BLADDERS - NO TURNING BACK NOW

[DCarlton]

So far so good with my F's bladder install.  Access plates removed; vent tubes drilled out and removed; fuel cap adapter ring drilled out and removed; fuel senders removed.  Removing the fuel pickup tubes should be next.  Several types and layers of sealant built up over the years from patches.  More to come... 

[BDPetersen]

When you start torque wrenching the clamps, Tekton sells a compact one as I recall.

[Immelman]

Interesting to see sealant applied to the inside of wing skin. I wonder what the thought process was there.

[N201MKTurbo]

After looking at the repair work done on your tanks, no wonder you are putting in bladders.

[N201MKTurbo]

If you stripped those tanks before you put the bladders in, you would probably gain 10 Lbs of payload.

[DCarlton]

  On 1/31/2025 at 9:49 PM, N201MKTurbo said:

After looking at the repair work done on your tanks, no wonder you are putting in bladders.

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Yep; nothing close to the beauty of a weep no more job. I'm trying to convince myself the extra 10 lbs of sealant will provide a cushion between the bladders and any sharp edges; along with the foam provided in the STC kit.  

[N201MKTurbo]

What I see is sealant put over sealant. And mystery sealant. And sloppy application. The only repairs approved in the maintenance manual requires the leaking area to be cleaned of all sealant down to bare metal. Then a bead coat of the specified sealant and after it cures, a brush coat of sealant. After that cures a top coat is applied. The repaired area should look like a brand new tank. That’s not what I see in your tanks.

[MikeOH]

  On 2/1/2025 at 1:08 PM, N201MKTurbo said:

What I see is sealant put over sealant. And mystery sealant. And sloppy application. The only repairs approved in the maintenance manual requires the leaking area to be cleaned of all sealant down to bare metal. Then a bead coat of the specified sealant and after it cures, a brush coat of sealant. After that cures a top coat is applied. The repaired area should look like a brand new tank. That’s not what I see in your tanks.

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What is your point?

[DXB]

Does anyone else with bladders worry there's spar corrosion hidden under their old sealant, and now permanently hidden upon bladder installation?

[MikeOH]

  On 2/1/2025 at 8:05 PM, DXB said:

Does anyone else with bladders worry there's spar corrosion hidden under their old sealant, and now permanently hidden upon bladder installation?

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Does anyone drain their tanks and strip off old sealant just to inspect for spar corrosion?

[DCarlton]

  On 2/1/2025 at 1:08 PM, N201MKTurbo said:

What I see is sealant put over sealant. And mystery sealant. And sloppy application. The only repairs approved in the maintenance manual requires the leaking area to be cleaned of all sealant down to bare metal. Then a bead coat of the specified sealant and after it cures, a brush coat of sealant. After that cures a top coat is applied. The repaired area should look like a brand new tank. That’s not what I see in your tanks.

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Not a great example of how to seal or patch tanks.  I'm sure the folks at the tank strip and seal shops have seen it all.  The new bladder STC install procedure calls for removing the sealant from inside the tank around the sender holes 1/2" wide; it doesn't call for stripping the tanks.     

[DCarlton]

  On 2/1/2025 at 8:05 PM, DXB said:

Does anyone else with bladders worry there's spar corrosion hidden under their old sealant, and now permanently hidden upon bladder installation?

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Would be interesting to ask the tank reseal shops if they have ever encountered corrosion inside a fuel tank or under the sealant.  They've seen thousands.  Someone with a good line of comms with Paul at Weep No More should ask.  My gut and no more says that's an unlikely location.  In the case of a bladder install, I like the fact that the old sealant covers the sharp edges inside the tank in addition to the materials and procedures provided in the STC.  

[N201MKTurbo]

I would think any corrosion would cause blistering or flaking of the sealant. It is hard to imagine any corrosion would start on the tank side, so inspecting in the wheel well should show it first.

[DCarlton]

For the folks that might be interested in the hardware involved, here's a few more random pics of my bladder install.  Vents and drains get removed, relocated and replaced, holes are enlarged in the ribs for the bladder interconnect tubes and covered with centipede grommet, additional small vent/drain holes are drilled in each bladder bay, foam pads are installed in the bottom of the tanks, stringers and rivet heads are taped (the original sealant provides protection too), the inboard bladder is held up by a snap plate, the middle and outboard bladders are held up in position with the plates shown (temporarily out of position) that screw to the original access panels, the original fuel cap adapter ring is removed and new fuel cap adapters and caps are installed, new improved fuel pickup tubes are installed, fuel senders get overhauled or replaced and the gages get fresh labels.  I need to make a picture of the new drain valves and tank vent opening (it's an interesting design).  I should have made a pic of the spring clamps that get torqued over the bladder interconnect tubes but didn't.  Bottom line, there's significant work involved.  After seeing the original gunked up fuel pickup tubes and vent tubes, I'm glad those got replaced.  I wouldn't say it's superior to a high quality tank reseal but it's an alternative solution that should be field serviceable by any mechanic if needed in the future (a plus if you live in an area where no one wants to patch or reseal tanks).  I expect the bladders to outlast the airplane at this point.  Looking forward to filling the tanks soon and making sure there are no leaks before we reinstall the interior.  Should be downhill from here.  

[kortopates]

  On 2/1/2025 at 8:18 PM, MikeOH said:

Does anyone drain their tanks and strip off old sealant just to inspect for spar corrosion?

Well yes, every time they have their tanks properly stripped and re-sealed. Of course it’s not frequent at all, but generally more than once over the plane’s lifetime and likely to be in time for finding issues.

I know my tanks don’t have rated fuel capacity because my tanks look just as bad as these if not worse. i think someone added a sloshing compound at one time to fix leak(s) They’ve been very abused in prior ownership patch jobs - but don’t leak so in no hurry to fix this.


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[MikeOH]

  On 4/7/2025 at 2:38 AM, kortopates said:

Well yes, every time they have their tanks properly stripped and re-sealed. Of course it’s not frequent at all, but generally more than once over the plane’s lifetime and likely to be in time for finding issues.

I know my tanks don’t have rated fuel capacity because my tanks look just as bad as these if not worse. i think someone added a sloshing compound at one time to fix leak(s) They’ve been very abused in prior ownership patch jobs - but don’t leak so in no hurry to fix this.


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Agree, if you are stripping for a reseal then inspection makes perfect sense. Why wouldn't you?

I was just pointing out that I can't imagine anyone strips their tanks JUST to inspect for spar corrosion!

[DCarlton]

  On 4/7/2025 at 3:01 AM, MikeOH said:

Agree, if you are stripping for a reseal then inspection makes perfect sense. Why wouldn't you?

I was just pointing out that I can't imagine anyone strips their tanks JUST to inspect for spar corrosion!

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The condition of the rest of the plane has a lot do with your decisions too.  We opened EVERY inspection and access panel before we started this work and spent a significant amount of time inspecting the airframe (lights, mirrors, cameras, eyeballs).  Yes the old sealant is ugly and it goes against my usual obsessive tendencies to leave it alone but it does provide a good cushion for the bladders around the nut plates and structure.  The only way I would want it stripped is to do it the way Weep No More does it.  I almost didn't post any pictures to avoid potential criticism but I wanted folks to see how their tanks might actually look inside; stripping tanks that have been patched is not an easy job at all.  I'm fairly critical and I'll be satisfied if we get this buttoned up and don't have any leaks.  I'm not at all concerned about corrosion under the sealant.  

[FredG]

What is going to be the added weight of the bladder installation?

[DCarlton]

  On 4/7/2025 at 5:45 AM, FredG said:

What is going to be the added weight of the bladder installation?

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I’ll look it up tomorrow and post the exact weight but I think it’s around 35 lbs.  I’ll be carrying 54 gal now instead of 64 so I’m actually gaining useful load.  Five hours is enough fuel for me.  

[Hank]

  On 4/7/2025 at 6:27 AM, DCarlton said:

I’ll look it up tomorrow and post the exact weight but I think it’s around 35 lbs.  I’ll be carrying 54 gal now instead of 64 so I’m actually gaining useful load.  Five hours is enough fuel for me.  

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Based on flying time and gallons to refill, my standard C with 52 gallons is good for almost six hours (4:45 flying, refilled with 41 gallons; did this twice. Don't recall gallons to refill after two more recent 4:30 flights).

[DCarlton]

  On 4/7/2025 at 5:45 AM, FredG said:

What is going to be the added weight of the bladder installation?

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29.7 lbs 

[kortopates]

  On 4/7/2025 at 6:27 AM, DCarlton said:

I’ll look it up tomorrow and post the exact weight but I think it’s around 35 lbs.  I’ll be carrying 54 gal now instead of 64 so I’m actually gaining useful load.  Five hours is enough fuel for me.  

Actually you’re losing ~30 lbs in useful load but gaining ~60 lbs in payload and maybe about an hour less in range.


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[DCarlton]

  On 4/7/2025 at 4:28 PM, kortopates said:

Actually you’re losing ~30 lbs in useful load but gaining ~60 lbs in payload and maybe about an hour less in range.


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Ok I looked up the definitions.  Thanks for that rusty pilot refresher training exercise.    

Here's the fuel capacity info from the Supplemental Flight Manual for anyone that might be considering bladders.  We verified these figures when adding fuel the first time.  

FUEL LIMITATIONS:
2 Standard Tanks:  28.65 U.S. Gallons Each
Total Fuel:  57.3 U.S. Gallons
Usable Fuel:  54.8 U.S. Gallons
Unusable Fuel:  2.5 U.S. Gallons