Drilling 6A Main Gear Weldments, need advice

[WingsOnWheels]

If the weather is good this weekend, I plan to pull the fuselage out of the shop, mount the wing, and drill the main gear mounts. However, there is an issue I would like to get some input on. I am hoping Vans will be open Friday so I can give them a call.

The forward flange on the gear weldments that bolts to the lower longeron doesn't match the plans. The plans show the strut welded to a midpoint in the flange and a bolt forward and aft of the tube (see image)

The weldment as provided has the strut tube biased more towards one end of of the flange. The red dots in the second picture would be the plans drilling locations (the dots are just for representation, not exact points), but putting a bolt below the tube on the corner of the flange would not provide sufficient edge distance or the nut would interfere with the weld. I could put two bolts on one side of the tab (black dots), but the edge distance on the longeron would then be questionable.

How did others deal with this part of the weldments? Pictures would be appriciated.

 

[mcencula]

Horizontal holes

The holes on my weldments (-7A) were horizontal. If it were me, I'd maintain the edge distance on the aluminum lower longeron and let the edge distance go smaller on the steel flange. Going from memory, I believe the minimum edge distance for steel is 1.5D for steel anyway, not 2D like on aluminum. Edit: I was corrected by Matt R (wildblue37) that the standard edge distance is 2D for aerospace regardless of material.

Here are a couple pictures that show where the starter holes were located on the flange for my -7A weldments. Note one of them shows the paint stripped away because I had to have the flange cut off and have it re-welded to fit correctly.

Check with Vans to be sure.

 

[az_gila]

Shims

I did mine at the two red dots location as the plans show, squeezing the rear one in.

In my case, rather than cutting and re-welding, I made a tapered shim to correct the misfit. I think most of the RV-6A weldments did not fit precisely - I know some builders repositioned the ends with a hammer, but i prefer the shim method...

 

[WingsOnWheels]

Without grinding down a washer, the best edge distance I can get on that small corner of the flange is 5/16. If I grind the washer just a bit I can get it up to the minimum 6/16 which will do the job. It isn't ideal, but acceptable. I'll check with Vans, but it sounds like my best bet.

Thanks for your input.

 

[flion]

Yes, the ground washer will do the trick for you. I had more trouble with the bolts through the spar; in a couple of spots the webbing really interfered with getting washers and nut in place. But I managed, with perseverance.

 

[WingsOnWheels]

Yes, the ground washer will do the trick for you. I had more trouble with the bolts through the spar; in a couple of spots the webbing really interfered with getting washers and nut in place. But I managed, with perseverance.

I can see where there will be some trouble with four of the big bolts. The plans have you put the two center seat ribs with the web dead-center over the bolt hole. I'll have some fun with that one for sure...

 

[wildblue37]

For aerospace, 2D is usually the minimum edge distance regardless of the material. Fastener strength is measured at 2D and 1.5D, with 1.5 less obviously. So 2D is the no-brainer edge distance. Less than that deserves some structures evaluation.

 

[Rick6a]

How did others deal with this part of the weldments?.....

I often encountered that situation with the weldments in my -6A and handled it the way pros would likely do. I used a spot face or sometimes called a reverse spot face to machine the perimeter of the hole to provide a perfectly flat surface for the nut and washer to sit upon. Typically, you chuck a spot face shaft into your cordless drill then insert the shaft through the hole. Then you affix an appropriately sized spot face onto the shaft. The self locking feature on the nose of the shaft prevents the spot face from coming loose when operating the drill motor. Using a relatively slow RPM, you PULL the spot face through the hole. The spot face machines the surface of the material. You stop when the paint just starts to scuff. In your case, a spot face will just remove a small portion of the conflicting weld producing a perfectly flat surface for the nut and washer.

Spot faces come in many different hole diameters and sizes. There is sure to be a size ideal for your situation, check with tool vendors for more information. Spot facers frequently show up on eBay too.

 

[az_gila]

I often encountered that situation with the weldments in my -6A and handled it the way pros would likely do. I used a spot face or sometimes called a reverse spot face to machine the perimeter of the hole to provide a perfectly flat surface for the nut and washer to sit in. Typically, you chuck a spot face shaft into your cordless drill then insert the shaft through the hole. Then you affix an appropriately sized spot face onto the shaft. The self locking feature on the nose of the shaft prevents the spot face from coming loose when operating the drill motor. Using a relatively slow RPM, you PULL the spot face through the hole and it machines the surface of the material. You stop when the paint just starts to scuff. In your case, a spot face will just remove a small portion of the conflicting weld thus allowing the nut and washer to fit without conflict.

Spot faces come in many different hole diameters and sizes. It all depends upon the particular application. There is sure to be a size ideal for your situation. Check tool vendors for more information. Spot facers frequently show up on eBay too.

<snip pic>

Rick, is it good practice to spot face and cut into the weld?

I would think a modified washer would be more structurally correct for this particular problem bolt.

PS - I do like the spot face in other locations.

 

[Rick6a]

..... is it good practice to spot face and cut into the weld?......

Problem with potentially compromising the structural integrity of the weld? When queried, Van's suggested I grind off the portion of the offending weld using a ball file or whatever else would work to achieve adequate clearance. My view is that while that may be okay to do, that is taking a meat axe approach because you run the risk of removing more material than you really have to. A spotface is a dedicated tool, it produces an extremely clean result and by design removes only just enough material to allow the nut and washer to do their job.

 

[WingsOnWheels]

Rick,

Thanks for the tip on the spot face, that is a great idea. I will check with vans before using it for a particular application, but I sure like the idea.

----------------

I spent today fitting and drilling the main gear, that was just a barrel of fun...

I still have some cleanup items to complete, so right now the plane gets to spend the night in the driveway (not something I'm particularly comfortable with). At least the hard part is over with.

For the 3/16 holes I used a 3/16 OD X 1/8 ID bushing to drill a pilot and then finished it with a 3/16 drill.

For the 1/4 holes I used the same pilot and bushing, then a 3/16 bit, then a 7/32 bit, then finished it with a chucking ream.

I'm pretty happy with the fitment. There are a coule spots that are going to very difficult to get a nut on due to proximity to a weld. I will see what Vans says about these spots.

 

[WenEng]

Help on fitting gear weldment RV-6A

I am starting to fit the main gear weldments prior to drilling and am confused about a couple things.
1) There is a gap of maybe 3/16 inch between the fuselage longeron and the extended weldment brace if I hold the weldment tight to wooden false spar, or if I instead hold it tight against fuselage and corner of wing spar, the furthest bottom inboard weldment at the spar has the same size gap. In other words one end or the other has that gap depending on how I hold it tight.
2) With the quickbuild fuselage bottom not open for easy clamping of the weldment, how did you proceed to clamp up the weldment to the spar and fuselage side before drilling?

I guess I expected the weldment to be a more precise fit and I don't knwo if those outer weldment braces can be flexed at all. I only can find pictures of all ends c-clamped tight but don't know if flexing is involved.

Thanks.

 

[Rick6a]

.....one end or the other has that gap depending on how I hold it tight......

Wendell,

You don't want to flex that weldment bracing in an effort to pull out the 3/16" gap. By forcing the weldment into place you will almost certainly introduce a permanent preload condition on the weldment and the preload you created may encourage fatigue cracking leading to ultimate failure at some unknown point in the future. Ouch.

If I were faced with the same situation, I would not hesitate to pick the gap that seems easiest to work with and then fill in that gap with a correctly sized shim. Standard sheet metal stuff.

For peace of mind, contact Van's and run the problem by them.

 

[koda2]

Gear Weldment Shims

Colin,
You may get lucky and have your gear weldments fit the fuselage. Maybe not.

Vans sent the wrong gear leg weldments out with the 6AQB kit I have and they did not fit at all. I had to tig weld shut 50-some holes and re-match drill them to the fuselage with the plane upright and built. It took several months. No one fessed up to where the weldments came from or who made them.

Just my opinion but I would get the corners of the weldments tightly in the corners of the bulkhead and fuselage side, using clamps and then position your gear legs per plans. At that point you may find the foward fuselage extensions don't fit at all. Either not sufficient edge distance or way out in space. I had to machine wedge-shaped spacers on both sides to get them to fit.

Here is what I started with and ended with:

The top 3 holes on the spacer are just lightening holes.

Dave A
6A build

 

[WenEng]

Thanks Dave and Rick..

That picture of a tapered shim looks exactly like what I may have to contend with on my gear weldment. At least I know its something that has been done in other builds. I will also write to Vans. The last thing I wanted to do was to put any preload on the weldment with C clamps, even though at this point I don't know how I would clamp the weldment to the fuselage longerons after the quickbuild floor is already on. I'll think on that one for awhile.
So, I will proceed as follows.
Install the two wings temporarily, Bolt the gear legs to the weldments and position them correctly according to the plans measurements. See where the gap resides (spar or fuselage side) and make the appropriate shim.

I have read some build sites where they actually cut and rewelded the gapped weldment leg, or some have bent it by leverage or hammering, but I don't want to go there....
Thanks.

 

[koda2]

Weldments

Colin,
I had to resort to some pretty off-beat tools and jigs to get mine on, including concentric brass tubing for drilling up and some bolt-on jigs that I made out of steel scrap. I went through a lot of drill bits.

However, since your bottom skin is not on it should be relatively a lot easier.

Its hard to see the closeup details from your first pictures but everything looks pretty good. The spar-weldment interface should be tight with no gaps. If the "back" side flanges are not against the side of the fuselage, recheck all your measurements. If things are good, they will need shims too but they ought to be pretty close.

I suspect the bolt holes for your gear legs were already match drilled in the weldments so your toe-in should be correct. Mine were not correct and one was "wallowed-out", so I welded them shut and resorted to some tricks to re-match drill them from the inside out.

If the weldments are in the corners and the gear legs are the right distance apart and equi-distant from the center (found by dropping a string line from the brace), they are as good as it gets. There is another measurement to make sure the ends are far enough aft. I think it was seven inches but its in the plans.

Anyway, your weldments are already bolted to the spar so you will have to shim the forward extensions where they are. If the fuselage sides have pilot holes and they do not fit the extensions, you can "pull" the holes to a degree using jeweler's files and ultimately reamers to salvage the holes. Its tedious work.

Remember that a reamer will not move an off center hole, it just makes it bigger. If you have to go to oversize bolts they are hard to find and easily cost a hundred dollars or more. Plus the edge distance margins go away in a hurry. I suspect all you are going to need are some correctly sized shims.

Dave A.

 

[RViter]

Faux spar --- think twice.

I am starting to fit the main gear weldments prior to drilling and am confused about a couple things.
1) There is a gap of maybe 3/16 inch between the fuselage longeron and the extended weldment brace if I hold the weldment tight to wooden false spar, or if I instead hold it tight against fuselage and corner of wing spar, the furthest bottom inboard weldment at the spar has the same size gap. In other words one end or the other has that gap depending on how I hold it tight.

I guess I expected the weldment to be a more precise fit and I don't know if those outer weldment braces can be flexed at all. I only can find pictures of all ends c-clamped tight but don't know if flexing is involved.

Thanks.

I also have a QB and my FIRST impression of the weldment was that it was overly preloaded to fit against the false spar. HOWEVER, when the wings were inserted, the thickness of the main spar is greater than the wooden shipping spar. This completely changed the fit on mine (and probably your's). So, I would think twice before judging the fit of the gear mounts at this stage.

 

[WenEng]

Thank you Gary....

If the rain stays away I will slip the wings in today, leave it out in the driveway and position the gear weldments tomorrow. You right about the false spar being narrower than the real spar. I will be ready to make whatever shims are necessary after the legs are aligned correctly. The leg alignment is the deciding factor anyways, I think. Maybe I'll have to put a shim on two faces. I decided I don't want any preload on the gear weldment braces.

 

[WingsOnWheels]

Wendell,

I lucked out and my gear legs went in just fine with no gaps once the wings were bolted in place. I used a series of bushings for the drilling 12" drill bits and reamers are the way to go for the drilling. I made the bushings using brass and stainless tube from the hobby store. Stainless is better if you can get it. Make sure your bushings fit in the holes before you get everything bolted up. I had to spin my bushings in the drill press with some sandpaper to cut the diameter down just a hair to fit the holes in the spar.

I also lucked out and the toe-in was correct in the pre-drilled gear legs.

My only complaint is the horizontal alignment of holes in the spar vs the position of the webs and doublers in the weldment. The holes are not in the ideal locations (not where I would put them anyway) and come to close to the web in the weldment and to some of the welds. I spoke to Vans and they said to just grind away some of the weld and web as required to get the bolts in. Not my ideal solution, but the only other option would be to make my own weldments.

 

[WenEng]

Thanks Colin..

Wings went on really easily. I was surprised. The gear weldments seem to fit better with the real spar, but tomorrow will tell all when I set the gear legs to proper dimensions. Anyone have any suggestions for clamping down low on the spar and fuselage with the Quickbuild skins already on and in the way? Looks like I need to go find a 9 inch deep C clamp.

 

[RViter]

Lead at the top and the bottom will follow?

You could maybe clamp the top of the spar/bulkhead/mount and the bottom extension will follow (fit close enough to start). Drill and bolt up the top edge in a couple of holes, and also secure/drill the lower corner to the fuselage side skin, bolt a couple and THEN deal with securing those extended braces.

Just thinking out loud ... but I didn't have to drill mine. Surprised that for a QB you have to drill the mounts. Good luck.

Sent you a PM re: PICS?