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SB 12-09-26: Loose U-1202 Attach Bolts

It is getting a little confusing knowing which thread to use to continue this discussion now that there are three..... however....

Point 2 in the addendum is not entirely clear to me. Are they sayiing to jack up the airplane while doing the entire procedure, or just when ready to final torque the bolts? It seems to me that having the gear hanging with the outer bolts and U-1202 removed would put a lot of stress on the inner hardware.

Anybody else wonder about this?
 
Jacking for SB

I too wondered about this. By jacking to take the weight off the wheels, I assume that means the weight off the gear by putting the aircraft on the heavy stands. I also agree that with the weight off the gear it would not be wise to take out the F-1202 Bracket bolts.

The SB can be done with the wings installed, but I have not tried to put the aircraft on the stands with the wings on. I think I would want to remove the wings to put it up.

Bet'ya we will get clarification on this, John.

Tony
 
Point 2 in the addendum is not entirely clear to me. Are they sayiing to jack up the airplane while doing the entire procedure, or just when ready to final torque the bolts? It seems to me that having the gear hanging with the outer bolts and U-1202 removed would put a lot of stress on the inner hardware.

Letting the legs hang from the inboard attachment point is not a problem (just don't push down on the legs while the outboard brackets are removed).
The bending load induced is minute compared the landing loads.
 
Van's is on it!

Glad to see that Van's engineers are working on a fix. Hope that all of those who are flying will find that the fix is the end to the problem. I expect that to be the case.

As for those of us who are not yet to the fuselage in our builds, I hope that Van's will offer us a pre-flying fix as well - a beef up or??? Thanks again to the people at Van's for giving us excellent support.
 
re did the SB except for the chamfer at the corners for rivet interference. I don't have rivet interferenceafter chamfering the original way. The addendum has a better method as there is no chance the bolt head bearing area is diminished by the new proceedure.

Jacking it up for torqueing resulted on no change in torque at the bolts/nuts, however. Clarification on the gap was helpful.

Doug Dahl
 
U1203 / U1202 Gaps

In working the gear SB today, I decided to take a look at U1202 and U1203 using a 3.9 mm VJ articulating video borescope. All of the bolts have been seated and torqued per the SB (no weight on gear). The AN6 bolt in the U1203 is a -23.

As you can see in the photos, the U1203 is fully seated thur the AN6 bolt area, however there are gaps between the U1203 and the U1203B plate at both AN4-22 bolts. The same gap appears on the U1202 - U1202B combination at the AN5-20 bolts. The gaps are uniform on both the port and starboard sides, as well as fore and aft.

Has anyone else seen these gaps, as in are they normal, or have I missed something in the assembly?

20121006073010.jpg

U1202Gap_zps38918ab8.jpg


Thanks.

John Salak
RV-12 #116
 
U1203 / U1202 Gaps

Thanks for the quick reply.

I read the "full contact" part of the SB as the U1202 contacting the U1202B wear plate and F1204 channel. I was expecting no gaps unless the U1202 was not properly torqued or one side was hung up on a rivet head. Perhaps a nominal gap value could be defined as a check.

The gaps in the U1203 are not mentioned in the SB or revised p35-03 (rev 2). Again, it may be helpful to specify a nominal gap value as a post installation final check.

John Salak
RV-12 #116
 
Thanks for the quick reply.

I read the "full contact" part of the SB as the U1202 contacting the U1202B wear plate and F1204 channel.

Nope, it means check that the U-1202 is in full contact with the gear leg. The way to confirm that being to verify the gap is equal at each end. No nominal gap measurement is really needed since all you need to know is that there should be a gap, and that it should be equal at both ends.
 
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Working the SB - Hints on removing the U-1202 brackets.

Began working on the SB yesterday. Had a lot of trouble removing the U-1202 brackets. The protruding rivets below the brackets make dropping it straight down impossible. I finally obtained enough wiggle room by sliding the wear plates inboard and out of the way. I also had to disconnect the brake lines, which means the brakes will have to be bled after reassembly. I pass this along for the benefit of those who have not yet started the SB. If your airplane was assembled like mine, you will need to slide the wear plates out of the way and disconnect the brakes lines to get the 1202's out.
 
Cracks not at the hole

When I originally examined my outer landing gear forward bolt holes I could only see a single crack that started at the forward edge of the Center Section and terminated in the bolt hole on both sides of the airplane. I sent photographs of all 4 of the outer bolt holes to Van's for their assessment. "Eagle Eye" Rian found a 2nd crack in the forward right hand cut out that was not at the hole. The 2nd crack was outboard of the crack that terminated in the bolt hole and looks very similar to the outboard crack in the photo that DonFromTX posted in the thread ?Loose Main Gear Legs?. The photo is on page 4 post #34 of that thread. That photo also shows a 3rd crack inboard of the bolt hole. Both of the holes have been stop drilled. After Rian pointed out the crack I had a difficult time finding the crack. I used more Acetone to remove the primer in the area and took more photos. I then used Picasa 3 to magnify the area in the photo and finally could see the crack. I removed the ELT, tied off the wire bundle, got my high tech LED flashlight and could finally see the 2nd crack. I am still having trouble making sure that I can see the end of the crack. Peterk suggested that I spray paint the area and then wipe the paint off going across the crack area. Some residual paint should be visible and I should be able to see the end of the crack. Rian has instructed me to stop drill the crack with a #30 drill and he confirmed that I should use a Center Punch at the end of the crack to keep the drill bit from walking. Peterk also suggested that I use a right angle drill because it is less likely to walk. Sorry for the long winded explanation buy overlooking a small crack know will result in a big crack later. The next part of the SB will inform the builder how to stop drill their cracks. Bob Kibby N712BK.
 
SB 12-09-26: loose U1202 attach bolts

Performed SB today. Drilled 3/8 holes per addendum. AN5 at U-1202 took 3/4 to 1 turn each to restore original torque spec. No cracks found in F1204. AN6 at U-1203 was at torque spec but both bolts could be turned with small wrench. Added second NAS1149F0663P washer to each assembly, re-torqued to spec. Now bolt cannot be turned. Torqued bolts with plane on gear and checked torque again with plane jacked up. Airframe has 158 hours and 267 landings on paved runways,(only one hard one, the rest grease). Also had a left main gear tube blowout on my 25th landing with lots of vibration and pull.
SN:120135, first flight 10/9/10.
Frank
 
Peterk suggested that I spray paint the area and then wipe the paint off going across the crack area. Some residual paint should be visible and I should be able to see the end of the crack.Bob Kibby N712BK.

What you want to use is a dye penetrant. Here's one from Aircraft Spruce - you want a can of spray and a can of developer. Forget the spray paint.....

http://www.aircraftspruce.com/catalog/topages/magnaflux.php

Bob Bogash
N737G
 
Finished the SB

Yesterday I finished the SB without incident. Three out of four bolt holes had no cracks and no uneven shoulder under the washer. The left rear hole does have a slight shoulder, but no cracks. It also displays thread marks on the inside circumference that indicated to me that the bolt was moving around some when it was loose. Picture of the bolt hole available here.

I torqued all bolts to the top number plus 1 ft/lb for the nut friction. I will recheck after a few flights. Also replaced the AN6-24 bolts with the -23's. The -24's were obviously too long - I guess I never really looked for that when I built the plane.

I checked for cracks by eyeball. Wish I had thought of using dye, but didn't read Bob's post until this morning. Good idea Bob!
 
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Close Tolerance Bolts

With all of the talk of moving parts in the gear area, is there any thought to us using close tolerance bolts??? We may have to put them in the freezer for awhile, and use a drift to seat them, but they shouldn't mover around anymore! Could that possibly prevent the cracking that is showing up? What say you more experienced folks??
.............Tom
 
With all of the talk of moving parts in the gear area, is there any thought to us using close tolerance bolts??? We may have to put them in the freezer for awhile, and use a drift to seat them, but they shouldn't mover around anymore! Could that possibly prevent the cracking that is showing up? What say you more experienced folks??
.............Tom

My thought is....

Changing to a close tolerance fastener to fix a problem caused by the original fasteners not being tight, is not a good choice, and the fact that these bolts for the most part are loaded in tension, not in shear (unlike the majority of fasteners in an aircraft).
The cracks are likely caused by the impact loading of the loose bolts. If the currently specified bolts are kept tight there should be no problem with cracking.
Why do they get loose? Hard to say for certain, but it is likely a combination of a number of things, which doing a retorque after the first few hrs of flight will likely resolve.
 
For what it is worth, one of the individuals reporting cracks of the channel, claimed his bolts were still at original torque specs.
 
Yesterday I finished the SB without incident. Three out of four bolt holes had no cracks and no uneven shoulder under the washer. The left rear hole does have a slight shoulder, but no cracks. It also displays thread marks on the inside circumference that indicated to me that the bolt was moving around some when it was loose. Picture of the bolt hole available here.

I torqued all bolts to the top number plus 1 ft/lb for the nut friction. I will recheck after a few flights. Also replaced the AN6-24 bolts with the -23's. The -24's were obviously too long - I guess I never really looked for that when I built the plane.

I checked for cracks by eyeball. Wish I had thought of using dye, but didn't read Bob's post until this morning. Good idea Bob!
All of my bolts were at torque and no cracks were found at 61 hrs TT, however I also have one hole (LH forward) with a slight shoulder that looks like your picture. The bolt was also slightly bent in the thread area. With the advice of a good friend and retired Sikorsky Aircraft airframe engineer I will use self-aligning washer sets in lieu of the NAS1149F0563P washers for reassembly. They can be found at http://www.mcmaster.com/#self-aligning-washers/=jnzfnx
Longer bolts will also be required to accommodate the thicker washers
 
All of my bolts were at torque and no cracks were found at 61 hrs TT, however I also have one hole (LH forward) with a slight shoulder that looks like your picture. The bolt was also slightly bent in the thread area. With the advice of a good friend and retired Sikorsky Aircraft airframe engineer I will use self-aligning washer sets in lieu of the NAS1149F0563P washers for reassembly. They can be found at http://www.mcmaster.com/#self-aligning-washers/=jnzfnx
Longer bolts will also be required to accommodate the thicker washers

I'm not sure that will help, the self aligning washers are used when the two mating surfaces are flat but not parallel.
The problem in our case is a "step" i.e. "not flat" surface.

all 4 of my nut locations have a significant step, I'm hoping Vans will come out with a further updated SB with instructions on what to do about these steps.
 
My thought is....

Changing to a close tolerance fastener to fix a problem caused by the original fasteners not being tight, is not a good choice, and the fact that these bolts for the most part are loaded in tension, not in shear (unlike the majority of fasteners in an aircraft).

I'd have to dig out my engineering texts and - zero in the def of "close tolerance", but these bolts - especially the AN6-23A - do not exactly slide in! How about a lot of pounding with a heavy hammer - a lot. I even considered packing the bolts in dry ice.

Bob Bogash
N737G
 
If the bolts are that tight I wonder if they are creating a hoop stress on the hole contributing to crack initiation around the hole.
 
The AN6 bolts are the inner center bolts. Haven't heard of any cracks at that location.

And Nasa's is the first I've heard of that didn't "slide in". I pretty much went by the rule, "if it doesn't fit, you've done something wrong."
 
I'm not sure that will help, the self aligning washers are used when the two mating surfaces are flat but not parallel.
The problem in our case is a "step" i.e. "not flat" surface.

all 4 of my nut locations have a significant step, I'm hoping Vans will come out with a further updated SB with instructions on what to do about these steps.

Van's is well aware of the "step" as myself and others have sent photos. Their Landing Gear Analysis publication indicates that they are working on an engineered solution, although it is not specific yet how they are going to do it. Also, in feedback to me from my photo they indicated that there will be "update parts" and the step in the center section will become a "non issue".

At this point, they have indicated that those with flying aircraft should do the SB as directed in order to prevent any damage. Those with damage should wait for the engineered solutions.

I think it can be safely assumed that hardware will be offered that will address the "step" in the center section.

Tony
 
And Nasa's is the first I've heard of that didn't "slide in". I pretty much went by the rule, "if it doesn't fit, you've done something wrong."

Well, the SB does describe seating the bolt with a hammer, and using a wood block to protect the head.

I can tell you I destroyed several wood blocks, and anticipating another bolt change, have laid in a supply of red oak flooring strips for the next time around.

It could be I have a problem, but they sure didn't just slide in!

Bob Bogash
N737G
Waiting for the "Final Solution"
 
Well, the SB does describe seating the bolt with a hammer, and using a wood block to protect the head.

I can tell you I destroyed several wood blocks, and anticipating another bolt change, have laid in a supply of red oak flooring strips for the next time around.

It could be I have a problem, but they sure didn't just slide in!

Bob Bogash
N737G
Waiting for the "Final Solution"

I don't think they should have been THAT tight.
one of mine went in with a single rubber mallet tap
the other took a pretty good pounding with the soft mallet, but not anything that would have broken an oak plank !
(I'm talking about the AN6 through bolt)
 
I'm not an aeronautical engineer ...

I'm not an aeronautical engineer ... I'm not even a good builder ... that said, it seems to me the landing gear "problem" could have been prevented by beating all the landing gear bolts and brackets with a hunk of wood and a hammer to be sure as heck they were properly seated and then torque the devil out of all the nuts and bolts (extra torque for bolt TIGHTNESS in hole and nut torque)! When the next revision for Section 35-3 is published ... it must say much, much more than "when the leg is properly positioned, tighten all hardware" as it states in revision 10-5-11.

Remember, I'm not an aeronautical engineer ... I'm not even a good builder ... but ...
 
Well, the SB does describe seating the bolt with a hammer, and using a wood block to protect the head.

I can tell you I destroyed several wood blocks, and anticipating another bolt change, have laid in a supply of red oak flooring strips for the next time around.

It could be I have a problem, but they sure didn't just slide in!

Bob Bogash
N737G
Waiting for the "Final Solution"

You were not the only one having this problem. My AN6 bolts didn't split wooden blocks but I needed a hammer to get them seated in those holes and it took quite a while. The smaller ones went in ok.
 
Yet mine bottomed out easily, all 6 of them, by just pushing them up with my fingers. No force required.
 
What we're seeing here is VARIATION - the subject of my last 10 years at Boeing.

Variation is the ENEMY of QUALITY. Boeing document D1-9000 or the current Aerospace Industry Standard AS-9100 describe it in detail - I have neither the time nor energy to describe them here and now.

But, as a bottom line - when the same installations demonstrate finger "push-in" tolerances at one end of the goalpost, and "pound-in" with a sledge hammer at the other, there's a problem.

However this variation originated, or built up, they demonstrate a manufacturing/installation situation that is not good. The end result is reflected in some airplanes that show no damage (sometimes despite abuse) and others that wrinkle structure despite gentle handling and smooth landings.

I have no idea idea if tight bolts or loose bolts are the solution (or culprit.) Or tail section movement rotating around the bottom of the aft bulkhead, Computerized Finite Element Analysis are tools useful these days, but sometimes trial and error works well too. Did in the old days!

I'm glad the "problem" has been analyzed and escalated to the status of "a problem", and that better minds than mine are working the problem..

This forum DOES have an impact (and- thanks again - DonfromTx! - we all owe you, Man!)

Bob Bogash
N737G
 
Not sure if this is the best thread to use but thought it worthwhile to give an update on our SB 12-09-26 experience. Before the SB came out we had checked the torque on the U-1202 bolts and found they all needed tightening between ? and ? a turn after roughly 100 hours operation. See my post http://www.vansairforce.com/community/member.php?u=15004
and this link which gives an idea of the field we operate from http://www.youtube.com/watch?v=IERK-JVieM0&feature=relmfu

We had only flown a few hours since our previous inspection so didn?t expect to find any problems but thought it would be reassuring to check under the nuts for cracks which we obviously couldn?t do at our first inspection. As before we did the work with the aircraft on stands and the wings removed for ease of access.

We added a washer to the AN6 bolts as per the SB to ensure the nuts don?t bottom out and found they were both a pretty tight fit in the holes.
On removing the nuts/washers from the U-1202 bolts no cracks were found but all four positions have slight steps in the channel and the washers had deformed slightly to ?take up? the step. There was no apparent interference between the U-1202 blocks and rivets so we did not remove them. However, it did look as though had there been any interference it would have been more or less in line with the centreline of the bolt hole so chamfering the U-1202 as per the SB would not have helped. All four bolts were also a tight fit in the holes and we fitted new washers before torqueing up the nuts.

As before there was no indication of wrinkling or deformation in the skin or structure around the landing gear.

All back together again and now hoping that by ?fixing something that wasn?t broke? we haven?t introduced any new problems! Anyhow our plan is to recheck the torques after a few landings on our bumpy grass field.

Alan
 
Removable F-1275G cover plate ?

Completed the SB on my 12 today. I drilled off the two Cover Plates to get a good look at the hardware after 168 hours, and a lot of landings, all on hard surface.
As found, one of the U-1202 brackets did have a small rivet interference and gaps on each side did not look quite equal. The other U-1202 bracket looked square. There were a lot of threads showing beyond the nuts on the AN6-24A bolts. I believe these nuts were bottomed out on the bolts, but some clamping was taking place because there was an imprint of the washer in the powder coating on the bracket.

After taking off the nuts on the outboard AN5 bolts I found no cracks in the C-channel but it was apparent that the washers do not bear the full 360?, as was noted in previous posts:
i-RMxzhH3-M.jpg




I corrected the rivet interference by slightly grinding the U-1202 per the SB. I used the even torquing sequence and verified the U1202s were holding the gear leg evenly. I added an additional washer on each of the AN6-24A bolts per the SB.

One thing that I would like to see is a change from rivets to nutplates and screws holding on the F-1275G left and right Cover Plates. This might be something we could do individually, post AW inspection.

Tony

Tony or anyone else - did you pursue the idea of adding nutplates to the F-1275G cover plates?

Thanks,
Tom
 
Nutplates for the covers...

It looks like it would be possible to install nutplates for the cover plates but it would require removing the first side cover skin foreward of each cover plate to get access to install nutplates. That means drilling out an additional dozen or so rivets on each side of the fuselage. Also, some of the tabs won't have enough room to install a standard nutplate so some mini ones will have to be used.
Removing the side covers makes it quite a bit easier to work on the gear, but by drilling the 3/8" diameter tool access holes per the S.B. it should not be necessary to remove the side covers.

Tony
 
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I'm doing mine now - -

and I removed the 'covers'. They had us 'glue' the wear plates in originally, and cleaning the surfaces off with them on is another good reason to have them off. I put them on last time without painting the rivets. You have to be almost laying on the ground to see them, so not a big deal to me. Only a few rivets. Drilling all those on the doublers is another matter. I may post results when I get the entire project(s) done.

John Bender
 
Tony - I haven't looked yet but what about this? Install all of the easy nut plates. Then CUT the cover plate (just like cutting the aft bulkhead behind the fuel tank. See the Modification sticky for details) Add a little backer plate with nutplates to hold the resulting 2 pieces together. Re-rivet that aft part of that into the skins where the nut plates are too difficult to get at. Does the resulting removable forward partial piece give enough access to make this worthwhile?
 
and I removed the 'covers'. They had us 'glue' the wear plates in originally, and cleaning the surfaces off with them on is another good reason to have them off.

I think the only thing specified previously was to coat them with grease so they didn't rust... that must be quite some grease you guys use on your combines there in Iowa...
 
Hey Scott - -

Haven't gone back to check. Maybe I did that to hold them in place for easier assembly. It worked. Had to pry them off. Anyway, still think it is easier to have them off. Hand size can make a difference also I'm sure. I remembered I used a swivel socket on those 2 original bolts. Not sure the 3/8" holes help much. Only a 1/4" drive extension goes thru a 3/8" hole. I'll reflect when I get done.

John Bender
 
Drill the holes

I drilled the 3/8 holes and used 1/4 inch extensions-- put one up inside the airplane, stick the other through the hole and then slip the two together and add the socket. That makes it very easy to torque from the bottom (only about 5 in-lb bolt drag), and the 1/4 extensions didn't seem to be a problem. With the holes drilled as per the SB there's a slight angle to the rear bolt but that worked OK, too.

I looked at adding nutplates and as said above, there isn't room to use standard ones-- either right-angle or very small arms will be required. And fitting them to the inside of the fuselage wo't be fun. All in all, the holes were faster, worked well, and are capped with 3/8 inch plastic plugs form the aviation supply aisle at Lowes.

Wayne 120241/143WM
 
Hey Wayne - -

there are 4 - 3/8" plastic plugs in my kit. You had to buy some ? Yes a 1/4" longer extension goes thru the hole just fine. At the airport, I only had a 3/8" drive and adapter, so more tools on this mornings trip. Forgot another item, so here I am home again. I have one of the wifes old C-pap hoses that are very flexible and will work for getting the pieces out of the inside area.

This is not a simple few hour job, but I am moving along nicely. Taking lots of pictures, and will post as an album when I feel I am done. Will also post hours. I am painting the doublers at home also, so that is adding a little time.

John Bender
 
Just finished the landing gear mod. We used the wing tie down eye bolts screwed into the top of the wings to raise the landing gear one side at a time using our engine hoist. This worked well as you could vary the height to make taking the landing gear out and reinstalling it easier. Also, we bolted all four new plates together and stack drilled the 1/4" holes on our drill press at home. Then we bolted them temporarly to the bottom of the spar, purchased a 1/4"X12" drill bit and drilled the spar from the bottom side up using the plates as a guide. The two outer holes are a straight shot with no obstruction. The two inner holes required drilling a 1/4" hole thru the bottom of the fuselage. Not counting removing the wheel pants, inspection plates, seats etc. it took about 3 hours per side. I think this improvement is a good one and thank Vans for making it available to us.
 
I would like to respectfully suggest that future posts regarding installation of SB 12-11-09 be placed in the "other" thread, started by Tony T., entitled "Service Bulletin 12-11-09 (Main Landing Gear Upgrade)". I think that title is more representative of where we are now (installation of the SB), and it will reduce confusion and the necessity to check two separate threads to keep up to date on how the first SB implementers are faring. JMHO.
 
2johns-- wings on??

I admit to not having read the SB instructions yet, but I was under the impression that the wings had to come off to the the SB mod. If that's NOT the case then it's easy to jack up one side using the gear jack and put a horse under the wing (on a rib, please!). That's what I did to do the original check for bolt tightness.

Wayne 120241/143WM
 
A long shot...

Eagle's Nest -3 is ready for the gear legs and rather than just build around the SB, I thought I would first check to see if anyone in Texas or surrounding states who has received their SB kit but are waiting to install it would consider shipping it to us. We'll pay the shipping, and as soon as our SB kit arrives we'll replace the "loaner". Any takers?

Have a great day!
 
Time Schedule with dates

If someone sends you there kit - your kit may arrive at the same time or sooner.

I am also ready to put on my side skins and it would be nice if vans would post some time schedule of when builders will get there kits.




Eagle's Nest -3 is ready for the gear legs and rather than just build around the SB, I thought I would first check to see if anyone in Texas or surrounding states who has received their SB kit but are waiting to install it would consider shipping it to us. We'll pay the shipping, and as soon as our SB kit arrives we'll replace the "loaner". Any takers?

Have a great day!
 
John -great pics! 2 questions - do you think you could have marked the lower wing edge skin for "shaving" on initial removal if you had these pictures, and avoided the reinstall for that purpose? And, what special tools were needed? I have the same right-angle chuck and two step drills starting at 1/8 inch. I do not have a "long" bit other than a #30.
 
Thanks so much John for recording and sharing the process. It sure helps us who are anxiously awaiting our turn at it.
 
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