I have been thinking about taking a 2-3" section of step tubing making a clam shell to reinforce by welding to the heavy base. Make the clam split on the neutral axis (leading/trailing edge) and shape the lower end like a torpedo to prevent a sharp stess riser perpendicular to the tube axis. Further don't weld the lower part, silver braze it. This will spread the load over a larger area for the stiffener not a single welded line. This is just an idea for a design and truly needs a test piece or FEA to verify the benefits.

Take a look at the fuel injection tubes and how they are brazed They have an uneven transition for the connecting sleeve to the tubes. This prevents the sharp transition from the sleeve joints to the tube.

I took pictures of Vans demonstrator RV7A yesterday.
RV7_step.JPG
 
rocketbob said:
It is mind-boggling that step cracks continue to be a problem that the factory never has had an interest in addressing. "When in doubt build it stout". Doubling the thickness of the steel parts in the steps 2x would solve the problem. Who cares if it gains two pounds in weight.
Click to expand...

Bingo!

Mike you should at least take the time to send an email to Vans. Not that they're going to change anything today, but maybe someday they'll think about it.

Welcome to the broken step club. :(
 
By freind's RV6A with something like 750 hrs on it cracked in the same place on the co-pilot side. It started cracking at least a year ago.

Like most I don't believe this is caused from normal use. It sure looks like a resonance issue to me as well.
 
jimbower said:
That would be Mr. Mark Phillips of the Possumworks! Met him at OSH one year and marveled at the step. Lots more fussing than I want to do, but it was fun to watch.
Click to expand...

Yes, it is indeed Possum.....I was going to allow him to remain anonymous. :)
 
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Suggestion

I would drill a hole at the very top of the weldmend and then one at the bottom. Take a large syringe like a turkey injector full of resin and inject from the bottom hole to the top filling the tube 100%. Might solve the problem and could be done without removing anything.
 
Berchmans said:
I would drill a hole at the very top of the weldmend and then one at the bottom. Take a large syringe like a turkey injector full of resin and inject from the bottom hole to the top filling the tube 100%. Might solve the problem and could be done without removing anything.
Click to expand...

Filling it with sand versus resin would be a better idea - the dead-blow-hammer effect will absorb energy to prevent resonance, whereas a fixed rigid mass like a resin blob will still resonate.
 
Neither approach will strengthen the part.

The resin will exotherm inside the tube. You don't want that.

The effect of the sand will be to drastically lower the natural frequency of the step (resin will do that too) and add some damping. But these will only help if the problem is resonance and if there's not another excitation source at the lower frequency. If it isn't resonance, e.g. if it's the load on the step that's causing this, then it won't help a bit.

Dave
 
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JB Weld Clarificaiton

Just for the record, I was never suggesting a "FIX" with JB weld, my use of it was to just get a few more months out of the stop so I don't have to be down for several weeks fixing the step. Summer is the best time of year up here, so I will not be doing anything with the step and plan to be as gentle with it as I can.

Thanks for all the information.

Cheers
 
RKellogg said:
The fact that the crack develops on the compression side leads me to suspect that the failure is caused by the resonant ferquency of the step being the same as or a harmonic of an engine roll frequency vibration at cruise.....
Click to expand...

I'm not a beleiver of the resonance thoery since my pax step was cracked before the engine was ever started. It cracked on the compression side, it is half way thru, and is being monitored at 400hrs and counting.
 
curtis said:
I'm not a beleiver of the resonance thoery since my pax step was cracked before the engine was ever started. It cracked on the compression side, it is half way thru, and is being monitored at 400hrs and counting.
Click to expand...

That makes it sound like a manufacturing issue with the way the weld heating is stressing the metal to pull tension on that area after it cools.
 
With the amount of pounding and bending to make my steps fit against the fuselage, I will be surprised if it isn't cracked already. If I had known about the step cracking problem before I did my step, I think I would have moved it to a little better location that didn't involve bending and shaping the mounting flange.

I agree with Rocketbob that the problem could be solved with thicker material used when they are being produced. The photo of the Vans 7A demonstrator looks like it has had some repairs or strengthening on their stair.

Don't take these thoughts as ragging on Vans - I believe their design is exactly what they wanted. It is a light, fun, economical, plane to fly. It is not perfect for everyone. I am willing to give up a little economy, fun, and weight, to make it perfect for me. A pound or so for the steps so I don't have to replace them and maybe 10 pounds to keep my A nose gear from rolling up and me tipping over. Well - it is an experimental - maybe I need to start experimenting!
 
WELDING THE STEP

Just a thought. Will welding the step on the plane cause trouble with the computers on the plane? I know when we have to weld on an implement on the farm we unhook the tractor to save the tractors computers.
 
Step crack

I had the same thing happen to me on my -8.
I see that your crack has progressed to your fairing, mine wasn't quite that far. You might have to trim the fairing a bit to give access.;)
I called in a welder and he did a nice job with his tig welder. Only took about 30 inutes. Has been just fine ever since.;)
 
Protect electronics

Jim Wright said:
I had the same thing happen to me on my -8.
I see that your crack has progressed to your fairing, mine wasn't quite that far. You might have to trim the fairing a bit to give access.;)
I called in a welder and he did a nice job with his tig welder. Only took about 30 inutes. Has been just fine ever since.;)
Click to expand...

Thanks Jim, as another person noted about welding with the step on the plane, did you take any steps to protect your avionics? My thought is to remove the boxes and ground straps to protect things to include removing the electronic ignition.

Thank fully I know a master welder, he has done some other work for me like my aileron push rods, if anyone can do this job he can. As you noted I will have to slice my flap fairing. In the build I was able to make a nice fitting hole and avoid the splice in the flap fairing, I was so proud of myself now I wish I had made the entire thing removable.

Cheers
 
Where is Allan from Antisplat, he came up with the idea of filling the step with sand, and he confirmed the repair with a transducer mounted on the step in flight.
 
Step Repair

I did this a few months ago but wanted to post this. My step cracked and to totally remove the step on the RV-8A would be very evolved, so I decided to try a splint.

I bought some of the same airfoil tubing used on the original step, in hindsight I should have gone up one size as it needs to fit around the original.

I split the tube lengthwise then drilled for rivets over the crack area. My step was cracked across the entire back of the step.

I cut away the portion of the flap fairing to gain access to the step crack area.

I applied JB weld as I riveted the splint in place and after that set I applied JB Weld putty to fair the front and back where the splint was located as well as a big area on the back of the step to give it more support.

All that was left was to install a cover piece to cover the area of the flap fairing I cut way.

This is now more rock solid that the original and I have been using it for two months now. It is not the prettiest fix but after painting it will be hardly noticeable. This was sure a lot less effort than removing floors and fairings to get access to remove the entire step.

Crack

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Splint

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Finished

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Cheers
 
I had a customer with a cracked step. It was a toss up weather to fix the original step or replace it. I went for the replacement. The time needed to do the work would have been about the same either way.
 
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