fuel cap - probably a stupid question...

[ayavner]

on the Jab fuel cap, what is the thing that pokes up into the airstream, is that meant to provide ventilation?

 

 

[facthunter]

And probably a bit of positive pressure. Nev

 

 

[JabSP6]

on the Jab fuel cap, what is the thing that pokes up into the airstream, is that meant to provide ventilation?

Hi Ayavner

 

The fuel tanks on Jabs in the wings do have ventilation pipes attached to the fuel caps sticking up in the air. These also have covers fitted when the planes are not in use to stop the possibility of water entering.

 

Safe Flying

 

JabSP6

 

 

[Admin]

No such thing as a stupid question here Mate!

 

 

[ayavner]

mate if there's a way, I'll find it

 

 

[jetjr]

Theres small holes in the top which must face forward, if these become blocked by insects (what the covers are for) its possible fuel can no feed evenly from tanks

 

 

[Eric McCandless]

I think there is a design issue with the Jabiru fuel cap that may cause the cap to leak or come loose in flight, and I am surprised there is not a service bulletin on it. It has happened a couple of times with me in the short time I have owned my J170, until I realised what was happening.

 

If the Allen nut is loosened too much (more than a couple of turns), the small o-ring between the bottom and upper plates can become dislodged from its locating groove. It is not noticeable until you re-tighten the Allen nut. With the o-ring out of its groove, tightening the nut will result in the cap not seating properly in the tank and may leak or worse, come loose in flight.

 

I would recommend to never undo the Allen nut more than a few turns and always check that the cap fits flat and firm when tightened again. There should be no movement of the cap in its seat after it is secured with the Allen key. I always gently grab hold of the vent and give it a gentle shake to make sure it is firm. If it moves, then undo it and check that the inner o-ring is properly seated in its groove before re-tightening.

 

Have others noticed this?

 

 

[mlpinaus]

"I always gently grab hold of the vent and give it a gentle shake to make sure it is firm. If it moves, then undo it and check that the inner o-ring is properly seated in its groove before re-tightening.

 

Have others noticed this?"

 

Yes. "Wiggle the fuel caps" has become a part of my walk around. I think that the problem is eased by using a T bar type Allen key available at Repco, rather than the standard

 

one supplied with the air craft. I am also 6' 5, so that helps looking over the wing.

 

Marcus

 

 

[Ultralights]

blocked fuel tank vents can cause some issues, if they become blocked, they can stop the flow of fuel, as the fuel is drained out, it can cause a vacuum inside the tank, stopping the flow, in some aluminium tanks it has been know to cause the tank to implode. more than one aircraft has been bought down by blocked fuel vents.

 

 

[jetjr]

Checking fuel cap security is part of most aircraft preflights Ive been involved with

 

Did see a C185 take off with a cap off, fuel was sucked out in minutes and could clearly see the fuel streaming from wing in flight

 

 

[Guernsey]

Do you all carry a spare fuel cap???

 

Alan.

 

 

[jakej]

Do you all carry a spare fuel cap???Alan.

How many items do we then carry spares for Alan, no need IMO just do the proper checks in this case before flying.

 

In the 'certified' aircraft market there is a requirement for a restraining system (eg chain or cable etc) for fuel caps that can't be seen while in pilots seat - a very good idea for ALL aircraft, but I wonder how many meet this requirement

 

Jake J

 

 

[jetjr]

My J200 has restrained caps, , only holds lower half of the cap though. Havent had a problem in 800hrs with fuel caps, even flying once with one not done up tight.

 

I have found regularly replacing large o rings helpful so they dont stick and jam so much, also a smear of lube helps. Sometimes this is the cause of over loosening nut

 

 

[facthunter]

Having a chain on a fuel cap is not an answer for having it come off in flight. I HAVE seen what a seat belt strap does to the fabric and I think a fuel cap on a chain would do similar damage to the upper wing surface. Rubber tanks can contract to a crushed condition and most of the fuel is lost, w2ith the cap off. The gauge can register anything but will not mean anything. CHECK your fuel caps for condition. Most motorbikes would have better ones than some aircraft . Nev

 

 

[Old Koreelah]

...more than one aircraft has been bought down by blocked fuel vents.

I almost joined their ranks, but discovered it in time and had an alternate tank. How to check the vent is not blocked? Tape a square of tissue paper over the vent and blow into the open tank. Tissue paper should move.

 

 

[jakej]

Agreed Nev re damage to fabric however on an aircraft where you can't see the cap, having it on a wire or chain will surely get your attention, there will be some minor damage in fiberglass or metal aircraft but you will know the cap is off. Without the tethering of the caps you could lose a lot of fuel (you generally won't see it flowing out) before it will show on the 'trusty' fuel gauge, a fuel computer won't be of any use in this situation as it only measures fuel used. Not an ideal situation if on a long cross country trip miles from anywhere.

 

Doing the checks is always the answer to minimising the risks - I still ocassionally get out of the plane (despite just buckling up) to check the oil dipstick security as a result of being distracted etc then not absolutely sure that I did tighten it - still happens now after 2900 + hrs.

 

Jake J

 

 

[Guest Howard Hughes]

No such thing as a stupid question here Mate!

The only stupid question is the one you don't ask!

[Guernsey]

How many items do we then carry spares for Alan, no need IMO just do the proper checks in this case before flying.In the 'certified' aircraft market there is a requirement for a restraining system (eg chain or cable etc) for fuel caps that can't be seen while in pilots seat - a very good idea for ALL aircraft, but I wonder how many meet this requirement

 

Jake J

Hi Jake you are absolutely correct regarding carrying a spare fuel cap however, it is human beings that fly these aircraft so mistakes happen. I know of a few occasions where people have refueled, then been distracted (shouldn't happen but it does) and forgot to put the cap back on, in all cases the aircraft were high wing except one which was a Trike.

 

Alan.

 

 

[Guest Howard Hughes]

Even on our aircraft, the last thing we do is a quick walk around to visually inspect caps, lockers, etc...

 

It is s good habit to be in!

 

PS: I don't see the need to carry a spare fuel cap!

 

 

[sfGnome]

I recall hearing a story once of a jab cap being put on with the vents facing backwards, and the fuel being sucked out by venturi force. Does that seem possible, or just a myth?

 

Diverging from topic slightly (but blame JakeJ - he mentioned oil ), I did get interrupted doing the oil check one day and left the oil cap in the engine bay. Luckily (purely luck), I did a final check of the engine and found it, so these days I leave the cap on top of the cowling where it's obvious.

 

 

[jetjr]

The riser with holes in it is bonded into fuel cap and theres a locating lug on the cap to ensure it faces forward - pretty tough (near impossible) to put it on backwards

 

I did hear of a guy who had the riser pipe come out and he reinserted it backwards, no fuel came out but it didnt feed properly.

 

 

[Old Koreelah]

I recall hearing a story once of a jab cap being put on with the vents facing backwards, and the fuel being sucked out by venturi force. Does that seem possible, or just a myth?Diverging from topic slightly (but blame JakeJ - he mentioned oil ), I did get interrupted doing the oil check one day and left the oil cap in the engine bay. Luckily (purely luck), I did a final check of the engine and found it, so these days I leave the cap on top of the cowling where it's obvious.

When refuelling my car I religiously leave the fuel cap on the driver's seat for the same reason.

 

 

[Eric McCandless]

I recall hearing a story once of a jab cap being put on with the vents facing backwards, and the fuel being sucked out by venturi force. Does that seem possible, or just a myth?

I believe this is a myth, as the vent has a one way plastic ball valve which allows air into the tank, but will not allow fuel to escape from the tank. I have tested this by being able to blow air through the top of the vent but unable to suck air back out.

 

 

[billwoodmason]

Eric,

 

In my experience 1 turn is enough to remove Jab wing tank fuel caps but is not enough to displace the rubber seal.