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12-20-2015, 07:27 AM
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Join Date: Mar 2013
Location: Prince Edward Island, Canada
Posts: 138
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Tank Baffle change
Since I'm nearing completion of my tail kit I've been reviewing the build manual and plans for the next stage of construction, my wings. A little background to my project. Kit #658 circa 1986 was purchased from EAA105 who sold on behalf of an estate. Some components had been lost over the years and I purchased new parts from Vans to replace them. I have the factory built Phlogiston Spar option and the wings are completely untouched.
As always, a problem when mixing new and old parts you run into design changes that create a lot of head scratching. I realized this weekend that the wing tank baffle (T-402) had been changed from a forward facing flange to an aft facing flange that slips over the Spar Web Doubler (W-406B) as per the new drawing 17A
My kit came with drawing 17 so the tanks are the old style where the baffle faces forward. I can see that with the new design the forward row of screws through the tank skin and the baffle to the spar doubler flange. This seems be a more secure method of attaching the tanks.
My plans show the forward row of screws that attach the tank skin to the main spar flange only.
My question is whether there are known issues with the older design. From what I understand, if I wanted to change to the new design I'd have to change the forward spar doubler to the new dimension part which would allow the tank baffle to fit over it's flanges. This would require disassembling the main spar and retrofitting the new spar web doubler. I wouldn't want to do this unless it was absolutely necessary. I plan to call Van's on Monday but I'm sure there is great experience to glean here on VAF?
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12-20-2015, 01:31 PM
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Join Date: Jan 2007
Location: Benton, Kansas
Posts: 259
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I knew it wasn't just me out there!
...Okay, so here is the deal on the tanks. I had the exact same scenario that you mentioned, and I too talked to Van's.
My wing kit was a second hand, incomplete kit, that had basically nothing done to it, other than a lot of pieces lost. I had to buy so many new parts, that only part original are the spars and some of the ribs.
Feel free to take a look at my buildlog, as this procedure was fairly well documented there too:
So, the older kits had a forward facing baffle, and the tank ribs were recessed at the root to accept the baffle flange. The new baffles have the aft facing flange, which moves the web of the baffle forward about a half an inch or so. This is no good, because now your tank ribs will stick forward a half inch of the outboard leading edge of the wing. So, you guessed it, ALL NEW TANK RIBS. But the joys of mixing new and old are just getting started. The height of the new baffle, is exactly the same height as the spar. (In other words, you cannot step the flanges over the spar flange per the drawing, or you will be too tall.
Here is the HYBRID solution of new and old that I used, and was given the thumbs up from Vans:
The new baffle flanges are roughly 1" wide. Remove half of that width, so the baffle flanged are now ~.5" As the baffle and spar flanges are the same height, you will make a butt joint of these two sections. The tank skin will fit really nice over the spar flange this way. There are still the SAME number of screws attaching the tank to the wing. It's a lot of work, but a good method of using new tank parts on the older spars.
Feel free to PM me if you want to chat further on this. I'll see what I have for pictures.
Gregg
__________________
Gregg J. Brightwell
Benton, KS
CFII/MEII, ATP, AGI, A&P
-4 Emp and Wings complete!
Fuselage out of the jig!
www.mykitlog.com/gbrightwell
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12-20-2015, 03:23 PM
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Join Date: Mar 2013
Location: Prince Edward Island, Canada
Posts: 138
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Thanks Greg, I was reading through your Kitlog yesterday, a great resource so thank you for well documenting your build. What wasn't clear to me was if there were any issues with building the tanks the "old" way. I noticed the new tank baffle is the exact same height as it's always been, 7 25/32" but the flange has been increased from 9/16" to 1". I had expected that if I was to build the tanks the "old" way I could simply trim this down and face the flange forward. I have all the original tank ribs so no worries there. Going this route means the only material attaching the tank to the spar will be the skin. Granted there would be the same number of fasteners but I was worried there was a reason it was changed. Cracking around the screw holes or elongation of the holes possibly??
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01-14-2016, 04:20 AM
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Join Date: Sep 2006
Location: Trento, northern Italy
Posts: 622
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I had similar problem
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01-16-2016, 05:15 AM
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Join Date: Jan 2016
Location: South California
Posts: 244
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Baffeled
Has the discussion of putting a step down to allow the end of the baffle to slide into the ID of the spar flange. Something a bead roller with step dies may do. I have to ask or I will not learn..
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01-17-2016, 07:57 PM
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Join Date: Mar 2013
Location: Prince Edward Island, Canada
Posts: 138
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I kinda thought the same thing, that or add a strip to the inside of the baffle flange that extends back and inside the spar web doubler. There are a few areas where one could run into trouble though.
1. The tank skin is dimpled for the #8 machine screws that attach it to the spar doubler which would make it near impossible to slip the flange of the spar web doubler in the tiny gap.
2. The plate nuts would then become part of the tank baffle web instead of being attached to the spar. Obviously this is not how Van designed it so proper stress analysis has not been considered.
For these reasons I've decided to build the tanks the old way. I called builder support but they couldn't tell me why the design had been changed other than likely to make it easier to build.
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08-13-2016, 03:37 PM
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Join Date: Mar 2013
Location: Prince Edward Island, Canada
Posts: 138
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I'm nearing the stage on my left wing where I'll have to start fitting the leading edge skin and assembling fuel tanks concurrently to match. I had been thinking I would modify the tank baffle and build the tanks as per my original plans but this means using AK-42H (sealed CS 3/32" pull rivet) to attach the wing skin to the baffle. This won't have quite as nice a finished look and I wonder whether these will leak over time. Since you can't put a dab of sealant on the tail after setting the rivet there seems like it would be a path for fuel to leak out between the rivet and the dimpled skin.
So two thoughts:
1. Keep calm and build on.
2. replace the tank ribs and build with a rear facing flange baffle. Alternatively to buying all new ribs, I could trim the original internal 3 ribs and replace the flange with a length of .032 angle?
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08-13-2016, 07:02 PM
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Join Date: Jun 2011
Location: Nashua, NH
Posts: 536
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Keep calm and build on. The hole in the rivet head can be filled and smoothed out to where you won't know the difference. Remember- K.I.S.S.
__________________
Mike
RV-4 #2750
N654ML
IO-360
WW150C Prop
1018 lbs
Flying
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08-14-2016, 05:47 AM
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Join Date: Mar 2013
Location: Prince Edward Island, Canada
Posts: 138
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more than the appearance of the rivet head is my (unfounded?) concern of future leaking. How likely is it for fuel to weep between the rivet and the skin? I imagine most of the sealant would be forced out. I'm interested to know if anyone has any direct experience with using these rivets and whether the old way of building the tanks was more prone to leaking. Van changed the design for likely good reason. Was leaking part of that reason?
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08-14-2016, 08:29 AM
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Join Date: Jun 2011
Location: Nashua, NH
Posts: 536
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The self sealing rivets I believe are used to close the tanks up even in the new design, and they don't seem to be leaking. Dip the rivet in proseal and indont think you will have any issues.
__________________
Mike
RV-4 #2750
N654ML
IO-360
WW150C Prop
1018 lbs
Flying
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