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Thread: PA-18 Fuel Tank Popping Noise On Landing

  1. #1

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    PA-18 Fuel Tank Popping Noise On Landing

    Not sure if anyone has any experience with something like this happening in their plane. About a year ago I noticed occasionally after landing during the rollout I could hear a slight "popping" noise coming from either the wing or behind in the fuselage. It seemed hit or miss at first. I didn't really think much of it I thought maybe something was shifting around in the belly pod. Flash forward to now, it happens very frequently and I believe I have it pin pointed to the left fuel tank. It happens all the time in the landing rollout after the plane has slowed to maybe 20mph. It DOES NOT happen upon touchdown, it happens after. I hypothesized that the fuel tank has some kind of dent in it, and during flight the vented cap is allowing enough pressure to keep it from popping, and during the rollout as the plane slows the pressure reduces and whatever it is, a dent or flimsy part of the tank would pop due to decreased pressure. It happens when the tank has anything less than 1/2 to 3/4 fuel.

    I have the standard piper fuel caps for my 160HP O-320-B2B. I tried using a single atlee pressure vent cap on that side and it seemed to help for a little while but then it would do it again at lower fuel amounts in that tank.

    I have a CGR-30P engine monitor and fuel flow is always fine, plane runs great. At this point its more of annoyance that makes me cringe, but worried it could lead to bigger issues. The plane was never in any kind of accident or anything that would have dented the tank.

    Yesterday I was taxiing on a little bit rougher of strip and it popped so loud I thought I had hit something at first. I think it may have been from fuel sloshing around aggravating it.

    Mechanic is going to look at the tank but just curious if anyone has ever experienced this. They are stock 18 gallon tanks on a normal left, right off system.

    Also if we do have to end up replacing the tank is there any difference between the Univair and Dakota cub 18 gallon tanks?

    Thanks in advance.

  2. #2
    Steve Pierce's Avatar
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    No change with an Atlee snorkel front facing vented cap I would think it is a mechanical, tank moving, flexing or something issue. Be curious what you find when you get the tank cover off.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  3. #3

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    Strange,
    maybe have a good look at all wing attach hardware as well.
    something maybe loose enough to allow wallowing, shifting, clunking.

  4. #4
    cubdriver2's Avatar
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    Quote Originally Posted by Oliver View Post
    Strange,
    maybe have a good look at all wing attach hardware as well.
    something maybe loose enough to allow wallowing, shifting, clunking.
    20 mph is about when the wing unloads and starts to carry its own weight?

    Glenn

  5. #5

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    Any difference with fuel full and empty in that tank? That would be my first troubleshooting step. Have you gone out to the wing tip and tried lifting and releasing to see if you can duplicate it?

  6. #6

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    If you have some slop in the lift strut bolt hole at the fuselage you’ll get a clunk when the wing is unloaded. Try picking the plane up out board of the lift struts and see if it moves.
    Likes BC12D-4-85, flynlow liked this post

  7. #7
    39-J3's Avatar
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    I had the same problem with my Clipped wing J3. It was driving me crazy trying to figure out where the noise was coming from. It was the holes at the fork attachment points to the fuselage that was elongated, and when the wing would unload it would make a popping sound.

    Larry.

  8. #8
    BC12D-4-85's Avatar
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    I had something like this on a leased PA-18. Loose lift strut forks at the fuselage. Lifting and releasing the wing tips made it talk. Yours may be another issue. You might try blowing via a hose into the tank vent to see if it bonks when pressure is altered.

    Gary

  9. #9
    cubdriver2's Avatar
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    Quote Originally Posted by 39-J3 View Post
    I had the same problem with my Clipped wing J3. It was driving me crazy trying to figure out where the noise was coming from. It was the holes at the fork attachment points to the fuselage that was elongated, and when the wing would unload it would make a popping sound.

    Larry.
    25 plus years ago my Vagabond had the same problem. My IA put zero tolerance bolts in and it was fine.

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

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