What is your experience with drawdown from J's wet wings?

[Captain]

I am hoping for feedback from any other J owners or users with wet wings, and apologise if this has been discussed before but I have done a search and can't find anything.

 

 

 

When I built my 230 I went to the trouble of trying to route the fuel supply to the head tank so that it would draw evenly from both wings ..... and ran fuel lines separately from each wing to a T-piece just before the head tank which is located behind the sound curtain.

 

 

 

What I am experiencing is that with both tanks chockers @ take-off, the sight gauge appears to show that my aircraft draws fuel from the starboard wing on climb-out and for the first hour or so, and then the port side wing sight glass starts to draw down.

 

 

 

For the last few flights I have super concentrated on keeping the ball right in the guts for all stages of the initial couple of hours and the result is the same.

 

 

 

Do you experience anything similar or if not, what do you see with yours?

 

 

 

And if you get the same, why do you reckon that happens and does anybody have a proven solution to even up the draw-down thru all stages of the flight?

 

 

 

Regards Geoff

 

 

[BigPete]

G'day Geoff,

 

my factory built 160 does exactly the same thing. I start of with say 50 litres (on the sight gauges) and one side always drains more (can't rember which side ) and it might finish up as 45 on one side and 40 on the other.

 

By the time I get down to 10/15 litres aside it has evened out and I nearly always add the same amount of fuel each tank when I fill up again.

 

There has never been a "fill up" difference of more than 5 litres.

 

regards

 

:big_grin:

 

 

[facthunter]

Common system.

 

As a general rule, with a common system, whether gravity or fuel pumps . very small variations in balance/pressure will cause uneven fuel usage. The only way to stop this happening, is to SELECT a tank in isolation, to even the levels or have an individual fuel pump and a non-return valve fitted to each tank. In the interests of simplicity and therefore an improvement in safety and cost this is rarely done. When the tanks are full then, for a while, loss of fuel by venting is always possible, and the uneven levels that you have observed are not uncommon. I tend to think that wing down or a bit of ball out of centre is often the cause, though some systems have a return line to one tank that may have a tendency to cause imbalance. nev

 

 

[Yenn]

I have a theory about wing tanks. Two problems.

 

1. The vents can experience different pressures, which could cause uneven flow rates.

 

2. The port tank should vent out beyond the stbd. tank and the stbd. tank vent out past the port tank, that will stop the siphoning of fuel when parked on a slope and also any venting problems.

 

 

[Guest ROM]

We have the same uneven fuel useage in our club's J230.

 

I think Yenn is on the right track with the uneven Vent pressures.

 

I have suspected something like this since soon after we got our J230 and experienced the uneven useage of fuel from the wing tanks.

 

As pilots you should all be well aware of how the effects of flow and turbulent flow around an object affect the pressures on that object which is why we use streamlining on struts, fairings and wheel spats.

 

Even slight variations between the two wing profiles both upstream and downstream of the vertical fuel tank vent tubes would make a significant difference to the pressures around the vents and therefore between the pressures in the tanks.

 

As well we have very small manufacturing differences between vent tubes which would also change pressures in the wing tanks.

 

A crossover vent tube between tanks would probably have to be at least a 12 or 15mm ID to handle the differential airflow between tanks.

 

With both tanks full even this crossover pipe would be filled with fuel and the problem would still be there regardless.

 

If the uneven flow and useage worries you, maybe you could put in a sealed cap on each tank and install a static type tube high up on the fin with a vent line to each tank starting at the common static tube.

 

Some high performance gliders use this idea to maintain equal pressure in their water ballast wing tanks and equal release when dumping small amounts of ballast water.

 

Don't use the ASI static as a common static as any fuel backflowing up the lines would make your ASI adopt a very non co-operative attitude probably just when it's work experience would be sorely needed.

 

A possible alternative idea and I haven't seen it used yet, is to place a small streamlined fairing on the round lower part of each vertical vent tube and lengthen or shorten the chord and / or the length of this fairing until you get a steady even useage from both tanks.

 

Try one vent first and see if it makes a significant difference. If it does then you are on the way. If not then that idea is a dead end.

 

Don't know if that would work but it would be very simple to mould something around the vent tubes to experiment.

 

 

[brilin_air]

Hi Geoff,

 

Our 160 seems to use fuel from the port tank first and then the starboard, at first I was a bit concerned but I did a few close circuits when I had about 10 litres in the port tank and about 50 litres in the starboard tank as a test, when I returned I still had about 10 litres in the port tank and the starboard tank had reduced its level. I have run my fuel lines very similar to how you have done yours and I can't see any viable reason for using more fuel from one side more than the other, all I do is make sure my total fuel for my trip is enough and just keep an eye on both levels, and as long as I can see fuel in both tanks I do not worry about it too much. I have also parked my plane on uneven ground, and by doing this I can move fuel from one tank to the other just by gravity, it works both ways so I am confident that the way that the fuel feeds to the header tank is ok.

 

All the best

 

Brian

 

 

[Guest brentc]

Mine has a SINGLE vent and it still feeds unevenly so you're damned if you do and damned if you don't as they say.

 

 

[jetjr]

Fuel pump turned on for the second half helps it to even out.

 

I believe new Jabs cant turn one side off? taps on the pillar were deleted.

 

Mine has visual glass guages and they look terribly uneven but when you turn a tank off it rises to same level on both sides.

 

Ive given up worrying about it , sometimes when refilling theres a difference between sides but only up to 10L, probably because I wasnt level when flying.

 

I hope to never being down to my last 10L and not over a strip.

 

JR

 

 

[Captain]

Mine has a SINGLE vent and it still feeds unevenly so you're damned if you do and damned if you don't as they say.

Thanks for the feedback everyone, & G'day Brent.

 

Which talk feeds 1st after takeoff with your single vent?

 

 

[Guest brentc]

G'day captian, depends on which way the wind blows! (metaphorically speaking)

 

There seems to be no definite order. It's hard to work out as my plane sits on a lean due to undercarriage and therefore the left one always has more to start with. If it was a big problem for me, I still have the taps if I want to use them.

 

 

[bushpilot]

My factory J160 tanks do drain unevenly, but I find if I deliberately fly with the ball a poofteenth off centre (which way depends on the tank that is lowest), then they even up over about 10 minutes.. I'm sure it's not necessary, but it feels better to have them roughly even...

 

 

[Guest J430]

You all have a G296 or higher don't you:big_grin:

 

Use the tank Timer function. Those who have flown many GA types Pipers and Beech etc will have experience on Left or Right fuel selectors and fuel management. Do that!

 

I can not solve it any other way. As Brent says....Damned either way! And its not just Jabs and other rec A/C.

 

J

 

 

[Bruce Robbins]

Last time I took some friends for a local sightseeing trip in a rented Cessna 182, I got a severe fright after 45 minutes or so. Checked the fuel guages for the first time since take-off, after having been questioned/pestered non stop about the fabulous sights passing by below.

 

.............Whoah, whats happened to all the fuel out of the left tank!! Needle seems to be bouncing on empty!!

 

........Quick change from "Both" to "Right", listen very intently to the engine noise for the next five minutes, and then enjoy the afterglow of adrenaline induced thump, thump, thump noises in the chest cavity slowly subsiding.

 

For a bit of light reading on drawing fuel from high wing wing tanks (no I'm not stuttering) try this ........

 

http://www.moonflight.org/Documents/Fflow.pdf

 

Cheers,

 

Bruce

 

 

[Captain]

That is a cracker of an article Bruce. Thanks for the link.

 

It looks like uneven fuel flow will result from sitting more on one cheek, or if your aviation-smile is not dead centre.

 

 

[ianboag]

Great forum. All these things about the J2xx that I thought were just me - hard starting - running out of forward trim - uneven tank drain.

 

My J200 is an old one and came without the header tank mod. If I tried to run on just one tank I always got the dreaded choke-cough-splutter-sweat. Now I've done the HT mod - tanks still drain at different rates. If it looks too extreme I turn the tap off on the lower tank for a while. So long at I can see fuel in the header tank vent pipe (runs up next to me) I know there are no problems.

 

IB