Why is managing fuel so complicated?

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VictorValencia

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VictorValencia
I'm a sport pilot and all my time is in a Skycatcher so I've never had to deal with
managing/balancing fuel between tanks. The C162 gives you "on" or "off". That's
it. No "Left", "Right" etc. Pretty simple. I like that.

So I watch this video:
and the gist of the story is he had a ferry tank with a pump and did not
configure his fuel system correctly prior to taking off from a sandbar and the
engine died before making it to the next sandbar. He was not hurt fortunately
and the only damage to the plane was the spinner since the water was only a
foot or two deep. I have also seen stories of people forgetting to switch tanks.

Here's my question. I understand why you can end up with more fuel in one tank
than another but why hasn't this problem been solved so the pilot does not have
to manually intervene to manage fuel tank levels? For example if you have a tube between
the two tanks won't they always end up at the same level (for the most part). I understand
if you're in a long turn that the fuel can flow into the tank of the "lower" wing but if
the tube is small enough not much will pass through and, over time, the tanks will remain
fairly even once you level out.

I must be missing something here :)
 
You are indeed, bigly. Trainers usually have tanks with really simple fuel setups. My Cessna 150 has a "both" setting to get fuel from the wing tanks, the Cherokee had a "Left/off/Right" switch. My Mooney has one of those, though it's located at my feet and half impossible to use. However, many aircraft have auxiliary tanks, and lots sport tip tanks. These are more complex and take more attention to manage properly.
 
But if you just had 2 wing tanks shouldn't it be simpler? In the C150 I assume there's a left, right, both and off setting. Why not just "both" and "off"? You said the Cherokee has left/off/right.
That seems overly complicated and adds more pilot workload and the possibility of having the engine die while still having plenty of fuel.

I can definitely understand the required complexity if you have more than 2 tanks.
 
Just about everyone drives a car that has only one fuel tank and never had to switch tanks before flying airplanes. I used to have a pickup that had 3 fuel tanks holding a total of 84 gallons. Only the original tank had a gauge on it. I knew by mileage when I should start expecting a drop in fuel pressure indicating I needed to switch tanks, so airplane fuel planning was no big deal for me.
 
Sometimes even with a "Both" option, you'll get a heavy wing and R/L option (if it's fuel related) can let you isolate the heavy wing and draw from there. Management isn't hard. Most GPS system have nag alerts based on time for tank change alerts (shouldn't be necessary).
 
It's definitely not "hard" to manage but what if, for example, a re-tractable gear aircraft had 3 separate buttons to control the gear? One for each gear. It's not hard to push 3 buttons instead of one
but most of the time there's just one button/lever right? The manufacturers cleverly designed it so you don't have to manage each one separately. With 3 buttons I bet you'd see
lots of landing accidents where less than 3 were deployed although I agree that there are plenty of sans-gear landings with just one button :)

As I mentioned earlier for the 2-tank scenario with a tube between them, the fuel level would remain the same for the most part between the 2 tanks so you would not need to balance
the tanks you're drawing from.
 
Actually there is a tube between Cessna tanks. But it's the Vent tube.

90% of High Wing operation is with selector on BOTH. Although, sane pilots use the selector on the ground to confirm both tanks are drawing.

Ex:
Park the plane on Left. Prevents cross feeding the fuel.
Start the plane on Left and start taxiing. Confirms Left is feeding
Switch to Right while taxiing. Confirms Right is feeding
BEFORE RUN-UP, Switch to Both. Do you run-up and go fly.

If needed in flight (the heavy wing example stated previously) you can switch "away" from the heavy wing to balance stuffs out.
 
What if you parked the plane on an incline. Fuel could migrate from the higher tank to the lower and then out the vent. What if one cap had a slight air leak, creating a partial vacuum in that tank? What if you needed to drain one tank for some reason? There are any number of scenarios where you might want to isolate the tanks from each other. On a simple two-tank system like the high-wing Cessnas, "Both" makes it pretty foolproof 99% of the time.
 
VictorValencia said:
I understand why you can end up with more fuel in one tank
than another but why hasn't this problem been solved so the pilot does not have
to manually intervene to manage fuel tank levels? For example if you have a tube between
the two tanks won't they always end up at the same level (for the most part). I understand
if you're in a long turn that the fuel can flow into the tank of the "lower" wing but if
the tube is small enough not much will pass through and, over time, the tanks will remain
fairly even once you level out.
Click to expand...
Couple thoughts

(A)
I like having separate independent fuel tanks.. this can be a life saver in a situation with contaminated fuel, a leak in a tank, etc,

(B)
Cessna builds piles of complete trash, their "both" option doesn't draw even fuel flow do to how the vents are designed. Inevitably you will have one tank at 1/4 and the other at 2/3. In addition, the tanks aren't actually isolated.. there is a connection tube

..for planes with multiple independent tanks (Cirrus, Bonanza, Pipers, really any real airplane) fuel management for anyone even with a 10% level of competence is not hard. Switch your tanks on a set time interval, etc.

..oh also, if you run out of gas and have only one tank, or have it on both, then if you run out of gas you're screwed.. at least with multiple tanks you can switch and buy yourself a little bit of time to get on the ground


PS - the new CEO of Cirrus threw this idea out there "why do I have to switch L and R?? Can't the plane just do that?"<- many current GA pilots though think we hit the epitome of GA tech in 1953 so this idea was readily lambasted
 
On the C150 (I own one, N19477), it only has on or off. It does draw from the right side faster than the left, it's a common "problem" with the 150, because of the venting design. But, if the one tank does go empty before the other one, the engine doesn't quit.
 
I have most of my hours in Pipers with L/R tanks. Have a 30min timer set in my GNS530 that pops up a message to switch fuel tanks. So every 30, just switch. It works well for me. If you really want to see crazy look at planes like the earlier Cherokee 6s that have 4 tanks to switch between... or the twins/others that deal with stuff like cross-feeding tanks.

But I think the answer to your question of why haven't we come up with a solution is complexity and reliability. It's hard to think of a system much simpler or more reliable than a hand operated selector valve. Anything to automate that is probably going to be electronic which means at a minimum some kind of electronically actuated valve and control system. Then you need some kind of redundancy in that system because it's electronic... and you've added more opportunities for user error/confusion because of course you still need the pilot to be able to manually select one tank.

I can understand why someone used to a high wing with a "both" or "on/off" selector would be worried about it but really once you fly a plane with a simple L/R selector for a while it's not difficult at all just come up with some method like a timer to make sure you don't run one dry.
 
Imagine having two glasses, one filled with a drink and the other empty. Each glass has a straw. If you try to drink from both straws at once you will get only air, no drink. That is a low-wing airplane. You "drink" only from one straw at a time.

When you have a high-wing, gravity maintains a positive pressure in both straws and the weight of the fuel from the tank with fuel will win over the air from the empty one.
 
Larry in TN said:
Imagine having two glasses, one filled with a drink and the other empty. Each glass has a straw. If you try to drink from both straws at once you will get only air, no drink. That is a low-wing airplane. You "drink" only from one straw at a time.

When you have a high-wing, gravity maintains a positive pressure in both straws and the weight of the fuel from the tank with fuel will win over the air from the empty one.
Click to expand...

What would be nice though is a single header (footer?) tank that all could drain into and then the fuel is drawn from. Then if on both/all if one does go dry it still is pulling from the footer tank without interruption
 
My M35 Bonanza had 6 tanks... 2 mains, 2 Aux and 2 tip....
I fly a V35B now with 2 tanks 40 gallons each.
I like the 2 tanks better :)
 
Almost 25 years ago I was a flight engineer on DC8. DC8s have as many as ten fuel tanks. I'm not sympathetic! LOL
 
My Comanche has two tanks with 30 gallons each. I usually fill them to 25 gallons each because there is actually two level markers in the tanks. I run 30 minutes per side and switch sides based on which way the hand is pointing in the 8 day clock on my dash. From 00-30 I run off the right tank and from 30 to 60 I run off the left tank. This has worked well so far.
 
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jd21476 said:
My Comanche has two tanks with 30 gallons each. I usually fill them to 25 gallons each because there is actually two level markers in the tanks. I run 30 minutes per side and switch sides based on which way the hand is pointing in the 8 day clock on my dash. From 00-30 I run off the right tank and from 30 to 60 I run off the left tank. This has worked well so far.
Click to expand...
Your Crazy Ivans would be very predictable. ;)
 
Managing fuel is easy. Managing the air in the empty tanks is the real challenge.

Fuel shouldn’t flow to the lower tank in a coordinated turn. Only a slip, skid, or tilted parking space should drain fuel from one tank into the other.

There are planes that automatically pump fuel around to maintain balance. But they are ... I’m going to go with “more expensive.” And that system is one more complication that can fail. With airplanes, simpler systems that require a little more of the pilot are generally considered safer, because pilots should be less likely to fail than automated machines.

Of course, the accident records seem to send a different message.
 
Tantalum said:
Couple thoughts
Click to expand...

I liked your post. I could t find the option to like it about ten times. So I’ll just quote a part of your post and say I like it about ten times.

Set a timer. After 30 mins, switch tanks. Another hour goes by, switch tanks. Repeat. Landing before then? Switch to the fullest tank before landing. It’s the G in gumps. At least for low wings.

not sure what the G in gumps stands for in high wings.... maybe G for Get a low wing. :biggrin:
 
The Bo I recently bought has six but you are only drawing off of four. My tips just have pumps that push the fuel to the aux tanks. @pigpenracing - was yours different?
 
VictorValencia said:
It's definitely not "hard" to manage but what if, for example, a re-tractable gear aircraft had 3 separate buttons to control the gear? One for each gear. It's not hard to push 3 buttons instead of one
but most of the time there's just one button/lever right? The manufacturers cleverly designed it so you don't have to manage each one separately. With 3 buttons I bet you'd see
lots of landing accidents where less than 3 were deployed although I agree that there are plenty of sans-gear landings with just one button :)

As I mentioned earlier for the 2-tank scenario with a tube between them, the fuel level would remain the same for the most part between the 2 tanks so you would not need to balance
the tanks you're drawing from.
Click to expand...

If you want to pay for the software development, actuators, testing, backup, and the weight penalty, you could come up with a one-touch multi-tank fuel system. Otherwise, some time studying, thinking ahead and keeping one’s head in the game works.
 
ateamer said:
If you want to pay for the software development, actuators, testing, backup, and the weight penalty, you could come up with a one-touch multi-tank fuel system. Otherwise, some time studying, thinking ahead and keeping one’s head in the game works.
Click to expand...
It works until it doesn't. Then people die.
 
Matthew Rogers said:
It works until it doesn't. Then people die.
Click to expand...
A severe and rather a slippery slope assessment..

Most modern commercial jets manage their own fuel.. coding and developing a system like this surely would not be hard, but with only a few hundred GA planes sold per year with most of the current fleet about as old as Methuselah there simply is no financial incentive to do so.. incidentally, accurate fuel senders have alluded aeronautical engineers on piston aircraft for decades, so we'd have to cross that hurdle first

I'm not aware of a single fuel starvation incident that was the result of some software or automation failing, to the contrary, they've all been caused by humans and in some cases like the Air Transat Airbus incident humans made the situation worse
 
Deelee said:
not sure what the G in gumps stands for in high wings.... maybe G for Get a low wing
Click to expand...
I like that, I'm going to use it next time I'm flying with a buddy in a highwing. Thanks!
 
Zeldman said:
Just about everyone drives a car that has only one fuel tank and never had to switch tanks before flying airplanes. I used to have a pickup that had 3 fuel tanks holding a total of 84 gallons. Only the original tank had a gauge on it. I knew by mileage when I should start expecting a drop in fuel pressure indicating I needed to switch tanks, so airplane fuel planning was no big deal for me.
Click to expand...
They used to have fuel tanks in planes, but they had an unfortunate habit of crushing pilots in forced landings or nose-overs when they were behind the pilot, blocking the view when they were in front of the pilot (that's why Lindbergh couldn't see forward in the Spirit of St Louis), and incinerating them either way. Moving fuel to the wings was a big safety improvement, but it meant having (at least) two tanks instead of one.

With high wings, you can still have a "Both" setting with gravity feed; with low wings, you can't — to see why, put one straw in a full glass of water and one on an empty, then try to drink through both at the same time.
 
David Megginson said:
to see why, put one straw in a full glass of water and one on an empty, then try to drink through both at the same time
Click to expand...
I like this illustration, makes it very easy to understand

But this is not an insurmountable problem, simple connect the bottom of both cups with another straw

One thing I've wondered is how aircraft with anhedral wings manage fuel consumption. Presumably the pickup ports are on the outboard, not inboard, portions of the tanks..

upload_2020-11-12_22-31-24.png
 
Matthew Rogers said:
It works until it doesn't. Then people die.
Click to expand...
Which is why we train on it, and maintain complete situational awareness of the aircraft's systems. The same can be said about the engines themselves. Why should we have to manage our own mixture, carb heat, mags, etc? Why can't they be like cars, so we just turn the key, punch the "go" lever and never have to think about it? Because those automated systems fail sometimes, and pilots need to be able to take immediate action to rectify the problem if possible. Nothing makes that easier than simple manual control valves, not to mention it's yet another cue for the pilot's situational awareness regarding fuel. If someone's screwing up and running tanks dry, the problem is with improper planning on the pilot's part, and not with the fuel system. Automated or not, it's imperative to be aware of fuel levels in your tanks.

ateamer said:
If you want to pay for the software development, actuators, testing, backup, and the weight penalty, you could come up with a one-touch multi-tank fuel system.
Click to expand...

I'd personally find it easier to reconcile with "I screwed up and ran a tank dry, but was able to switch over and revive the engine," rather than "a 38-cent microchip fried, preventing me from switching tanks, and now i'm in big trouble." Just IMHO.
 
The most important tool for fuel management, no matter how many tanks...is a timer. It's really not very hard. It is among the least complex tasks for flying. If you can't manage fuel with a timer, you will have more significant bandwidth problems with other aspects of flying.
 
Tantalum said:
I like this illustration, makes it very easy to understand

But this is not an insurmountable problem, simple connect the bottom of both cups with another straw

One thing I've wondered is how aircraft with anhedral wings manage fuel consumption. Presumably the pickup ports are on the outboard, not inboard, portions of the tanks..

View attachment 91766
Click to expand...
Motive flow.
 
KSCessnaDriver said:
Oh boy, this is going to get good... Trying to explain motive flow to people who can't figure out to switch tanks every 30 minutes
Click to expand...
It's basically a venturi.. right? I've seen this referenced to aircraft fuel systems like the VC-10
 
I believe most of it is not the complexity of the system, but rather some pilots try to “push it”, as not to make a fuel stop.
 
drummer4468 said:
Which is why we train on it, and maintain complete situational awareness of the aircraft's systems. The same can be said about the engines themselves. Why should we have to manage our own mixture, carb heat, mags, etc? Why can't they be like cars, so we just turn the key, punch the "go" lever and never have to think about it? Because those automated systems fail sometimes, and pilots need to be able to take immediate action to rectify the problem if possible. Nothing makes that easier than simple manual control valves, not to mention it's yet another cue for the pilot's situational awareness regarding fuel. If someone's screwing up and running tanks dry, the problem is with improper planning on the pilot's part, and not with the fuel system. Automated or not, it's imperative to be aware of fuel levels in your tanks.
Click to expand...
But where do we draw that line on the spectrum?

The main reason I've been told why GA is stuck in the 1950s is because of low volume, high costs, and FAA.. which makes sense. There are what, fewer than 2K piston planes sold in a year?? Ford pumps that many cars out in one afternoon. Everything we have now is basically because of stuff that was designed and built in the 1950s. Even the Cirrus, outside of having a chute and being made not of metal, still uses the same crappy engine

Take a look at commercial air travel. We used to have flight engineers managing all these systems, and then some smart people came along and developed FADEC and automation to reduce workload, increase safety, and reduce costs. It's certainly possible, and I don't think the reason it hasn't been done in small planes is out of a pragmatic concern for safety but because there simply hasn't been a reason to

The DA62 is full FADEC, by the way, and Continental does have a FADEC engine that I believe will be going in the Tecnams that Cape Air is getting. So there definitely are piston GA planes that have the capability to auto-lean.

Can we attribute any air crash to automation? Some people blame autopilots for plane crashes (like flying in ice, complacency), but I'd bet that autopilots have saved many more lives through workload ease then the handful of accidents it *may* have played a role in

For every crash that was the result of someone taking off on an empty tank, or mismanaging their fuel, I have to think that $0.38 chip is less likely to be having a bad day
 
Tantalum said:
One thing I've wondered is how aircraft with anhedral wings manage fuel consumption.
Click to expand...
The C17, in your picture, has fuel pumps. Big, 3-phase, AC fuel pumps. LOL At least two per tank.

For what it's worth, those C17s are slow. Once watched one load up and taxi out at Yokota AB in west Tokyo. We were discussing the tail markings and what they meant. Seven-plus hours later, as we were getting in the van that would take us to customs in Singapoe (Paya Lebar AB), that same C17 lands. We must have passed him somewhere over the Philippines.
 
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