J160 wet wing feeding uneven

[glenns]

Has anyone had any issues with the J160 feeding fuel from the wet wings uneven. I have been having issues with uneven feed since the aircraft was picked up 6 weeks ago.

 

It is not always an issue but quite often fuel tends to feed from only one tank and certainly not evenly from both tanks.

 

It was quite scary when we were ferrying the aircraft from bundaberg and on the first stop we found the right hand tank empty and the left still full of fuel.

 

After speaking with Jabiru they advised that this can sometimes be caused by overfilling one of the tanks which then block's a breather pipe. This then favours the other tank.

 

I am not completely convinced however and would welcome any feedback from other owners.

 

glenns

 

 

[BigPete]

Hi Glenn,

 

funny thing my 160 has been OK - sometimes 5 to 10 liters difference. BUT - today when I refuelled - left tank nearly empty and right tank still around 35 liters.

 

I will talk to Cliff Banks tomorrow and see if he has any ideas.

 

regards

 

 

[Guest Guest]

From my personal experience, it's usually caused by rudder / ball position. If your balance is too far off,fuel may evendrainout thevent in the cap. There is a header tank under the seat and the tanks just feed into the header. As long as they both feeding, even if unevenly, there should be no problems.

 

Cliff will sort you out.

 

 

[River]

G'day Glenn,

 

Whilst there can be quite a number of reasons it does sound like it may be a pressure/venting problem. Maybe a incorrectly seating fuel cap seal or the likes off?

 

Rodger

 

 

[Ross]

Hi Jabiru J type Kit flyers and builders

 

I am assembling a J160 kit and have heard of this uneven fuel flow problem in wet wings before but not only for the J160. I have yet to hear of an engine stopping from one tank being dry but it could give quite an uneven load on the wings. Is this a problem?

 

In the J160 kit #14 version each wing tank has two feed outletsthat go to its own twin inlet single outlet valve before continuing in a single tube to a Tee piece behind the seats where it is joined by the single tube from the other wing tank with a similar feed and valve arrangement.

 

From the tee piece behind the seatsa single feed continues to the header tank under the passengers seat from where any air should escape back to the wing tanks..

 

The wing tanks are joined by a tube across the cabin ceiling that connects to an uluminium tube in each wing tank that goes inside the tank to the top of theextreme outer end of each wing tank. If this tube is not full of fuel it should allow the fuel pressures from each tank to equalise provided that .........

 

The header tank has a breather outlet that should allow the header tank to fill with fuel and any trapped air or air coming in with fuelto escape back tothe tube across the cabin ceilingvia a tee piece in the ceiling in that joining tube between wing tanks.

 

Since the wings are at aone degree dihedralthe outer ends should be higher than elsewhere. So if there is any air in the tanks that is where it should be in the outer end of the wing tanks connected to the other wing by the breather tubeacross the cabin ceiling (provided we have balanced flight).

 

There aremany combinations of possibilities here of where the fuel might go depending on the positions of the breather tube(s) in the wings, the fuel cap vents orientation, the cleanliness of the finger filters in the tank feeds, the diameter of the fuel lines and tubes (capillary action), the location of paper filters in the system, the trim and rigging of the aeroplane and which way up is the aeroplane.

 

Are the fuel cap vents set up to be air pressure positive, negative or neutral?

 

If the resultant tank pressuresare differenr fuel must flow from one wing tank to the other.

 

It could move via the tee piece behind the seats or even via the breather tube across the ceiling unless the breather pipe across the ceiling has a shut off valve each side of the header tank tee piece connection.

 

An extra two valves would then make the fuel system more complex but allow each tank to be operated independently but would increase the risk of engine failure due to fuel starvation and uneven loading of the aeroplane.

 

If anyone knows for sure what is the cause of this problem please let me know before I get my J160 airborne.

 

Regards

 

 

[Guest Guest]

Ithink you'll find the fuel system on the Jabs to be tried, tested and proven. There have been aircraft that actually did "run out of fuel." This was prior to the fittment of the Header Tank under the passenger seat. Initially it was just two tanks feeding into a t-piece then into the engine. The problem with that was that when one tank ran out it had the potential to feed air into the t-piece and cause fuel starvation (this happened to me too), particularly if the aircraft was unbalanced. As an interim measure, Jabiru recommended that the fuel pump be turned on when the combined fuel quantity was below 50 litres.

 

After they put the header tank in (retro-fit available) the problem to the best of my knowledge was completely solved. I would advise not modifying the Jabiru fuel system- it is simply not required.

 

The J160 shares the same 140'ish (more like 128) litre tanks that the J200/J230/J400/J430 use, however there has been a recent change in the last 10 or so kits where the tanks have a modified profile - they are shorter in the wing and have a wider chord length; I am unsure on why they made this modification.

 

NEVER underestimate the power of the NUT at the controls who isn't flying the aircraft in balance!!!

 

Nos

 

 

[Wilfred]

With the J200 we had the header tank mod installed at the factory and then at a later date did some flow tests, and found much the same thing . The tanks do seem to feed slightly unevenly and will tend to pull form one and then the other. This was done on the ground so had no bearing to out of balance flying. The difference only appears to be 5 - 6 litres at a time and then evens up with the other tank feeding. Over a full fuel load i do not think that it would cause one empty tank before the other once you allow for reserve. This happens with or without the electric fuel pump on so seem to be a "nature of the beast"thing. Once again the eneven flow does not seem to be enough to cause an inflight problem and dont forget the header tank would take care of any slight prblems.

 

 

[glenns]

Thanks for the great responses guys.

 

I tend to agree with just about all the responses. None however explains our initial experience over 2 days where we were getting 1 tank draining completely before the other. I can assure all that balanced flight was not the issue ( at least in this case).

 

This is a factory complete (recently) aircraft so header tank and all mods are done.

 

At the moment when I check the tanks they are about 5 ltrs different so that seems to fit in with turtle and others comments. However over the last couple of weeks there have been significantly greater differences up to 20ltrs.

 

Glenn

 

 

[Wilfred]

Have you tried doing a drain test with the fuel caps off, to eliminate any pressure changes due to blocked or insufficient venting.

 

 

[Wilfred]

just another quick one. At one time we had a similar problem in the Jab and the only thing i could find different was the angle that the fuel caps were put on at tjhe last refueling. The vent on the cap is at the rear of the cap and it can be tightened with the vent in any position. one would think that the direction of the holes in the vent to the airflow could possibley effect the tank venting. We make a prctice of allways putting the caps back on with the vent shaft to the rear of the aircraft.

 

 

[Guest Ken deVos]

turtle wrote: The vent on the cap is at the rear of the cap and it can be tightened with the vent in any position.

 

Now I'm confused!

 

On the two, fairly new factory built J160s, I'm sure that the fuel caps are keyed so that the vent holes on the upright tube faces forward into the airflow.

 

 

[Wilfred]

They are probably different caps as ours were changed when the header tank was fitted

 

 

[glenns]

Yes I can confirm that on the recent J160C's the fuel caps are keyed to prevent the vents facing backwards, I have checked and confirmed that.

 

Drain test is next on my list of things to try.

 

 

[Wilfred]

Have you spoken to someone at Jabiru about this.

 

You may find that it is not a problem and just the way they feed.

 

 

[glenns]

Yes, see first entry. I rang Jabiru as soon as the office was open and received the advise about fuel getting into the breather line of one of the tanks when they are filled completely to the top. This they said would tend to favour the other tank.

 

This seem's to improve things by not filling tanks completely but thier can still major differences between the 2 tanks.

 

glenns

 

 

[Wilfred]

it sounds like what happens when flying out of balance.

 

if it works fine on the ground this would more than likely be the problem. it only takes a short while out of balance for the fuel to transfer over to the other tank this could be whats happeniing rather than the one tank feeding. also if slightly out of balance it would not be difficult for the fuel to block the breather and restrict flow from that tank. i dont know about the 160 but on the 200 the fuel can transfer between tanks. this seems to happen even when parked on uneven ground and with close to full tanks will spill out the breather on the low side.

 

 

[glenns]

Maybe a combination as there are lots of different pilots flying the aircraft including students.

 

So the initial issue may have been caused by overfueling when we left Bundaberg and not being aware of the possible consequences of this. Then as the aircraft is being flown by students etc some out of balance flight might be causing the not so drastic differences. i.e. 5 to 20 ltrs.

 

One other piece of info which for some reason I didn't find relevant to bring up at the time (whoops) was the fact that the rudder and rudder pendals have required adjustment (new adjustable pedals were fitted a the last minute) and at one stage unless you kept pressure on the right rudder then you would be out of balance. I was obviously doing this but other pilots may not have been especially any students.

 

So I will monitor but I get the feeling that the mystery maybe solved.

 

Thanks All

 

 

 

[Guest Guest]

Just spoke to instructor with several hundred hours in J160's and he said that in their examples (3 x J160's) that the tanks always feed unevenly, even draining completely empty on one side on occasions. Luck of the draw I suspect.

 

 

[glenns]

Yo may just be right. I thought it was going ok but when I refuelled on the weekend there was still a 20ltr difference between the 2 tanks.

 

 

[theoy]

We found the small o ring in one of the fuel caps was damaged, after it was replaced both tanks would empty together. I think maybe the laminar airflow over the fuel cap caused a negative pressure holding the fuel flow back OR about the same time we adjusted the rudder / rudder pedals so not to apply rudder all the time. :;)4:

 

Cheers

 

Theo

 

 

[glenns]

Thanks Theo will have a check of the O rings but hadn't noticed any issues.

 

I refuelled on the weekend and they were pretty even so who knows. I also had some feed back of another aircraft leaving bundaberg and being ferried back to SA and they had exactly the same experience with one tank draining completely and the other still full.

 

Glenn

 

 

[Wilfred]

Since you first mentioned this topic I have been taking more notice and in our aircraft it seems more of a problem with certain pilots. This leads me to go more for the flying out of balance as the cause. The pilot that has the least noticble difference is a high hour senior instuctor who i would have to think would be more in tune with the aircraft.

 

PS I checked the O Rings and they are like new.

 

 

[glenns]

OK, I will try and keep an eye on that as well. Problem is I do not always fill up the aircraft to take note of the tanks but I suspect you may be right.