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  #1  
Old 02-21-2017, 05:40 AM
BruceMe's Avatar
BruceMe BruceMe is offline
 
Join Date: Feb 2005
Location: Shawnee, Kansas
Posts: 566
Default RV-6 tank fit saga

I'm having fits fitting my RV-6 tank. The original was all dented in from a flip-over accident, so I'm rebuilding.

For background on me... I built a 'slow-build' (non-pre-punched anything) RV-4 from 2003-2008 so I thought this wouldn't be that hard. Boy was I wrong.

I [ahem] "winged" the first new tank build referencing the plans for left/righ layout, parts and measurements but really just eye-balled from the broken tank. It all went together as smoothly as pro-seal (bleck)... Fit, drilled, dimpled, cleaned gooped and I was happy enough. The trouble came when I went to fit it to the wing. I was also repairing the outboard leading edge skin and had it off when I fit the tank... <<<< BIG MISTAKE HERE

A rebuilt this tank using the special oversized W-601 skin. They have long flanges (by design) which are there to be trimmed to match the outboard skins. Except... I didn't have them on and I didn't realize that until _AFTER_ I put the outboard skin on at which time the 1/2" gap on the leading edge looked so amateur-built-hour.

For the second attempt; I was fed up making tanks. I gave it to a very RV experienced friend who I have subsequently learned has only worked on and built pre-punched airframes. Yeah... <<< SMALLER MISTAKE HERE

A slow-build airframe is a one of a kind. Think 1960's vintage English car looks beautiful but you can't swap parts.

My kind friend made the cardinal sin of thinking the plans as gospel and the instructions are there to answer any residual quandaries.

I had to let out a good laughed when he said... "The instructions don't say anything about trimming the flang?!" To this I chuckled and replied, "The slow-build instructions are filled with sage advice like 'Attach F-401', That's it... nothing else." If you get this, you built one.

Where modern pre-punched RV kits are like hiking the Appalachian trail with a guide dog, the old builds are more like doing the same with a ratty old miners map from 1904.

So I'm on my third attempt. My first build was closest; we'll do it that way again and now that the outboard skin is on, I will trim the aft tank flang to match the bracket to the fuselage and the tank to the outboard skin. Third time's a charm

Keep the hammer down!

-Bruce
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  #2  
Old 02-21-2017, 08:56 AM
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JonJay JonJay is offline
 
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Location: Battleground
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Sounds frustrating! It has been a long time, but aren't the tank skins drilled in assembly with the wing, same as the RV4 you built?
I recall strapping the tank skin down with the wing in the jig and lots of filing edges to fit and refit to match up with adjoining leading edge and main skins. The tank was then finished in a cradle off the wing.
I can not imagine building a tank from plans and then trying to make it fit on a 6 even with the larger flanges.
Perhaps I am not understanding or am misinterpreting what you have done.
Anyway, keep at it.
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  #3  
Old 02-21-2017, 01:21 PM
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az_gila az_gila is offline
 
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Location: 57AZ - NW Tucson area
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Quote:
Originally Posted by JonJay View Post
Sounds frustrating! It has been a long time, but aren't the tank skins drilled in assembly with the wing, same as the RV4 you built?
I recall strapping the tank skin down with the wing in the jig and lots of filing edges to fit and refit to match up with adjoining leading edge and main skins. The tank was then finished in a cradle off the wing.
I can not imagine building a tank from plans and then trying to make it fit on a 6 even with the larger flanges.
Perhaps I am not understanding or am misinterpreting what you have done.
Anyway, keep at it.
Yes, they are match drilled upon assembly.

One option may be to cut off the flange area from the old tank and use it a marking template on the new tank flange with lots of careful measurement.

On the -6 wings there is not a lot of tolerance in this area since the spar flanges are quite narrow, 9/16 for the forward row of #8 screws.
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  #4  
Old 02-22-2017, 05:24 AM
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BruceMe BruceMe is offline
 
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Yes and yes... It will get done and right and I'm sure it will be long forgot like all my other mistakes.

-Bruce
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Once RV-3 3456B
Now RV-6 4074V
Once and soon again RV-4 254MM
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  #5  
Old 02-22-2017, 05:51 AM
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JonJay JonJay is offline
 
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Quote:
Originally Posted by BruceMe View Post
Yes and yes... It will get done and right and I'm sure it will be long forgot like all my other mistakes.

-Bruce
I hear ya. I'll chalk your post up to a need to vent!
As you know being an experienced builder of the early kits, nothing comes easy and a rebuild is even harder still.
I have no doubt you will get it done and done right.
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RV1 - Proud Pilot.
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  #6  
Old 02-22-2017, 08:52 AM
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RV6_OKLA RV6_OKLA is offline
 
Join Date: Jan 2005
Location: Yukon Ok
Posts: 91
Default RV6 Fuel Tank

Been there done that! Dinged the leading edge of the left tank. Friends said just bondo it, but I said nope, new tank. I did not know what I was saying!! After 3 sets of tank parts, mission completed. I built my slow build RV6. It had prepunched skins on the wings, but no prepunched ribs. During the building process the wings had to be jigged and drilled. There lies the problem. The new parts for the tank had a drilled skin which matched my old skin, but ribs weren't drilled. So how do you jig a tank to a wing that is already attached to the airplane???

It's been several years, but here's what I remember from the process.

I used the new prepunched skin to determine where the ribs should be riveted to the new baffle. I drilled holes in each rib so I could insert two threaded rods to hold ribs in position at a later point then clecoed ribs to the baffle. Using the old tank, I determined the distance that the rear of the baffle was from the spar web and made spacers from hard wood that were about 1"x1". Carefully position the spacers and hot glue to web face. Now, the baffle with ribs clecoed to it is positioned to where it needs to be and I drilled and clecoed(fill with rivet and proseal later) the baffle to the wood spacers. If you had wasted skins from previous tries, you can prepare the attach holes for the screws and then cut it apart and screw a section on bottom of spar and another section on top of spar and also at the ends where tank attaches to wing. This acts as an alignment tool. Then uncleco ribs from baffle and add the threaded rods and nuts and reattach to baffle. Using the nuts on the rod, space ribs to match skin holes. Baffle should now be in position and ready for drilling and a center line drawn on ribs for drilling reference. Skin should be prepared with dimples for screws. The next step is to pull skin over the ribs/baffle using straps, so flap is removed and a spacer made to go full length behind the rear spar. I cut down a 2x4 taped it in place. From memory, I think I placed skin over ribs and screwed the skin to bottom of spar, then used the straps to tighten skin until screw holes lined up on top of spar, but may have been the opposite. What you are wanting to do is get screw holes to match and rib center lines to line up. This took several attempts!! Ribs needed to be tweaked to line up. It took a lot of cussing, but it eventually came together. An extra set of hands is a plus. Once drilled, remove tank and remove baffle spacers and finish tank. I used the straps to help get it back on. Replace flap and go flying. Hope this helps.
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