What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

12 Stiffener Kit

Piper J3

Well Known Member
I?m thinking about adding the Stiffener Kit to my already-built & painted RV-12 and have a few questions?

The kit contains three pieces ? one diagonal mounted brace on each forward fuselage side skin and one piece for the lower right firewall. My concern is about the pieces that get added to the fuselage side skins. I prefer not to add rivets to my already painted airplane especially in such a conspicuous place on the front side of the forward fuselage. I guess I can paint the new rivets but I prefer to not have it look like a repair to a nice pristine surface. So my question is? can these braces be fastened to the side skins with adhesive bonding in place of rivets? Modern-day aerospace and aircraft manufacturing are using a lot of structural adhesive bonding in place of rivets. This is being done for carbon fiber material and aluminum.

I would appreciate advise from anyone who has done this install on a finished & painted aircraft.
 
That's a really interesting question. I believe (and someone please correct me if I'm wrong) that the intent of those pieces is to stiffen the firewall and forward skins to reduce "drumming" and noise, not to provide additional structural strength. It does seem like using a good adhesive on the sides wouldn't be unreasonable. For that matter, I've been thinking about installing the stiffener on the firewall and using some strips of Dynamat on the sides, since I have some in the garage left over from a truck quieting project a few years ago.
 
I have bonded stiffeners and NACA ducts to the fuselages of several RVs that i have built with no issues. I dont see why it wouldnt work here. I installed the same kit to my RV12 before paint but if it had been painted i would probably bond it in place.
My favorite adhesive is JB Weld and i have never had anything bonded with it come loose, as long as you do it correctly.
Tape off the fuselage area for the stiffener and rough it up with 40 or 60 grit sand paper. Same for the stiffener. That and the prepunched holes in the stiffener, will give good bond strngh.
You could do one rivet in each end of the stiffener to help, making only a couple of rivet heads to touch up.
 
There are aluminum aircraft that have been almost entirely built by adhesive bonding parts together (Single engine Grumman, etc), so using adhesive is possible.

The question that needs to be answered is if adhesive is substituted for rivets, are you able to assure that what you are using will have the same strength?

The two angles you are asking about were added for a structural purpose.
 
Bond Prep

A simple preparation process that I've used comes from the Cri-Cri builders manual. The Cri-Cri uses a lot of structural bonding to aluminum.

Scrub the mating surfaces with Ajax cleanser and maroon Scotchbrite until the surface is a uniform gray color and water runs without beading, rinse while continuing to scrub until clean, then dry and bond within two hours.

I've used this with the G-flex epoxy, the thickened version with success.

The process actually says to bond within a "few" hours, but recommends the sooner the better.

Dave
RV-3B, currently building the fuselage
 
Stiffener Kit

Can someone help out with some info on this forward fuselage stiffer kit, part number and when was it introduced please? :confused:
 
Can someone help out with some info on this forward fuselage stiffer kit, part number and when was it introduced please? :confused:

Andrew, search on Vans order site for:
RETRO F.WALL/S.SKIN
12 STIFFENER KIT
$25.00
Introduced around 2013 if I remember correctly.
 
12 Stiffner kit $25.00
Contents: ff-1204d, ff-1204e, f-1295-mod, bag 2738 and doc 12 man sect 54.
 
12 Stiffner kit $25.00
Contents: ff-1204d, ff-1204e, f-1295-mod, bag 2738 and doc 12 man sect 54.
Is that the right one, those numbers look like center section parts on my CD plans?

How can one tell by just looking if this has been installed or not? Anyone have a photo?
I think the stiffeners if I I'm thinking of the correct parts (mine came with them as part of the kit) can be seen in the first picture on here.
They are the two yellow primmer strips attached to the inside the forward side skin on both sides that I think are what the OP is talking about.
My CD plans show these as F-1295-R and F-1202N-1-R on page 29A-03 which can be seen at https://www.vansaircraft.com/pdf/revisions/RV-12/RV-12_29A.pdf
 
Is that the right one, those numbers look like center section parts on my CD plans?


I think the stiffeners if I I'm thinking of the correct parts (mine came with them as part of the kit) can be seen in the first picture on here.
They are the two yellow primmer strips attached to the inside the forward side skin on both sides that I think are what the OP is talking about.
My CD plans show these as F-1295-R and F-1202N-1-R on page 29A-03 which can be seen at https://www.vansaircraft.com/pdf/revisions/RV-12/RV-12_29A.pdf

Yes - F-1295 horizontal side wall stiffener and also the diagonal stiffener on the firewall. Both were added as upgrades to the earlier kits.
 
Last edited:
There are aluminum aircraft that have been almost entirely built by adhesive bonding parts together (Single engine Grumman, etc), so using adhesive is possible.

The question that needs to be answered is if adhesive is substituted for rivets, are you able to assure that what you are using will have the same strength?

The two angles you are asking about were added for a structural purpose.

Please forgive me if I seem obtuse, but if the angles that attach to the side skins serve a critical structural purpose then I would think it would be a mandatory retrofit. If they don't, then it doesn't seem that the strength of the attachment of the side skin angles would be critical. Certainly there would be some attachment strength required to perform its intended purpose, but if that purpose is just to keep the skin from flexing it seems that a good adhesive would do it.

Stated another way, if the piece isn't required on a plane that didn't originally have it, bonding seems like as good an idea as riveting. But I'm no engineer, and I'm more than happy to have my errors pointed out. :)
 
The reason I started this thread, and asked the question about the stiffener, is because I fly off a grass runway. We roll the runway in the spring but suffice to say it is not smooth. See video https://www.youtube.com/watch?v=enwOI_Ye1zI&t=80s

I purchased my 12 from the original builder knowing that landing gear and fuel tank SB's were not complied with. I'm now making these alterations and reviewing all SB's for compliance. That is how I stumbled upon the stiffener.

I'd really like to know if the Stiffener is for rigidity or if its needed for additional strength. Perhaps Scott will reply to this thread once again and shed some light on this. If the purpose is to add strength then I may go ahead and rivet to the side skins.
 
Last edited:
I'd really like to know if the Stiffener is for rigidity or if its needed for additional strength.

It provides both (because in may ways those are the same thing).

Whether any particular RV-12 actually needs it?

That depends on how the pilots flying it, treat it.

The change was made when the re-evaluation of the main gear (and subsequent design change) was done.

Why was the re-evaluation done?
Even though the gear was originally designed and tested to the ASTM requirements, service history began to make it obvious that meeting the ASTM requirements doesn't necessarily mean the airplane would tolerate all of the level of treatment it would receive depending on who was flying it.

The fwd stiffeners add some additional margin for nose gear loads on the fwd fuselage.
 
Please forgive me if I seem obtuse, but if the angles that attach to the side skins serve a critical structural purpose then I would think it would be a mandatory retrofit. If they don't, then it doesn't seem that the strength of the attachment of the side skin angles would be critical. Certainly there would be some attachment strength required to perform its intended purpose, but if that purpose is just to keep the skin from flexing it seems that a good adhesive would do it.

Stated another way, if the piece isn't required on a plane that didn't originally have it, bonding seems like as good an idea as riveting. But I'm no engineer, and I'm more than happy to have my errors pointed out. :)

I don't think I ever said they met a critical structural purpose... Just that why bother adding them if you don't know what structural benefit it is providing (other than a possible false sense of security).

A safety rope when rock climbing isn't required (some climbers actually free climb high elevations).

Using a rope provides an added level of safety margin.

If you are going to go to the trouble to use a rope would you feel ok just with the knowledge that you have a rope (of unknown strength) connected to you, or would you prefer to know for certain that it will catch you if you fall?

The design change wasn't issued as mandatory because not everyone needs or wants more load margin than was originally designed in (the demonstrator RV-12 had been flown for many years and many hundreds of hours without any indication that the design change was needed). For those that do, a extra safety rope is available.
 
Last edited:
Scott - Thank you for taking time out of your Saturday schedule.

Your explanation is concise and clear. I now have the information I need and will decide how to proceed. Thanks again...
 
I don't think I ever said they met a critical structural purpose... Just that why bother adding them if you don't know what structural benefit it is providing (other than a possible false sense of security).

A safety rope when rock climbing isn't required (some climbers actually free climb high elevations).

Using a rope provides an added level of safety margin.

If you are going to go to the trouble to use a rope would you feel ok just with the knowledge that you have a rope (of unknown strength) connected to you, or would you prefer to know for certain that it will catch you if you fall?

The design change wasn't issued as mandatory because not everyone needs or wants more load margin than was originally designed in (the demonstrator RV-12 had been flown for many years and many hundreds of hours without any indication that the design change was needed). For those that do, a extra safety rope is available.
No disagreement there. I was asking because I don't recall ever seeing an explanation of why the change was made in the first place.

Obviously just blindly deciding to stick it in there with Elmer's (per your safety rope analogy) would be a poor choice. However, it seems fairly straightforward to calculate the strength of an assembly with rivets, and compare that to the strength of a bonded joint. Both of the adhesives I looked at seemed to provide substantially more strength than rivets... at least in the off-hand example I used as a quick comparison. But again, I could be completely wrong. It's at least an interesting learning opportunity to take up some of my cold winter down time. In the mean time I'll continue not dropping the thing in on its nose. :)
 
Adhesives

Well this is the first post after several years watching.
I was involved years back with a company called Robertson STOL we used
bonded leading edge cuffs on the Piper series AC only across the fuel tanks. We also did this with the newer C210 with wet wings.
Part of the installation requirements, FAA, was to rivet the four corners of the part to the tank. The idea behind this was to prevent it from starting to peel from any of the edges. This section was separate from the rest of the cuff which extended to the wing tip.
Grumman AC also had SBs issued for the same reason years later when they came out. I was flying that series of AC at the time while getting my pilots ticket.
About JB Weld, it works great on bonding aluminum, scuff, clean and bond. Use it quite often in my hobbies and it machines quite well. I tried a Loctite adhesive that was recommended and it did not hold no matter how it was done.
 
Last edited:
Weight

I don't think I ever said they met a critical structural purpose... Just that why bother adding them if you don't know what structural benefit it is providing (other than a possible false sense of security).

A safety rope when rock climbing isn't required (some climbers actually free climb high elevations).

Using a rope provides an added level of safety margin.

If you are going to go to the trouble to use a rope would you feel ok just with the knowledge that you have a rope (of unknown strength) connected to you, or would you prefer to know for certain that it will catch you if you fall?

The design change wasn't issued as mandatory because not everyone needs or wants more load margin than was originally designed in (the demonstrator RV-12 had been flown for many years and many hundreds of hours without any indication that the design change was needed). For those that do, a extra safety rope is available.

Is weight much of a consideration when adding this kit material..?
 
Last edited:
I am still trying to decide if I have them or not. Don't this photo indicate by the rivet pattern that I have them installed?
10cq895.jpg
[/IMG]
 
Don, your photo shows the stiffeners are not installed, when the mod is done, there is another row of rivets a little below the line at the side skin and cowling intersection. There is also a diagonal brace on the passenger side firewall, running from upper right to lower middle. That one would present some grief with the engine installed, I would think.
Cheers,
DaveH
120485
 
Thanks guys, I have a kit on the way! Us ham fisted rusty pilots need all the stiffeners we can get:)

Don, your photo shows the stiffeners are not installed, when the mod is done, there is another row of rivets a little below the line at the side skin and cowling intersection. There is also a diagonal brace on the passenger side firewall, running from upper right to lower middle. That one would present some grief with the engine installed, I would think.
Cheers,
DaveH
120485
 
Back
Top