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  #1  
Unread 03-11-12, 10:11 AM
n86121's Avatar
n86121 n86121 is offline
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Talking Fuel Management Questions - various strategies

Good Morning Gents,

I have a T337D. While the T C&D models return fuel goes to the manifold, instead of the main tank, I am still totally paranoid about running a tank dry. Probably a good thing.

The mains have 92 usable, and the aux 36, for a total of 128 gals. If I remember correctly thats out of 131 on board, or about 4 gals in various fuel lines, etc.

My car has a nice way of expressing fuel: X miles to empty.
Would that it be so simple.

I dont want to run a tank until an engine quits. That seems like a bad idea.

I have a totalizer on board. Very nice, but....

For whatever paraboid reason, I assume the tanks may not really be full (even though I fill them), as 210's dont always get full unless perfectly level. Also the heater draws fuel that doesnt run through the totalizer. Etc.

What should I plan to leave in a tank before switching? 4 gals? 2 gals? More? Less?

Whatever the moosh factor, it should apply to all four tanks. If the moosh factor is 4 gals per tank, then that effectively means assume 16 gallons less than 128 available, or 112 available. Maybe too conservative?

My general strategy has been to mostly use the mains. My habit is to refuel always and often. For lots of shorter flights, this means the totalizer is always indicating simply and the aux fuel is 'along for the ride'.

For longer flights, I run the main until they have about 16 gals left, (worst case safely over 30 mins), then switch to aux.

Then run aux down until 8 gals left (4 in each, in case not filled completely or whatever), then back to mains to land.

Thoughts? Discussion? New TSA jokes?

I'm about 1 month from getting my 'thrasher back. She's going to be very very pretty.

D
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  #2  
Unread 03-11-12, 05:49 PM
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n86121 n86121 is offline
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Red face Fuel burn profile

This graph shows the tanks volumes and switchover points.

I assume like a 210 that even though I fill the tanks, they may not be 100% full.

The shadin is set to flash 'low fuel' once 76 gals used, i.e. 16 in mains and 36 in aux

Then burn down 28 of the aux, leaving 8 in the aux just in case.

The shadin also flashes with 40 minutes left, to remind me to go back to mains.

Then switch back to the main for landing, etc.

The 8 in the aux just in case.
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  #3  
Unread 03-13-12, 12:53 AM
sns3guppy sns3guppy is offline
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I like to think in terms of time in the tanks, rather than gallons. I don't ever want to be at less than IFR reserves, but at a minimum, an hour remaining, or better.

It's hard to run out of fuel if you don't burn off the bottom half of the tanks. This doesn't mean that one should never burn below a half-tank, but simply means that so long as one keeps a healthy margin and doesn't abuse it, running out of fuel isn't an issue.

A good practice is dipping the tanks, rather than simply looking in the tank. It's easy to have a tank appear full, especially with an extended filler neck, and still be able to squeeze considerable fuel into the tank.

In the case of the 210, filling to the bottom of the filler neck leaves the tanks down by a considerable margin; about an hour in each tank.

Simply watching the fuel level in the tank isn't enough. Know how much you anticipate putting into the tank, and verify it with the fuel flow meters on the truck or pump when you do fill the tanks.

Another good practice is to deduct an hour from what you think is in the tanks, and start there. If your best calculation shows five hours of fuel, then plan on four hours max, and take your reserve out of that. I've flown with a lot of individuals who think that being able to squeak the last drop out of each tank of fuel, and being able to run it to the last few ounces was somehow a hallmark of a good aviator. I strongly disagree. I had a new employer once tell me that he expected me to run a tank dry so I'd know just how far I could stretch the fuel. I quit and went elsewhere. No need working around that kind of stupidity.

Fuel flow meters and totalizers work great so long as you've got correct data to begin with. Aircraft gauges are notoriously wrong. If I'm flying cross country, I like to keep a fuel log and compare it to what I calculated I'd have burned when passing each waypoint. Rough calculations are useful, too; half-way there I should see half of the fuel that I calculated in the preflight, gone. Three quarters of the way, three quarters of my planned trip fuel, gone, and so on.

Keep track of your bypass fuel in your tank and burn calculations. There are two basic ways to get silent in flight; one is running out of fuel, but the other is mismanaging (misplacing, misfeeding, etc) the fuel. When fuel is transferred or bypassed from one tank to the other, keep the amount in mind and use accordingly.

Remember, you can always land earlier and take on more fuel. You run out of options, however, if you push it too far. I've flown skymasters with up to a 12 hour endurance if flown properly, and I could do it, but personally I have about a three hour bladder and that's enough. I've done a lot of 6+ hour flights in Skymasters, and that's too long. Land, take a break, and get more fuel. No sense pushing any farther or longer than necessary. Remember, it's supposed to be fun!
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Unread 03-13-12, 03:18 PM
Ed Coffman Ed Coffman is offline
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I run my tanks the way the owners manual recommends. If you fill them all and refill to take care of any slant caused by unequal fuel weight you should have very close to 128 gallons. Run your mains for the first hour. Then switch to one aux and write down the time. 15 minutes later switch to you other aux. This is so you won't have both tanks running dry at the same time. At cruise you it will take approximately 49 minutes to exhaust your aux tanks. If you pay attention to your fuel flow you will see minor fluctuations before the tank runs dry. Switch then and you won't even notice the event. 15 minutes later you will need to switch your other tank. You will notice yours mains will almost be full again. That is all the fuel you have and you won't be dilly dallying around with "how much do i have in my aux tanks". Also switching from dry mains to aux's is a good way to kill your self. The aux's aren't connected to the aux fuel pumps.
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  #5  
Unread 03-13-12, 10:39 PM
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hharney hharney is offline
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I agree with Ed, do it by the book. I take off and climb to cruise altitude and after about 1 hour on the main tanks, I select both aux tanks. I start my 1 hour timer and after 1 hour I switch the front back to main and leave the rear on the aux. When the rear coughs I switch the rear back to the main and then switch the front back to the aux. When the front coughs I switch the front back to the main. Usually total time on the aux's is 1.25 to 1.3 hours. I watch my clock, fuel gauge and fuel flow for indications. Once in a while the cough will catch me by surprise.

Depending on terrain or location I will stay on mains longer than 1 hour. But for the most it's right around an hour like the book says.

Once the aux's are drained you know that all the fuel you have is in the main tanks. I calculate the time very conservatively and figure my reserve. I know my fuel gauges even though lots of people and pilots in the right seat point and question them. Mine are only trustworthy when they are 1/4 or lower. For the most part they work pretty good and after flying this airplane for 35 years you get to know the systems.

I know have a JPI with fuel flow and I am starting to learn to use it as a tool also. It is amazingly accurate. I have it tied into the Garmin 530 and it continues to amaze me with it's right on numbers.

At times I will put 10 gallons in each aux just to have some fuel sloshing around in the tanks and I have used that hour or so of fuel in some cases but never because the mains were too low. I almost always top the mains after each flight but only use the aux's for cross country flights. I almost never let the mains below 1/2.
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  #6  
Unread 03-14-12, 09:23 PM
Walter Atkinson Walter Atkinson is offline
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Quote:
Originally Posted by hharney View Post
Once the aux's are drained you know that all the fuel you have is in the main tanks. I calculate the time very conservatively and figure my reserve.
Excellent advice. I run tanks dry routinely. It's a safety issue. It was SOP in the piston airliners for decades. (There IS a reason not to run tanks dry on turbines. Different animal)

You want ALL of your fuel in one tank (per engine) when making a max range trip and having your "one hour reserve" IN ONE PLACE. Low, on an approach, sweating weather or nav issues, is NO time to be looking for fuel spread around different tanks, That can kill you and has killed others. Do you want your reserve all in one place and all fuel decisions made or do you want it spread around various tanks, not knowing exactly how much is where when the chips are down?

RUN THEM DRY IN FLIGHT and determine exactly how much REAL usable fuel you have in each tank. Unless you do that, you do not know. Draining the fuel on the ground is not the same and does not work.
Knowing this information could save your life one day.

If you are not comfortable running a tank dry, get an instructor who is and get comfortable with it. It is a safety issue.
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