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crack in the inside corner of the left fuselage skin (F-1270L)

jrich

Active Member
After 260 hrs., I have an approx. 1.5? long crack in the inside corner of the left fuselage skin (F-1270L) where the Upper Firewall (F-1201A) meets the Firewall Shelf (F-1201B). See photos:

distviewofcrack_zpsaacda0dd.jpg


crackinfuseskinF-1270L_zpsc7fcb565.jpg
 
Firewall reinforcement

I had some down time and installed the optional firewall reinforcement. When I did this I felt it would strengthen this area of the fuselage. I am not an engineer but it just made sense and how this added angle will support this area. IMHO

My opinion is to stop drill the crack and install the firewall reinforcement sub-kit for the around $22 price tag.
 
Off subject, but...

I was wondering if you could expound on the pros/cons of the vinyl you used. I'm building an -8 and am thinking of using some.:rolleyes:
 
Pros/cons vinyl

AA flyer,
I've done vinyl since 79,from cut to printed full wraps etc.
I'm building a 4 and may do numbers or limited graphics but not a wrap.
The best 3M vinyl will get you 7-10 yrs, most of the "high performance" vinyls today won't last much more than 5-7 yrs. Printed vinyls are 5-7 tops with great potential for fade, remember there is only one layer of thin ink on a printed vinyl even with a UV protective laminate. Look at the rivets in the photos and you have the problem of adhesive failure from stretch around the rivets. If your racing and changing sponsors every 2-4 years go for a full wrap-but plan on changing it. I'm painting mine with something that will last 20-30 yrs,besides the cost is going to be about the same. The only upside to a wrap would be for a very colorful or even a photographic scheme, but remember it just won't last like paint because there isn't much color going on and the carrier (vinyl) doesn't last in weather/uv like paint on aluminium IMHO
Mike
 
After 260 hrs., I have an approx. 1.5? long crack in the inside corner of the left fuselage skin (F-1270L) where the Upper Firewall (F-1201A) meets the Firewall Shelf (F-1201B). See photos:

I am wondering, do you trailer this aircraft?
 
Here is how I would fix that: cut the skin 1/4 in from the last line of vertical rivets, drill out all rivets, remove the piano hinges and the stiffener as well as the ventilation door. Use the cut skin as a template to cut a new skin plus 1/2 inch to overlap the vertical rivet line. Match drill all holes, rivet back everything into place .
Don't ask me how I know it's possible :eek:
 
I am interested in a reinforcement BEFORE it breaks, but don't quite understand your description. Any chance of a crude drawing or photo?
Here is how I would fix that: cut the skin 1/4 in from the last line of vertical rivets, drill out all rivets, remove the piano hinges and the stiffener as well as the ventilation door. Use the cut skin as a template to cut a new skin plus 1/2 inch to overlap the vertical rivet line. Match drill all holes, rivet back everything into place .
Don't ask me how I know it's possible :eek:
 
John,

Did you report this to Vans? It's interesting that the two cracks reported on the forum appear so similar but others haven't reported them. The similarity suggests a possible generic issue while the small number could mean there is something else contributing. On the other hand the lack of numbers may just reflect limited hours on a new product. That's why it would be nice to have Vans weigh in.

I have no experience with the firewall stiffener mod because it came along after mine was completed, but the diagonal appears to be on the side opposite from the cracks and the side stiffeners seem to be further back than the affected area. Does anybody know if these stiffeners really address the fatigue crack issue? I guess that's another question for Vans.

Maybe Scott could shed some light on this.

Rich
 
... the only difference with a stock RV-12 is the skin overlap at the last vertical line of rivets before the firewall.

Not quite true Jean-Pierre. The other difference is that the skin is now relying on the last vertical line of rivets to transfer all the loads between the new and old skins at the seam, whereas before those rivets would probably not have seen much load as the skin was continuous. Does it matter? I don't know. But if you haven't already, I'd suggest running this repair past Vans just to make sure, as the load path is now different from the stock RV-12. They may say for example, that you need more rivets joining the two skins. It may be fine, but better to be safe than sorry!
 
So for those of us finishing our fuselage kits, should we be worried, or do something to reinforce the side skins?

Mine has the holes for the diagonal and horizontal reinforcements (which I guess is now standard in the newer kits), but I haven't gotten to that point yet....but plan to in the next few days.

Should I add some reinforcement now while I have pretty good access, or not worry about it?

Thanks for the thoughts in advance.

Here is a pic of the newer skin with the secondary line of holes...thinking I am ok...but.... (PS - pardon the overspray - long story)

11qtzpk.jpg
 
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Uh! Oh! I think I'm about to spin the thread slightly off topic. Geez, I hate when people do that!

But looking at Winged Frog's air vent cover-up, and CactusPilot's bare, naked vent - not yet born....

Does everybody think there's enough fresh air coming in? I like a LOT of fresh air and often think it's a little "sparse." Like maybe the vents should be bigger. I've even thought of adding a second vent below. And I don't even live in a warm place, much less HOT, like some of you guys.

Am I the only guy who craves more cool, fresh air???

Bob Bogash
N737G
 
John,

If you are building ELSA you don't have any option but to build to plan unless you get Vans approval. If I was in your shoes I'd build to plan, get licensed, fly off the PAPs and then install external doublers at the corner where the stress riser causes initiation. Then paint the plane.

Rich
 
One question?

Bob do you have the optional interior package with the side panels where the vents are?
 
I don't think so - I don't have an interior (actually I have just a few items - side pockets, stick boots - but not the sidewall and floor carpeting etc.)

I have the single small air vent on each side as in cactuspilot's picture.

Bob
 
So for those of us finishing our fuselage kits, should we be worried, or do something to reinforce the side skins?

Mine has the holes for the diagonal and horizontal reinforcements (which I guess is now standard in the newer kits), but I haven't gotten to that point yet....but plan to in the next few days.

Should I add some reinforcement now while I have pretty good access, or not worry about it?

[/IMG]

The extra reinforcement in the stiffener kit will prevent the formation of the diagonal skin cracks that have been posted here. Vans didn't go to the trouble of redesigning this area and releasing a stiffener kit for no reason. It would be cheap insurance to install it IMHO.
 
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Mine has the holes for the diagonal and horizontal reinforcements (which I guess is now standard in the newer kits), but I haven't gotten to that point yet....but plan to in the next few days.

That is good news since I went ahead and installed the fuselage skin stiffener on my old kit so now I can say it is part of the standard build :)
 
Not quite true Jean-Pierre. The other difference is that the skin is now relying on the last vertical line of rivets to transfer all the loads between the new and old skins at the seam, whereas before those rivets would probably not have seen much load as the skin was continuous. Does it matter? I don't know. But if you haven't already, I'd suggest running this repair past Vans just to make sure, as the load path is now different from the stock RV-12. They may say for example, that you need more rivets joining the two skins. It may be fine, but better to be safe than sorry!

I appreciate your advice which makes lots of sense and will examine carefully this issue with my A&P (who did the repair). I am afraid that VAN's answer will be their standard: "We have not tested this configuration and cannot guarantee it's fine" (they did it to me once and I don't blame them, they cannot test all variations of their design). FYI, this repair is the result of a dent made while moving the plane to my hangar. The Aternative was to change the whole skin that goes to the back of the fuselage, including the doubler :eek:
 
Bob,

I've seen conjecture by several members about the stiffeners being the fix for this issue, but I've never seen anything from Vans saying that is the case. It seems strange that there would be no SB if that's the case. After all Vans put out the SB on the oil tank bracket to address nuch smaller cracks.

Rich
 
Bob,

I've seen conjecture by several members about the stiffeners being the fix for this issue, but I've never seen anything from Vans saying that is the case. It seems strange that there would be no SB if that's the case. After all Vans put out the SB on the oil tank bracket to address nuch smaller cracks.

Rich
 
Vent Works, Bob

Having flown my AA-1 Yankee for 14 summers with the canopy open for more coolness, (Fahrenheit, not appearance) I was very skeptical of the vents and bought some RV-7 vents from a builder who'd used better ones. I purposely did not paint the airplane before flying so I could add those vents after getting the AW. Much to my surprise, I didn't need them. I AM still trying to get a good seal at the corners of the canopy for this cold weather, though.

Wayne 120241/143WM
 
You're right Rich. I haven't seen any explanation from Vans either, yet they thought the modification sufficiently worthwhile to incorporate it into the kit and make the retro-fit kit available. Maybe not enough builders officially reported the cracking problem to them, so they didn't feel it necessary to make a formal statement. To be fair, there haven't been many reports here either, but maybe enough for them to take another look at the drawings and think; "Hmm, stresses will tend to concentrate in that corner, and we really should do something about it because it's not a good design detail." Whatever the reason, the sidewall stiffeners will carry the loads well into skins and away from that sharp corner where the lower firewall shelf, upper firewall and cowl attachment points all come together. It's a busy junction point with a lot of potential sources of stresses focussed in a small area, and that's usually not a good idea in a fatigue-prone structure. Again, I'm not an aero engineer, so these are just my thoughts.
 
Bob,

Your bio says you are a structural engineer, so I'm reluctant to challenge your opinion. This nuke engineer specializes in neutrons!

I put a lot of faith in Vans. I would think they would jump on this with an SB if it was a fleet issue. I hope my faith is not misplaced.

BTW thanks for the D180 schematic you sent me.

Rich
 
Glad to help with the D180 Rich. (I'll send you the Skyview drawing when you upgrade :D). Yes, I make my living as a structural engineer and an airframe is essentially just another structure, but that doesn't make me an aero engineer. I have no doubt that if Vans had a major concern, they would issue an SB, but I agree that releasing this retro-fit kit and then saying nothing much about it while at the same time upgrading the current kits is not very helpful. However they are very good at what they do, so I interpret this modification as more of a process of design improvement rather than fault fixing. I also think it shows that Vans take their work seriously and are not afraid to improve their designs from time to time. To me this additional stiffener makes a lot of engineering sense in the way it strengthens the fuselage side and eliminates a potential trouble spot, so I was happy to install it. My view is that if Van's thinks its a good idea, then so do I. However, at this point in time it's not mandatory, and so there's no obligation on a builder to do anything.
 
I received my landing gear upgrade kit right after I painted the plane and fortunately had some touch up paint left. I try to avoid screwing up my paint unless it's a safety issue!

Rich
 
I have a theory about the cracks that initiate at the corner between the top firewall vertical section and the "shelf". Today I had my cowling off and when I put it back I noticed the bottom hinge section seems to preload that corner in tension so I shaved about 3/32" off the bottom hinge. It made a big difference in ease of fitting the bottom cowling, and got me thinking that may be part of the conditions that start a crack. May be unrelated, but bought I would throw it out there for comment.
 
Just a few questions!

jrich, was wondering if you have had your prop balanced?:confused: Also do you use the Vans Softfield Takeoff and Landing technique on every takeoff and lands.;)
 
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