Cracking on steps

Fred.Stucklen · #1 03-11-2011, 08:47 PM

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????

Ron Lee · #2 03-11-2011, 09:42 PM

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/communit...rack+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.

N941WR · #3 03-11-2011, 09:54 PM

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.

Geico266 · #4 03-12-2011, 06:30 AM

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

swisseagle · #5 03-12-2011, 07:35 AM

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

Russ McCutcheon · #6 03-12-2011, 09:52 AM

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.

gasman · #7 03-12-2011, 09:57 AM

Quote:

Originally Posted by Geico266

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...............

rvbuilder2002 · #8 03-12-2011, 05:00 PM

Quote:

Originally Posted by Russ McCutcheon

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.

roadrunner20 · #9 03-12-2011, 05:21 PM

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.

turbo · #10 03-12-2011, 06:20 PM

quit a few years but when it failed i cut it off. must say my knees are a bit stronger since then, and if i need a step i have a spare on the right side. now lets hope that one lasts foe ever. anyways, no fat chicks allowed. http://http://img340.imageshack.us/i...92/img2268.jpg