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#31
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The flight school where I rent from has all late-model Cessnas, and there
is no doubt that they do not drain evenly. I've heard several "urban-legend" style explanations for the uneven drainage issue, and I don't claim to know which one is accurate. However, they don't generally seem to drain unevenly enough to have any significant impact on weight and balance... Now I actually did all my PPL training in a low-wing Tampico that did not have a "both" option. And a year or so later, when I started flying Cessnas, I saw the "both" selector as a major convenience, and I took advantage of it. But a while ago, I flew in a friend's Bonanza, a low- winger, and we were talking about fuel management. And he reminded me of an EXCELLENT reason to switch tanks during flight even if there is a Both selector. I think someone on this thread mentioned briefly... Basically, let's say your flying West, into a headwind. It's a little stronger than expected, and so you're all ****ed off, and gunning the engine up a bit to try to make up some of the ground speed. Maybe you're at a different altitude than planned, and for whatever reason you're not leaned out as well as you could be. Based on your "optimum" calculations, you think you have 5 hours of fuel. But between the headwind, and not flying optimally as planned, you use 10% more fuel than expected, and you are going to use 10% more time than expected... Bottom line, you now need a fuel stop, but you don't know it... If your fuel selector is on Both, you get one shot. Your right tank may run dry first, but you won't have any idea until your completely dry in both tanks. You get to glide to the nearest golf course and call for help. If you are switching tanks every 1/2 hour, and your right tank runs dry, it's like an alarm. Your engine fails, and you do your ABC checklist, switch tanks, and get your power back. You can take a moment to calm down, figure out what happened, and find the nearest airport with services and fuel up. You get a "second chance". Of course, it's not guaranteed - you might only have a drop of fuel in the other tank. But flying on both guarantees you to be a glider on empty... Ever since that conversation, I fly "low-wing" style once airborne, and switch tanks to both on taxi, takeoff, and landing only... Peter R. wrote in : Koopas Ly ) wrote: Is the procedure of only using one tank only applicable to certain C172 year/models? I've flown a variety of 172's from late 60's models to brand new 2002's, and have always used "both" tanks during flight...just wondering... Switching tanks is not in the '02 172 CRUISE checklist, but it is something that I do to maintain an even balance across both tanks. This is because the difference (at least in the '02 172SP I fly) between the two after a long flight can be substantial. |
#32
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Rules To Fly By And Not Run Out Of Fuel:
I routinely run the outboards dry on long cross countries (know your airplane on this issue).. This cross checks my fuel burn against the clock since I know exactly how much was in the tank when I selected it... Running it dry removes fuel gauge error from the equation... I'm usually within five minutes... I fly by the clock, not the fuel gauge... If the gauge gets too far from what the clock says it should be (either full or empty), we put down and refuel to see what the heck is going on... this only happened once - a sticky gauge Lastly, I never get into the last hour of fuel for any reason... 60 minutes of fuel left on the clock is "bingo time" and it is put it on the ground.. I have landed and refueled just twenty minutes from my destination because I hit bingo before I got there... One of the locals back at the home field thought I was nuts... But then, he has had an engine run out of fuel while taxing in from the runway one time, so what do you think I feel about his opinion... Denny - an old pilot... "Dave Butler" wrote in message ... Dan Thomas wrote: Lots of old pilots didn't trust fuel gauges, which is still a wise attitude. |
#33
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"Judah" wrote in message ... I've heard several "urban-legend" style explanations for the uneven drainage issue, and I don't claim to know which one is accurate. However, they don't generally seem to drain unevenly enough to have any significant impact on weight and balance... The crossfeed issue on the 172 (why the left tank drains faster) is not an urban legend. If you are a Cessna Pilot's Association member they will send you a brief on what it is and how to fix it by tweaking the tank vent. |
#34
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I have an oblique answer to this question. I'm building an airplane that seats four and is a high wing monoplane. The fuel tanks are in the wing root, just like most high wing Cessnas. The plans show that the fuel outlets should be placed near the wingroot but in different locations fore and aft from each other. One tank has an outlet near the wingroot by the trailing edge, the other tank has the outlet near the wingroot but towards the leading edge. Since it's a homebuilt, you have some flexibility in how you do things. Why not put in two ports for each tank - one fore one aft. That way you can slip and nose down and get fuel no matter which tank is selected? Try talking with the designer of the plane about this - it might be worth considering. Jose -- (for Email, make the obvious changes in my address) |
#36
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Judah wrote: If you are switching tanks every 1/2 hour, and your right tank runs dry, it's like an alarm. Right. You switched tanks 3 minutes ago. Hope you're right over an airport. George Patterson Some people think they hear a call to the priesthood when what they really hear is a tiny voice whispering "It's indoor work with no heavy lifting". |
#37
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Dan
From an 'old' pilot. We used to fly 30 minutes on a tank and then switch to other tank (back and forth). This manual switching kept the fuel inbalance to a max of 30 minutes fuel which was very manageable. Trying to feed from both tanks for any period of time always caused a inbalance. Also knew fuel burn and could compare fuel used and remaining, to fuel gauge. For landing, fuel was switched to fullest tank (check list item). In 'heavy iron' and max range, would run tank dry. In GA, never planned that long a duration so never had a engine stoppage caused by empty tank. Safety is as safety does. Big John On 4 Dec 2003 17:19:07 -0800, (Dan Thomas) wrote: "Tony Cox" wrote in message thlink.net... "Koopas Ly" wrote in message om... The only time that fuel is set to one particular tank is on the ground. I've never used fuel from only one tank in flight. Why would someone do that? Some models of 172 *require* you to select a single tank above 5000', due (supposedly) to vapor lock problems. Check your POH. Lots of old pilots didn't trust fuel gauges, which is still a wise attitude. They'd sometimes fly on one tank until it ran dry and the engine quit, then switch to the other and know exactly how much they had left and how much they'd burned. This doesn't work well if the tanks are very far off the airplane's centreline, as the imbalance can require increases aileron input, causing more drag and tiring the pilot. It can also panic passengers and create unpleasant cabin odors and extra janitorial work after the flight. Dan |
#38
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I don't have a "both" on my Mooney and I DO NOT miss it. "Both" just
means that if you ever run out of gas, you're really out of gas. The Cessna 140 I used to fly would drain all the gas from the left before touching the gas in the right (its not the same as the C-150, there is no interconnecting hose in the 140). -Robert (Koopas Ly) wrote in message . com... Good day all, With regards to fuel tanks in a C172, why does the takeoff and landing checklists both call for the fuel selector handle to be in the "both tanks" position? The only time that fuel is set to one particular tank is on the ground. I've never used fuel from only one tank in flight. Why would someone do that? Also, why is the fuel selector set to one tank during refueling? Is it to minimize crossfeeding? Thanks, Alex |
#39
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#40
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An an example, the Swift (low wing) is just "both". There are a lot of
examples of low wing planes with "both". In my Mooney, if I ever run out of gas, I'll just switch tanks. Thank God there isn't a "both"! There is a significant difference here between low wing, and high wing designs. If you have a low wing aircraft, and have a 'both' selector, if one goes empty, air is sucked into the system by the fuel pump, and fuel delivery stops. Hence low wing aircraft with a 'both' position, have to have a central 'sump' from which the fuel is drawn. On high wing aircraft, where the fuel is delivered by gravity, if one tank goes dry in the both position, fuel will still feed from the other. Hence 'both', is relatively unusual on low wing designs, but more common on high wing planes. This is why your RV6, doesn't have a 'both'. Best Wishes |
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