RV-6A Step Installation Question

After putting it off for some time, I today tackled installing the steps on
my RV6A fuselage. Everything went really well, especially bending the flange around the step to conform to the fuselage (no more than 5 minutes a side). The only downside (and it's not something I did...for once!) is that the tube does not reach all the way to the F-626 web - it's about a half inch too short. This also means that I cannot pass the bolt through the F-6125 plastic block - the bolt hole is right even with the end of the tube (see pix below).



The fuse is a quickbuild fuse, so I'd expect that it's put together correctly. Some sanity measurements show that to be the case, so what I have are two steps whose tubes are too short. I can think of three possible remedies :

1) Have a longer piece of 1.5" 4130 Chrome-molly tubing welded to the existing tubes

2) Double up the F-6125 plastic blocks

3) Get another set of steps from Van's - hopefully ones with the correct tubing lengths

My preferred solution is #2, but before I go this route I was hoping some other builders might offer their thoughts on how to proceed.

Thanks!

wider blocks

it would seem to me that wider blocks would move the force away from the rib and give it a twisting motion. there are only two bolts holding this in IIRC i would opt for #3 and get vans to send what you paid for. if you weld you will have to grind the weld off . a no no in ACM. option 2 would be just that, option 2
good luck

Brad:

I had a similar situation with my very slow build 6A. What I did was to make a shim out of extra spar flange material...the 1/8in stuff. I stacked two of these shims between the step tube bearing blocks and the bottom fuselage ribs, essentially making a 1/4" shim. It requires longer bolts of course to bolt the blocks, shims and then the ribs together. You will notice that there are only two bolts mounting the bearing blocks to the bottom fuselage rib. The shim is oriented diagonally across the bearing block so that the bolts pass through them and support the bearing blocks as well.

Has worked with no ill-effects.

Regards,

#1

cytoxin said:

it would seem to me that wider blocks would move the force away from the rib and give it a twisting motion. there are only two bolts holding this in IIRC i would opt for #3 and get vans to send what you paid for. if you weld you will have to grind the weld off . a no no in ACM. option 2 would be just that, option 2
good luck

Click to expand...

Brad

I'd go for option 1, and if you get a short internal sleeve, and use rosette welds, no grinding will be required. Definitely this option if you have the skin rivet holes already drilled.
The welded portion only has to go through the fuselage hole anyway... and at the fus. skin side all of the loads are taken by the multiple rivets. This hole could be slightly enlarged with no problems.... no weld grinding should be involved anyway...

At the inner rib, there are a LOT of forces created by heavy passengers putting all of their weight on the steps.... As previously stated, shims would put more of a twisting load on the rib, which is only 0.025 thick.

Do you have a good aircraft welder around??

gil in Tucson

Regarding twisting of the fuselage bottom rib with the shim I mentioned above.....

I too was concerned about that. After all was secured, when all my weight was placed on the step, I observed no such twisting, this before the baggage floor skins were in place which give the ribs more rigidity.

As I said, I have had no problems with how this was assembled. YMMV.

ChiefPilot said:

.......but before I go this route I was hoping some other builders might offer their thoughts on how to proceed.......

Click to expand...

ChiefPilot said:

.......... but before I go this route I was hoping some other builders might offer their thoughts on how to proceed.Thanks!

Click to expand...

You have any number of ways to deal with the problem. There is no one right way, and I only offer another data point to consider. A POSSIBLE fix I would personally feel comfortable with is illustrated below. Fabricate a tapered .125 doubler plate extending several inches on either side of bearing block. Lay out a double row of AD4 rivets, equal spacing. Shim remaining gap as required. This situation highlights why I prefer my alligator squeezer over the common "C" type. An alligator would make very short work of squeezing those rivets. This repair may seem like overkill on an RV, but I built mine like I was still on the F-18 production line.

I doubled up the plastic blocks and drove longer bolts through both.

You may wish to consider placing the step flange on the inside of the sideskin (perhaps with a doubler on the flange as well to move it in even further) - this would give you a little extra length to play with, and some have suggested it even looks better.
Bill Brooks
RV-6A, slow build fuselage (still).

Thanks for all the responses! I talked to Van's today to see what their take on it was and the conversation was one of those that answered the question but didn't make me feel any better .

Their approach is to shim the F-6125 block to get enough edge clearance to drill the hole through the steel tubing. When I asked about the twist that would be induced, the technician on the other side (Bruce) said it shouldn't be a problem. He then went on to also suggest that I tell passengers to back onto the step when exiting the aircraft rather than jumping down on it and that (here's the thing) they have had to replace the step on their -7A demonstrator three times. I know the demo planes get a lot of usage, but ...wow.

Still not sure what to do, but I think I have some better ideas on how to address this now - thanks to everyone for your help!

Shim

Hi Brad,
Our 6A had the same problem and I cut a 1/4" piece of plastic from the lid of a Roundup drum....the perfect thickness and used longer bolts. I've had a 260 lb guy and two 240 pounders...no problem so far. The outer rivets take almost all the load and rotating force since the arm dramatically reduces the loads on the inner attach point.
Regards,

Another THought

When I was building my Quickbuild RV-7A, I noticed the same thing. The problem was that the weld was not allowing the step to fully insert into the fuse. I made the hole bigger in the fuse side to allow the weld to fit into the hole and it made difference.

Just a thought.

Brian