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7A Wing Attach Close Tolerance Bolts

keitht

Well Known Member
Just put the wings on for the last time with the close tolerance bolts at the airport. The top row of bolts are no problem. The bottom row of bolts are a piece of engineering nobody could be proud of. There are major interference issues with the gear leg support weldments that prevent getting a wrench on the nut to do anything other than stop the nut turning. You have to insert the bolts with just a couple of threads through, get the nut started, tap the bolt in, turn the nut a quarter turn, tap the bolt and repeat until there are enough threads into the nut that the bolt can be drawn in by turning the bolt. I cooled the bolts down in the freezer overnight before inserting them in the spar fitting (with grease) but even so the bolt turning friction was significant so I don’t have a good feel for what final torque I have on the bottom bolts. More of an issue for the AN4 size bolts. Having this poor quality of engineering in such a critical area just beggers belief. I am really surprised that there hasn't been more calls for Vans to fix the design in this area. This may get a pass grade from a FEA viewpoint but is totally unacceptable from an assembly and maintenance viewpoint.
 
I’m not looking forward to this. I’m not far behind on what you are doing. I just transported my fuselage to the airport on Monday and installed wings with temporary bolts. Going to try putting the close tolerance bolts into place tonight. Hope to maybe catch up with you one of these days since I’m not to far from you. I’m based at willapa harbor airport 2s9
 
Keith

Just read your rant and feel your pain. My went on last week and there was the same issue, although I think the problem was my creation.

When the assembly of parts for the center section (F704D & F704E) are assembled, I used the small AN5 size close tolerance bolts for alignment. Looking back, that was a mistake since the long pole in the tent would eventually become the issue of getting the larger close tolerance bolts in place. Hard lesson learned and another example of an easy to add note that was omitted from the directions.

The best I could do with the issue was to use drill rod of the right size (7/16") with tapered ends in EVERY hole during assembly. Lube them up, tap them all way in, and tap them back out with the close tolerance bolt.

After torque, check the washers to make sure they don't spin. I plan to recheck the torque on those at the first condition inspection. But they are only working in shear, and the friction in the sandwich of parts only adds a little.

Down in Vernonia this week doing some flying, hoping for my first flight next week! Look forward to visiting with you soon.
 
The good news is that those bolts are for shear only, so torquing the nut is not a concern. The nut is just to keep the bolt from coming out 😎 There are numerous designs (sailplanes for example) that just use a washer and cotter pin to keep the bolt in place.
I have a modified open end wrench (ground down to be able to actually fit on the nut) that a few of us at my airport used to install those bolts. Not a fun job.
 
Keith

Just read your rant and feel your pain. My went on last week and there was the same issue, although I think the problem was my creation.

When the assembly of parts for the center section (F704D & F704E) are assembled, I used the small AN5 size close tolerance bolts for alignment. Looking back, that was a mistake since the long pole in the tent would eventually become the issue of getting the larger close tolerance bolts in place. Hard lesson learned and another example of an easy to add note that was omitted from the directions.

The best I could do with the issue was to use drill rod of the right size (7/16") with tapered ends in EVERY hole during assembly. Lube them up, tap them all way in, and tap them back out with the close tolerance bolt.

After torque, check the washers to make sure they don't spin. I plan to recheck the torque on those at the first condition inspection. But they are only working in shear, and the friction in the sandwich of parts only adds a little.

Down in Vernonia this week doing some flying, hoping for my first flight next week! Look forward to visiting with you soon.
Bill,
Most of the problem for me was the gear leg weldment interference issue - should have built a taildragger like you are doing. I made up 3 shop bolts for the smaller dia bolts that had tapered ends but were long enough to get the taper all the way through. I put two in the top and one in the bottom inboard. Made up a tool (modified pry bar) to be able to remove the lower shop bolt by getting under the head and levering. The big bolts lined up well and freezing them down helped get them in without the need for muscle. Then the fun started with getting the nuts on. In the end I gave up trying to use a torque wrench on the lower bolts- just tightened until resistance increased and then “felt it” from there to get it nipped up and stop the washers turning. Not what I would prefer but don’t see any other alternative.
I am really familiar with all the different methods used on sailplanes to attach wings and fuselage- mostly two much larger dia single pins in double shear to hold both wings and fuselage together in an easy to assemble and dis-assemble arrangement- nothing I have seen on sailplanes compares with the RV- 7A arrangement which is a major assembly challenge and likely to be impossible to dissassemble without damaging something.
Had two guys that had both built RV-6s helping me put the wings on - both were shaking their heads at the arrangement for the lower wing bolts on the RV-7A.
 
I had a quantity of cheap wrenches I collected from yard/garage sales. I than cut, ground, or bent them to shape specifically for each nut around the gear weldment. Remember, you need a Left & Right version of each custom shaped wrench.
 
Bummer ... well, good news is that it'll be done soon and I'm sure your wings will stay on just fine!

Of course, you say you should have built a taildragger ... now I'm trying to learn how to LAND a taildragger!!

Lots of new stuff in the GA world to wrap my head around. Feel like the FNG again!

Hang in there!
 
A rivet gun will make quick work of installing close tolerance bolts.

Not the ones he's having issues with. They have to go in slowly to allow the nut to be screwed on a few threads at a time. They then have to be torqued from the bolt head with run-on torque added.
 
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You can go to your local welding shop and purchase dry ice; Dry ice is substantially colder than your freezer (-109F). I have used it replacing valve guides in a flat head water cooled engine on one of our forklifts: worked well and the dry ice lasted a few days in our foam cooler.
 
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It is one of the worst jobs on the build, it took us three weekends to get all the bolts in and nuts on, using freezing spray helped by chilling the bolts and using lube but what a total pig of a job. I cannot see any way that we would ever get the wings removed if we had a forced landing in a field somewhere as there is no way that you could get to drift the lower bolts out and it would be impossible to pull them. The RV14 has a much better design with the bolts OUTSIDE the fuselage.

Nige

Ivybridge, Devon UK
RV9A G-CSAM
 
You can go to your local welding shop and purchase dry ice; Dry ice is substantially colder than your freezer (-109F). I have used it replacing valve guides in a flat head water cooled engine on one of our forklifts: worked well and the dry ice lasted a few days in our foam cooler.

Dry ICE AND 91% Isopropyl alcohol slurry is even better, -78C (acetone also same temp).

I used burnishing plugs to pre-size the holes - it only addressed the tiny misalignment of spar layers. (RV7)
 
I've heard liquid nitrogen is even better than dry ice. You can buy it from a gas supplier from Linde/Praxair and Air Liquide. Some ice cream shops even use it.
Just need a dewar container to put it in. They sell them on Amazon.

That's my plan (as well as the modified tools as suggested) for installation.
 
I've heard liquid nitrogen is even better than dry ice. You can buy it from a gas supplier from Linde/Praxair and Air Liquide. Some ice cream shops even use it.
Just need a dewar container to put it in. They sell them on Amazon.

That's my plan (as well as the modified tools as suggested) for installation.

I’d urge a little caution here. You can ‘burn’ (actually freeze) your skin if there’s a spill. There’s also the possibility of asphyxiation if in a closed space. Finally, I don’t know enough metalargy to know if the steel bolt loses its properties and becomes brittle, but I’d check.
 
Liquid nitrogen is colder than dry ice. But given the precautions you would need to take to handle something at -150f I’m thinking it may not make things easier.
 
Liquid nitrogen is colder than dry ice. But given the precautions you would need to take to handle something at -150f I’m thinking it may not make things easier.

Boiling point for liquid nitrogen is more like -320 F - it’s really cold!
 
LN2

I see a potential problem with using liquid nitrogen (LN2). Since the bolt is shrinking in both dia and length, I am curious if using LN2 would cause the bolt to shrink too much in length. The scenario is that the bolt shrinks too much in length, and when it goes back to room temperature, there develops a gap between the head and the spar. since it is very tight bolt, and the nut is in a tight space, it might be very hard to draw the bolt in by torquing the nut. If this happens, now what? Trying to re cool the bolt wont help since it is now in contact with the spar.
 
Gezz guys get real. You don't work with liquid nitrogen with no protective equipment and gloves. Also you don't think dry ice will freeze your skin if your not careful? Always work with protective equipment and precautions accordingly. The bolt doesn't shrink to raisin if you cool it down. Typical shrinkage on steel is about 0.003" per inch diameter of the bolt. This is a common process called - Shrink Fitting. It's often used in machining and fabrication shops. Why do you think you can buy this stuff from welding supply shops?

You don't need to bath the bolt in -320deg liquid overnight if you don't want to. You can pour it on the bolt, or dip it in the nitrogen just enough to help get it pretty cold just before you slip it into an aligned hole. And the bolt isn't so tight you won't get the head tight to the spar. If your having those problems your using the wrong size bolt or you have done something wrong.

https://www.youtube.com/watch?v=y2fctNYMRoE

https://www.alliedpipefreezing.co.uk/services/shrink-fitting/
 
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There is a reason that the construction manual doesn’t mention using any special process to freeze the bolts. It’s just not necessary.
A little bit of lube on the bolt and driving them in with a heavy plastic mallet or a rivet gun works just fine. If you want a little extra help then removing them one at a time quickly from a freezer will help a little.
 
Now you're just taking the fun out of it Scott. How are we supposed to 'mad-scientist' this now?:rolleyes: I mean locked down and bored out of our tree...I had some real ideas going. I didn't even get to mounting the flux capacitor on the baggage bulkhead yet, or how to place the Mr Fusion on the slider canopy. Roads?!....where we are going we don't need roads!.
 
Spar bolts

There is a reason that the construction manual doesn’t mention using any special process to freeze the bolts. It’s just not necessary.
A little bit of lube on the bolt and driving them in with a heavy plastic mallet or a rivet gun works just fine. If you want a little extra help then removing them one at a time quickly from a freezer will help a little.

Scott,
I would agree that serious freezing shouldn’t be necessary. You are missing the main point of the thread. The design of the gear leg support bracket and the serious interference with the installation of the lower spar bolts was the point. This area of the design is not worthy of Vanns and shouldn’t even have got to the point of cutting metal for the prototype aircraft let alone become the standard for the 7A kit design. There are many ways to solve the challenges posed by the need to have the undercarriage weldment where it is and make the installation, retention and extraction of the lower wing spar bolts conform to normally accepted aircraft engineering standards. I understand the need for “ inexpensive”, “simple” “reliable” when it comes to homebuilding a kit airplane - just designing and manufacturing a set of two part expanding bolts installed from the rear of the lower spar would have provided dual load path and an easy acceptable way to meet the challenge. You guys have FEA models already in place (I hope) so it just needs somebody with production engineering design skills to flesh out the bolt design, run the numbers and contract with a machine shop to produce the bolts. Too late for those of us that have already followed the existing drawings - not to late to fix some unacceptable amateurish engineering.
KT
 
Scott,
I would agree that serious freezing shouldn’t be necessary. You are missing the main point of the thread. The design of the gear leg support bracket and the serious interference with the installation of the lower spar bolts was the point. This area of the design is not worthy of Vanns and shouldn’t even have got to the point of cutting metal for the prototype aircraft let alone become the standard for the 7A kit design. There are many ways to solve the challenges posed by the need to have the undercarriage weldment where it is and make the installation, retention and extraction of the lower wing spar bolts conform to normally accepted aircraft engineering standards. I understand the need for “ inexpensive”, “simple” “reliable” when it comes to homebuilding a kit airplane - just designing and manufacturing a set of two part expanding bolts installed from the rear of the lower spar would have provided dual load path and an easy acceptable way to meet the challenge. You guys have FEA models already in place (I hope) so it just needs somebody with production engineering design skills to flesh out the bolt design, run the numbers and contract with a machine shop to produce the bolts. Too late for those of us that have already followed the existing drawings - not to late to fix some unacceptable amateurish engineering.
KT

We admit the A model main gear attachment on the RV-7 is not as refined as it could be. As you already said, it was an engineering compromise towards simplicity which does make me take slight offense at it being referred to as amateurish. Some times simplicity and absolute priority in weight reduction causes engineering choices that may not be easy to execute but in a case where it is a one and done, like this, I think it can be justified.

Having said that, that understanding is what drove the design of the RV-10 and RV-14A, that came after the RV-7, to have a different configuration center section so that the wing attach bolts are on the outside of the fuselage and not common with the hardware for landing gear attachment.
 
We admit the A model main gear attachment on the RV-7 is not as refined as it could be. As you already said, it was an engineering compromise towards simplicity which does make me take slight offense at it being referred to as amateurish. Some times simplicity and absolute priority in weight reduction causes engineering choices that may not be easy to execute but in a case where it is a one and done, like this, I think it can be justified.

I think we are both entitled to our own point of view. Yours seems to me to be equal to putting lipstick on a pig and then falling in love with it. Its still a pig - you guys have demonstrated your capability to fine tune the necessary compromises and produce good engineering - you need to apply those skills to this area of the design. As one of the old sages at the big kite factory in Seattle was often heard to say to young engineers at design reviews “you can do better- we wouldn’t have hired you if we though this was all you were capable of.”
KT
 
Another Guy's Opinion on Wing Installation

When reading this thread a few weeks ago, right before I started my own wing installation, I wasn't sure what to think and I was DREADING performing this task based on what I read in this thread.

I installed the wings on my own using sawhorses for supporting the wings as I positioned / inserted them. A little tricky but doable (I had a lot of wood scraps that I used to shim the horses to the proper heights). Getting the rear spar to properly engage also took a little finesse, but doable. I made drift pins using cheap hardware store bolts.

The NAS bolts were indeed a snug fit, and I'm not sure if "shrinking" them using dry ice helped, but I'll go ahead and believe it did. The top bolts / holes are a breeze. The bottom holes are certainly a challenge which required me laying down in the fuse with my head under the panel to get to the nut side, but with a crows foot I was able to get to the nuts and get everything tightened up. Of course it was a pain (literally) but doable.

I guess the point of my rambling is that while this was a bit of a challenge, it wasn't as bad (in my opinion) as previous posters made it out to be.
 
Good to hear a new builder isn’t having the problems of those above. I did mine on a Saturday morning with the help of a non-aviation friend as wing-wiggler. Done before lunch. (Before any internet warnings).
No ice, no nitrogen needed. That was 700 flite hours ago. Barely remember it. I’m sure most others had a similar experience.
 
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