Why is managing fuel so complicated?

Larry in TN said:
For what it's worth, those C17s are slow
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I just did some mild Googling and it seems like 0.7 to 0.74 speed plane. That does seem slow doesn't it? Don't most modern jets cruise 0.8 - 0.85?
 
Tantalum said:
I just did some mild Googling and it seems like 0.7 to 0.74 speed plane. That does seem slow doesn't it? Don't most modern jets cruise 0.8 - 0.85?
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Cruise is .74 to .78, but most often .74 for fuel efficiency and for crossings.
 
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.
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Our Comanche has 30 a side in the mains plus 15 a side in the aux tanks. Our practice is to start, taxi, takeoff, climb on one main, then switch to the opposite aux for 1 hour, back to the other aux for 1 hour, then alternate mains each hour. The Comanche 250 nominally burns 14 gph, for planning I round to 15. That means I have one hour in each aux, and two hours in each main. My burning the aux for an hour, I'm also checking my fuel burn to verify its at least 15 gph or less.
 
I want to know where these fuel level markers are. All I have is the blackness of the bladders in the main tanks.
 
Tantalum said:
I just did some mild Googling and it seems like 0.7 to 0.74 speed plane. That does seem slow doesn't it? Don't most modern jets cruise 0.8 - 0.85?
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Well, we were flying a DC8-62 or DC8-72 (can't remember which) which isn't exactly "modern". Our normal cruise speed was 0.80 and a high-speed cruise was 0.82.

0.74 is a bit on the slow side for transports though some others are in that range. I'm normally 0.76 - 0.80 in the 737 and that probably averages just a small bit above the long range cruise as we adjust our cruise mach based on scheduled arrival time. The long-haul airplanes, with which the C17 has many other things in common, are faster; typically in the mid .8x range. 0.70 - 0.74 would be more common in jets designed for short, frequent legs such as many of the RJs. On those routes the speed difference makes very little difference in overall flight time.
 
Since my low-wing PA-28 doesn't have a "Both" setting, I've decided make the most of it and treat it as a bug rather than a feature.

If I have a problem like an undetected fuel hose leak increasing my fuel use, both my tanks won't run dry at the same time (as would happen with a high wing and a "Both" setting).

If one tank runs dry earlier than it should have, the other likely still has enough fuel for me to get to the nearest airport for a precautionary landing, instead of having to dead-stick into the nearest clearing.
 
Aren't there are systems where the fuel pump delivers more gph than the engine burns and you have to consider the extra fuel gets collected back into a tank?

Don't Bonanzas have something like that?
 
Cessnas get away with a BOTH position because fuel isn't pumped FROM the tanks. It runs to the fuel selector by gravity. Most low wings have to pump fuel out of the tanks. Can't be done if one tank is empty (try sucking up your soft drink with one straw in the glass and one out). The Navion has both main tanks drain to a small center tank, so it has (by default) only an ON-OFF fuel selector (there's only one filler for both sides as well, the left tank fills through the center).

Of course, as you put on more fuel, the problem gets more involved. My B model came with a baggage tank that gravity feeds into the right main, but you need to close it off when you're not transferring because you can throw fuel overboard if you leave it open while the main is full. A later mod adds tip tank fuel which doesn't count against your gross weight, being out on the far end of the wing, but uneven flows make for a heavier wing with slight imbalances so there's almost always a way to run either the left or right there.

The 172 has the fun feature is that it can transfer fuel through the vent line in flight, so even if you set the fuel selector on RIGHT the left tank can go down until the fuel tank is burned down below the level of the vent line. A later AD advises you also to run either LEFT or RIGHT at higher altitudes to increase the fuel flow through the lines through the doorpost to avoid vapor locking.
 
Matthew said:
Aren't there are systems where the fuel pump delivers more gph than the engine burns and you have to consider the extra fuel gets collected back into a tank?

Don't Bonanzas have something like that?
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I'm painting with a broad brush here, but most of the Continental fuel injection setups return fuel to a fuel tank and most Lycomings do not.

You need to have knowledge of how each aircraft you fly work (this is why DPEs ask systems questions on checkrides). Early Bonanzas return all fuel to the left main tank regardless of which tank you have selected (plus they only have one fuel gauge). Newer ones return the fuel to the selected tank. Twin Cessnas return fuel to the main tanks, even if you're running on the aux tanks, and if you have a locker tank you don't burn directly off that tank. It is also important to know what, if any fuel system STCs are installed and how they work.

Generally speaking, the older the airplane is, the more complex the fuel system is. In the 1940s and 1950s the designers expected pilots to have some mechanical aptitude. That expectation went away as time carried on.
 
Tantalum said:
. Even the Cirrus, outside of having a chute and being made not of metal, still uses the same crappy engine.
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I really get tired of that. Which of you following this thread can design and build an engine that produces half a horse per pound at a low RPM that a propeller is happy with and that will run reliably at very high power levels for 2000 hours?

None of you. You have NO IDEA of the difficulties involved. You've been spoiled by modern cars, which operate under completely different and more benign conditions and demands.
 
It's not worth going through this whole exercise again, but asking a 9 liter engine to wheeze out 250 horsepower at 2,400 RPM is not that crazy.. and God forbid you look at it wrong or dare operate it slightly outside of ideal conditions and it will fall apart on you 1,000 hours in.. never mind all the internet forum lore and "but Mike Bush said.." nonsense

Diesel would be your answer by the way, diamond seems to have okay success with that now at this point and Cessna tried it on their lineup as well but unfortunately there's just not that much demand for improvement there, given the tiny volume and extremely high costs.. people just accept it, and if they want more reliability or power they move to turbines

If it wasn't for commercial aviation we'd still be sitting here with Messerschmitt equivalent turbines saying that it's simple and the best we can do given our current materials etc
 
Tantalum said:
It's not worth going through this whole exercise again, but asking a 9 liter engine to wheeze out 250 horsepower at 2,400 RPM is not that crazy.. and God forbid you look at it wrong or dare operate it slightly outside of ideal conditions and it will fall apart on you 1,000 hours in.. never mind all the internet forum lore and "but Mike Bush said.." nonsense
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You make my point. Are you a mechanic of any type? An engineer? A tecnician?
 
When I did some work on an SMA diesel 182 ten years ago, SMA had spent $1 billion US on it at that point and had 50 engines flying worldwide.

Think about that. Then think about trying the same thing in litigious America intead of France.
 
Dan Thomas said:
I really get tired of that. Which of you following this thread can design and build an engine that produces half a horse per pound at a low RPM that a propeller is happy with and that will run reliably at very high power levels for 2000 hours?

None of you. You have NO IDEA of the difficulties involved. You've been spoiled by modern cars, which operate under completely different and more benign conditions and demands.
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I don’t know about that. The Austro AE300 in the DA40 is a actually a tweaked Mercedes OM640 diesel. With the FADEC, dual ECUs, and water cooling, that engine is a dream to operate. Sure the maintenance can be more expensive, but the advantages more than make up for that in my opinion. I love being able to pull the power all the way back to idle and watch the engine temp barely budge.
 
Not certified in the US. And 100lbs+ heavier than 100LL equivalents, which could cause W&B issues on retro fits.
 
EdFred said:
How many car engines do that though?
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Who said anything about car engines? Maybe someone else did, but it wasn't me. My response is to the OP wondering why fuel management is difficult (it's not).. and an illustration from me that due to various reasons (just about all of them economical) private ga really hasn't advanced at all. Part of the reason new plane sales suck.. why would you spend close to $1M on a new Bonanza or Baron when you can find one for a fraction of the cost, often with more capable W&B specs.

Dan Thomas said:
Think about that
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There are plenty of economic reasons why our planes are as antiquated technologically as they are. But those are economic reasons. Given enough money and the desire we can achieve great things technologically. We shouldn't limit our imagination and pretend that what a handful of engineers offered in the 1940s as a cheap, economical, and somewhat reliable powerplant for the burgeoning world of private aviation is the best we'll ever get. Are there big leaps? No, probably not.. but can we try to ameliorate many of the issues here people are plagued with (mixture settings, weird roughness caused by maybe poorly timed mags, hard starts, etc.) .. sure, we should!

Take for example.. on more than one occasion my right seater was blown away that the Cirrus will alert you if the parking break is on. Or the fact that to use the heat or air vents on many legacy planes it's a who's who of push and pull knobs that either roasts you or blasts you with cold air. Why not make it a simple hot cold mixing dial (the TTx, and others have solved this). There are a lot of small improvements like that

Cervieres said:
I don’t know about that. The Austro AE300 in the DA40 is a actually a tweaked Mercedes OM640 diesel. With the FADEC, dual ECUs, and water cooling, that engine is a dream to operate. Sure the maintenance can be more expensive, but the advantages more than make up for that in my opinion. I love being able to pull the power all the way back to idle and watch the engine temp barely budge.
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shhhhh... you're upsetting the status quo
 
Matthew said:
Aren't there are systems where the fuel pump delivers more gph than the engine burns and you have to consider the extra fuel gets collected back into a tank?

Don't Bonanzas have something like that?
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Yep. Early Bonanzas like mine, return 3gph to the left tank. So if you have 4 or 5 tanks, you need to plan your fuel burn to keep at least 10 gallons in a main tank for take off and landing, and not overfill the left tank and pump fuel overboard. Aux tanks are only to be used in level flight. Newer Bonanzas return fuel to the tank you are using, so no way to pump fuel overboard by mismanagement.
 
Tantalum said:
By the way.. for everyone saying that we can't modernize our legacy engines and that fadec is "bad" because what if it goes crazy or whatever..
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Some might say that but I don't think that has anything to do with the reason modernization hasn't happened at a faster rate.

Look at the age of the typical airplane people are flying and look at the technology that was available at that point in time. Anyone whining that a 1965 airplane should have 2015 style engine controls is unrealistic.
 
EdFred said:
And the W&B issues? People already complain about nose heavy 6 cyls. Add another 100lbs on the front and how are the handling characteristics?
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You’re right. What’s the point of innovation if it doesn’t mesh with a 50 year old airframe.
 
Matthew said:
Aren't there are systems where the fuel pump delivers more gph than the engine burns and you have to consider the extra fuel gets collected back into a tank?
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If I'm remember correctly, back about 35 years, the C-310 does that. Excess fuel is returned to the main (tip) tanks. If you have fuel in the AUX tanks you can't burn it first, as you would otherwise want to for structural reasons, as the excess fuel would be pumped overboard out the vent if the mains are still full. You have to burn the mains down to a point (that I don't remember) before switching to the AUX tanks. The AUX tanks empty much faster than the engine's flow rate and fill the mains back up in the process.
 
Cervieres said:
You’re right. What’s the point of innovation if it doesn’t mesh with a 50 year old airframe.
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Well, if it's only going in new planes, then we circle back to Tantalum's point of the new planes being 1MM plus, and (almost) no one is going to buy them. So what's the point of the engine if it can't be retrofitted?

I mean if you're going to provide an example of a suitable replacement, then I don't know, provide an example of a..........suitable replacement.
 
What about those with 3 fuel valves, but only two tanks to draw from?
 
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EdFred said:
Well, if it's only going in new planes, then we circle back to Tantalum's point of the new planes being 1MM plus, and (almost) no one is going to buy them. So what's the point of the engine if it can't be retrofitted?

I mean if you're going to provide an example of a suitable replacement, then I don't know, provide an example of a..........suitable replacement.
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Never said anything about replacement engines for older aircraft, just that better technology already exists and is commercially available. Beech, Piper, and Cessna pistons are already on borrowed time. Bonanza and Baron production are barely seeing double digits and will soon go the way of Mooney. Cessna and Piper might hang on for a while with the trainer market and the 206/M350. Diamond, Cirrus, Pipistrel and Tecnam make better products and embrace new technology and manufacturing processes which will lead to more and more market share. You can argue all you want that an O-540 powered aluminum airplane is better than a diesel or Rotax powered Diamond/Tecnam/etc., but the market disagrees.

I totally agree the cost of new aircraft is almost prohibitive and driven by forces that we can’t really control, but 1 million + is a bit of a high number. There are a whole lot of modern low time and new aircraft in the $250-500K range.
I know lots of people who balk at airplane prices that drive $100K trucks and boats which will depreciate down to nothing in a few years. The price of a new SR20 or DA40NG isn’t totally unreasonable.
 
EdFred said:
Yup, there are no marks in the tanks. Black bladders is all.
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When you open the cap there should be a sleeve. If you fill to the bottom then that is 25 gallons and to the very top is 30 gallons.
 
jd21476 said:
When you open the cap there should be a sleeve. If you fill to the bottom then that is 25 gallons and to the very top is 30 gallons.
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Maybe they changed it in later SN#s, but I can't fill to the top of the sleeve.
 
mondtster said:
Some might say that but I don't think that has anything to do with the reason modernization hasn't happened at a faster rate.

Look at the age of the typical airplane people are flying and look at the technology that was available at that point in time. Anyone whining that a 1965 airplane should have 2015 style engine controls is unrealistic.
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That's just it. In North America, the number of private pilots flying planes built since 2000 is minuscule. We mostly fly inexpensive old planes, where the retrofit cost of $40,000 or more for each diesel engine is prohibitive, and the benefits, dubious. In Europe, where fuel is more expensive, cross-country flying is more restricted, and pilots tend to fly lighter, newer planes, diesel has a more obvious market.
 
There are new engines available, as has been mentioned. But pilots/owners are cheap and unrealistic about costs, so they don't sell. Lycoming's iE2 has been around a long time already--maybe 14 or 15 years. The SMA is available for STC retrofit in the 182Q, because the SMA is heavy and in that airplane the battery can be relocated to the tailcone and the heavy metal prop replaced with the MT composite prop. SMAs are heavy because they have to withstand much higher compression and combustion pressures. The heads are air and oil cooled and there's a huge oil cooler and a big turbo intercooler. It all adds up. The Austro engine is smaller and turns at a high RPM to generate its horses, so a redrive reduces the RPM to propeller speeds and increases the torque in doing so. The redrive weighs something, too, and it also (unless things have changed) needs replacement several times over the life of the engine. None of this is cheap, and there are limited service centers for any major repairs for the engine.

Yes, with enough money we can change a lot of stuff. But that money thing is a stinker, as the iE2 proves. Parking brake warning lights or horns are stupidly easy to create and they're cheap and light and they impress the buyer and his friends, but they do absolutely nothing for performance unless you try to take off with the brakes on. WHen I've worked in Cirruses and Cessna Corvalises I've seen a lot of cockpit bells and whistles, but those airplanes still have all the usual power and control systems as an older airplane, because those are the systems that cost real big money to change and certify.

And, in any case, automated fuel and engine management won't cure the oblivious-pilot problem. Even in really simple airplanes that have a fuel on-off valve, pilots still run out of fuel and crash. Or they neglect to do a decent preflight and sump the tanks and strainer, and crash. Or they cheap out on maintenance and stuff fails or malfunctions. The endless stories on this forum about failed alternators and vacuum pumps and magnetos are proof of that. And automated stuff is completely unnoticed until it decides to quit without warning, so in an airplane you need manual overrides and the skills to use them. But when many pilots can't even manage a common problem like carb ice, I don't think they'll manage manual overrides well either unless they're awfully simple, like SMA's manual throttle linkage that the pilot engages when the FADEC quits. You'd need a whole training course on manual overrides, and periodic refresher courses. Or several redundant automated systems. It's just easier and cheaper to learn how to use the old-fashioned stuff every day.
 
David Megginson said:
That's just it. In North America, the number of private pilots flying planes built since 2000 is minuscule. We mostly fly inexpensive old planes, where the retrofit cost of $40,000 or more for each diesel engine is prohibitive, and the benefits, dubious. In Europe, where fuel is more expensive, cross-country flying is more restricted, and pilots tend to fly lighter, newer planes, diesel has a more obvious market.
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Diesel is a big deal in Africa, which has n o refineries that make 100LL. When I was there 14 years ago, Avgas was between $8 and $11 per litre, or $30 and $40 per gallon. The SMA runs on Jet, which is plentiful in Africa.

The SMA I worked on was a $100K conversion in Canada ten years ago. New fuel stuff, new engine mount, many other mounts for coolers and so on. New exhaust system. Installation of the FADEC computer and controls. New composite propeller. New cowling. Move the battery and install all new cabling and contactor control wiring. And the ambient temperature limits for starting are much higher than for a gasoline engine. Not much below freezing at all.

Now you now why there aren't many out there.

There are new aircraft gasoline engines. Jabiru and UL Power. Funny thing, though: They look a lot like Lycomings and Continentals and produce about the same power for weight. Which tells one--or should tell one--that Lycs and Conts are built like they are because that's what works reliably at minimal weight.
 
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