Cessna style fuel system

Do the SC's with cessna style fuel systems feed exclusively out of the specific tank chosen, or do they crossfeed when on left or right only?

I've recently had the opportunity to put long hours in a cessna 180 and wanted to accurately judge my fuel in each tank. So I would use from both till I got to a quarter hour (so my feeble mind could keep track easily), then 1 hr left tank, two hours right tank, then 1 hour on left tank and go till it ran out or I arrived at a fueling stop. figuring then I could judge how much fuel I had remaining in the other tank like I do the Super Cub. Every thing worked perfectly the first morning. But in the afternoon, I switched sides. Both for a short period, then right 1 hour, left 1 hr and 45 minutes and my engine quit !!!! Now I had to sweat out the next 45 minutes on the right tank till I got to a refueling point, thinking I must be loosing gas or the engine suddenly started burning excessive amounts of fuel. Nope still took 12 GPA. (22" and 2300 rpm) So now I just plan for 4 hrs flight and be within half hour of refueling point. I still don't know how much fuel I can really get out of each tank.
Now I got to thinking if this is how the SC with the Cessna fuel system is, it must suck when you want to get close to all you can out of a tankload.
What are any of you that have the cessna systems experiencing.

They feed from the tank selected. I ran one out of gas over the airport just to see what I had left. A few quarts each tank was all. I could get it to run momentarily by rocking the wings.

My 12 has a L/R/Both fuel selector, but there is no crosstube between the tanks. It can't crossfeed. My C-180 has only crossfed on the ground. Park on uneven ground and the fuel moves downhill. It's never done it in flight that I was aware of.
SB

The Cessna style fuel system works great. It feeds from the tank selected. It does crossfeed when in the OFF and Both positions. It crossfeeds through the selector valve. When parked on unlevel ground, select either the rt. or lt. tank and it won't grossfeed. I install this system in all the PA18's and 12's that I build.

Stewartb,

If you have a right/left/both fuel selector, the two tanks ARE connected--at the fuel selector.

Like the 180, if parked on an incline, your 12 will crossfeed, though maybe not as much, or as fast since the tanks are smaller, and closer together.

Don't fool yourself that the tanks aren't connected, though. They both attach to that selector.

The difference is that most Cessnas have a cross-tube between tanks at the top of the tanks.

MTV

Mike,
Read the initial question. Will it crossfeed when either R or L is selected?The Cessna will crossfeed through the top tube no matter where the selector is, if the fuel level is high enough and slope is great enough. My 12 will not.

In flight I've never noticed any crossfeeding in the Cessna, but I generally try to keep a balance between tanks. I use the both position because I don't want to run out of gas, ever. If I leave with adequate fuel and the selector on both, I don't really care which tank it's running on at a particular moment. I do rock the wings when I'm getting low just to make sure the needles will bounce a little. If I ever land with less than an hour's fuel in the tanks, I've screwed-up. That's my personal rule.
SB

Stewart,

Yep, I agree, though it's got to be a pretty steep slope for a Cessna to port fuel through the top tube, but can be done, I reckon.

With the advent of really good fuel flow computers, certified for virtually any airplane, though, I really can't imagine why everyone doesn't have one.

It's not there to help you stretch your fuel, it's just there to make you more comfortable with what you're doing.

When I switched mine over to L/R/Both I put a cross feed at the top of the fuel gauges (very near the top of the tank). If one tank is topped off it will cross feed until the level of the full tank falls below the top of the gauge.

Aren't fuel flow computers just calculations based on what you programmed in??
36 hrs of flying with each flight between 3.6 and 4.2 hrs @ 22" and 2300 rpm my fuel flow ranged between 11.9 and 12.2 GPA.
Today I decided to bump it up to 23" and 2400 RPM to see what kind of fuel flow I had at that setting. after 3.8 hrs, my guages were bouncing on empty and I had no idea what I had left. wound up using 13.2 gpa. Would the fuel flow computer adjust for that different setting or would I still have to manually set it ?

Fuel flow computers use a transducer that measures the actual fuel flow into the carb. You have to tell it what you put in, it'll tell you exactly what is used.

I still like to land with extra. If you ever get the chance to orbit around waiting for clearance to enter controlled airspace for a special, the extra fuel is nice to have. Especially since the last couple of minutes into Lake Hood are over the water.
SB

Pardon my ignorance, but I have never understood the advantage of the Cessna-type fuel system. Doesn't this reduce your useable by a couple of gallons? I think knowing exactly how much fuel you have in which tank is a lot more reliable method of fuel management. Am I overlooking something? :roll:

Ron, The ones I've done wern't done as a fuel management improvement but a safety improvement. Some people don't like having the header tank full of gas in front of them.

As Stewart noted, the fuel flow computers use a transducer in the fuel line to determine precisely how much fuel is being transferred to the engine.

It takes some calibration to start with, and you have to accurately note how much fuel you put in the tanks, but that's not too tough.

They are wonderful devices, and as I noted, I don't use them to extend my range, but rather to know precisely where I'm at in fuel useage. This can be important, and relevant early in a flight, as well as at the end. For example, if I'm doing a cross country flight, I get airborne, the GPS tells me my progress over the ground, which isn't as fast as I'd hoped. Now I look at my fuel computer, which tells me precisely what fuel I'm burning. I can play with the power settings, and sometimes, this gives me the confidence to decide to press on. On the other hand, occasionally, it tells me early on that I'm going to need gas. The computer tells you your current flow, time to dry tanks at present flow, amount of fuel remaining, amount of fuel used, and a bunch of other, less important stuff.

Has anyone here ever noted that different airports have different prices for gas? Will one of these things pay for itself over time?

Even if you don't push fuel range, these things can save you heartburn by letting you know up front that you will need fuel, and give you time to plan for it.

MTV

Has anyone here ever noted that different airports have different prices for gas? Will one of these things pay for itself over time?

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I always use www.airnav.com



Tim

Ruidoso Ron said:

Pardon my ignorance, but I have never understood the advantage of the Cessna-type fuel system. Doesn't this reduce your useable by a couple of gallons? I think knowing exactly how much fuel you have in which tank is a lot more reliable method of fuel management. Am I overlooking something? :roll:

Click to expand...

A little late to the party...been busy. You don't have to pardon any ignorance Ron. The only advantage of the Cessna style fuel system is to those not smart enough to handle a left-right-off gravity feed system in a single engine airplane. It does cross feed, it does have less useable fuel, and anyone who really thinks it reduces fire hazard is just kidding themselves...period...

Put in HD headers, a Univair valve, and most importantly, learn how your system works, manage it properly, and you will have the safest fuel system flying.

Mark,


Thank You! You are right on, in my book.

MTV

The way you choose to manage your fuel system is of course your choice. The advantage to the Cessna type system is less management. You don't have to worry about switching tanks if you don't want to. The system crossfeeds only in the OFF and Both positions. If you don't want it to crossfeed, then choose either left or right position. The unuseable fuel has nothing to do with the type of valve you use. It's where the fuel pickups are located in the tank. Part of the mod includes fuel pikups in the front of the tanks also, thereby giving you fuel delivery no matter what attitude you're in. With this setup you wind up with a quart or two of unuseable fuel. I've installed this system in every cub I've built and flown with it for years. I've run different tanks dry and checked the amount of fuel left after I landed and it's the same every time. Every customer that I've installed this system in likes it. So now that you have more facts...make your choice.

Seems to me, if I remember correctly, the second most common way to crash a plane is to run it out of gas(behind VFR into IFR). Given that a lot of smart folks have made this mistake it seems to me that keeping things simple would help eliminate this pitfall. Two tanks with a selector on both pretty much qualifies as a "no-brainier". Know what you start with, know what your burn is, and then be very conservative. DO NOT TRUST FUEL GAUGES.
If you are routinely flying one tank til dry then going down to less than 1/2 hour fuel in the other you are dancing at the edge of the cliff and you will eventually fall off. Stay away from the cliff. You might be a great dancer but we are all human and we all make mistakes. Leave yourself a little room for error.

Just something to consider.

Bill

Bill Rusk said:

Seems to me, if I remember correctly, the second most common way to crash a plane is to run it out of gas(behind VFR into IFR). Given that a lot of smart folks have made this mistake it seems to me that keeping things simple would help eliminate this pitfall. Two tanks with a selector on both pretty much qualifies as a "no-brainier". Know what you start with, know what your burn is, and then be very conservative. DO NOT TRUST FUEL GAUGES.
If you are routinely flying one tank til dry then going down to less than 1/2 hour fuel in the other you are dancing at the edge of the cliff and you will eventually fall off. Stay away from the cliff. You might be a great dancer but we are all human and we all make mistakes. Leave yourself a little room for error.

Just something to consider.



Bill

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Oh if only life were that easy.

Let me qualify my statement about running a tank dry. I did that in a test flight over my airport just to check what the unuseable fuel was. I'm not fond of running a tank dry on an actual mission, that's why I chose the BOTH system.

When you buy the STC to remove the header tanks what parts do you get? How many hours to install?

I just bought the paperwork and drawings, not the kit. took about 16 hrs to install with all new fuel lines.

How much was that?

I think it was about 200 for the paper and drawings

So if shop rate is 60.00 I would be looking at 960.00 for labor, 200.00 for a new vavle and 200.00 for stc = $1360.00?

Or buy HD header tanks for 275.00 and a new valve for 200.00 plus 4 hours labor =$715.00?

Does this sound about right

looks pretty close, valve can be modified instead of new needed, 10 minute change.

Both system

The comments about less usable fuel with the "Both" system are incorrect. If you are counting the quart of fuel in each header tank on the stock system, then I guess you are technically right, but I wouldn't want to get down to cutting it that close. The tanks are the same in both systems. The difference is the headerless (Cessna, Headerless or "Both" all the same) system is feeding to the fuel selector valve with four 3/8" fuel lines, one in each corner of the tank. The stock system you are feeding the valve with two 3/8" lines and one 1/4" line, so which one is going to get more gas out of the tanks? I would say it is the one with a 3/8" port at each corner of the tank.

Picture this in your mind. The shunt (center of the valve the handle is mounted to) in a STOCK fuel selector is drilled out in an "L" shape. The fuel selector valve body has three ports, left tank, right tank, and engine. The fuel flows from the tank selected (left or right), into the valve body and through, lets say, the leg of the "L", makes a 90 degree turn inside the shunt then flows on to the engine through the foot of the "L". So depending on the position (Left, Right, Off, Off) the fuel coming out of the valve only comes from one direction, left or right tank. No magic here.

In the "Both" system, a 3/8" (actually it is 1/2" with a finger strainer that reduces it to 3/8") port is welded into the front of the right hand tank (it only has a rear 3/8" port with the stock system). The front fitting in the left had tank is increases from 1/4" feed to 3/8" as well. The tanks feed from both front and rear (ports) fuel lines into a "T" fitting that is located close to the fuel selector, then with a single line going from the "T" to the stock location on the fuel selector. The fuel selector "shunt" is then modified from the "L" configuration to a "T" configuration by drilling through the shunt.

Now when the valve is turned to "Both", it will feed from the left and right tank at the same time (think of the top cross bar of the "T" as left and right tank and the leg as going to the engine, the valve is turned on its side but you get the idea). With the selector in the in the right or left position the "T" is on its side and you are feeding from only one tank with no cross over. In the off position the engine port is cut off but you have cross over between the tanks.

Either system has it's merits. I wouldn't call someone an idiot if they prefer one system or the other. I had one of each a couple of years ago but now have both of my planes set up without header tanks ("Both" system) and like it that way. All of Cub Crafters planes have the "Both" set up.

Take care. Crash

Crash, with two ports in each tank, won't a boost pump suck in air when one of the ports is uncovered?

Always felt extremely uncomfortable with a header full of fuel over my lap. With all due respect for those who think that fire risks are the same as for wing tanks, I sorely disagree: I'd rather have a post-crash fire (or any fire, actually...!) starting somewhere else than right in my face.

mvivion said:

Stewart,


With the advent of really good fuel flow computers, certified for virtually any airplane, though, I really can't imagine why everyone doesn't have one.

It's not there to help you stretch your fuel, it's just there to make you more comfortable with what you're doing.

Click to expand...

Couldn't agree with you more. Not to mention engine diagnostics.

All these are valid points. Another one worth pondering is isolating the two sides for T/O. Though feed from two tanks buys more fuel feed insurance, my preference is, design permitting, to T/O on one tank (the side I landed on, and taxied out on) even when selection to "both" is available." There's still a lot of bad fuel out there (water, kerosene mix, urine, whatnot), especially up in the Arctic (Just watch some of those yahoos drag the nozzle in the snow when they rewind the hose).

When I pick up fuel, I fill the empty tank first. Most contaminants are in the nozzle, and on the bottom of storage tanks, bladders and bowsers, so they will most likely end up in the first few gallons.

Two small details--and probably personal obsessions-- (yes, a healthy dose of pathalogical paranoia is part of the pilot's to survival kit), but they could mean the difference between landing back at the field with the engine coughing or crashing at the end of the runway.

Live and learn.