Toobuilder

Toobuilder

Well Known Member
...Can it?


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A slotted wing attach fitting?

Somebody please tell me this is not "Van approved".
 
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That's normal... see drawing 38 in the RV-7 plans, or whatever the equivalent "wing attach and control system detail" sheet is for the RV-8. :)

mcb
 
Standard deal. Supposed to pull free in a wreck instead of ripping out the inboard tank rib. Flight loads are vertically directed or so I've been told.
 
You've got to be kidding me!

I realize that the fwd attach serves very little purpose (especially since I see the limited structure the fitting is attached to), but wouldn't it be easier to simply drill a hole?

Edit: So it's designed to pull out... OK. (because that's exactly what it will do!)
 
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Toobuilder said:
...Can it?

A slotted wing attach fitting?
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Its done that way to allow the fuel tank to pull away from the fuselage in a crash (presumably most of the flight load is in the vertical). I think the idea is that a closed hole could result in the tank being ripped open.
 
This fitting is NOT a wing attach fitting. It is simply a fuel tank support and is designed to only support the fuel tank loads on the ground. The notch is so that if the wing is pulled away, it will not rip out the end of the fuel tank.
 
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If I'm not mistaken, this change was made to the plans many, many moons ago as a direct result of a accident that removed wings from an RV and ruptured the tanks. Some of the old fogies on here can probably tell us all about it.
 
Well, let's don't say too many, many moons ago!

Jamie said:
If I'm not mistaken, this change was made to the plans many, many moons ago as a direct result of a accident that removed wings from an RV and ruptured the tanks. Some of the old fogies on here can probably tell us all about it.
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I can verify that it was after 1993. My -6 originally had the "hole" and had to be later modified.
 
My -6 has holes and not slots, that's the way it was when I bought it. I'm not inclined to remove the tanks just to change this... But i'll keep it in mind if I ever have to ditch off-airport.
 
Snowflake said:
My -6 has holes and not slots, that's the way it was when I bought it. I'm not inclined to remove the tanks just to change this... But i'll keep it in mind if I ever have to ditch off-airport.
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Mine had holes too (1996). But I changed them. I kind of like the idea of heading between two trees in the dense forest....to rip the wings off, along with the complete fuel tanks...

BTW, as I remember, you can slot either side. That way, you could remove just the angle pieces that bolt to the fuselage.

L.Adamson ---- RV6A
 
L.Adamson said:
Mine had holes too (1996). But I changed them. I kind of like the idea of heading between two trees in the dense forest....to rip the wings off, along with the complete fuel tanks...
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In a -6? Forget about it. I think that spar is waaay too strong to "snap" off by flying between two trees. You're more likely to come to an abrupt, screeching, and possibly painful, halt.

BTW, as I remember, you can slot either side. That way, you could remove just the angle pieces that bolt to the fuselage.
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Well, that just makes waaaaay too much sense. I'll take a look and see where the bolts are in the cockpit, that might be do-able. I've got to pull my wing intersection fairings soon anyway so I can polish them, maybe I can do this while i'm in there as well.
 
My -6 wings plans show only the hole. The plans are also real blue-prints and pre date the mod... Yes, my attach brackets will also be slotted when the time comes.
 
Toobuilder said:
...Can it?A slotted wing attach fitting?....Somebody please tell me this is not "Van approved".
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Bob Kuykendall said:
I'm curious: Do you have the plans set for your airplane? Thanks, Bob K.
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Toobuilder,

It is unclear that the RV-8 you fly is actually owned by you. If it is, you should inspect that detail and determine if a fuel tank attach (support) bracket is modified with a slot so that the assembly complies with Van's advice, engineering and the accurate information already presented on this thread.
 
Rick6a said:
Toobuilder,

It is unclear that the RV-8 you fly is actually owned by you. If it is, you should inspect that detail and determine if a fuel tank attach (support) bracket is modified with a slot so that the assembly complies with Van's advice, engineering and the accurate information already presented on this thread.
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No, this airplane is not mine, but I am its "caretaker". It resides in my hangar and I am helping the new owner through the maintenance process. What started out as a simple oil pump change (no record of AD compliance) has tuned into a project of major proportions because I keep uncovering gross errors in workmanship. As a result of the overall quality of the airplane, I am "spring loaded" to question things like this fuel tank support. I figured someone simply slotted the hole to make it easier to install.

I really should round up a set of plans...
 
On the RV-6 plans...

...Drawing # 46 (Wing / Fuselage Attach) shows the details of the "slot". This is noted as Rev 9, dated 3/98.
 
I certainly appreciate the quick responses everyone! This forum has once again proven to be a wealth of information.

Thanks a million :D
 
If you didn't allow it to pull out, and you just bolted it in there, there'll be some pulling out anyway, but it will be the inboard rib of the fuel tank that will pull out.
 
Huh?

Mel said:
This fitting is NOT a wing attach fitting. It is simply a fuel tank support......
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I'm confused by your narrow interpretation of the function the parts. You clearly stress the point that the part is NOT (your emphasis) a "wing attach fitting" and you go on to assert it is really is a fuel tank "support." I would think a precise description (thus understanding) is helpful to the builder. In any event, how do you reconcile your opinion with drawings that clearly describe those parts as "tank attach angle" or "tank attach bracket?" Nowhere can I find a reference that describes the parts serviing as fuel tank supports. Please clarify.

dwqpky.jpg
 
Wing vs. Tank attach.

OK, I'll concede that it is a "tank attach" angle.
I still maintain that it is not a "wing" attach fitting.
 
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I would think a precise description (thus understanding) is helpful to the builder.
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Methinks Mel's description was quite precise. The nomenclature on the drawing probably predates the changeover to a slotted fitting.
 
Timely catch. I am getting ready to attach/proseal that angle.

It would be much easier to make that slot beforehand.
Here are the images from my 6A plan. Shows the slot, etc.

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20100516_122812.jpg
 
Very interesting ! I just looked at my preview plans for the 4 and found the same thing . I'm pretty sure mine is not slotted and will put it on the to do list .

I am curious about the need for a platenut and safety wired bolt . Why not a simple bolt/washer/locknut ?

Any ideas ?

Marc
 
777drvr said:
I am curious about the need for a platenut and safety wired bolt . Why not a simple bolt/washer/locknut ?
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Probably because you don't want to apply full torque on the bolt/nut assembly. It only holds for shear in this case. You want the bolt to be able to pull clear in case of an accident.
 
Mel has it right. The tank attach bracket is there to control flight loads in the vertical (+6,-3 G's) on some 120 pounds of fuel/tank. The reason you have the fasteners called out is because it isn't supposed to be tight. The light torque allows the parts to separate as said in other posts to lessen the likleyhood of a post-crash fire. The slot allows support in the vertical plane to provide G loading on a heavy area of the wing. In a crash, the major load is latteral (aft). I'm pretty sure the wing would either separate or at least bend back a ways if you ran into something with it at 50 knots.
 
That's what I thought . I understand that you might not get full torque on the platenut but that may not keep people from trying . You could just as easily use the bolt nut combo and not tighten it up too much . Just food for thought because I don't see any explanation as to how the junction should be tightened.

Marc
 
777drvr said:
You could just as easily use the bolt nut combo and not tighten it up too much.
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If you are going to use a bolt/nut combo, it's best to use a drilled bolt and castle nut. That way you can "lock" the amount of torque that you want. It's never a good idea to use a nylok nut and not torque to spec.
 
Thanks Mel . I didn't build my plane but I'm trying to learn as much as I can in order to improve and maintain it . I love getting these little nuggets of old timer knowledge !

Marc
 
When originally designed, a bolt with a castlated nut could have been used, but the nutplate was chosen to help keep the bolt from tipping and binding the joint as it slides apart. Because of the slot, once the bracket starts to move the bolt is only supported by the .125' thickness of the aft bracket. That is also the reason the nutplate is specified to be installed horizontal. It is the orientation which has the most resistance to the bolt tipping because of the bending resistance of the nutplate.
The safety wire is specified for two reasons...

The intent is that the bolt only be tightend just enough that the AN970 washer can't be rotated by hand.

The joint is technically one that is subject to rotation. Under high G's, there is enough wing flex to induce a very small amount of movement it this joint (same reason a castlated nut is used on the rear spar attach point).
 
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