Fuel Bladder


New Member
Can someone point out the advantages of using fuel bladders as opposed to fuel tanks? When flying the old 172s, I only had 3 sumps to drain durring my preflight, but when I fly the new SPs I have to drain 13 sumps. Why the change to fuel bladders instead of the integral fuel tanks? Weight? Cheaper? Thanks for the input....

When flying the old 172s, I only had 3 sumps to drain durring my preflight, but when I fly the new SPs I have to drain 13 sumps.

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<font color="purple"> Lawsuits. </font>
lawsuits? I'm not a mechanic, but it would seem to me that a tank would be much more safe than a bladder as far as trapping water in the tank goes because the bladder could develop a wrinkle or somthing that would prevent water from reaching the sump. I may be way off base here, so if I am wrong, somebody please let me know.

I am not knowledgable in construction but is it easier or cheaper on the assemply line to use bladders?

You have two, seperate issues here.

The fuel bladder/intergral tanks are one issue.

The number of sumps are a second.

Apparently, the reason Cessna now has 13 sumps on the new 172s (I flew Rs for my primary and am quite familar with all 13 of 'em!) is because of lawsuits in the late '60s and primarily in the '70s. Morons ... sorry "pilots," would head out to their bird, hop in, turn the engine over and fly away, never having sumped the fuel tanks. Then - surprise, surprise - when the engine would choke due to water in the line the "pilot" would invaribly bungle the "emergency" landing and in turn he or she would sue Cessna citing that they "had sumped the aircraft" but the "sumps didn't get it all." The lawsuits got so bad that most GA manufacturers quit making small GA aircraft which is why all of us are flying around in old beat up tin cans.

As a precautionary measure the new Cessnas have an insane number of sumps partly as legal protection against would be morons.

The tank/bladder issue is an engeneering/manufacturing measure. Each has it's merits and drawbacks but I'm not sure this change is directly related to the number of sumps or if they even did, infact, change from one storage method to the other.
I have no idea if this is a reason but it seems plausible:

With bladders, in the event that your fuel vent became clogged, the bladder would then become void of all fuel. On the other hand, if flying a fuel tank, if the fuel vent became clogged, then a vacuum could set up inside the tank and eventually arrest fuel flow to the engine.

Additionally, when sumping the fuel you are checking for, among other things, H20. If a bladder colapses, the volume of air in the bladder it able to get smaller and thus deminish the propensity for H20 vapors to be in the air and therefore eventually condense into the fuel.