Dissymetric fuel consumption

[Gordon Boggs]

Hello to all

I'm member in a flying club in France and we have 3 CTLS LSA planes

On the latest one a 2019 model, we are experiencing a problem where the left tank is emptying itself before the right one, i.e. if we put 60 liters in each tank and fly for 2 hours we returen with  about 30 liters in the left tanks and 57 in the right.

We have checked fuel caps, thank vents and fuel lines; all ok

Anyone know about this?

thanks

Gordon

[andyb]

i  have the very same problem in my 2014 CTLSi.  My understanding is that it's caused by not applying correct rudder, but for me it happens when I have the ball centered, and the plane seems to be flying with the correct trim.  I've wondered wither my ball is calibrated correctly.

For the CTLSi, I think it's not an issue, as both tanks empty into the header tank.  Not sure how it impacts the other models.

It's disconcerting.

Andy

[GrassStripFlyBoy]

Hello Gordon,

Flying the airplane off coordinated rudder, and steep bank angles, are situations where fuel can transfer between the tanks.  On my SW this occurs through the main fuel line even if fuel is shut off, so know unlevel parking can create a similar result when parked on ground too.  Is your LS a carburetor type, or fuel injected?  I’m not intimate with what differs on that note, but those here with more insight will want to know that question.  I believe LS has a fuel transfer tube between tanks separate from fuel feed, that may increase the tendency of fuel transfer.

I would suggest clamping off a fuel line from tank on each side, one at a time, and inspecting the flow at engine, possibly just drain fuel at gascolator, to ensure there is no difference on the RH supply, and it is simply transfer between tanks.

[Gordon Boggs]

Hi,

Thanks for the replies

It's a carb type. We have flown it making sure ball was well centered. We might try clamping one of the fuel lines and see what happens.

P.S. what we find strange is we don't have the same problem with the other 2 CTLS that we have at the club. One is a 2013 model and the other is 2014. 

 

[ct9000]

I think that the fuel return line from the pressure regulator only goes to the left tank. 

[Roger Lee]

Hi Gordon,

This is very common in the FD aircraft and even in some certified aircraft. In the CT it is part flat fuel tank design andthe fact that your instrument panel and or instruments are not perectly set up. So when you think the ball is centered in the imstrument in actuallity it isn't. So what we all do for longer flights many times is fly 1/2 ball out towards the wing that drains faster. Remeber the fuel follows the ball. If you wanted to transfer fuel from the right side to the left then fly one complete ball out to the keft. The transfer isn't fast, but does work. Don't bother trying  to re-rig and square everything up. It's far easier to just fly 1/2 ball out to the fastest draing wing.

[FlyingMonkey]

What Roger said.  Also remember these airplanes are hand-made and no two are 100% the same.  It's possible the bottom of one tank has a slight tilt to it and is not 100% flat, which would also make this problem worse. 

When I fly short, hour hops I carry plenty of fuel and don't really worry about it.  For longer cross-country flights I just periodically check the sight tubes and balance per Roger's procedure if the levels become significantly out. 

Remember too, the CT will happily fly with an empty tank with no issues.  The way people come to grief is when one tank goes empty and the other gets low.  Then an uncoordinated turn away from the empty tank can cause the remaining fuel to run away from the pickup near the cockpit and interrupt fuel flow to the engine.  If you never run the fuel very low and/or balance your tanks when one gets way out of whack, you'll be fine. 

[Anticept]

Head pressure, which is dictated by the vertical column height of the fluid, and fluid flow restrictions, are what matters for considering which will drain faster. How you get that level difference doesn't matter. If the top of the fluid level in one tank sits slightly higher than the other tank, then the tank with the higher fluid level is going to drain faster until they equalize. If you got there by filling one tank more than the other, or are flying with one wing low, it's the same thing for fuel draining.

A tank with different geometry won't change that, not by itself anyways. It will drain until the fluid level is level with the other tank, and then they will drain equally...

Even if one tank were a 10 foot high, 1 inch round tube and the other were a 10 foot wide, 1 inch high tank, the tall one will drain until equalized, then drain equally in regards to height with the wide tank.

[Tip]

I had the same issue with a new LS back in 2008. The fuel line between the wing root and the A pillar was kinked. It was fixed by putting a 90 degree elbow in-line. Make sure that isn’t your problem.
Your Dynon is probably not level as Roger mentioned. You can verify that by zip tying a line level on the crossbar.

[Jim Meade]

FD says level is measured at the channel between the seats, so setting that to level and then verifying that the crossbar or other feature is level is probably a good idea.

[Tip]

I have put a 3’ or 4’ level across the wing roots and set the line level to match.

[Jim Meade]

A friend taught me to take a carpenters level and set it on the wing outboard of where the wing joins the fuselage and set a good digital level on it.  Should be about 1.7°.  Repeat for other wing.  Adjust tire pressure or shims under tires until the two dihedral values are equal.  That should have the fuel tanks set about as level as one could get.

Some also use a long hose and a water level.  More monkey business than than the digital level but cheaper.

[FlyingMonkey]

41 minutes ago, Jim Meade said:

A friend taught me to take a carpenters level and set it on the wing outboard of where the wing joins the fuselage and set a good digital level on it.  Should be about 1.7°.  Repeat for other wing.  Adjust tire pressure or shims under tires until the two dihedral values are equal.  That should have the fuel tanks set about as level as one could get.

Some also use a long hose and a water level.  More monkey business than than the digital level but cheaper.

That's an interesting method.  When you say outboard do you mean with the inside edge of the level up to the wing/fuse seam line, or somewhere else?  I could see the exact position where the level is placed making a difference.

[Jim Meade]

Where the wing root abuts the fuselage.  Find a "flat" spot on the wing and go from about that position outward.  Granted, some wings are very slightly wavy but a long enough level (4") seems to negate that problem.

[FlyingMonkey]

Thanks.