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Thread: Fuel Vent

  1. #41
    nanook's Avatar
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    Quote Originally Posted by Clayton Harper View Post
    I'm not sure about SCs but the 150 HP fuel system in a Pacer will not meet CAR 3 fuel flow with out the pressure tube. Who know how Piper got it passed. Ed Trimmer discovered this when he STCed 180 HP in the Pacer.
    The header-tank fuel system that Piper designed for the PA-18, kept a positive head to the carburetor as long as you used the left wing tank. For cruise configuration the right wing tank & header was adequate. Both right & left fuel tanks required a vented cap only, no ram air caps were/are needed.

  2. #42
    skywagon8a's Avatar
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    Quote Originally Posted by cubflier View Post
    ...Keep in mind that after blowing the tank back up that cap was used for the entire time and no issues. If the cap had been plugged by some other cause the problem of tank collapse would have persisted. It did not.
    Jerry
    Did it ever occur to you that it is possible, due to many fuelings over time both with a gas hose and a Jerry can that the filler portion of the tank may have been pushed down a little? When this happens the vent in the cap can be pressed against the cover filler neck gasket thus blocking the air vent. Over time you may not even realize that the filler cap was lower than it should be.

    Some gas caps are very close to the top of the wing. Enough so that it is difficult to handle the cap.
    N1PA

  3. #43
    cubflier's Avatar
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    Quote Originally Posted by skywagon8a View Post
    Did it ever occur to you that it is possible, due to many fuelings over time both with a gas hose and a Jerry can that the filler portion of the tank may have been pushed down a little? When this happens the vent in the cap can be pressed against the cover filler neck gasket thus blocking the air vent. Over time you may not even realize that the filler cap was lower than it should be.

    Some gas caps are very close to the top of the wing. Enough so that it is difficult to handle the cap.

    This was not the case. If it were the venting issues would have been constant. I know we looked things over and there was no issue with the cap conflicting with the cover gasket. The cap was used on that tank for the rest of the trip and in fact he used this cap and tank combo for years after the incident. The tank was not pushed down a little, it was wadded up way down in side the tank bay. When we blew the tank back up it never fully returned to it's original condition so from then on his filler cap set lower and at an angle but vented just fine.

    Jerry
    If it looks smooth...it might be

    If it looks rough...it is!!

  4. #44
    180Marty's Avatar
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    The header-tank fuel system that Piper designed for the PA-18, kept a positive head to the carburetor
    Maybe that's why my 12 has the snorkel vents in the caps. I don't have a header tank. Haven't looked too close but with the Air research tanks, there is an outlet both front and back with lines going to a Dakota fuel valve. Pretty much like my 54 180 except it doesn't have forward tank outlets. It still has one above the cabin snorkel vent.

  5. #45

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    As it so happens..., I now have six (6) fuel caps that are new..., I only need two! I have four from Dakota Cub (two with the "lolly Pop" and two without). I also have two from Atlee that I think I will use...., any interest?

  6. #46
    RatCub Redux FrankO's Avatar
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    Read thru this & several other similar threads, trying to solve a problem I had with my cub after this year's extensive annual & engine swap. Right side tank had a pressurization problem, would initiate fuel starvation/involuntary leaning after flying on that tank for a period of time (no problem on the left). Had what looked like the original caps from the 50's, found that neither cap had been modified per the AD issued in the 50's, cap on the right side had rusted internal parts; replaced both with the milled aluminum caps from Univair @ $100 each. Additional flying showed the problem persisted, fuel starvation on the right tank only. Did find info on this site about a possible low pressure area on top of the wing causing the problem, at least on the one side. Also found a comment about one tank being slightly elevated relative to the other, perhaps adding to the problem. Took the tank cover panels off, examined both tanks and did find one that was higher (the right tank). At the same time, I tested the caps by pressing down on & releasing pressure on each (capped) tank, could hear air expelling as I pushed down and being inhaled as I released pressure on each tank; caps (both original and new) worked as designed. However, I had attached new felt strips to the straps securing each tank (replacing ancient duct tape) and in the case of the right tank, I speculated it was likely the tank cover was putting undue pressure on that tank due to the addition of 1/8" of felt, would not allow the right tank to fully re-expand as fuel was consumed & created low press within the tank as a result; removed the felt, reassembled and flew the airplane. Problem solved, no more symptoms. Anyone having what they perceive as pressurization issues would do well to test the tanks/caps as I did to narrow down the problem, which in my case was never the caps, just my own well intended but ill thought out mod.....

  7. #47

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    Will Univair's $100 milled aluminum caps handle 180hp? I'm using snorkel now. Milled aluminum are beauties.

  8. #48
    Steve Pierce's Avatar
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    Quote Originally Posted by King Brown View Post
    Will Univair's $100 milled aluminum caps handle 180hp? I'm using snorkel now. Milled aluminum are beauties.
    Which 180 hp STC do you have? I know Cub Crafter's requires the snorkel type caps. Can't remember on the AERO (Penn Yann) STC.

    As far as the felt Piper used 1/16" SAE50 felt. This is the best thing I have found to be the right thickness and crush. I found a vendor although they only sell in mass quantities and I started selling it in kits. https://www.freewebstore.org/piercea...61_115078.aspx
    Steve Pierce

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  9. #49

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    Thanks, Steve. I should have mentioned I'm Bushmaster 180hp experimental, using snorkels in the air and Univair's parked because they seal better against moisture. After months on the ground in our relatively cool/moderate climate, I've drained little more than a couple tablespoons of water from the five drains, almost always from the port tank. It would be a shame to use snorkels if the beautifully crafted Univairs would keep the engine running!

  10. #50
    skywagon8a's Avatar
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    King, what about something like this on the vent tube? Make a small leather gasket to seal the end when it's closed.

    N1PA

  11. #51

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    Thanks. It's worth a try. Changing caps at tie-down is a humbug.

  12. #52
    RatCub Redux FrankO's Avatar
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    Quote Originally Posted by King Brown View Post
    Thanks, Steve. I should have mentioned I'm Bushmaster 180hp experimental, using snorkels in the air and Univair's parked because they seal better against moisture. After months on the ground in our relatively cool/moderate climate, I've drained little more than a couple tablespoons of water from the five drains, almost always from the port tank. It would be a shame to use snorkels if the beautifully crafted Univairs would keep the engine running!
    The Univair caps are spiffy (now there's a word you don't hear anymore!) but the snorkels are required on the 180 due to the strength of the fuel draw, from what I understand. Just for the hell of it, I ordered a pair of the $7.95 el cheapo caps from Wag Aero...they are vented, they do fit & if a person wanted something to use just for storage, save yourself $92 each & use these. I don't doubt you could probably fly with them (for other than the 180) and not have any problem, except they're not PMA.

  13. #53

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    Towed banners at a very high power setting all day in a 180 horse super cub had to use full power the first hour or so with a 65' high panel when the wind was off land knocking me all over the place.. anyway we never used ram tube caps just plane old wag aero cheapo vented 7.95 caps, wide open 180hp O-360 and engine never hiccupped.. wonder why you need more fuel flow than the engine can take?

  14. #54

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    One of them there government things.

    § 3.434 Fuel flow rate for gravity feedsystems. The fuel flow rate for gravity feedsystems (main and reserve supply) shall be 1.2pounds per hour for each take-off horsepower or150 percent of the actual take-off fuelconsumption of the engine, whichever is greater.

    DENNY

  15. #55
    AdirondackCub's Avatar
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    As a practice I always remove my vented caps and put a sealed cap on when the airplane sits outside. No bugs, bees, mud dobbers clogging my vents. Its just part of my pre-flight when adding and checking fuel. ADK

  16. #56
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    Quote Originally Posted by AdirondackCub View Post
    As a practice I always remove my vented caps and put a sealed cap on when the airplane sits outside. No bugs, bees, mud dobbers clogging my vents. Its just part of my pre-flight when adding and checking fuel. ADK
    So......as the temp goes up and down during the day/night where does the + and - pressure come and go from?

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

  17. #57
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    I installed a Biplanes, Inc 12 gallon tank in the right wing of my 11. Those tanks come with and the STC requires, the "snorkel" vented cap. I assume that is because of the method of plumbing the tank into the fuel system. Mine was plumbed similar to a SC system instead, with the deviation noted in the 337.

    In any case, in the first couple months, everyone who saw the plane asked why a snorkel on one side, but not on the other. So, I installed a snorkel cap on the stock tank. Nobody has since asked why I have those caps......go figure.

    i like the snorkel caps, though....it'd be pretty hard to plug a vent with them....not impossible, but...

    MTV

  18. #58
    nanook's Avatar
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    Quote Originally Posted by DENNY View Post
    One of them there government things.

    § 3.434 Fuel flow rate for gravity feedsystems. The fuel flow rate for gravity feedsystems (main and reserve supply) shall be 1.2pounds per hour for each take-off horsepower or150 percent of the actual take-off fuelconsumption of the engine, whichever is greater.

    DENNY
    It has been awhile since I worked on a 180hp conversion, the fuel line diameter needed to be the next size up to meet the fuel feed requirements. The goose-necked caps were a quick fix for if you were using the original fuel system lines. The positive pressure flow made up for the smaller diameter gravity feed rate.

  19. #59

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    Quote Originally Posted by nanook View Post
    It has been awhile since I worked on a 180hp conversion, the fuel line diameter needed to be the next size up to meet the fuel feed requirements. The goose-necked caps were a quick fix for if you were using the original fuel system lines. The positive pressure flow made up for the smaller diameter gravity feed rate.
    That makes sense than because the towing super cubs were restricted cat and all rebuilt with newer larger fuel line, I have 1,000 + hours towing in several 180 hp super cubs and never used a gooseneck cap, just plain old wag aero style vented caps

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