Ed Cesnalis Posted August 25, 2014 Author Report Share Posted August 25, 2014 There is a T above the fuel valve Link to comment Share on other sites More sharing options...
Anticept Posted August 25, 2014 Report Share Posted August 25, 2014 But there is a Y connection somewhere above the fuel valve, right? Doesn't that serve a similar purpose? The fuel Y is different from what I am talking about. In gravity feed systems where you can draw from multiple tanks at once, there is a separate pneumatic line which is supposed to run between tanks to keep differential pressure in balance. I don't have an SW, so I'll take Tom Baker's word for it. Here's an example of two fuel systems (not FD specific): Now, if you notice, the top system only has ONE fuel vent. This would, in theory, work, but as Cessna found out, it actually doesn't. See this article about it. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted August 25, 2014 Report Share Posted August 25, 2014 But that diagram is different form a CTSW...our fuel lines don't both go into the fuel valve, they T together and then run in a common line to the valve. My point is that doesn't the T (or Y, whatever) act as a de facto cross feed line? If it didn't, we would not be able to transfer fuel between tanks by flying uncoordinated. Link to comment Share on other sites More sharing options...
Anticept Posted August 25, 2014 Report Share Posted August 25, 2014 I meant those as an example of tank configuration vs low wing systems (edited for clarification). You don't need an air interconnect line if you can only select one tank. As in the case of SWs, there is no fuel selection, it's just a fuel "Y". Unfortunately, they didn't put an air interconnect line, so it's much easier to empty one tank vs another. If they did put in an interconnect, then for the most part, it would be installation or uncoordinated flight that is emptying one tank faster. Link to comment Share on other sites More sharing options...
FredG Posted August 25, 2014 Report Share Posted August 25, 2014 Anticept, it is only "much easier to empty one tank vs another" if the two vents have sufficiently unequal resistance to the flow of makeup air. True enough, a balance tube to equalize pressure in the space over the fuel in the tanks would solve that problem. Andy, yes, my CTsw has the fuel line configuration you described. Link to comment Share on other sites More sharing options...
Anticept Posted August 26, 2014 Report Share Posted August 26, 2014 FredG: That's a given. My statement was about gravity feed with multiple tanks being easier to empty one tank faster when it lacks an interconnect tube, vs one that has it. Link to comment Share on other sites More sharing options...
ctspain Posted June 24, 2015 Report Share Posted June 24, 2015 HI, I have been reading the forum for a long time but it is the 1st time I post. I am from Spain and I bought my 2007 CTSW about 1 year ago. I have the same problem than most you for differences on fuel ussage, I tried to fly uncoordinately and use to work but not always all that I need. I checked the fuel vents and are ok but as previous owner was a dissaster on plane mantainance, I am not 100% sure if the align is correct. I am nearly sure the short part of the skirt, goes forward, right? I tried to look for pictures of other ct's and also the manual but I could not find any. Thanks. Link to comment Share on other sites More sharing options...
Anticept Posted June 24, 2015 Report Share Posted June 24, 2015 Anticept, it is only "much easier to empty one tank vs another" if the two vents have sufficiently unequal resistance to the flow of makeup air. True enough, a balance tube to equalize pressure in the space over the fuel in the tanks would solve that problem. Andy, yes, my CTsw has the fuel line configuration you described. I just now noticed, you said your SW has it. That's interesting, the fuel system diagram that I recall reviewing did not indicate it. I could very well be wrong Link to comment Share on other sites More sharing options...
Jacques Posted June 24, 2015 Report Share Posted June 24, 2015 HI, I have been reading the forum for a long time but it is the 1st time I post. I am from Spain and I bought my 2007 CTSW about 1 year ago. I have the same problem than most you for differences on fuel ussage, I tried to fly uncoordinately and use to work but not always all that I need. I checked the fuel vents and are ok but as previous owner was a dissaster on plane mantainance, I am not 100% sure if the align is correct. I am nearly sure the short part of the skirt, goes forward, right? I tried to look for pictures of other ct's and also the manual but I could not find any. Thanks. Bienvenido en el forum CTSPAIN, yes , the short part goes forward. The CTSW maintenance manual shows a drawing on page 6-7 Link to comment Share on other sites More sharing options...
FredG Posted June 24, 2015 Report Share Posted June 24, 2015 "I just now noticed, you said your SW has it. That's interesting, the fuel system diagram that I recall reviewing did not indicate it. I could very well be wrong :)" Corey - I may not have been clear. My SW does not have a balance tube to equalize pressure over the fuel in the tanks. It has the conventional SW configuration, i.e., the tanks fuel feed lines are connected (a "Y" or "T" connection) before the fuel valve. Pressure over the tank is equalized to ambient by the fuel vent on the fuel cap. With this arrangement, the fuel flow from each tank is not under pilot control. Rather, fuel flow from each tank is a function of resistance of the fuel line from each tank to the union of lines (assuming clear vents). Fuel level in the tanks is a function of flight coordination (level wings) and, possibly, differential fuel flow (if the difference is substantial). Just my opinions. Link to comment Share on other sites More sharing options...
Anticept Posted June 24, 2015 Report Share Posted June 24, 2015 Hi Fred! It has been very well documented that even a small difference in pressure will noticeably affect drain rate of fuel tanks in gravity feed systems with both tanks open. In fact, it's a checklist item on cessna 172s for maintenance to ensure the vents are aligned and shielded by the strut properly, as even with a working crossover tube, it can still unevenly drain. What will happen is it pushes some of the fuel to the other tank, in addition to the relatively miniscule amount being drawn by the engine (fuel lines are required to be significantly oversized). It's actually a federal regulation, in fact, to have a crossover tube in standard airworthiness aircraft, in gravity feed systems, where both can feed at once. Speculation, but I bet people have died over it because one tank emptied more than the other, slipped the airplane, and unported the fuel. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 24, 2015 Report Share Posted June 24, 2015 With this arrangement, the fuel flow from each tank is not under pilot control. Rather, fuel flow from each tank is a function of resistance of the fuel line from each tank to the union of lines (assuming clear vents). Fuel level in the tanks is a function of flight coordination (level wings) and, possibly, differential fuel flow (if the difference is substantial). Just my opinions. I think until the latest LS/LSi models, FD chose to trust fuel management to physics rather than the pilot. A single fuel lever controls flow, and tank drain is handled by pressure vent pressure and coordination. That method has an advantage, in that it is pretty darn hard to starve a CT of fuel if everything is working -- about the only way is to run one tank dry and let the other one get insanely low (2-3 gallons) and then go into an uncoordinated turn that drains the available fuel away from the pickup. Unlikely, but not impossible...this is exactly the scenario in the Daniel Barnath accident. The disadvantage is clear to all of us -- the pilot is not in direct control of fuel management between tanks, and flying uncoordinated (aka inefficiently) is the only option for pilot control. As human beings we *like* being in control of things, and being able to flip a LEFT/RIGHT/BOTH lever appeals to our sense of control. FD seems to have acknowledged this with their latest fuel system design. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 24, 2015 Report Share Posted June 24, 2015 On another note...if we have one tank draining obviously faster than the other (in my case it's the left tank draining faster), is there anything we can do or adjust other than coordination to improve the situation? For example, if I turn the left tank vent so that it's less directly pointed forward (say 30° or 45° away from directly forward) is it possible this the will provide higher vent pressure on the right side and compensate for the left preferential fuel drain? Just spit-balling here. Link to comment Share on other sites More sharing options...
Roger Lee Posted June 24, 2015 Report Share Posted June 24, 2015 Back in early Feb. 2007 when I first saw the uneven tank drain on my SW I thought it may be the vents. Negative verses positive pressure. I took the FD vent and flew several long legs with the vent turned at 90 degree angles. None made a difference. Then I made a set of vents that would positive pressure the system to a tiny degree. These are 6" tall and have a 90 degree sweep forward about 4". You can see these types on planes over the many years. I tried these with the holes facing forward and then facing rearward. These made no difference. These new vents did however keep all fuel from splashing out onto the wing when fuel levels were high or when the wing had a high bank angle. On the SW I could find no vent angle that made a difference. The only thing I found was trim. I then experimented with trim. I put a piece of string on the front windshield like many helicopters have for trim indication. (my copter did) I found the string was straight when my ball was 1/2 out to the left and my wings drained evenly. If I leave the ball centered my left wing to this day drains 3 times faster than my right. I still have my swept forward vents and have never spilled another drop of fuel on the wing. FD a long time ago published an article about the uneven drain and one empty tank. They said it was the flat tank design in the article which makes it sensitive to trim. Other aircraft on the market have the same issue. I believe that some tanks may be affected by the vent, but I couldn't find any indication of that when I did my research in 2007 on the SW. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 24, 2015 Report Share Posted June 24, 2015 I put a piece of string on the front windshield like many helicopters have for trim indication. (my copter did) I found the string was straight when my ball was 1/2 out to the left and my wings drained evenly. If I leave the ball centered my left wing to this day drains 3 times faster than my right. I still have my swept forward vents and have never spilled another drop of fuel on the wing. It sounds like maybe your ball is off, and a half ball out to the left might be the "true" coordinated position...? Link to comment Share on other sites More sharing options...
Roger Lee Posted June 24, 2015 Report Share Posted June 24, 2015 Hi Andy, It is. I don't worry much about it. I just trim for that 1/2 ball out. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted June 24, 2015 Author Report Share Posted June 24, 2015 I now have mostly even drain. #1 I moved my binnacle until a centered ball equaled coordinated flight. I confirmed by using rudder pedals to move levels in both sight tubes, After finding nose left and nose right unbalanced levels I could then recognized nose into the wind levels and then moved my binnacle till the ball was centered. #2 in flight I keep the now correct ball perfectly centered, this means I move my rudder trim for initial climb, cruise climb, cruise, descent and final approach. My plane transfers fuel in the hangar to regain balance, this helps a lot too. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted June 24, 2015 Author Report Share Posted June 24, 2015 Nose into the wind has no bearing on this. I meant nose into the relative wind, or coordinated flight. Thanks for pointing that out. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 24, 2015 Report Share Posted June 24, 2015 #1 I moved my binnacle until a centered ball equaled coordinated flight. Wouldn't it be easier to adjust/shim your EFIS or slip/skid ball to correct this, than moving the whole binnacle around? Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted June 24, 2015 Author Report Share Posted June 24, 2015 Wouldn't it be easier to adjust/shim your EFIS or slip/skid ball to correct this, than moving the whole binnacle around? Is yours fastened or just sitting on the cabin floor? I moved mine to center the ball in flight, it isn't heavy. Link to comment Share on other sites More sharing options...
FlyingMonkey Posted June 24, 2015 Report Share Posted June 24, 2015 Is yours fastened or just sitting on the cabin floor? I moved mine to center the ball in flight, it isn't heavy. Honestly I don't know, lol! I guess I should look. Link to comment Share on other sites More sharing options...
Ian Posted June 24, 2015 Report Share Posted June 24, 2015 Just let some air out of one tire. Or get a heavy passenger? Link to comment Share on other sites More sharing options...
gbigs Posted June 24, 2015 Report Share Posted June 24, 2015 I use the autopilot as much as possible. It keeps the ball centered and the tanks drain about as evenly as needed. If one tank is a gallon lower, I just add it back....and make sure total fuel is nowhere near reserve levels. Link to comment Share on other sites More sharing options...
Doug G. Posted June 24, 2015 Report Share Posted June 24, 2015 The autopilot will not correct for uneven flow from the tanks. Link to comment Share on other sites More sharing options...
FastEddieB Posted June 24, 2015 Report Share Posted June 24, 2015 The autopilot will not correct for uneven flow from the tanks. Nor center the ball. Still. Link to comment Share on other sites More sharing options...
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